Abstract: An object is to provide a method for manufacturing a highly reliable semiconductor device including thin film transistors which have stable electric characteristics and are formed using an oxide semiconductor. A method for manufacturing a semiconductor device includes the steps of: forming an oxide semiconductor film over a gate electrode with a gate insulating film interposed between the oxide semiconductor film and the gate electrode, over an insulating surface; forming a first conductive film including at least one of titanium, molybdenum, and tungsten, over the oxide semiconductor film; forming a second conductive film including a metal having lower electronegativity than hydrogen, over the first conductive film; forming a source electrode and a drain electrode by etching of the first conductive film and the second conductive film; and forming an insulating film in contact with the oxide semiconductor film, over the oxide semiconductor film, the source electrode, and the drain electrode.

Abstract: A protective circuit includes a non-linear element, which further includes a gate electrode, a gate insulating layer covering the gate electrode, a pair of first and second wiring layers whose end portions overlap with the gate electrode over the gate insulating layer and in which a conductive layer and a second oxide semiconductor layer are stacked, and a first oxide semiconductor layer which overlaps with at least the gate electrode and which is in contact with side face portions of the gate insulating layer and the conductive layer of the first wiring layer and the second wiring layer and a side face portion and a top face portion of the second oxide semiconductor layer. Over the gate insulating layer, oxide semiconductor layers with different properties are bonded to each other, whereby stable operation can be performed as compared with Schottky junction. Thus, the junction leakage can be decreased and the characteristics of the non-linear element can be improved.

Abstract: To provide a transistor having a favorable electric characteristics and high reliability and a display device including the transistor. The transistor is a bottom-gate transistor formed using an oxide semiconductor for a channel region. An oxide semiconductor layer subjected to dehydration or dehydrogenation through heat treatment is used as an active layer. The active layer includes a first region of a superficial portion microcrystallized and a second region of the rest portion. By using the oxide semiconductor layer having such a structure, a change to an n-type, which is attributed to entry of moisture to the superficial portion or elimination of oxygen from the superficial portion, and generation of a parasitic channel can be suppressed. In addition, contact resistance between the oxide semiconductor layer and source and drain electrodes can be reduced.

Abstract: A pixel portion and a driver circuit driving the pixel portion are formed over the same substrate. At least a part of the driver circuit is formed using an inverted staggered thin film transistor in which an oxide semiconductor layer is used and a channel protective layer is provided over the oxide semiconductor layer serving as a channel formation region which is overlapped with the gate electrode. The driver circuit as well as the pixel portion is provided over the same substrate to reduce manufacturing costs.

Abstract: A display device includes a pixel portion in which a pixel electrode layer is arranged in a matrix, and an inverted staggered thin film transistor having a combination of at least two kinds of oxide semiconductor layers with different amounts of oxygen is provided corresponding to the pixel electrode layer. In the periphery of the pixel portion in this display device, a pad portion is provided to be electrically connected to a common electrode layer formed on a counter substrate through a conductive layer made of the same material as the pixel electrode layer. One objection of our invention to prevent a defect due to separation of a thin film in various kinds of display devices is realized, by providing a structure suitable for a pad portion provided in a display panel.

Abstract: A flexible display device with high viewability is provided. The display device includes a first substrate, a second substrate, a first element layer, and a second element layer. The first element layer is positioned between the first substrate and the second substrate. The second element layer is positioned between the first substrate and the second substrate. The first element layer and the second element layer overlap with each other in a region. The first substrate and the second substrate have flexibility. The first element layer includes a display element and a first circuit. The display element is electrically connected to the first circuit. The second element layer includes a sensor element. The sensor element has a function of sensing distortion.

Abstract: In order to take advantage of the properties of a display device including an oxide semiconductor, a protective circuit and the like having appropriate structures and a small occupied area are necessary. The protective circuit is formed using a non-linear element which includes a gate insulating film covering a gate electrode; a first oxide semiconductor layer over the gate insulating film; a channel protective layer covering a region which overlaps with a channel formation region of the first oxide semiconductor layer; and a first wiring layer and a second wiring layer each of which is formed by stacking a conductive layer and a second oxide semiconductor layer and over the first oxide semiconductor layer. The gate electrode is connected to a scan line or a signal line, the first wiring layer or the second wiring layer is directly connected to the gate electrode.

Abstract: An object is to improve field effect mobility of a thin film transistor using an oxide semiconductor. Another object is to suppress increase in off current even in a thin film transistor with improved field effect mobility. In a thin film transistor using an oxide semiconductor layer, by forming a semiconductor layer having higher electrical conductivity and a smaller thickness than the oxide semiconductor layer between the oxide semiconductor layer and a gate insulating layer, field effect mobility of the thin film transistor can be improved, and increase in off current can be suppressed.

Abstract: An object is to provide favorable interface characteristics of a thin film transistor including an oxide semiconductor layer without mixing of an impurity such as moisture. Another object is to provide a semiconductor device including a thin film transistor having excellent electric characteristics and high reliability, and a method by which a semiconductor device can be manufactured with high productivity. A main point is to perform oxygen radical treatment on a surface of a gate insulating layer. Accordingly, there is a peak of the oxygen concentration at an interface between the gate insulating layer and a semiconductor layer, and the oxygen concentration of the gate insulating layer has a concentration gradient. The oxygen concentration is increased toward the interface between the gate insulating layer and the semiconductor layer.

Abstract: To provide an oxide semiconductor film having stable electric conductivity and a highly reliable semiconductor device having stable electric characteristics by using the oxide semiconductor film. The oxide semiconductor film contains indium (In), gallium (Ga), and zinc (Zn) and includes a c-axis-aligned crystalline region aligned in the direction parallel to a normal vector of a surface where the oxide semiconductor film is formed. Further, the composition of the c-axis-aligned crystalline region is represented by In1+?Ga1??O3(ZnO)m (0<?<1 and m=1 to 3 are satisfied), and the composition of the entire oxide semiconductor film including the c-axis-aligned crystalline region is represented by InxGayO3(ZnO)m (0<x<2, 0<y<2, and m=1 to 3 are satisfied).

Abstract: An object is, in a thin film transistor including an oxide semiconductor layer, to reduce contact resistance between the oxide semiconductor layer and source and drain electrode layers electrically connected to the oxide semiconductor layer. The source and drain electrode layers have a stacked-layer structure of two or more layers in which a layer in contact with the oxide semiconductor layer is formed using a metal whose work function is lower than the work function of the oxide semiconductor layer or an alloy containing such a metal. Layers other than the layer in contact with the oxide semiconductor layer of the source and drain electrode layers are formed using an element selected from Al, Cr, Cu, Ta, Ti, Mo, or W, an alloy containing any of these elements as a component, an alloy containing any of these elements in combination, or the like.

Abstract: It is an object to provide an oxide semiconductor which is suitable for use in a semiconductor device. Alternatively, it is another object to provide a semiconductor device using the oxide semiconductor. Provided is a semiconductor device including an In—Ga—Zn—O based oxide semiconductor layer in a channel formation region of a transistor. In the semiconductor device, the In—Ga—Zn—O based oxide semiconductor layer has a structure in which crystal grains represented by InGaO3(ZnO)m (m=1) are included in an amorphous structure represented by InGaO3(ZnO)m (m>0).

Abstract: An object is to reduce to reduce variation in threshold voltage to stabilize electric characteristics of thin film transistors each using an oxide semiconductor layer. An object is to reduce an off current. The thin film transistor using an oxide semiconductor layer is formed by stacking an oxide semiconductor layer containing insulating oxide over the oxide semiconductor layer so that the oxide semiconductor layer and source and drain electrode layers are in contact with each other with the oxide semiconductor layer containing insulating oxide interposed therebetween; whereby, variation in threshold voltage of the thin film transistors can be reduced and thus the electric characteristics can be stabilized. Further, an off current can be reduced.

Abstract: A pixel portion and a driver circuit driving the pixel portion are formed over the same substrate. At least a part of the driver circuit is formed using an inverted staggered thin film transistor in which an oxide semiconductor layer is used and a channel protective layer is provided over the oxide semiconductor layer serving as a channel formation region which is overlapped with the gate electrode. The driver circuit as well as the pixel portion is provided over the same substrate to reduce manufacturing costs.

Abstract: It is an object to provide a highly reliable semiconductor device with good electrical characteristics and a display device including the semiconductor device as a switching element. In a transistor including an oxide semiconductor layer, a needle crystal group provided on at least one surface side of the oxide semiconductor layer grows in a c-axis direction perpendicular to the surface and includes an a-b plane parallel to the surface, and a portion except for the needle crystal group is an amorphous region or a region in which amorphousness and microcrystals are mixed. Accordingly, a highly reliable semiconductor device with good electrical characteristics can be formed.

Abstract: A structure by which electric-field concentration which might occur between a source electrode and a drain electrode in a bottom-gate thin film transistor is relaxed and deterioration of the switching characteristics is suppressed, and a manufacturing method thereof. A bottom-gate thin film transistor in which an oxide semiconductor layer is provided over a source and drain electrodes is manufactured, and angle ?1 of the side surface of the source electrode which is in contact with the oxide semiconductor layer and angle ?2 of the side surface of the drain electrode which is in contact with the oxide semiconductor layer are each set to be greater than or equal to 20° and less than 90°, so that the distance from the top edge to the bottom edge in the side surface of each electrode is increased.

Abstract: A flexible display device with high viewability is provided. The display device includes a first substrate, a second substrate, a first element layer, and a second element layer. The first element layer is positioned between the first substrate and the second substrate. The second element layer is positioned between the first substrate and the second substrate. The first element layer and the second element layer overlap with each other in a region. The first substrate and the second substrate have flexibility. The first element layer includes a display element and a first circuit. The display element is electrically connected to the first circuit. The second element layer includes a sensor element. The sensor element has a function of sensing distortion.

Abstract: Homogeneity and stability of electric characteristics of a thin film transistor included in a circuit are critical for the performance of a display device including said circuit. An object of the invention is to provide an oxide semiconductor film with low hydrogen content and which is used in an inverted staggered thin film transistor having well defined electric characteristics. In order to achieve the object, a gate insulating film, an oxide semiconductor layer, and a channel protective film are successively formed with a sputtering method without being exposed to air. The oxide semiconductor layer is formed so as to limit hydrogen contamination, in an atmosphere including a proportion of oxygen. In addition, layers provided over and under a channel formation region of the oxide semiconductor layer are formed using compounds of silicon, oxygen and/or nitrogen.

Abstract: To provide a transistor having a favorable electric characteristics and high reliability and a display device including the transistor. The transistor is a bottom-gate transistor formed using an oxide semiconductor for a channel region. An oxide semiconductor layer subjected to dehydration or dehydrogenation through heat treatment is used as an active layer. The active layer includes a first region of a superficial portion microcrystallized and a second region of the rest portion. By using the oxide semiconductor layer having such a structure, a change to an n-type, which is attributed to entry of moisture to the superficial portion or elimination of oxygen from the superficial portion, and generation of a parasitic channel can be suppressed. In addition, contact resistance between the oxide semiconductor layer and source and drain electrodes can be reduced.

Abstract: An object is to provide a method for manufacturing a highly reliable semiconductor device including thin film transistors which have stable electric characteristics and are formed using an oxide semiconductor. A method for manufacturing a semiconductor device includes the steps of: forming an oxide semiconductor film over a gate electrode with a gate insulating film interposed between the oxide semiconductor film and the gate electrode, over an insulating surface; forming a first conductive film including at least one of titanium, molybdenum, and tungsten, over the oxide semiconductor film; forming a second conductive film including a metal having lower electronegativity than hydrogen, over the first conductive film; forming a source electrode and a drain electrode by etching of the first conductive film and the second conductive film; and forming an insulating film in contact with the oxide semiconductor film, over the oxide semiconductor film, the source electrode, and the drain electrode.