REDUCED CAPACITANCE DISPLAY ELEMENT
A display element, such as an interferometric modulator, includes a transparent conductor configured as a first electrode and a movable minor configured as a second electrode. Advantageously, the partial reflector is positioned between the transparent conductor and the movable mirror. Because the transparent conductor serves as an electrode, the partial reflector does not need to be conductive. Accordingly, a greater range of materials may be used for the partial reflector. In addition, a transparent insulative material, such as a dielectric, may be positioned between the transparent conductor and the partial reflector, for example, in order to decrease a capacitance of the display element without changing a gap distance between the partial reflector and the movable minor. Thus, a capacitance of the display element may be reduced without changing the optical characteristics of the display element.
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This application is a continuation of U.S. patent application Ser. No. 11/155,939, filed Jun. 17, 2005, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/613,542, filed on Sep. 27, 2004, both of which are hereby expressly incorporated by reference herein in their entirety. In addition, this application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/613,488, filed on Sep. 27, 2004.
FIELD OF THE INVENTIONThe field of the invention relates to microelectromechanical systems (MEMS).
DESCRIPTION OF THE RELATED TECHNOLOGYMicroelectromechanical systems (MEMS) include micro mechanical elements, actuators, and electronics. Micromechanical elements may be created using deposition, etching, and or other micromachining processes that etch away parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. One type of MEMS device is called an interferometric modulator. As used herein, the term interferometric modulator or interferometric light modulator refers to a device that selectively absorbs and/or reflects light using the principles of optical interference. In certain embodiments, an interferometric modulator may comprise a pair of conductive plates, one or both of which may be transparent and/or reflective in whole or part and capable of relative motion upon application of an appropriate electrical signal. In a particular embodiment, one plate may comprise a stationary layer deposited on a substrate and the other plate may comprise a metallic membrane separated from the stationary layer by an air gap. As described herein in more detail, the position of one plate in relation to another can change the optical interference of light incident on the interferometric modulator. Such devices have a wide range of applications, and it would be beneficial in the art to utilize and/or modify the characteristics of these types of devices so that their features can be exploited in improving existing products and creating new products that have not yet been developed.
SUMMARY OF CERTAIN EMBODIMENTSThe systems, methods, and devices of the invention each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of Certain Embodiments” one will understand how the features of this invention provide advantages over other display devices.
In some embodiments, a display element comprises: a substantially transparent conductive layer; a partially reflective insulator having a thickness of between about 40 and 150 Angstroms; a moveable reflective layer, the partially reflective insulator being positioned between the conductive layer and the moveable reflective layer, wherein a voltage applied between the conductive layer and the moveable reflective layer induces movement of the moveable reflective layer; and a first dielectric layer positioned between the conductive layer and the partially reflective insulator.
In some embodiments, a method of forming a display element comprises: forming a substantially transparent conductive layer; forming a moveable reflective layer; forming a partially reflective insulator having a thickness of between about 40 and 150 Angstroms, the partially reflective insulator being formed between the conductive layer and the moveable reflective layer, wherein a voltage applied between the conductive layer and the moveable reflective layer induces movement of the moveable reflective layer; and forming a first dielectric layer between the conductive layer and the partially reflective insulator.
In some embodiments, a display element comprises: first means for transmitting light and conducting electricity; second means for partially reflecting light and insulating, the second means having a thickness of between about 40 and 150 Angstroms; third moveable means for reflecting light, the second means being positioned between the first means and the third means, wherein a voltage applied between the first means and the third means induces movement of the third means; and fourth dielectric means positioned between the first means and the second means.
The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the following description, the embodiments may be implemented in any device that is configured to display an image, whether in motion (e.g., video) or stationary (e.g., still image), and whether textual or pictorial. More particularly, it is contemplated that the embodiments may be implemented in or associated with a variety of electronic devices such as, but not limited to, mobile telephones, wireless devices, personal data assistants (PDAs), hand-held or portable computers, GPS receivers/navigators, cameras, MP3 players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., odometer display, etc.), cockpit controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices of similar structure to those described herein can also be used in non-display applications such as in electronic switching devices.
One interferometric modulator display embodiment comprising an interferometric MEMS display element is illustrated in
The depicted portion of the pixel array in
The optical stacks 16a and 16b (collectively referred to as optical stack 16), as referenced herein, typically comprise of several fused layers, which can include an electrode layer, such as indium tin oxide (ITO), a partially reflective layer, such as chromium, and a transparent dielectric. The optical stack 16 is thus electrically conductive, partially transparent and partially reflective, and may be fabricated, for example, by depositing one or more of the above layers onto a transparent substrate 20. In some embodiments, the layers are patterned into parallel strips, and may form row electrodes in a display device as described further below. The movable reflective layers 14a, 14b may be formed as a series of parallel strips of a deposited metal layer or layers (orthogonal to the row electrodes of 16a, 16b) deposited on top of posts 18 and an intervening sacrificial material deposited between the posts 18. When the sacrificial material is etched away, the movable reflective layers 14a, 14b are separated from the optical stacks 16a, 16b by a defined gap 19. A highly conductive and reflective material such as aluminum may be used for the reflective layers 14, and these strips may form column electrodes in a display device.
With no applied voltage, the cavity 19 remains between the movable reflective layer 14a and optical stack 16a, with the movable reflective layer 14a in a mechanically relaxed state, as illustrated by the pixel 12a in
In one embodiment, the processor 21 is also configured to communicate with an array driver 22. In one embodiment, the array driver 22 includes a row driver circuit 24 and a column driver circuit 26 that provide signals to a display array or panel 30. The cross section of the array illustrated in
In typical applications, a display frame may be created by asserting the set of column electrodes in accordance with the desired set of actuated pixels in the first row. A row pulse is then applied to the row 1 electrode, actuating the pixels corresponding to the asserted column lines. The asserted set of column electrodes is then changed to correspond to the desired set of actuated pixels in the second row. A pulse is then applied to the row 2 electrode, actuating the appropriate pixels in row 2 in accordance with the asserted column electrodes. The row 1 pixels are unaffected by the row 2 pulse, and remain in the state they were set to during the row 1 pulse. This may be repeated for the entire series of rows in a sequential fashion to produce the frame. Generally, the frames are refreshed and/or updated with new display data by continually repeating this process at some desired number of frames per second. A wide variety of protocols for driving row and column electrodes of pixel arrays to produce display frames are also well known and may be used in conjunction with the present invention.
In the
The display device 40 includes a housing 41, a display 30, an antenna 43, a speaker 44, an input device 48, and a microphone 46. The housing 41 is generally formed from any of a variety of manufacturing processes as are well known to those of skill in the art, including injection molding, and vacuum forming. In addition, the housing 41 may be made from any of a variety of materials, including but not limited to plastic, metal, glass, rubber, and ceramic, or a combination thereof. In one embodiment the housing 41 includes removable portions (not shown) that may be interchanged with other removable portions of different color, or containing different logos, pictures, or symbols.
The display 30 of exemplary display device 40 may be any of a variety of displays, including a bi-stable display, as described herein. In other embodiments, the display 30 includes a flat-panel display, such as plasma, EL, OLED, STN LCD, or TFT LCD as described above, or a non-flat-panel display, such as a CRT or other tube device, as is well known to those of skill in the art. However, for purposes of describing the present embodiment, the display 30 includes an interferometric modulator display, as described herein.
The components of one embodiment of exemplary display device 40 are schematically illustrated in
The network interface 27 includes the antenna 43 and the transceiver 47 so that the exemplary display device 40 can communicate with one ore more devices over a network. In one embodiment the network interface 27 may also have some processing capabilities to relieve requirements of the processor 21. The antenna 43 is any antenna known to those of skill in the art for transmitting and receiving signals. In one embodiment, the antenna transmits and receives RF signals according to the IEEE 802.11 standard, including IEEE 802.11(a), (b), or (g). In another embodiment, the antenna transmits and receives RF signals according to the BLUETOOTH standard. In the case of a cellular telephone, the antenna is designed to receive CDMA, GSM, AMPS or other known signals that are used to communicate within a wireless cell phone network. The transceiver 47 pre-processes the signals received from the antenna 43 so that they may be received by and further manipulated by the processor 21. The transceiver 47 also processes signals received from the processor 21 so that they may be transmitted from the exemplary display device 40 via the antenna 43.
In an alternative embodiment, the transceiver 47 can be replaced by a receiver. In yet another alternative embodiment, network interface 27 can be replaced by an image source, which can store or generate image data to be sent to the processor 21. For example, the image source can be a digital video disc (DVD) or a hard-disc drive that contains image data, or a software module that generates image data.
Processor 21 generally controls the overall operation of the exemplary display device 40. The processor 21 receives data, such as compressed image data from the network interface 27 or an image source, and processes the data into raw image data or into a format that is readily processed into raw image data. The processor 21 then sends the processed data to the driver controller 29 or to frame buffer 28 for storage. Raw data typically refers to the information that identifies the image characteristics at each location within an image. For example, such image characteristics can include color, saturation, and gray-scale level.
In one embodiment, the processor 21 includes a microcontroller, CPU, or logic unit to control operation of the exemplary display device 40. Conditioning hardware 52 generally includes amplifiers and filters for transmitting signals to the speaker 45, and for receiving signals from the microphone 46. Conditioning hardware 52 may be discrete components within the exemplary display device 40, or may be incorporated within the processor 21 or other components.
The driver controller 29 takes the raw image data generated by the processor 21 either directly from the processor 21 or from the frame buffer 28 and reformats the raw image data appropriately for high speed transmission to the array driver 22. Specifically, the driver controller 29 reformats the raw image data into a data flow having a raster-like format, such that it has a time order suitable for scanning across the display array 30. Then the driver controller 29 sends the formatted information to the array driver 22. Although a driver controller 29, such as a LCD controller, is often associated with the system processor 21 as a stand-alone Integrated Circuit (IC), such controllers may be implemented in many ways. They may be embedded in the processor 21 as hardware, embedded in the processor 21 as software, or fully integrated in hardware with the array driver 22.
Typically, the array driver 22 receives the formatted information from the driver controller 29 and reformats the video data into a parallel set of waveforms that are applied many times per second to the hundreds and sometimes thousands of leads coming from the display's x-y matrix of pixels.
In one embodiment, the driver controller 29, array driver 22, and display array 30 are appropriate for any of the types of displays described herein. For example, in one embodiment, driver controller 29 is a conventional display controller or a bi-stable display controller (e.g., an interferometric modulator controller). In another embodiment, array driver 22 is a conventional driver or a bi-stable display driver (e.g., an interferometric modulator display). In one embodiment, a driver controller 29 is integrated with the array driver 22. Such an embodiment is common in highly integrated systems such as cellular phones, watches, and other small area displays. In yet another embodiment, display array 30 is a typical display array or a bi-stable display array (e.g., a display including an array of interferometric modulators).
The input device 48 allows a user to control the operation of the exemplary display device 40. In one embodiment, input device 48 includes a keypad, such as a QWERTY keyboard or a telephone keypad, a button, a switch, a touch-sensitive screen, a pressure- or heat-sensitive membrane. In one embodiment, the microphone 46 is an input device for the exemplary display device 40. When the microphone 46 is used to input data to the device, voice commands may be provided by a user for controlling operations of the exemplary display device 40.
Power supply 50 can include a variety of energy storage devices as are well known in the art. For example, in one embodiment, power supply 50 is a rechargeable battery, such as a nickel-cadmium battery or a lithium ion battery. In another embodiment, power supply 50 is a renewable energy source, a capacitor, or a solar cell, including a plastic solar cell, and solar-cell paint. In another embodiment, power supply 50 is configured to receive power from a wall outlet.
In some implementations control programmability resides, as described above, in a driver controller which can be located in several places in the electronic display system. In some cases control programmability resides in the array driver 22. Those of skill in the art will recognize that the above-described optimization may be implemented in any number of hardware and/or software components and in various configurations.
The details of the structure of interferometric modulators that operate in accordance with the principles set forth above may vary widely. For example,
In embodiments such as those shown in
As described above with respect to
In the exemplary interferometric modulator 100, the transparent conductor 140 is shown positioned between the partial reflector 116 and the substrate 120. In this embodiment, the transparent conductor 140 is configured as an electrode of the interferometric modulator and, thus, the interferometric modulator 100 may be actuated by placing an appropriate voltage difference, e.g., 10 volts, between the moveable minor 114 and the transparent conductor 140. In an exemplary embodiment, the transparent conductor 140 comprises Indium Tin Oxide (ITO), Zinc Oxide, Florine doped Zinc Oxide, Cadmium Tin Oxide, Aluminum doped Zinc Oxide, Florine doped Tin Oxide, and/or Zinc Oxide doped with Gallium, Boron or Indium. In this embodiment, the partial reflector 116 is not required to be conductive and, thus, the partial reflector 116 may comprise any suitable partially reflective material, either conductive or nonconductive.
In certain embodiments of interferometric modulator, a reflectivity of the partial reflector 116 is within the range of about 30-36%. For example, in one embodiment the reflectivity of the partial reflector 116 is about 31%. In other embodiments, other reflectivities are usable in connection with the systems and methods described herein. In other embodiments, the reflectivity of the partial reflector 116 may be set to other levels according to the desired output criteria for the interferometric modulator 100. In a typical interferometric modulator, as a thickness of the partial reflector increases, the reflectivity of the partial reflector also increases, thus reducing the effectiveness of a dark state and limiting the contrast of the interferometric modulator. Therefore, in order to achieve a desired reflectivity of the partial reflector, in many embodiments reduction of a thickness of a partial reflector is desired.
In the embodiment of
In one embodiment, the partial reflector comprises silicon nitride, which is a non-conductive, partially reflective material. In other embodiments, oxides of chromium are used, including, but not limited to, CrO2, CrO3, Cr2O3, Cr2O, and CrOCN. In some embodiments, low conductivity dielectric materials are used as the partial reflector. These low conductivity dielectric materials are generally referred to as “high-k dielectrics”, where “high-k dielectrics” refers to materials having a dielectric constant greater than or equal to about 3.9. High-k dielectrics may include, for example, SiO2, Si3N4, Al2O3, Y2O3, La2O3, Ta2O5, TiO2, HfO2, and ZrO2, for example.
In other embodiments, the partial reflector 116 comprises a dielectric stack having alternating layers of dielectrics with different indices of refraction. As those of skill in the art will recognize, the output characteristics of the interferometric modulator 100, e.g., the color of light that is reflected from the interferometric modulator 100, are affected by the reflectivity of the partial reflector 116. Accordingly, tuning of the reflectivity of the partial reflector 116 may be performed in order to achieve desired output characteristics. In one embodiment, the index of refraction of the partial reflector 116 can be fine-tuned by using a partial reflector 116 comprising a combination of dielectric materials in a stack structure. For example, in one embodiment, the partial reflector 116 may comprise a layer of SiO2 and a layer of CrOCN. In an exemplary embodiment of an interferometric modulator having a partial reflector comprising a dielectric stack, the material layers above substrate 120 include a layer of ITO that is about 500 Angstroms thick, a layer of SiO2 that is about 1000 Angstroms thick, a layer of CrOCN that is about 110 Angstroms thick, a layer of SiO2 that is about 275 Angstroms thick, an air gap that is about 2000 Angstroms thick, and an Al reflector. Thus, in this exemplary embodiment, the partial reflector comprises a layer of SiO2 that is about 1000 Angstroms thick and a layer of CrOCN that is about 110 Angstroms thick. Those of skill in the art will recognize that there are many other suitable conductive or non-conductive materials that may be used alone, or in combination with other materials, as part of the partial reflector 116. Use of these materials in combination with the systems and methods described herein is expressly contemplated.
In a typical display, as a capacitance of the individual display elements, e.g., interferometric modulators, increases, a power required to change voltages across the display elements also increases. For example, as a capacitance of any actuated display elements in an interferometric modulator display increases, the current required to change voltage levels on the columns of the display also increases. Accordingly, display elements with reduced capacitance are desired. The display elements of
As described above with respect to
In one embodiment, an optical gap (including the air gap 303 and the dielectric 306) of the reverse interferometric modulator 300 is much smaller than an optical gap of an interferometric modulator that produces black in an actuated state and color or white in a released state (e.g.,
Due to the decreased distance between electrodes, the capacitance of reverse interferometric modulators is generally higher than regular interferometric modulators. Accordingly, reverse interferometric modulators may consume additional power when changing voltages across their row and/or column terminals. In order to reduce the capacitance of the reverse interferometric modulator 300, the dielectric layer 308 is positioned between the terminals of the interferometric modulator. For example, the interferometric modulator 300 includes a dielectric 308 adjacent to the transparent conductor 310. In the same manner as discussed above with respect to
The interferometric modulators 100, 200, and 300 each include a movable minor (mirror 114 in
Various embodiments of the invention have been described above. Although this invention has been described with reference to these specific embodiments, the descriptions are intended to be illustrative of the invention and are not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention.
Claims
1-28. (canceled)
29. A display element comprising:
- a substantially transparent conductive layer;
- a partially reflective insulator having a thickness of between about 40 and 150 Angstroms;
- a moveable reflective layer, the partially reflective insulator being positioned between the conductive layer and the moveable reflective layer, wherein a voltage applied between the conductive layer and the moveable reflective layer induces movement of the moveable reflective layer; and
- a first dielectric layer positioned between the conductive layer and the partially reflective insulator.
30. The display element of claim 29, wherein when the voltage is applied between the conductive layer and the moveable reflective layer, at least a portion of the moveable reflective layer moves so that the at least a portion of the moveable reflective layer physically contacts the partially reflective insulator.
31. The display element of claim 29, further comprising a second dielectric layer positioned between the partially reflective insulator and the moveable reflective layer.
32. The display element of claim 29, wherein the first dielectric layer includes a material selected from the group consisting of SiO2, Al2O3, and Silicon Nitride.
33. The display element of claim 29, wherein the partially reflective insulator includes a material selected from the group consisting of Silicon Nitride, CrO2, CrO3, Cr2O3, Cr2O, and CrOCN.
34. The display element of claim 29, further comprising a circuit configured to drive the moveable reflective layer such that light reflected by the moveable reflective layer and the partially reflective insulator can be modulated so as to form part of a viewable image.
35. The display element of claim 34, wherein the display element includes a display element in a reflective display.
36. The display element of claim 29, wherein the display element is included with a plurality of other display elements to form an image by selectively modulating incident light.
37. The display element of claim 29, wherein the moveable reflective layer includes a metal.
38. A method of forming a display element, the method comprising:
- forming a substantially transparent conductive layer;
- forming a moveable reflective layer;
- forming a partially reflective insulator having a thickness of between about 40 and 150 Angstroms, the partially reflective insulator being formed between the conductive layer and the moveable reflective layer, wherein a voltage applied between the conductive layer and the moveable reflective layer induces movement of the moveable reflective layer; and
- forming a first dielectric layer between the conductive layer and the partially reflective insulator.
39. The method of claim 38, wherein when the voltage is applied between the conductive layer and the moveable reflective layer, at least a portion of the moveable reflective layer moves so that the at least a portion of the moveable reflective layer physically contacts the partially reflective insulator.
40. The method of claim 38, further comprising forming a second dielectric layer between the partially reflective insulator and the moveable reflective layer.
41. The method of claim 38, wherein the first dielectric layer includes a material selected from the group consisting of SiO2, Al2O3, and Silicon Nitride.
42. The method of claim 38, wherein the partially reflective insulator includes a material selected from the group consisting of Silicon Nitride, CrO2, CrO3, Cr2O3, Cr2O, and CrOCN.
43. The method of claim 38, wherein the display element includes a display element in a reflective display.
44. The method of claim 38, wherein the moveable reflective layer includes a metal.
45. A display element comprising:
- means for transmitting light and conducting electricity;
- means for partially reflecting light, the partially reflecting means having a thickness of between about 40 and 150 Angstroms, and the partially reflecting means including an insulator;
- moveable means for reflecting light, the partially reflecting means being positioned between the transmitting means and the movable reflecting means, wherein a voltage applied between the transmitting means and the movable reflecting means induces movement of the movable reflecting means; and
- means for insulating positioned between the transmitting means and the partially reflecting means.
46. The display element of claim 45, wherein the transmitting means includes a substantially transparent conductive layer, the partially reflecting means includes a partially reflective insulator layer, the movable reflecting means includes a moveable reflective layer, and the insulating means includes a first dielectric layer.
47. The display element of claim 46, wherein when the voltage is applied between the conductive layer and the moveable reflective layer, at least a portion of the moveable reflective layer moves so that the at least a portion of the moveable reflective layer physically contacts the partially reflective insulator.
48. The display element of claim 46, further comprising a second dielectric layer positioned between the partially reflective insulator and the moveable reflective layer.
49. The display element of claim 46, wherein the first dielectric layer includes a material selected from the group consisting of SiO2, Al2O3, and Silicon Nitride.
50. The display element of claim 46, wherein the partially reflective insulator includes a material selected from the group consisting of Silicon Nitride, CrO2, CrO3, Cr2O3, Cr2O, and CrOCN.
51. The display element of claim 46, further comprising a circuit configured to drive the moveable reflective layer such that light reflected by the moveable reflective layer and the partially reflective insulator can be modulated so as to form part of a viewable image.
52. The display element of claim 51, wherein the display element includes a display element in a reflective display.
53. The display element of claim 46, wherein the display element is included with a plurality of other display elements to form an image by selectively modulating incident light.
54. The display element of claim 46, wherein the moveable reflective layer includes a metal.
Type: Application
Filed: Aug 22, 2011
Publication Date: Feb 23, 2012
Applicant: QUALCOMM MEMS Technologies, Inc. (San Diego, CA)
Inventors: William J. Cummings (Clinton, WA), Brian J. Gally (Los Gatos, CA)
Application Number: 13/215,138
International Classification: G02B 26/00 (20060101); B05D 1/36 (20060101); B05D 5/06 (20060101);