Display device, electronic device and method of driving display device
The present invention provides a display device which can display characters clearly and display images smoothly. An area gray scale method is adopted and a configuration of one pixel is changed depending on a mode, by selecting one or more display regions in each pixel. When characters are needed to be displayed clearly, one pixel is configured by selecting a stripe arrangement. Thus, clear display can be conducted. When images are needed to be displayed, one pixel is configured by selecting an indented state. Thus, smooth display can be conducted.
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This application is a divisional of application Ser. No. 11/474,227 filed on Jun. 23, 2006 now U.S. Pat. No. 7,898,623.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to display devices having a display screen on which characters and images are displayed, and relates to a technique for improving visibility of a display screen.
2. Description of the Related Art
In recent years, a so-called self-luminous display device has been attracting attention, which has pixels formed with a light-emitting element such as a light-emitting diode (LED). As a light-emitting element used in such a self-luminous display device, there is an organic light-emitting diode (also called an OLED, an organic EL element, an electroluminescence (EL) element, or the like), which has been attracting attention and used for an EL display (e.g., an organic EL display). Since the light-emitting element such as an OLED is a self-luminous type, it is advantageous, as compared to a liquid crystal display, in that high visibility of pixels is ensured, no backlight is required, high response speed is achieved, and the like. The luminance of a light-emitting element is controlled by the value of current flowing therein.
As a driving method of controlling gray scales of light emission (luminance) in such a display device, there are a digital gray scale method and an analog gray scale method. In the digital gray scale method, gray scales are expressed by controlling ON/OFF of a light-emitting element in a digital manner. On the other hand, as for the analog gray scale method, there are a method of controlling the light-emission intensity of a light-emitting element in an analog manner, and a method of controlling the light-emission time of a light-emitting element in an analog manner.
In the digital gray scale method, only two states of a light-emitting element can be selected, which are a light-emission state and a non-light-emission state; therefore, only two gray scales can be expressed. Thus, the digital gray scale method is often used in combination with another method to achieve multi-grayscale display. As a method for achieving multi-grayscales, a time gray scale method is often used in combination (Reference 1: Japanese Patent Laid-Open No. 2001-324958 and Reference 2: Japanese Patent Laid-Open No. 2001-343933). In addition, an area gray scale method is used in some cases (Reference 3: Japanese Patent Laid-Open No. 2001-125526).
On the other hand, a pixel configuration for displaying clear images and characters both has been developed (Reference 4: Japanese Patent Laid-Open No. 2005-062416). In general, a delta array or a stripe array is adopted as a pixel configuration; however, in Reference 4, a hexagonal pixel configuration is adopted.
SUMMARY OF THE INVENTIONHowever, it is difficult to form pixels for each color when the hexagonal pixel configuration is employed. In particular, in a case of an organic EL element, since an organic layer is deposited for each color, the organic layer is not deposited so well, in the case of such a complex structure.
In view of the above problem, it is an object of the present invention to provide a display device in which a display method can be changed as appropriate, with a simple pixel configuration.
One feature of the present invention is a display device comprising: a first display region; a second display region; and a third display region, wherein in the first, second and third regions, the same color is displayed; wherein in a first state, a pixel includes the first display region and the second display region; wherein in a second state, the pixel includes the second display region and the third display region; and wherein an area of the first display region is equal to an area of the third display region.
Another feature of the present invention is that the pixel expresses a gray scale by selecting the display regions included in the pixel to emit light in the display device described above.
Note that various kinds of transistors can be used in the present invention. Therefore, transistors applicable to the present invention are not limited to a particular type. Thus, the present invention can employ a transistor such as a thin film transistor (W1) using a non-single crystalline semiconductor film typified by amorphous silicon or polycrystalline silicon. Thus, manufacturing can be done at a low manufacturing temperature, at a low cost, devices can be formed over a large substrate or a transparent substrate, or a transistor can transmit light. A MOS transistor, a junction transistor, a bipolar transistor formed with a semiconductor substrate or an SOI substrate, or the like can also be used. Thus, transistors with less variation, transistors with high current supply ability, or transistors with small size can be formed, or less power consumption circuits can be obtained. In addition, a transistor formed with a compound semiconductor such as ZnO, a-InGaZnO, SiGe or GaAs, a thin film transistor thereof or the like can be applied. Thus, manufacturing can be done at a low manufacturing temperature or at room temperature, or a transistor can be formed directly on a low heat resistant substrate such as a plastic substrate or a film substrate, for example. A transistor obtained by an ink-jet method or a printing method can also be used. Thus, manufacturing at room temperature or at a low vacuum degree, or a manufacturing with use of a large substrate is possible. Since manufacturing without a mask (reticle) is possible, layout of a transistor can be changed easily. A transistor using an organic semiconductor or a carbon nanotube, or other transistors can also be applied. Thus, such a transistor can be formed over a flexible substrate. In the case of using a non-single crystalline semiconductor film, it may contain hydrogen or halogen. In addition, a substrate over which transistors are formed is not limited to a particular type, and various kinds of substrates can be used. Accordingly, transistors can be formed over a single crystalline substrate, an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a paper substrate, a cellophane substrate, a stone substrate, a stainless steel substrate, a substrate including a stainless steel foil, or the like. Alternatively, after forming a transistor over a certain substrate, the transistor may be transferred to another substrate. By using such a substrate, a transistor having excellent characteristics or a transistor with low power consumption can be formed, or a nonbreakable device or a heat-resistant device can be manufactured.
Note also that the structure of a transistor is not limited to a particular type and various structures may be employed. For example, a multi-gate structure having two or more gates may be used. In the case of multi-gate structure, since channel regions are connected in series, a structure in which plural transistors are connected in series is obtained. By using a multi-gate structure, off-current can be reduced as well as the withstand voltage can be increased to improve the reliability of the transistor, and even when the drain-source voltage fluctuates at the time when the transistor operates in the saturation region, flat characteristics can be provided without causing variations of a drain-source current. In addition, such a structure that gate electrodes are formed to sandwich a channel may also be employed. By using such a structure that gate electrodes are formed to sandwich a channel, the area of the channel region can be enlarged to increase the value of current flowing therein, and a depletion layer can be easily formed to improve an S value. A structure in which plural transistors are arranged in parallel is obtained, when gate electrodes are formed to sandwich a channel. In addition, any of the following structures may be employed: a structure where a gate electrode is formed over a channel; a structure where a gate electrode is formed below a channel; a staggered structure; an inversely staggered structure; a structure where a channel region is divided into a plurality of regions, and the channel regions are connected in parallel; or a structure where a channel region is divided into a plurality of regions, and the channel regions are connected in series. In addition, a channel (or a part of it) may overlap a source electrode or a drain electrode. With a structure where a channel (or a part of it) overlaps a source electrode or a drain electrode, unstable operation caused by charges accumulated in a part of the channel can be prevented. In addition, an LDD region may be provided. By providing an LDD region, off-current can be reduced, and the withstand voltage can be increased to improve the reliability of the transistor. Even when the drain-source voltage fluctuates at the time when the transistor operates in the saturation region, stable characteristics can be provided without causing variations in a drain-source current.
Note that transistors in the present invention may be any type of transistors and may be formed over various types of substrates. Thus, all circuits may be formed over a glass substrate, a plastic substrate, a single crystalline substrate, an SOI substrate, or other substrates. By forming all circuits over one substrate, the number of parts can be reduced to lower manufacturing cost, or connection points with circuit components can be reduced to enhance reliability. Alternatively, such a structure may be employed that a part of circuits is formed over a substrate, while another part of the circuits is formed over another substrate. That is, all circuits are not required to be formed over the same substrate. For example, such a structure may be employed that a part of circuits is formed over a glass substrate with transistors, while another part of the circuits is Mimed over a single crystalline substrate so that the IC chip is attached onto the glass substrate by COG (Chip on Glass). Alternatively, the IC chip may be connected to the glass substrate by TAB (Tape Automated Bonding) or by using a printed board. In this manner, by fowling a part of circuits over the same substrate, the number of parts can be reduced to lower manufacturing cost, or connection points with circuit components can be reduced to enhance reliability. In addition, since a portion of high driving voltage or a portion of a high driving frequency consumes a lot of power, such a portion is not allowed to be formed over the same substrate, and thus, increase in power consumption can be prevented.
Note that a transistor is an element having at least three terminals of a gate, a drain, and a source. A channel region is provided between a drain region and a source region, and current can flow through the drain region, the channel region and the source region. Here, a source and a drain are exchangeable depending on a structure, an operation condition or the like of a transistor, and thus, it is difficult to determine which is a source or a drain. Thus, in some cases of the present invention, regions serving as a source and a drain are not referred to as a source or a drain. In that case, they are referred to as a first terminal or a second terminal, for example. Further, a transistor may be an element including at least three terminals, abuse, an emitter and a collector. Also in this case, an emitter and a collector may be referred to as a first terminal and a second terminal.
In addition, in the case of a multi-gate transistor, for example, a gate electrode of a transistor is connected to a gate eledtrode of another transistor with the use of a conductive film which is formed from the same material as the gate electrode in many cases. Since this region is a region for connecting a gate electrode to another gate electrode, it may be called a gate wire, while it may also be called a gate electrode since the multi-gate transistor may be regarded as one transistor. That is, such a region may be called a gate electrode or a gate wire as long as it is formed of the same material as the gate electrode or the gate wire and connected thereto. In addition, a part of a conductive film which connects a gate electrode to a gate wire, for example, may also be called a gate electrode or a gate wire.
Note that a gate terminal means a region of a gate electrode or a part of a region electrically connected to the gate electrode.
Note that a source means apart or a whole part of a source region, a source electrode, and a source wire (also called a source line, a source signal line, or the like). A source region is a semiconductor region containing a large amount of p-type impurities (e.g., boron or gallium) or n-type impurities (e.g., phosphorus or arsenic). Accordingly, it does not include a region containing a slight amount of p-type impurities or n-type impurities, that is, a so-called LDD (Lightly Doped Drain) region. A source electrode is a conductive layer formed of a different material from the source region, while being electrically connected to the source region. Note that there is a case where a source electrode and a source region are collectively referred to as a source electrode. A source wire is a wire for connecting source electrodes of different pixels, or a wire for connecting a source electrode with another wire.
Note that there is a portion functioning as both a source electrode and a source wire. Such a region may be called either a source electrode or a source wire. That is, there is a region where a source electrode and a source wire cannot be clearly distinguished from each other. For example, in the case where a source region overlaps a source wire which is extended, the overlapped region functions as both a source wire and a source electrode. Accordingly, such a region may be called either a source electrode or a source wire.
In addition, a region formed with the same material as a source electrode, while being connected to the source electrode may be called a source electrode. A part which overlaps a source region may be called a source electrode as well. Similarly, a region formed with the same material as the source wire, while being connected to the source wire may be called a source wire as well. In the strict sense, such a region does not have a function of connecting to another source electrode in some cases. However, there is a case where this region is formed with same material as the source electrode or the source wire, while being connected to the source electrode or the source wire in order to provide a sufficient manufacturing margin. Accordingly, such a region may also be called either a source electrode or a source wire.
In addition, a conductive film which connects a source electrode to a source wire may be called a source electrode or a source wire, for example.
Note that a source terminal means a part of a source region, a source electrode, or a region electrically connected to the source electrode.
Note also that this is true of a drain, similarly to the source.
In the present invention, a connection includes an electrical connection, a functional connection and a direct connection. Accordingly, in the configuration disclosed in the present invention, other connection than a predetermined connection are also included. At least one element which enables an electrical connection (e.g., a switch, a transistor, a capacitor element, an inductor, a resistor element, or a diode) may be interposed between an element and another element. In addition, at least one of a circuit which enables a functional connection (e.g., a logic circuit (such as an inverter, a NAND circuit or a NOR circuit); a signal conversion circuit (such as a DA conversion circuit, an AD conversion circuit or a gamma correction circuit); an electric potential level conversion circuit (a power supply circuit such as a boost circuit or a buck circuit, or a level shift circuit for changing electric potential level of H signal or L signal), a power source, a current source or a switching circuit, an amplifier circuit (such as an op-amp, a differential amplifier circuit, a source follower circuit, a buffer circuit, or a circuit which can increase a signal amplitude or a current amount); a signal generation circuit, a memory circuit; a control circuit and the like) may be arranged between an element and another element. Alternatively, connection may be conducted directly without interposing other elements or other circuits. Note that only the case that connection may be conducted directly without interposing other elements or other circuits is described as being “directly connected”. Meanwhile, description of “electrically connected” includes an electrical connection (i.e., a connection with another element interposed), a functional connection (i.e., a connection with another circuit interposed), and a direct connection (i.e., a connection without another element or another circuit interposed).
In the present invention, a pixel means a minimum unit of an image. Thus, in the case of a color display device having color elements of R (Red), G (Green), and B (Blue), one pixel is composed of a dot for R color element, a dot for G color element, and a dot for B color element. Note that the color element is not limited to three colors, and it may be composed of more than three colors. For example, there is RGBW (W means white), or RGB plus yellow, cyan, and/or magenta. In addition, a color similar to at least one color of RGB may be added. For example, R, G, B1 and B2 may be employed. B1 and B2 are both blue, but have slightly different frequencies. By using such color elements, an image like a real thing can be done or reduction of power consumption can be achieved. Note that plural dots for a certain color element may be included in one pixel. At that time, the plural color elements may have different sizes of regions contributing to displaying. In addition, by controlling plural dots of a circuit color element, gray scales may be expressed. This is called an area gray scale method. Alternatively, plural dots of a circuit color element may be used and signals to be supplied to each dot may be slightly different to widen a viewing angle.
Note that in the present invention, “semiconductor device” means a device including a circuit which includes a semiconductor element (such as a transistor or a diode). In addition, it is acceptable that “semiconductor device” means a general device which can operate with use of semiconductor characteristics. “Display device” means a device having a display element (such as a liquid crystal element or a light-emitting element). Further, it means a display panel itself in which a plurality of pixels including a display element such as a liquid crystal element or an EL element, or a peripheral driver circuit for driving the pixels are formed over a substrate. Moreover, “display device” may include a periphery driver circuit arranged over a substrate by wire-bonding or by using a bump, that is, a so-called chip-on-glass (COG). Furthermore, it may include a device to which a flexible printing circuit (FPC) or a printed wiring board (PWB) is attached (for example, IC, a resistor element, a capacitor element, an inductor, a transistor and the like.). It may include an optical sheet such as a polarizing plate or a phase plate. Moreover, it may include a backlight (such as a light guide plate, a prism sheet, a diffusion sheet, a reflecting sheet or a light source (e.g., LED or a cold-cathode tube). Moreover, “light-emitting device” means a display device having a self-luminous type display element such as an EL element or an element for FED, in particular. “Liquid crystal display device” means a display device having a liquid crystal element.
In the present invention, an expression that an object is “formed on” or “formed over” a different object does not necessarily mean that the object is in direct contact with the different object. The expression may include a case where two objects are not in direct contact with each other, with another object sandwiched therebetween. Accordingly, when it is described that a layer B is formed on a layer A (over a layer A), it means either case where the layer B is formed on and in direct contact with the layer A, or where another layer (e.g., a layer C or a layer D) is formed on and in direct contact with the layer A, and then the layer B is formed on and in direct contact with the layer C or D. In addition, when it is described that an object is “formed above” a different object, it does not necessarily mean that the object is in direct contact with the different object, and another object may be sandwiched therebetween. Accordingly, when it is described that a layer B is formed over or above a layer A, it means either case where the layer B is formed in direct contact with the layer A, or where another layer (e.g., a layer C or a layer D) is formed in direct contact with the layer A, and then the layer B is formed in direct contact with the layer C or D. Similarly, when it is described that an object is formed below or under a different object, it means either case where the objects are in direct contact with each other or not in contact with each other.
In accordance with the present invention, a unit constituting one pixel can be changed in accordance with an image. As a result, characters can be displayed clearly and imaged can be displayed smoothly.
In the accompanying drawings:
Hereinafter, the embodiment modes will be described with reference to the drawings. It is to be noted that the present invention is not limited to the following description, and it is easily understood by those skilled in the art that modes and details herein disclosed can be modified in various ways without departing from the spirit and the scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the description of the embodiment modes to be given below.
Embodiment Mode 1R1 and R2 constitute a red sub-pixel, G1 and G2 constitute a green sub-pixel, and B1 and B2 constitute a blue sub-pixel. One pixel is constituted by the sub-pixels of each color. Here, in R1 and R2, areas contributing to light-emission or displaying is set at R1 and R2=1:2. In G1 and G2, areas contributing light-emission or displaying is set at G1 and G2=1:2. In B1 and B2, areas contributing light-emission or displaying is set at B1 and B2=1:2. Gray scales can be expressed by selecting either, both or none of R1 and R2 so as to emit light (or contributes to displaying). In other words, an area gray scale method can be used. In
The portion shown by reference numeral 101 is square. When this square is regarded as one pixel unit, a stripe array can be conducted in a whole display screen. Consequently, a clear display can be conducted. In each color, subpixels are aligned in columns and thus, it is easy to form an organic EL element.
Next, a case is shown, where a portion shown by reference numeral 102 constitutes one pixel. In the red sub-pixel, R2 and R1 are aligned in this order, and in the blue subpixel, B2 and B1 are aligned in this order. In the green sub-pixel, G2 and G1 are aligned in this order. In the case of one pixel 101, the order of G1 and G2 is employed to form one pixel, whereas in the case of one pixel 102, the order of G2 and G1 is employed. Consequently, the shape of a portion constituting one pixel is indented. Thus, blurred display can be made, and because of the blurred display, smooth display can be made. This leads to a structure similar to the case where subpixels are arranged in a delta array.
By adopting a more indented shape, a portion 103 may constitute one pixel. Thus, a smoother display can be made.
In this manner, it is possible to change one pixel unit as appropriate, in other words, determine which subpixels constitute one pixel, and thus, how to express display can be changed. For example, when characters are displayed mainly, one pixel having a square shape is formed to display clearly, whereas when images are displayed mainly, one pixel having an indented shape, i.e., a non-square shape is formed by shifting the subpixels up and down. As a result, a smooth display can be performed.
Display region (contributing to displaying) in the subpixel of each color is divided into plural regions. The ratio of the sizes of the regions is set at 1:2. As a result, an area gray scale method can be applied.
It is to be noted that
For example, as shown in
As to
In
Note that in
Further, in
Note that
Note that in
In addition, in
In Embodiment Mode 2, supply of a signal to each sub-pixel will be described. In
R2 at a second row is connected to a signal line 421 via a selecting transistor 401. R1 at a second row is connected to the signal line 421 via a selecting transistor 402. In other words, R1 and R2 are connected to the same signal line. R2 at a third row is also connected to the signal line 421 via a selecting transistor 403.
A gate signal line is connected to each selecting transistor. A gate signal line 411 is connected to the selecting transistor 401. A gate signal line 412 is connected to the selecting transistor 402. A gate signal line 413 is connected to the selecting transistor 403. By selecting each gate signal line sequentially, a signal can be supplied to each subpixel via the signal line 421.
Here, the gate signal lines are arranged in an upper side and a bottom side of the portion 101. Thus, the gate signal lines can be arrayed as a straight line.
Next,
R2 at a second row is connected to a signal line 521 via a selecting transistor 501. R1 at the second row is connected to a signal line 522 via a selecting transistor 502. In other words, R1 and R2 are connected to different signal lines. Similarly, R2 at a third row is also connected to the signal line 521 via a selecting transistor 503.
Two selecting transistors of the upper and lower subpixels are connected to one gate signal line of the gate signal lines. In other words, one gate signal line is shared. The selecting transistor 501 is connected to a gate signal line 511, the selecting transistor 502 is connected to a gate signal line 512, and the selecting transistor 503 is also connected to the gate signal line 512. When the gate signal line 512 is selected, the selecting transistors 502 and 503 are turned ON at the same time. However, since the signal lines are different, a signal can be supplied to the subpixels without problems.
Note that this embodiment mode has been described in detail, relating to Embodiment Mode 1. Thus, this embodiment mode can be freely combined with Embodiment Mode 1.
Embodiment Mode 3Next, an example of a pixel circuit is shown.
A selecting transistor 4904 which is a first transistor is controlled by using a gate signal line 4901 which is a first wire. When the selecting transistor 4904 is turned ON, a video signal is input into a storage capacitor 4905 from a source signal line 4902 which is a second wire. At this time, a driving transistor 4906 which is a second transistor is turned ON/OFF depending on the video signal, and a current flows to an opposite electrode 4908 through a light-emitting element 4907 from a power supply line 4903 which is a third wire.
Note that the selecting transistor 4904 of
Next,
Note that the selecting transistor 4904 of
The pixel configuration is not limited to those shown in
As the pixel configuration for correcting characteristic variation, broadly classified, there is a pixel configuration for correcting variation of a threshold voltage or a pixel configuration in which a current is input as a video signal.
The configuration of
It should be noted that there are various pixel configurations for correcting variation of a threshold voltage; thus, the present invention is not limited to the configurations of
Next,
Note that there are various pixel configurations in which a current is input to correct variation; thus, the present invention is not limited to the configurations of
In
Note that a particular light-emitting element is not necessarily arranged in a pixel. Further, light-emitting elements can employ various modes. For example, there are display media whose contrast changes by an electromagnetic action, such as an EL element (e.g., an organic EL element, an inorganic EL element, or an EL element containing an organic material and an inorganic material), an electron-emissive element, a liquid crystal element, electronic ink, an optical diffractive element, a discharging element, digital a micromirror device (DMD), a piezoelectric element, or a carbon nanotube. In addition, a display device provided with an EL panel using an EL element includes an EL display; a display device using an electron-emissive element includes a field emission display (FED), a surface-conduction electron-emitter display (SED) or the like; a display device provided with a liquid crystal panel using a liquid crystal element includes a liquid crystal display; a digital paper type of a display device using electronic ink includes electronic paper; a display device using an optical diffractive element includes a grating light valve (GLV) type display; and a plasma display panel (PDP) type of a display using a discharging element includes a plasma display; a display device using a digital micromirror device (DMD) includes a digital light processing (DLP) display device; a display device using a piezoelectric element includes a piezoelectric ceramic display; and a display device using a carbon nanotube includes an NED (Nano Emissive Display) and the like.
Note that a storage capacitor, like the storage capacitor 4905, functions to hold a gate potential of the driving transistor 4906. Although the storage capacitor 4905 is connected between a gate of the driving transistor 4906 and the power supply line 4903, the present invention is not limited to this configuration. The storage capacitor 4905 may be provided anywhere as long as it can hold the gate potential of the driving transistor 4906. In addition, the storage capacitor 4905 may be omitted in the case where a gate capacitance of the driving transistor 4906 and the like can be used for holding the gate potential of the driving transistor 4906.
Note that various types of elements, such as an electric switch or a mechanical switch may be used, as an example, for the switches shown in
Although
On the other hand, in order to set an input of a circuit on the output side of the switch to be in a floating state, a switch shown in
In
This embodiment mode has been described in detail, regarding to Embodiment Modes 1 and 2. Thus, this embodiment mode can be freely combined with Embodiment Mode 1 or 2.
Embodiment Mode 4In using a digital gray scale method, only two states of a display element can be expresses, which are a light-emission state (also, referred to as a light-transparent state) and a non-light-emission state (also, referred to as a non-light-transparent state). Thus, the digital gray scale method is often used in combination with another method to achieve multi-grayscale display. A driving method of a pixel for multi-grayscale will be described.
As a method for conducting multi-grayscale, there are a time gray scale method and an area gray scale method. The time gray scale method is a method for expressing a gray scale by changing the length of a light-emitting time during a certain period. The area gray scale method is a method for expressing a gray scale by changing the size of a light-emitting area.
Note that the time gray scale method and the area gray scale method may be combined with each other.
As for the area gray scale method, as shown in
Herein, the time gray scale method will be described in detail. In a digital time gray scale method, one-frame period is divided into a plurality of sub-frame periods. Then, a gray scale is expressed by changing the combination of a lighting sub-frame period during each frame period.
By repeating similar operations, a gray scale can be expressed. At this time, it is possible to express various gray scales with a power of 2 for the length of the lighting period in each sub-frame period, like 1:2:4:8: . . . .
Moreover, the area gray scale method is combined with a time gray scale method, thereby expressing more gray scales. For example, in a case that two bits are expressed by the area gray scale method and six bits are expresses by the time gray scale method, 8 bits can be expressed as a whole.
A pixel configuration in this case may have configurations of
Note that, in a signal-writing period, potentials of a power supply line 4903 and an opposite electrode 4908 are controlled so that no voltage is applied to a light-emitting element 4907. For example, the potential of the opposite electrode 4908 is made high, so that no voltage is applied to the light-emitting element 4907, or the opposite electrode 4908 may be made in a floating state without supplying an electric charge. Consequently, the light-emitting element 4907 can be prevented from emitting light in the signal-writing period.
Next,
In a certain row, after writing of a signal and a predetermined light-emitting period are completed, a signal writing operation starts in a subsequent sub-frame. By repeating such operations, lengths of the light-emitting periods can each be controlled.
In this manner, many sub-frames can be arranged in one frame even if a signal is written slowly. In addition, since the ratio of a light-emitting period during one-frame period (a so-called duty ratio) can be high, it is possible to reduce power consumption, suppress deterioration of the light-emitting element, or suppress a pseudo contouring.
A pixel configuration in this case may have the configurations of
Note that, although
Note that details of such a driving method are disclosed in, for example, Japanese Patent Laid-Open No. 2001-324958, United States Patent Application Publication No. 2001/0022565 or the like, which can be applied in combination with the present invention. And, the entire disclosure of these patents is incorporated herein by reference.
Then,
In a certain row, after writing of a signal and a predetermined light-emitting period are completed, a signal writing operation starts in a subsequent sub-frame. In a case where a light-emitting period is short, a signal erasing operation is performed to provide a non-light-emitting state. By repeating such operations, the lengths of the light-emitting periods can be controlled.
According to this, many sub-frames can be arranged in one frame even if a signal is written slowly. Further, in the case of performing the signal erasing operation, data for erasing is not required to be obtained in a same method as the method of obtaining a video signal; therefore, the driving frequency of a source driver can also be reduced.
A selecting transistor 4904 is controlled using the gate signal line 4901. When the selecting transistor 4904 is turned ON, a video signal is input into a storage capacitor 4905 from the source signal line 4902. Thus, a driving transistor 4906 is turned ON/OFF in accordance with the video signal and current flows to the opposite electrode 4908 through the light-emitting element 4907 from the power supply line 4903.
When a signal is needed to be erased, a second gate line 1101 is selected to turn the erasing transistor 11040N, so that the driving transistor 4906 is turned OFF. Then, no current flows from the power supply line 4903 to the opposite electrode 4908 through the light-emitting element 4907. Consequently, a non-light-emitting period can be provided and the length of a light-emitting period can be freely controlled.
Although the erasing transistor 1104 is used in
When a signal is needed to be erased, the second gate line 1201 is selected (a high potential here) to turn the erasing diode 12040N, so that a current flows from the second gate line 1201 to the gate of the driving transistor 4906. Consequently, the driving transistor 4906 is turned off. Then, no current flows from the power supply line 4903 to the opposite electrode 4908 through the light-emitting element 4907. Consequently, a non-light-emitting period can be provided and the length of a light-emitting period can be freely controlled.
When a signal is needed to be held, the second gate signal line 1201 is not selected (a low potential here). Then, the erasing diode 1204 is turned OFF and the gate potential of the driving transistor 4906 is thus held.
Note that the erasing diode 1204 may be any element as long as it has a rectifying property. The erasing diode 1204 may be a PN diode, a PIN diode, a Schottky diode, or a zener diode.
In addition, a diode-connected transistor (a gate and a drain thereof are connected) may be used as well.
Note that a driving method as shown in
Note that details of such a driving method are disclosed in, for example, Japanese Patent Laid-Open No. 2001-324958, United States Patent Application Publication No. 2001/0022565 or the like, which can be applied in combination with the present invention. And, the entire disclosure of these patents is incorporated herein by reference.
Note that the timing charts, pixel configurations, and driving methods that are shown in this embodiment mode are just examples, and the present invention is not limited to the examples. It is possible to apply various timing charts, pixel configurations, and driving methods.
Then, an operation area of a driving transistor in the case of a digital gray scale method will be described.
For example, in the case where a driving transistor is operated in the saturation region, there is such an advantage that the value of current flowing in a light-emitting element does not change even when the voltage-current characteristics thereof degrade. Therefore, image burn-in is unlikely to occur. However, when the current characteristics of the driving transistor vary, a current flowing therein also varies. In such a case, display unevenness may occur.
On the contrary, when the driving transistor is operated in the linear region, the value of current flowing therein is hardly affected even when the current characteristics of the driving transistor vary. Therefore, display unevenness is unlikely to occur. In addition, since the gate-source voltage of the driving transistor (an absolute value of the voltage) can be prevented from increasing too much, power consumption can be reduced. Further, when the gate-source voltage of the driving transistor (an absolute value of the voltage) is increased, the value of current flowing therein is hardly affected even when the current characteristics of the driving transistor vary. However, when the voltage-current characteristics of the light-emitting element degrade, the value of current flowing therein may change. Therefore, image burn-in becomes more likely to occur.
In this manner, when the driving transistor is operated in the saturation region, the value of current flowing therein does not change even when the characteristics of the light-emitting element change. Therefore, in such a case, the driving transistor can be regarded as operating as a current source. Thus, such a drive is to be called a constant current drive.
In addition, when the driving transistor is operated in the linear region, the value of current flowing therein does not change even when the current characteristics of the driving transistor change. Therefore, in such a case, the driving transistor can be regarded as operating as a switch. In addition, it can be regarded that a voltage of a power supply line is directly applied to the light-emitting element. Thus, such a drive is to be called a constant voltage drive.
This embodiment mode has been described in detail, regarding Embodiment Modes 1 to 3. Thus, this embodiment mode can be freely combined with Embodiment Modes 1 to 3.
Embodiment Mode 5Next, a layout of a pixel in the display device of the present invention will be described.
Selecting transistors 4904 and 4804, driving transistors 4906 and 4806 and electrodes of light-emitting elements 4907 and 4807 are disposed. Sources and drains of the selecting transistor 4904 and 4804 are connected to a source signal line 4902 and gates of the driving transistors 4906 and 4806 respectively. A gate of the selecting transistor 4904 is connected to a gate signal line 4901, and a gate of the selecting transistor 4804 is connected to a gate signal line 4801. Sources and drains of the driving transistors 4906 and 4806 are connected to the power supply line 4903 and electrodes of the light-emitting elements 4907 and 4807 respectively. The storage capacitors 4905 and 4805 are each connected between the gate of the driving transistor 4906 or 4806 and the power supply line 4903.
The source signal line 4902 and the power supply line 4903 are formed of a second wire, while the gate signal lines 4901 and 4801 are formed of a first wire.
In the case of a top-gate structure, a substrate, a semiconductor layer, a gate insulating film, a first wire, an interlayer insulating film, and a second wire are formed in this order to form a film. In the case of a bottom-gate structure, a substrate, a first wire, a gate insulating film, a semiconductor layer, an interlayer insulating film, and a second wire are formed in this order to form a film.
Next,
In
A gate electrode 704 and a conductive layer 754 for forming the other electrode of the capacitor portion 751 are formed over the first insulating layer 703. A wire 707 connected to the TFT 750 is connected to a first electrode 708 of a light-emitting element 712. The first electrode 708 is formed over a third insulating layer 706. A second insulating layer 705 may be formed between the first insulating layer 703 and the third insulating layer 706. The light-emitting element 712 is formed of the first electrode 708, an EL layer 709, and a second electrode 710. Further, a fourth insulating layer 711 is formed to cover a peripheral end portion of the first electrode 708 and a connecting portion between the first electrode 708 and the wire 707.
Next, the details of the aforementioned structure will be described. The substrate 700 may be, for example, a glass substrate such as barium borosilicate glass or alumino borosilicate glass, a quartz substrate, a ceramic substrate, or the like. Alternatively, it may be a metal substrate containing stainless steel or a semiconductor substrate having a surface covered with an insulating film. In addition, a substrate formed of a flexible synthetic resin such as plastic may be used. The surface of the substrate 700 may be planarized by polishing such as chemical mechanical polishing (CMP).
The base layer 701 may be an insulating film formed of silicon oxide, silicon nitride, silicon nitride oxide, or the like. The base layer 701 can function to prevent diffusion of alkaline metals such as Na or alkaline earth metals which are contained in the substrate 700 into the semiconductor layer 702, which would adversely affect the characteristics of the TFT 750. Although
In addition, the surface of the glass substrate may be directly treated by high-density plasma with the conditions of microwave excitation, an electron temperature of 2 eV or less, ion energy of 5 eV or less, and an electron density of about 1011 to 1013/cm3. Plasma can be generated by using a plasma processing apparatus with microwave excitation with the use of a radial slot antenna. At this time, by introducing a nitrogen gas such as nitrogen (N2), ammonia (NH3), or nitrous oxide (N2O), the surface of the glass substrate can be nitrided. The nitride layer formed on the surface of the glass substrate has silicon nitride as its main component; therefore, it can be used as a blocking layer against impurities which are diffused from the glass substrate side. A silicon oxide film or a silicon oxynitride film may be formed over the nitride layer by plasma CVD, so as to be used as the base layer 701 as well.
Additionally, when a similar treatment is performed to the surface of the base layer 701 by using silicon oxide, silicon oxynitride, or the like, the surface of the base layer 701 or a part of the base layer 701, which exist in a depth of 1 to 10 nm from the surface, can be nitrided. Such an extremely thin silicon nitride layer can function as a blocking layer without giving an influence of stress to the semiconductor layer formed thereover.
Each of the semiconductor layer 702 and the semiconductor layer 752 is preferably formed with a patterned crystalline semiconductor film. Note that “patterning” means a process of transforming a film into a particular shape by a photolithography technique (e.g., forming a contact hole in photosensitive acrylic or processing photosensitive acrylic into the shape of a spacer), forming a mask pattern by a photolithography technique and etching using the mask pattern, and the like. The crystalline semiconductor film can be obtained by crystallizing an amorphous semiconductor film. As a crystallization method, there are laser crystallization, thermal crystallization using RTA or an annealing furnace, thermal crystallization using metal elements which promote crystallization, and the like. The semiconductor layer 702 has a channel formation region and a pair of impurity regions doped with an impurity element which imparts one conductivity type. Note that an impurity region which is doped with the aforementioned impurity element at a low concentration may be provided between the channel formation region and the pair of the impurity regions. The semiconductor layer 752 can have such a structure that the whole layer is doped with an impurity element which imparts one conductivity type or an impurity element which imparts the opposite conductivity thereto.
The first insulating layer 703 can be formed by stacking silicon oxide, silicon nitride, silicon nitride oxide, or/and the like, as a single layer or a multilayer. In this case, similarly to the aforementioned treatment, the surface of the insulating film may be oxidized or nitrided so as to be densified by a high-density plasma treatment with the conditions of microwave excitation, an electron temperature of 2 eV or less, ion energy of 5 eV or less, and an electron density of about 1011 to 1013/cm3. This treatment may precede the film deposition of the first insulating layer 703. That is, a plasma treatment may be performed to the surface of the semiconductor layer 702. At this time, a favorable interface with a gate insulating layer to be stacked thereon can be formed by performing the plasma treatment with the conditions of a substrate temperature of 300 to 450° C. and an oxygen atmosphere (such as O2 or N2O) or a nitrogen atmosphere (such as N2 or NH3).
Each of the gate electrode 704 and the conductive layer 754 may be formed to have a single-layer structure or a stacked-layer structure, with an element selected from Ta, W, Ti, Mo, Al, Cu, Cr, or Nd, or an alloy or compound containing such elements.
The TFT 750 is formed from the semiconductor layer 702, the gate electrode 704, and the first insulating layer 703 between the semiconductor layer 702 and the gate electrode 704.
The capacitor portion 751 includes the first insulating layer 703 functioning as a dielectric and a pair of electrodes, namely the semiconductor layer 752 and the conductive layer 754 facing each other by sandwiching the first insulating layer 703. Although
The second insulating layer 705 is preferably a barrier insulating film having a blocking property against ionic impurities, such as a silicon nitride film. The second insulating film 705 is formed from silicon nitride or silicon oxynitride. The second insulating layer 705 has a function of a protective film for preventing contamination of the semiconductor layer 702. After depositing the second insulating film 705, it may be hydrogenated by a high-density plasma treatment with microwave excited by introducing a hydrogen gas similarly to the aforementioned treatment. Alternatively, the second insulating film 705 may be nitrided and hydrogenated by introducing an ammonia gas. Further, the second insulating film 705 may be oxynitrided and hydrogenated by introducing an oxygen gas, an N2O gas, or the like, and a hydrogen gas. By performing a nitriding, oxidizing, or oxynitriding treatment with the aforementioned method, the surface of the second insulating layer 705 can be densified. Accordingly, its function as the protective film can be reinforced. The hydrogen introduced to the second insulating layer 705 made of silicon nitride can be discharged by performing a thermal treatment at 400 to 450° C., thereby hydrogenating the semiconductor layer 702.
The third insulating layer 706 can be formed with an inorganic insulating film or an organic insulating film. The inorganic insulating film includes a silicon oxide film formed by CVD, an SOG (Spin On Glass) film (silicon oxide film formed by coating), and the like. The organic insulating film includes a film made of polyimide, polyamide, BCB (benzocyclobutene), acrylic, a positive photosensitive organic rein, a negative photosensitive organic resin, or the like. In addition, the third insulating layer 706 may be formed with a material having a skeletal structure of silicon (Si) and oxygen (O). As a substituent of the material, an organic group containing at least hydrogen (e.g., an alkyl group or aromatic hydrocarbon) is used. As a substituent, a fluoro group may be used as the substituent. Further, both an organic group containing hydrogen and a fluoro group may be used as a substituent.
The wire 707 may be formed to have a single-layer structure or a stacked-layer structure of an element selected from Al, Ni, C, W, Mo, Ti, Pt, Cu, Ta, Au, or Mn, or an alloy containing such elements.
One or both of the first electrode 708 or the second electrode 710 may be formed as a transparent electrode. As a transparent electrode, there is indium oxide containing tungsten trioxide (IWO), indium oxide containing tungsten oxide (IWZO), indium oxide containing titanium oxide (ITiO), indium tin oxide containing titanium oxide (ITTiO), indium tin oxide containing molybdenum (ITMO), or the like. Needless to say, indium tin oxide (ITO), indium zinc oxide (IZO), indium tin oxide doped with silicon oxide (ITSO), or the like may be used as well.
At least one or both of the first electrode 708 and the second electrode 710 may be formed from a material which does not have a light-transmitting property. For example, it may be formed with alkaline metals such as Li or Cs, alkaline earth metals such as Mg, Ca, or Sr, an alloy containing such metals (e.g., MgAg, AlLi, or MgIn), a compound containing such metals (e.g., CaF2 or Ca3N2), or rare earth metals such as Yb or Er.
The fourth insulating layer 711 may be formed with a similar material to the third insulating layer 706.
The light-emitting element 712 is formed of the first electrode 708, the second electrode 710, and the EL layer 709 sandwiched therebetween. One or both ofr the first electrode 708 and the second electrode 710 serves as an anode, while the other thereof serves as a cathode. The light-emitting element 712 emits light with a current flowing through the anode to the cathode when a voltage higher than a threshold voltage is forwardly applied between the anode and the cathode.
The EL layer 709 is formed as a single layer or a multilayer. When the EL layer 709 is formed with a plurality of layers, these layers can be classified into a hole injecting layer, a hole transporting layer, a light-emitting layer, an electron transporting layer, an electron injecting layer, and the like in view of the carrier transporting property. Note that the boundary between each layer is not necessarily clear, and there may be a case where the boundary is unclear since a material for forming each layer is mixed with each other. Each layer may be formed using an organic material or an inorganic material. As the organic material, any of a high molecular compound, a middle molecular compound, and a low molecular compound may be used.
The EL layer 709 is preferably formed with a plurality of layers having different functions such as a hole injecting-transporting layer, a light-emitting layer, and an electron injecting-transporting layer. The hole injecting-transporting layer is preferably formed with a composite material containing an organic compound material with a hole transporting property and an inorganic compound material which exhibits an electron accepting property to the organic compound material. By employing such a structure, many hole carriers are generated in the organic compound which inherently has few carriers, thereby excellent hole injecting and transporting properties can be obtained. According to such an effect, driving voltage can be suppressed than that in a conventional one. Further, since the hole injecting-transporting layer can be formed to be thick without causing an increase of the driving voltage, short circuit of the light-emitting element resulting from dusts or the like can be suppressed.
As an organic compound material with a hole transporting property, there is, for example, copper phthalocyanine (abbreviated as CuPc); 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviated as MTDATA); 1,3,5-tris[N,N-di(m-tolyl)amino]benzene (abbreviated as m-MTDAB); N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (abbreviated as TPD); 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviated as NPB); 4,4′-bis{N[4-di(m-tolyl)amino]phenyl-N-phenylamino}biphenyl (abbreviated as DNTPD); or the like. However, the present invention is not limited to these.
As an inorganic compound material which exhibits an electron accepting property, there is titanium oxide, zirconium oxide, vanadium oxide, molybdenum oxide, tungsten oxide, rhenium oxide, ruthenium oxide, zinc oxide, or the like. In particular, vanadium oxide, molybdenum oxide, tungsten oxide, and rhenium oxide are preferable since they can be deposited in vacuum, and are easy to be handled.
The electron injecting-transporting layer is formed using an organic compound material with an electron transporting property. Specifically, there is tris(8-quinolinolato)aluminum (abbreviated as Alq3); tris(4-methyl-8-quinolinolato)aluminum (abbreviated as Almq3); bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviated as BAlq); bathocuproin (abbreviated as BCP); 2-(4-biphenylyl)-5-(4-tert-buthylphenyl)-1,3,4-oxadiazole (abbreviated as PBD); 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviated as TAZ); or the like. However, the present invention is not limited to these.
The EL layer 709 can be formed with, for example, 9,10-di(2-naphthyl)anthracene (abbreviated as DNA); 9,10-di(2-naphthyl)-2-tert-butylanthracene (abbreviated as t-BuDNA); 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviated as DPVBi); coumarin 30; coumarin 6; coumarin 545; coumarin 545T; rubrene; 2,5,8,11-tetra(tert-butyl)perylene (abbreviated as TBP); 9,10-diphenylanthracene (abbreviated as DPA); 5,12-diphenyltetracene (abbreviated as DPT); 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (abbreviated as DCM1); 4-(dicyanomethylene)-2-methyl-6-[2-(julolidine-9-yl)ethenyl]-4H-pyran (abbreviated as DCM2); or the like. Alternatively, the following compounds capable of generating phosphorescence can be used: bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C2′}iridium(picolinate) (abbreviated as Ir(CF3 ppy)2(pic)); tris(2-phenylpyridinato-N,C2′)iridium (abbreviated as Ir(ppy)3); bis(2-phenylpyridinato-N,C2′)iridium(acetylacetonate) (abbreviated as Ir(ppy)2(acac)); bis[2-(2′-thienyl)pyridinato-N,C3′]iridium(acetylacetonate) (abbreviated as Ir(thp)2(acac)); bis(2-phenylquinolinato-N,C2′)iridium(acetylacetonate) (abbreviated as Ir(pq)2(acac)); or the like.
Further, the EL layer 709 may be formed using a singlet excitation light-emitting material as well as a triplet excitation light-emitting material including a metal complex. For example, among light-emitting pixels for red emission, green emission, and blue emission, the light-emitting pixel for red emission which has a relatively short luminance half decay period is formed using a triplet excitation light-emitting material while the other light-emitting pixels are formed using singlet excitation light-emitting materials. The triplet excitation light-emitting material has high luminous efficiency, which is advantageous in that lower power consumption is required for obtaining the same luminance. That is, when the triplet excitation light-emitting material is applied to the pixel for red emission, the amount of current supplied to the light-emitting element can be reduced, resulting in the improved reliability. In order to suppress the power consumption, the light-emitting pixels for red emission and green emission may be formed using triplet excitation light-emitting materials, while the light-emitting element for blue emission may be formed using a singlet excitation light-emitting material. When forming the light-emitting element for green emission which is highly visible to human eyes using the triplet excitation light-emitting material, further lower power consumption can be achieved.
As a structure of the EL layer 709, a light-emitting layer having a different emission spectrum may be formed in each pixel to perform color display. Typically, light-emitting layers corresponding to the respective colors of R (red), G (green), and B (blue) are formed. Also in this case, color purity can be improved as well as a mirror-like surface (glare) of the pixel portion can be prevented by adopting a structure where a filter for transmitting light with the aforementioned emission spectrum is provided on the emission side of the pixel. By providing the filter, a circularly polarizing plate and the like which have conventionally been required can be omitted, and thus, light emitted from the light-emitting layer can be extracted without loss of the light. Further, changes in color tone, which are recognized when the pixel portion (display screen) is seen obliquely, can be reduced.
As the transistor, a transistor using amorphous silicon may be used, as well as a transistor using polysilicon as a semiconductor layer.
Next, a case of using an amorphous silicon (a-Si:H) film for a semiconductor layer of a transistor will be described.
The substrate may be any of a glass substrate, a quartz substrate, a ceramic substrate, and the like. In addition, the base film 2802 may be formed with aluminum nitride (AlN), silicon oxide (SiO2), and/or oxynitride silicon (SiOxNy), as a single layer or a multilayer thereof.
In addition, a wire 2805 and a wire 2806 are formed over the base film 2802, and an end portion of the pixel electrode 2803 is covered with the wire 2805. Over the wire 2805 and the wire 2806, an n-type semiconductor layer 2807 and an n-type semiconductor layer 2808 each having n-type conductivity are formed. A semiconductor layer 2809 is formed between the wire 2806 and the wire 2805, and over the base film 2802. A part of the semiconductor layer 2809 is extended over the n-type semiconductor layer 2807 and the n-type semiconductor layer 2808. Note that the semiconductor layer 2809 is formed with a non-crystalline semiconductor film such as amorphous silicon (a-Si:H) or a microcrystalline semiconductor (μ-Si:H). A gate insulating film 2810 is formed over the semiconductor layer 2809. In addition, an insulating film 2811 is fowled with the same material and in the same layer as the gate insulating film 2810, over the first electrode 2804. Note that the gate insulating film 2810 is formed of a silicon oxide film, a silicon nitride film, or the like.
A gate electrode 2812 is formed over the gate insulating film 2810. In addition, a second electrode 2813 is formed with the same material and in the same layer as the gate electrode 2812, over the first electrode 2804 with the insulating film 2811 therebetween. Thus, a capacitor element 2819 in which where the insulating film 2811 is sandwiched between the first electrode 2804 and the second electrode 2813, is formed. An interlayer insulating film 2814 is formed to cover an end portion of the pixel electrode 2803, a driving transistor 2818, and the capacitor element 2819.
A layer 2815 containing an organic compound and an opposite electrode 2816 are formed over the interlayer insulating film 2814 and the pixel electrode 2803 positioned in an opening portion of the interlayer insulating film 2814. Thus, a light-emitting element 2817 is formed in a region where the layer 2815 containing an organic compound is sandwiched between the pixel electrode 2803 and the opposite electrode 2816.
The first electrode 2804 shown in
A base film 2902 is formed over a substrate 2901. Further, a gate electrode 2903 is formed over the base film 2902. In addition, a first electrode 2904 is formed in the same layer and with the same material as the gate electrode 2903. As a material of the gate electrode 2903, polysilicon doped with phosphorus can be used. Not only polycrystalline silicon, but also a silicide which is a compound of a metal and silicon may be used as well.
In addition, a gate insulating film 2905 is formed to cover the gate electrode 2903 and the first electrode 2904. The gate insulating film 2905 is formed using a silicon oxide film, a silicon nitride film, or the like.
A semiconductor layer 2906 is formed over the gate insulating film 2905. In addition, a semiconductor layer 2907 is formed with the same material and in the same layer as the semiconductor layer 2906.
The substrate may be any of a glass substrate, a quartz substrate, a ceramic substrate, and the like. In addition, the base film 2902 may be formed with aluminum nitride (AlN), silicon oxide (SiO2), and/or oxynitride silicon (SiOxNy), as a single layer or a multilayer thereof.
N-type semiconductor layers 2908 and 2909 each having n-type conductivity are formed over the semiconductor layer 2906, while an n-type semiconductor layer 2910 is formed over the semiconductor layer 2907.
Wires 2911 and 2912 are formed respectively over the n-type semiconductor layers 2908 and 2909, and a conductive layer 2913 is formed with the same material and in the same layer as the wires 2911 and 2912, over the n-type semiconductor layer 2910.
A second electrode is formed of the semiconductor layer 2907, the n-type semiconductor layer 2910, and the conductive layer 2913. Note that a capacitor element 2920 is formed to have a structure in which the gate insulating film 2905 is sandwiched between the second electrode and the first electrode 2904.
In addition, a part of the wire 2911 is extended, and a pixel electrode 2914 is formed in contact with the top surface of the extended portion of the wire 2911.
An insulator 2915 is formed to cover an end portion of the pixel electrode 2914, a driving transistor 2919, and the capacitor element 2920.
A layer 2916 containing an organic compound and an opposite electrode 2917 are formed over the pixel electrode 2914 and the insulator 2915, and a light-emitting element 2918 is formed in a region where the layer 2916 containing an organic compound is sandwiched between the pixel electrode 2914 and the opposite electrode 2917.
The semiconductor layer 2907 and the n-type semiconductor 2910 which partially function as a second electrode of the capacitor element are not necessarily provided. That is, the conductive layer 2913 may be used as the second electrode so as to provide a capacitor element having such a structure that the gate insulating film 2905 is sandwiched between the first electrode 2904 and the conductive layer 2913.
Note that by forming the pixel electrode 2914 before forming the wire 2911 shown in
Although
A transistor with a channel-protective structure shown in
Similarly, a transistor with a channel-protective structure shown in
By using an amorphous semiconductor film for a semiconductor layer (e.g., a channel formation region, a source region, or a drain region) of a transistor which constitutes a pixel of the present invention, manufacturing cost can be reduced. For example, an amorphous semiconductor film can be used in the case of using the pixel structure shown in
Note that the structures of transistors or capacitor elements to which the pixel structure of the present invention can be applied are not limited to the structures described above, and various structures of transistors or capacitor elements can be employed.
Note also that this embodiment mode can be freely combined with Embodiment Modes 1 to 4.
Embodiment Mode 6Configurations of a pixel and a driver circuit of a display device of the present invention are described with reference to
An input terminal 25 for inputting signals from an external circuit to the scan line driver circuit 22, an input terminal 26 for inputting signals from an external circuit to the data line driver circuit 23, and an input terminal 29 for inputting signal to the monitor circuit 24 are provided in the periphery portion of the substrate 20.
The display region 30 constituting a subpixel includes a transistor 34 connected to the data line 31 and a transistor 35 which is connected in series between the power supply line 32 and the light-emitting element 37. A gate of the transistor 34 is connected to the scan line 33. When the transistor 34 is selected by a scan signal, it inputs a signal of the data line 31 to the display region 30 constituting a subpixel. The input signal is applied to a gate of the transistor 35 and charges a storage capacitor portion 36. In accordance with this signal, the power supply line 32 and the light-emitting element 37 become conductive, thereby the light-emitting element 37 emits light.
A power is required to be supplied from an external circuit so that the light-emitting element 37 provided in the display region 30 constituting a subpixel emits light. The power supply line 32 provided in the pixel portion 21 is connected to the external circuit at an input terminal 27. As resistance loss occurs in the power supply line 32 depending on the length of a wire to be led, it is preferable to provide input terminals 27 at a plurality of positions in the peripheral portion of the substrate 20. The input terminals 27 are provided at opposite end portions of the substrate 20 so that luminance variations in the area of the pixel portion 21 don't become notable. That is, it is prevented that one side of the screen becomes bright while the other side thereof becomes dark. Further, in the light-emitting element 37 having a pair of electrodes, an electrode on the opposite side to the electrode connected to the power supply line 32 is formed as a common electrode shared by the plurality of display regions 30 constituting subpixels. In order to reduce the resistance loss of this electrode, a plurality of terminals 28 are provided.
Next, an example of the display region 30 constituting a subpixel is described in details with reference to
The scan line 33 and the data line 31 are formed in different layers and cross each other with an insulating layer 57 interposed therebetween. The scan line 33 functions as a gate electrode of a transistor at a portion where it crosses a semiconductor layer 40 with a gate insulating layer 55 interposed therebetween. In this case, by providing the transistor 34 in accordance with the arrangement of the semiconductor layer 40 and making the scan line 33 diverge to cross the semiconductor layer 40 at plural portions, a so-called multi-gate transistor in which a plurality of channel formation regions are arranged in series between a pair of source and a drain can be provided.
It is preferable that the resistance of the power supply line 32 connected to the transistor 35 be low, therefore, it is preferable to use Al, Cu, or the like having particularly low resistance. In the case of forming a Cu wire, the Cu wire can be formed in an insulating layer in combination with a barrier layer.
A base insulating layer for semiconductor layers 40 and 41 is formed over the insulating layer 51. The structure of the base insulating layer is not limited; however, it is preferably formed from a silicon nitride layer 53 and a silicon oxide layer 54. Besides, as a structure of the insulating layer, an insulating layer 56 is formed of silicon nitride or the like as a protective film over the semiconductor layers 40 and 41 in addition to the gate insulating layer 55.
The power supply line 32 and the transistor 35 are connected by a wire 45 through a contact hole which passes through the aforementioned insulating layer. Moreover, a gate electrode 42 is connected to the transistor 34 by a wire 44. The gate electrodes of the transistors 34 and 35 may be formed by stacking a plurality of layers. For example, a first conductive layer and a second conductive layer may be combined in consideration of adhesion with a gate insulating layer and resistance. In addition, the shapes of the overlaying and underlying layers may be changed (for example, a hat-like shape having a visor) so that source and drain regions and a low concentration impurity (LDD) region may be formed in a semiconductor layer in a self-aligned manner.
An electrode 43 of a storage capacitor portion 36 provided by extending the gate electrode 42 is preferably formed to have low resistance by utilizing the combination of the first conductive layer and the second conductive layer, i.e., by providing a thin film portion of the first conductive layer and adding an impurity element imparting one conductivity type to the semiconductor layer as a lower layer. That is, the storage capacitor portion 36 is formed from the electrode 43 of the storage capacitor portion 36 provided by extending the gate electrode 42, a semiconductor layer 60 which is obtained by extending the semiconductor layer 41 of the transistor 35, and a gate insulating layer 55 sandwiched by them. The storage capacitor 36 can function efficiently by adding an impurity element imparting one conductivity type to the semiconductor layer 60 so as to have low resistance.
A pixel electrode of a light-emitting element may have a direct contact with the semiconductor layer 41 of the transistor 35, however, they can be connected through a wire 46 as shown in
A display panel described in this embodiment mode has a power supply line formed of a low resistant material such as Cu, therefore, it is efficient when a screen size is large in particular. For example, when a screen size is about 13-inch, a diagonal length of the screen is 340 mm while it is 1500 mm or longer in a screen of about 60-inch. In such a case, wire resistance cannot be ignored, therefore, a wire is preferably formed of a low resistant material such as Cu. Moreover, a data line and a scan line may be similarly formed when wire delay is considered.
It is to be noted that this embodiment mode can be freely combined with Embodiment Modes 1 to 5.
Embodiment Mode 7In Embodiment Mode 7, an evaporation apparatus used for manufacturing a display panel is described with reference to the drawings.
The display panel is manufactured by forming an EL layer over an element substrate in which a pixel circuit and/or a driver circuit is/are formed using transistors. The EL layer is formed so as to contain a material which exhibits electroluminescence at least in a portion thereof. The EL layer may be formed of a plurality of layers with different functions. In that case, the EL layer is, in some cases, formed by using layers with different functions, which are also called a hole injecting-transporting layer, a light-emitting layer, an electron injecting-transporting layer, and the like.
A substrate introduced from the load chamber 62 to the transfer chamber 60 is transferred to a predetermined treatment chamber by an arm type transfer means 66 capable of rotating. The substrate is transferred by the transfer means 66 from a certain treatment chamber to another treatment chamber. The transfer chambers 60 and 61 are connected by a film forming treatment chamber 70, where delivery of the substrate between the transfer unit 66 and a transfer means 67 is conducted.
Each treatment chamber connected to the transfer chambers 60 and 61 is kept under a reduced pressure. Therefore, in this evaporation apparatus, film forming treatment of an EL element is conducted continuously without exposing the substrate to air. A display panel having an EL layer to which film forming treatment has been applied may deteriorate by moisture or the like. Therefore, a sealing treatment chamber 65 is connected to the transfer chamber 61 for performing a sealing treatment to keep the quality before contacting to the air. The sealing chamber 65 is kept at an atmospheric pressure or under a reduced pressure close to the atmospheric pressure, therefore, an intermediate treatment chamber 64 is provided between the transfer chamber 61 and the sealing treatment chamber 65. The intermediate treatment chamber 64 is provided for deliver of the substrate and buffering the pressure between the chambers.
The load chamber 62, the unload chamber 63, the transfer chambers, and the film forming treatment chambers are provided with exhausting means for keeping the reduced pressure. As such exhausting means, various vacuum pumps such as a dry pump, a turbo molecular pump, and a diffusion pump can be used.
In the evaporation apparatus shown in
The thermal treatment chamber 68 performs a degasification treatment by heating a substrate over which a lower electrode, an insulating partition, or the like is formed. The plasma treatment chamber 72 performs a plasma treatment with rare gas or oxygen to the surface of the lower electrode. This plasma treatment is performed for cleaning the surface, stabilizing the surface condition, and stabilizing the surface physically or chemically (for example, a work function or the like).
The film forming treatment chamber 69 is a treatment chamber for forming an electrode buffer layer which contacts one electrode of an EL element. The electrode buffer layer has a carrier injecting property (a hole injecting property or an electron injecting property) and suppresses a
short-circuit of an EL element and a dark spot defect. The electrode buffer layer is typically formed of an organic and inorganic mixture material so as to have a resistance of 5×104 to 1×106 Ωcm with a thickness of 30 to 300 nm. The film forming treatment chamber 71 is a treatment chamber for forming a hole transporting layer.
A light-emitting layer of an EL element has a different structure in the case of a mono-color light emission and the case of white light emission. In the evaporation apparatus, film forming treatment chambers are preferably arranged in accordance with the light emission color. For example, in the case of forming three kinds of EL elements with different light emission colors in a display panel, a light-emitting layer in accordance with each light emission color is required to be formed. In this case, the film forming treatment chamber 70 can be used for forming a first light-emitting layer, the film forming treatment chamber 73 can be used for forming a second light-emitting layer, and the film forming treatment chamber 74 can be used for forming a third light-emitting layer. By changing the film forming treatment chamber for each light-emitting layer, mutual contamination of different light emission materials can be prevented, thereby improving the throughput of the film forming treatment.
Further, each of the film forming treatment chambers 70, 73, and 74 may be used to evaporate sequentially three kinds of EL materials with different light emission colors. In this case, evaporation is performed by moving a shadow mask in accordance with a region to be deposited.
In the case of forming an EL element which exhibits white light emission, light-emitting layers with different light emission colors are stacked vertically. In that case also, an element substrate sequentially can move from one film forming treatment chamber to another so as form each light-emitting layer. Alternatively, different light-emitting layers can be continuously formed in the same film forming treatment chamber as well.
In the film forming treatment chamber 76, an electrode is formed over the EL layer. The electrode can be formed by an electron beam evaporation method or a sputtering method, but a resistant thermal evaporation method is preferably used.
The element substrate in which up to the electrode has been formed is transferred into the sealing treatment chamber 65 through the intermediate treatment chamber 64. Inert gas such as helium, argon, neon, or nitrogen fills the sealing treatment chamber 65. In such an atmosphere, a sealing substrate is attached to a side of the element substrate where the EL layer is formed. In the sealed condition, inert gas or a resin material may fill a space between the element substrate and the sealing substrate. In the sealing treatment chamber 65, a dispenser for drawing a sealing material, a mechanical component such as an arm or a fixing stage for fixing the sealing substrate so as to oppose the element substrate, a dispenser or a spin coater for filling the resin material, and the like are provided.
In the treatment chamber, one or a plurality of evaporation sources is provided. In the case of forming a plurality of layers with different compositions or co-evaporating different materials, a plurality of evaporation sources are preferably provided. In
A substrate stage 86 and a substrate chuck 87 as a pair fix the substrate 89. The substrate stage 86 may be constituted with a heater incorporated therein so that the substrate 89 can be heated. The substrate 89 is transferred while being fixed on the substrate stage 86 by the substrate chuck 87. A shadow mask 90 provided with an opening portion can be used in accordance with a pattern to be deposited as required. In that case, the shadow mask 90 is provided between the substrate 89 and the evaporation sources 81a to 81c. The shadow mask 90 is fixed on the substrate or with a certain distance from the substrate by a mask chuck 88. When the shadow mask 90 requires alignment, a camera is provided in the treatment chamber and a positioning means is provided for the mask chuck 88 for slightly moving in X-Y-θ direction. Thus, positioning alignment is done.
An evaporation material supplying means for continuously supplying an evaporation material to the evaporation source is attached to the evaporation source 81. The evaporation material supplying means includes evaporation material supplying sources 85a, 85b, and 85c which are provided apart from the evaporation source 81, and a material supplying tube 84 which connects them. The material supplying sources 85a, 85b, and 85c are typically provided corresponding to the evaporation source 81. In
The evaporation material can be supplying by an air current transfer method, an aerosol method, or the like. By the air current transfer method, impalpable powder of the evaporation material is transferred on the air current such as inert gas to the evaporation source 81. The aerosol method is a kind of an evaporation method, in which a material liquid in which an evaporation material is dissolved or dispersed in a solvent is transferred and formed into aerosol by a sprayer so that the solvent in the aerosol is vaporized. In either case, a heating means is provided for the evaporation source 81, which vaporizes the transferred evaporation material to be formed as a film over the substrate 89. In the case of
In the case of applying the air current transfer method or the aerosol method, it is preferable that the films be formed in the film forming treatment chamber at an atmospheric pressure or lower, and preferably at a reduced pressure of 133 to 13300 Pa. The film forming treatment chamber is filled with inert gas such as helium, argon, neon, krypton, xenon, or nitrogen. Alternatively, the pressure can be controlled while supplying the gas (exhausting at the same time). Moreover, the film forming treatment chamber for forming an oxide film may have an oxygen atmosphere by introducing a gas such as oxygen or nitrous oxide. Further, a gas such as hydrogen may be introduced to the film forming treatment chamber for evaporating an organic material so as to have a reduction atmosphere.
As another method for supplying an evaporation material, a screw may be provided in the material supplying tube 184 so as to continuously push the evaporation material toward the evaporation source.
With the evaporation apparatus of this embodiment mode, a film can be continuously formed uniformly even for a large display panel. Moreover, an evaporation material is not required to be supplied every time the evaporation material is used up in the evaporation source, therefore, the throughput can be improved.
It is to be noted that this embodiment mode can be freely combined with Embodiment Modes 1 to 6.
Embodiment Mode 8In Embodiment Mode 8, hardware for controlling the display devices which have been described in Embodiment Modes 1 to 5, will be described.
In other words, transistors in the present invention may be any type of transistors and may be formed over any type of substrates. Therefore, all of the circuits may be formed over a glass substrate, a plastic substrate, a single crystalline substrate, an SOI substrate, or other substrates. Alternatively, such a structure may be employed that a part of the driver circuits is formed over a substrate, while another part of the driver circuits is formed over another substrate. That is, all circuits are not required to be formed over the same substrate. For example, in
A signal 2703 is input to the peripheral circuit substrate 2702, and a controller 2708 controls the signal so as to be stored in a memory 2709, a memory 2710, or the like. In a case where the signal 2703 is an analog signal, it is often subjected to analog-digital conversion and then, is stored in the memory 2709, the memory 2710, or the like. The controller 2708 outputs a signal to the substrate 2701 by using the signal stored in the memory 2709, the memory 2710, or the like.
In order to realize the driving methods described in Embodiment Modes 1 to 5, the controller 2708 controls various types of pulse signals, and outputs them to the substrate 2701.
Note that this embodiment mode can be freely combined with any of Embodiment Modes 1 to 6.
Embodiment Mode 9An exemplary structure of a mobile phone which has the display device of the present invention, will be described with reference to
A display panel 5410 is incorporated in a housing 5400 in an attachable/detachable manner. The shape and size of the housing 5400 can be appropriately changed in accordance with the size of the display panel 5410. The housing 5400 to which the display panel 5410 is fixed is set into a printed board 5401 so as to assemble a module.
The display panel 5410 is connected to the printed board 5401 through an FPC 5411. On the printed board 5401, a speaker 5402, a microphone 5403, a transmission-reception circuit 5404, and a signal processing circuit 5405 including a CPU, a controller or the like are formed. Such a module is combined with an input means 5406 and a battery 5407, and then incorporated into a housing 5409. A pixel portion of the display panel 5410 is disposed so that it can be seen from an open window formed in the housing 5412.
The display panel 5410 may be constructed in such a manner that a part of peripheral driver circuits (e.g., a driver circuit having a low operating frequency among a plurality of driver circuits) is formed over the same substrate as a pixel portion by using TFTs, while another part of the peripheral driver circuits (a driver circuit having a high operating frequency among the plurality of driver circuits) is formed in an IC chip. Then, the IC chip may be mounted on the display panel 5410 by a COG (Chip On Glass) method. Alternatively, the IC chip may be connected to a glass substrate by TAB (Tape Automated Bonding) or by use of a printed board.
In addition, by impedance-converting signals set to scan lines or signal lines with a buffer, time required for writing signals into pixels in each row can be shortened. Thus, a high-resolution display device can be provided.
In addition, in order to further reduce power consumption, such a structure may be employed that a pixel portion is formed over a substrate with TFTs, and all the peripheral circuits are formed in IC chips to be mounted on the display panel by COG (Chip On Glass).
With such a display device of the present invention, fine and high-contrast images can be provided.
Note that the configuration shown in this embodiment mode is just an illustrative example of a mobile phone, and therefore, the display device of the present invention can be applied to mobile phones with various structures, without limiting to the mobile phone with the aforementioned structure.
Note also that this embodiment mode can be freely combined with any of Embodiment Modes 1 to 8.
Embodiment Mode 10The control circuit 5706 corresponds to the controller 2708, the memory 2709, the memory 2710, or the like in Embodiment Mode 8. The control circuit 5706 mainly controls the arranging order of subframes or the like. The display panel 5701 may be constructed in such a manner that a part of peripheral driver circuits (e.g., a driver circuit having a low operating frequency among a plurality of driver circuits) is formed over the same substrate with a pixel portion by using Tiers, while another part of the peripheral driver circuits (a driver circuit having a high operating frequency among the plurality of driver circuits) is formed in an IC chip, so that the IC chip is mounted on the display panel 5701 by COG (Chip On Glass) bonding or the like. Alternatively, the IC chip may be mounted on the display panel 5701 by TAB (Tape Automated Bonding) or by use of a printed board.
In addition, by impedance-converting signals set to scan lines or signal lines with a buffer, time required for writing signals into pixels in each row can be shortened. Thus, a high-resolution display device can be provided.
In addition, in order to further reduce power consumption, such a structure may be employed that a pixel portion is formed over a glass substrate with TFTs, and all signal line driver circuits are formed in IC chips to be mounted onto the display panel by COG (Chip On Glass) bonding.
Note that such a structure is also desirable that a pixel portion is formed over a substrate with TFTs, and all of the peripheral driver circuits are formed in IC chips to be mounted onto the display panel by COG (Chip On Glass) bonding.
With such an EL module, an EL television receiver can be completed.
Among the signals received at the tuner 5801, audio signals are transmitted to an audio signal amplifier circuit 5804, and an output thereof is supplied to a speaker 5806 through an audio signal processing circuit 5805. A control circuit 5807 receives control data on a receiving station (reception frequency) or sound volume from an input portion 5808 and transmits signals to the tuner 5801 as well as the audio signal processing circuit 5805.
By incorporating the EL module in a housing, a TV receiver can be completed. A display portion of the TV receiver is formed with such an EL module. In addition, a speaker, a video input terminal, and the like are provided as appropriate.
It is needless to mention that the present invention is not limited to the TV receiver, and can be applied to various devices as a display medium having a large area such as a monitor of a personal computer, an information display board at the train station, airport, or the like, or an advertisement display board on the street.
In this manner, by using the display device of the present invention, fine and high-contrast images can be provided.
Note also that this embodiment mode can be freely combined with Embodiment Modes 1 to 9.
Embodiment Mode 11Embodiment Mode 11 will explain a method for manufacturing a semiconductor device using a plasma treatment as a method for manufacturing a semiconductor device including a transistor.
A semiconductor device shown in
Note that, in this embodiment mode, a semiconductor device shown in
In this embodiment mode, a method for manufacturing a semiconductor device by performing a plasma treatment to the semiconductor film 4603a, the semiconductor film 4603b, or the gate insulating film 4604 in the above
Initially, the end portions of an island-shaped semiconductor film provided over a substrate are formed to be almost perpendicular.
First, the island-shaped semiconductor films 4603a and 4603b are formed over the substrate 4601 (
Next, the semiconductor films 4603a and 4603b are oxidized or nitrided by a plasma treatment to form insulating films 4621a and 4621b over the surfaces of the semiconductor films 4603a and 4603b, respectively (
In addition, the plasma treatment is performed with an electron density of 1×1011 to 1×1013 cm−3 and an electron temperature of plasma of 0.5 to 1.5 eV in the atmosphere containing the gas described above. The electron density of plasma is high and the electron temperature around an object (here, the semiconductor films 4603a and 4603b) formed over the substrate 4601 is low. Thus, plasma damages to the object can be avoided. In addition, since the electron density of plasma is 1×1011 cm−3 or higher, the oxide film or the nitride film formed by oxidizing or nitriding the object by the plasma treatment has a superior evenness in film thickness as compared to a film formed by a CVD method, a sputtering method, or the like, and thus, can be a dense film. Moreover, since the electron temperature of plasma is 1 eV or lower, the oxidation treatment or the nitriding treatment can be performed at a lower temperature than a conventional plasma treatment or a thermal oxidation method. For example, the oxidation treatment or the nitriding treatment can be performed sufficiently even when the plasma treatment is performed at a lower temperature by at least 100° C. than a distortion point of a glass substrate. As the frequency for producing plasma, a high frequency wave such as a microwave (2.45 GHz) can be employed. Hereinafter, the plasma treatment is performed with the above conditions unless specifically referred.
Next, the gate insulating film 4604 is formed to cover the insulating films 4621a and 4621b (
Then, by forming the gate electrode 4605 or the like over the gate insulating film 4604, it is possible to manufacture a semiconductor device having the N-channel transistor 4610a and the P-channel transistor 4610b each using the island-shaped semiconductor films 4603a and 4603b as channel regions (
Before forming the gate insulating film 4604 over the semiconductor films 4603a and 4603b, the surface of each of the semiconductor films 4603a and 4603b is oxidized or nitrided by the plasma treatment. Consequently, a short-circuit or the like between the gate electrode and the semiconductor film due to a coverage defect of the gate insulating film 4604 in end portions 4651a and 4651b etc., of the channel regions can be prevented. In other words, in a case where the angles of the end portions of the island-shaped semiconductor films are formed to be almost perpendicular (θ=85 to 100°), when the gate insulating film is formed to cover the semiconductor films by a CVD method, a sputtering method or the like, there is a risk of a coverage defect due to breakage of the gate insulating film, or the like at the end portions of the semiconductor films. However, when the plasma treatment is performed to the surface of the semiconductor film to oxide or nitride the surface, coverage defects and the like of the gate insulating film at the end portion of the semiconductor film can be prevented.
In
In
In
Even when the end portions of the island-shaped semiconductor films are formed to be almost perpendicular, the plasma treatment is performed to the semiconductor films or the gate insulating film to oxidize or nitride the semiconductor films or the gate insulating film, thereby avoiding a short-circuit between the gate electrode and the semiconductor films caused by coverage defects of the gate insulating film at the end portions of the semiconductor films.
Next, a case will be described where the end portion of the island-semiconductor film has a tapered shape (θ=30° to less than 85°) in the island-shaped semiconductor film provided over the substrate.
First, the island-shaped semiconductor films 4603a and 4603b are formed over the substrate 4601 (
Next, the gate insulating film 4604 is formed to cover the semiconductor films 4603a and 4603b (
Then, the gate insulating film 4604 is oxidized or nitrided by a plasma treatment, and thus, an insulating film 4624 is formed over the surface of the gate insulating film 4604 (
Next, by forming the gate electrode 4605 or the like over the gate insulating film 4604, it is possible to manufacture a semiconductor device having the N-channel transistor 4610a and the P-channel transistor 4610b each using the island-shaped semiconductor films 4603a and 4603b as channel regions (
In this manner, by performing the plasma treatment to the gate insulating film, an insulating film formed of an oxide film or a nitride film is formed over the surface of the gate insulating film, and the surface of the gate insulating film can be enhanced in its film quality. The oxidized or nitrided insulating film by the plasma treatment is denser and has fewer defects such as pinholes as compared to a gate insulating film formed by a CVD method or a sputtering method, and thus, the characteristics of a thin film transistor can be enhanced. Further, it is possible to prevent a short-circuit between the gate electrode and the semiconductor film caused by the coverage defect of the gate insulating film or the like at the end portion of the semiconductor film, by forming the end portion of the semiconductor film into a tapered shape. However, by performing the plasma treatment after forming the gate insulating film, a short-circuit between the gate electrode and the semiconductor film, or the like can further be prevented.
A manufacturing method of a semiconductor device which is different from that in
First, the island-shaped semiconductor films 4603a and 4603b are formed over the substrate 4601 (
Next, before removing the resists 4625a and 4625b used for etching the semiconductor film, a plasma treatment is performed to selectively oxidize or nitride the end portions of the island-shaped semiconductor films 4603a and 4603b. An insulating film 4626 is fowled at each end portion of the semiconductor films 4603a and 4603b (
Then, the gate insulating film 4604 is formed to cover the semiconductor films 4603a and 4603b (
Next, by forming the gate electrode 4605 or the like over the gate insulating film 4604, it is possible to manufacture a semiconductor device having the N-channel transistor 4610a and the P-channel transistor 4610b each using the island-shaped semiconductor films 4603a and 4603b as channel regions (
When the end portions of the semiconductor films 4603a and 4603b are tapered, end portions 4652a and 4652b of the channel regions formed in parts of the semiconductor films 4603a and 4603b are also tapered. Thus, the thickness of the semiconductor film or the gate insulating film varies as compared to the center portion, and there is a risk that the characteristics of a transistor are affected. Thus, by selectively oxidizing or nitriding the end portions of the channel regions by the plasma treatment, an insulating film is formed over the semiconductor film which becomes the end portions of the channel region. Thus, an influence on the transistor due to the end portions of the channel region can be reduced.
Next, a manufacturing method of a semiconductor device will be explained with reference to the drawings. The method is different from the method described above. Specifically, a plasma treatment is applied to a semiconductor film having a tapered shape.
First, island-shaped semiconductor films 4603a and 4603b are formed over the substrate 4601 similarly as described above (
Next, a plasma treatment is performed to the semiconductor films 4603a and 4603b to oxidize or nitride the semiconductor films 4603a and 4603b, and thus insulating films 4627a and 4627b are formed on the surfaces of the semiconductor films 4603a and 4603b (
Then, the gate insulating film 4604 is formed to cover the insulating films 4627a and 4627b (
Next, by forming the gate electrode 4605 or the like over the gate insulating film 4604, it is possible to manufacture a semiconductor device having the N-channel transistor 4610a and the P-channel transistor 4610b using the island-shaped semiconductor films 4603a and 4603b as channel regions (
When the end portions of the semiconductor films are tapered, end portions 4603a and 4603b of the channel regions formed in a portion of the semiconductor films are also tapered. Thus, there is a risk that the characteristics of a semiconductor element are affected. By oxidizing or nitriding the end portions of the channel regions as a result of oxidizing or nitriding the semiconductor films by the plasma treatment, an influence on a semiconductor element can be reduced.
In
By performing the plasma treatment in this manner, impurities such as dusts attached to the semiconductor film or the insulating film can be easily removed. In general, in some cases, dusts (also referred to as particles) are attached to the film formed by a CVD method, a sputtering method, or the like. For example, as shown in
At this time, the dust 4673 can be easily removed from the surface of the insulating film 4674 by simple cleaning such as brush cleaning. In this manner, by the plasma treatment, even a minute dust attached to the insulating film or a semiconductor film can be removed easily. It is noted that this is an effect obtained by performing the plasma treatment, and this is true of other embodiment modes as well as this embodiment mode.
As described above, by improving the film quality of the surface of the semiconductor film or the gate insulating film by oxidation or nitriding by the plasma treatment, a dense insulating film having good film quality can be formed. In addition, dusts or the like attached to the surface of the insulating film can be removed easily by cleaning. Consequently, even when the insulating film is formed to be thin, defects such as pinholes can be avoided, and miniaturization and higher performance of a semiconductor element such as a thin film transistor can be realized.
Note that, in this embodiment mode, a plasma treatment is performed to the semiconductor films 4603a and 4603b or the gate insulating film 4604 in the above
Note that this embodiment mode can be freely combined with Embodiment Modes 1 to 10.
Embodiment Mode 12Embodiment Mode 12 will explain a half-tone method as a process of manufacturing a semiconductor device including a transistor.
In
As shown in
In
The transistor with the LDD on one side may be applied to a transistor where only positive voltage or negative voltage is applied between source and drain electrodes, and specifically may be applied to a transistor constituting a logic gate such as an inverter circuit, a NAND circuit, a NOR circuit, or a latch circuit, and to a transistor constituting an analog circuit such as a sense amplifier, a constant voltage generation circuit, or a VCO.
In
In
The resistor element may be made using a semiconductor layer including an impurity element at a high concentration or a metal layer that has a thin film thickness. The resistance of the semiconductor layer depends on the film thickness, the film quality, the impurity concentration, the activation rate, or the like. However, the metal layer is preferable, because the resistance of the metal layer is determined by the film thickness and the film quality, and thus it is less variable.
In
One or both of the semiconductor layer 5505 and the insulating layer 5508 may be subjected to an oxidation or nitriding treatment by a microwave-excited high-density plasma treatment that has an electron temperature of 2 eV or less, ion energy of 5 eV or less, and an electron density on the order of 1011 to 1013/cm3. In this case, the defect level at the interface between the semiconductor layer 5505 and the insulating film 5508 can be reduced by performing the treatment at a substrate temperature of 300 to 450° C. in an oxidizing atmosphere (O2, N2O, or the like) or a nitriding atmosphere (N2, NH3, or the like). By performing this treatment for the insulating film 5508, this insulating film can be made dense. In other words, generation of a charged defect can be suppressed to prevent variation in the threshold voltage of the transistor. In addition, in a case of driving the transistor at a voltage of 3 V or less, an insulating film oxidized or nitrided by this plasma treatment can be applied as the insulating film 5508. Alternatively, in a case where the driving voltage of the transistor is 3 V or more, an insulating film formed by this treatment on the surface of the semiconductor layer 5505 and an insulating film deposited by a CVD method (a plasma CVD method or a thermal CVD method) can be combined to form the insulating film 5508. Also, this insulating film can be used as the dielectric layer of the capacitor element 4004. In this case, a capacitor element with a large charge capacity can be formed because this insulating film formed by the plasma treatment has a thickness of 1 to 10 nm and is a dense film.
As explained with reference to
to change the shape of the mask pattern formed from a photoresist material.
In addition, a region where only the first conductive layer is foamed and a region where the first conductive layer and the second conductive layer are stacked can be formed continuously by using a photomask or a reticle provided with an assist pattern that is composed of a diffraction grating pattern or a semi-transparent film and has a function of reducing a light intensity. As shown in
In the case of
This embodiment mode shows that transistors that have different electrode structures, a capacitor element, and a resistor element can be formed to be separated in the same patterning process by using a photomask or a reticle provided with an assist pattern that is composed of a diffraction grating pattern or a semi-transparent film and has a function of reducing a light intensity. This allows elements having different modes to be integrated based on circuit characteristics without increasing the number of steps.
Note that this embodiment mode can be freely combined with Embodiment Modes 1 to 11.
Embodiment Mode 13Embodiment Mode 13 will explain an example of a mask pattern in manufacturing a semiconductor device such as a transistor with reference to
It is preferable to form semiconductor layers 5610 and 5611 shown in
In either case, the semiconductor layer to be formed first is formed over an entire surface or a part (a region having an area larger than a region to be determined as a semiconductor region of a transistor) of a substrate having an insulating surface. Then, a mask pattern is formed over the semiconductor layer by a photolithography technique. Island-shaped semiconductor layers 5610 and 5611 which have specific shapes and include source and drain regions and channel formation regions of transistors are formed by performing an etching treatment of the semiconductor layers with the use of the mask pattern.
A photomask for forming the semiconductor layers 5610 and 5611 shown in
The shape of the mask pattern 5630 shown in
An insulating layer partially containing at least silicon oxide or silicon nitride is formed over the semiconductor layers 5610 and 5611. One of purposes of forming the insulating layer is that it is used as a gate insulating layer. Then, as shown in
A photomask for forming these gate wires is provided with a mask pattern 5731 shown in
An interlayer insulating layer is a layer that is formed following the gate wires 5712, 5713, and 5714. The interlayer insulating layer is formed using an inorganic insulating material such as silicon oxide or an organic insulating material such as polyimide or acrylic resin. An insulating layer such as silicon nitride or silicon nitride oxide may be interposed between the interlayer insulating layer and the gate wires 5712, 5713, and 5714. In addition, an insulating layer such as silicon nitride or silicon nitride oxide may be provided over the interlayer insulating layer. The insulating layer can prevent the semiconductor layer and the gate insulating layer from being contaminated with impurities such as exogenous metal ions or moisture that is not preferable for a transistor.
An opening is formed in a predetermined position of the interlayer insulating layer. For example, the opening is provided corresponding to the gate wire or the semiconductor layer in a lower layer. In a wire layer formed from a layer or a plurality of layers of a metal or a metal compound, a mask pattern thereof is formed by a photolithography technique and a predetermined pattern is formed by an etching process. Then, as shown in
A photomask for forming these wires 5815 to 5820 is provided with a mask pattern 5832 shown in
In
Note that this embodiment mode can be freely combined with Embodiment Modes 1 to 12.
Embodiment Mode 14The present invention can be applied to various electronic devices. Specifically, the present invention can be applied to display portions of electronic devices. As examples of such electronic devices, there are cameras such as a video camera and a digital camera, goggle displays, navigation systems, audio reproducing devices (e.g., car audios or audio component sets), computers, game machines, portable information terminals (e.g., mobile computers, mobile phones, portable game machines, or electronic books), image reproducing devices provided with a recording medium (specifically, a device for reproducing the content of a recording medium such as a digital versatile disc (DVD) and having a light-emitting device for displaying the reproduced image), and the like.
With the digital camera having the display portion 35102 using the display device of the present invention, fine and high-contrast images can be provided.
As described above, the applicable range of the present invention is so wide that the present invention can be applied to electronic devices of various fields. The electronic devices of this embodiment mode may use a display device having any structure shown in Embodiment Modes 1 to 11.
The present application is based on Japanese Patent application No. 2005-194668 filed on Jul. 4, 2005 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.
Claims
1. A display device comprising:
- a gate signal line;
- a first signal line;
- a second signal line;
- a first pixel including a first display region, a first transistor, a driving transistor, a first switch, a second switch, a third switch, a fourth switch, and a capacitor element; and
- a second pixel including a second display region and a second transistor,
- wherein the first signal line is electrically connected to the first display region through the first transistor,
- wherein the second signal line is electrically connected to the second display region through the second transistor,
- wherein a gate of the first transistor is electrically connected to the gate signal line,
- wherein a gate of the second transistor is electrically connected to the gate signal line, and
- wherein an area of the first display region is different from an area of the second display region.
2. The display device according to claim 1,
- wherein the first switch is configured to initialize a gate electric potential of the driving transistor,
- wherein the second switch is configured to control conduction or non-conduction between a source of the driving transistor and a power supply line.
3. The display device according to claim 2, further comprising a first scanning line,
- wherein the first scanning line is configured to control ON/OFF of the third switch.
4. The display device according to claim 3, further comprising a second scanning line,
- wherein the second scanning line is configured to control ON/OFF of the fourth switch.
5. The display device according to claim 1,
- wherein the first pixel and the second pixel are aligned in a striped manner.
6. The display device according to claim 1, further comprising a fourth pixel including a fourth display region and a fifth display region,
- wherein in the first, fourth, and fifth display regions, the same color is displayed,
- wherein in a first state, the first display region and the fourth display region are used for a first subpixel, and the fifth display region is used for a second subpixel,
- wherein in a second state, the fourth display region and the fifth display region are used for the first subpixel, and the first display region is used for a third subpixel, and
- wherein an area of the first display region is equal to an area of the fifth display region.
7. The display device according to claim 1, wherein the first transistor includes a-InGaZnO.
8. The display device according to claim 1, wherein the first pixel expresses a gray scale by modulating a period when the first display region included in the first pixel emits light.
9. An electronic device comprising the display device according to claim 1.
10. A display device comprising:
- a gate signal line;
- a first signal line;
- a second signal line;
- a third signal line;
- a first pixel including a first display region, a first transistor, a driving transistor, a first switch, a second switch, a third switch, a fourth switch, and a capacitor element; a second pixel including a second display region and a second transistor; and
- a third pixel including a third display region and a third transistor,
- wherein the first signal line is electrically connected to the first display region through the first transistor,
- wherein the second signal line is electrically connected to the second display region through the second transistor,
- wherein the third signal line is electrically connected to the third display region through the third transistor,
- wherein a gate of the first transistor is electrically connected to the gate signal line,
- wherein a gate of the second transistor is electrically connected to the gate signal line,
- wherein a gate of the third transistor is electrically connected to the gate signal line, and
- wherein areas of the first display region, the second display region, and the third display region are different from each other.
11. The display device according to claim 10,
- wherein the first switch is configured to initialize a gate electric potential of the driving transistor,
- wherein the second switch is configured to control conduction or non-conduction between a source of the driving transistor and a power supply line.
12. The display device according to claim 11, further comprising a first scanning line,
- wherein the first scanning line is configured to control ON/OFF of the third switch.
13. The display device according to claim 12, further comprising a second scanning line,
- wherein the second scanning line is configured to control ON/OFF of the fourth switch.
14. The display device according to claim 10,
- wherein the first pixel and the second pixel are aligned in a striped manner.
15. The display device according to claim 10, further comprising a fourth pixel including a fourth display region and a fifth display region,
- wherein in the first, fourth, and fifth display regions, the same color is displayed,
- wherein in a first state, the first display region and the fourth display region are used for a first subpixel, and the fifth display region is used for a second subpixel,
- wherein in a second state, the fourth display region and the fifth display region are used for the first subpixel, and the first display region is used for a third subpixel, and
- wherein an area of the first display region is equal to an area of the fifth display region.
16. The display device according to claim 10, wherein the first transistor includes a-InGaZnO.
17. The display device according to claim 10, wherein the first pixel expresses a gray scale by modulating a period when the first display region included in the first pixel emits light.
18. An electronic device comprising the display device according to claim 10.
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Type: Grant
Filed: Feb 23, 2011
Date of Patent: Sep 13, 2011
Patent Publication Number: 20110141164
Assignee: Semiconductor Energy Laboratory Co., Ltd.
Inventors: Hajime Kimura (Kanagawa), Shunpei Yamazaki (Tokyo)
Primary Examiner: Rhonda S Peace
Attorney: Husch Blackwell LLP
Application Number: 13/032,829
International Classification: G02F 1/136 (20060101); G02F 1/1343 (20060101); G02F 1/133 (20060101); G02F 1/1335 (20060101); G02F 1/1337 (20060101);
