Liquid crystal display device

Abstract

To provide a display device that performs accurate display.SOLUTION: A circuit is formed by using a transistor that includes an oxide semiconductor and has a low off-state current. As a circuit, a precharge circuit or an inspection circuit is formed in addition to a pixel circuit. The off-state current is low since the oxide semiconductor is used. Thus, it is not likely that a signal or voltage is leaked in the precharge circuit or the inspection circuit to cause defective display. As a result, a display device that performs accurate display can be provided.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a semiconductor device, a display device, a liquid crystal display device, a light emitting device, or a method for manufacturing the same. In particular, a semiconductor device including a circuit including a transistor using an oxide semiconductor film, The present invention relates to a display device, a liquid crystal display device, a light-emitting device, or a method for manufacturing the same. [Background technology]

[0002] Conventionally, amorphous silicon has been used as a switching element for display devices such as liquid crystal display devices. Thin-film transistors (TFTs) that use a silicon layer formed from a material such as a capacitor as the channel layer Amorphous silicon thin-film transistors are widely used. Although the degree of reflection is low, it has the advantage of being able to accommodate larger areas of glass substrates.

[0003] Recently, transistors have been fabricated using metal oxides that exhibit semiconducting properties, and they have been used to develop electronic devices. For example, tungsten oxide is one of the most widely used metal oxides. Sten, tin oxide, indium oxide, zinc oxide, etc. are known to exhibit semiconductor properties. A transistor having a channel forming region made of such a transparent semiconductor layer made of metal oxide is A related art is disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-165532 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one embodiment of the present invention is to provide a semiconductor device or the like with low noise. Another object of one embodiment of the present invention is to provide a semiconductor device or the like having high withstand voltage. An object of one embodiment of the present invention is to provide a semiconductor device or the like with low power consumption. Another object of one embodiment of the present invention is to provide a display device or the like that performs correct display. The description of these problems does not preclude the existence of other problems. It is understood that an embodiment does not necessarily address all of the above problems. [Means for solving the problem]

[0006] In order to solve the above problems, a semiconductor device having an oxide semiconductor (OS) A circuit is constructed using transistors having an oxide semiconductor, particularly MOS transistors having an oxide semiconductor. The oxide semiconductor is substantially an intrinsic semiconductor. Therefore, the off-current is very low. low.

[0007] According to one aspect of the present invention, there is provided a pixel unit including a plurality of pixels, and a precharge circuit, The precharge circuit has a plurality of first transistors, and each of the plurality of pixels has a second The first transistor and the second transistor are made of an oxide A liquid crystal display device is provided that includes a semiconductor.

[0008] Alternatively, one aspect of the embodiment of the present invention is a pixel unit including a plurality of pixels and an inspection circuit, The inspection circuit has a plurality of first transistors, and each of the plurality of pixels has a second transistor. a first transistor and a second transistor including an oxide semiconductor The present invention provides a liquid crystal display device comprising:

[0009] Alternatively, one aspect of the embodiment of the present invention is a pixel circuit including a pixel unit and a circuit. The pixel includes a first transistor and a second transistor. a first transistor having a first gate electrode electrically connected to one another; The first terminals of the first transistors are electrically connected to each other, All of the second terminals of the first transistors are electrically connected to the pixel section, and the gates of the first transistors are The port is in a floating state, and the first and second transistors are A liquid crystal display device including an oxide semiconductor is provided.

[0010] Alternatively, one aspect of the embodiment of the present invention is a pixel circuit including a pixel unit and a circuit. The pixel includes a first transistor and a second transistor. a first transistor having a first gate electrode electrically connected to one another; The first terminals of the first transistors are electrically connected to each other, All of the second terminals of the first transistors are electrically connected to the pixel section, and the first terminals of the first transistors are electrically connected to the pixel section. The terminal of 1 is in a floating state, and the first transistor and the second transistor The present invention provides a liquid crystal display device having an oxide semiconductor.

[0011] In the above structure, the oxide semiconductor included in the first transistor and the second transistor The present invention provides a liquid crystal display device characterized in that the liquid crystal display device is an intrinsic semiconductor. Effect of the Invention

[0012] In the disclosed invention, a transistor including an oxide semiconductor and having low off-state current is used to This prevents unnecessary current from leaking into the circuit. Therefore, the circuit can operate normally. In a display device having a circuit with a transistor, accurate display can be performed. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a circuit diagram illustrating a semiconductor device. [Diagram 2] FIG. 1 is a circuit diagram illustrating a semiconductor device. [Diagram 3] FIG. 1 is a circuit diagram illustrating a semiconductor device. [Figure 4] FIG. 1 is a circuit diagram illustrating a semiconductor device. [Diagram 5] FIG. 1 is a circuit diagram illustrating a semiconductor device. [Figure 6] 4 is a timing chart illustrating waveforms of signals in a semiconductor device. [Figure 7] 4 is a timing chart illustrating waveforms of signals in a semiconductor device. [Figure 8] FIG. 1 is a circuit diagram illustrating a semiconductor device. [Figure 9] FIG. 1 is a circuit diagram illustrating a semiconductor device. [Figure 10] FIG. 1 is a circuit diagram illustrating a semiconductor device. [Figure 11] FIG. 1 is a circuit diagram illustrating a semiconductor device. [Figure 12] 1 is a cross-sectional view illustrating a semiconductor device. [Figure 13] 1A and 1B are a circuit diagram and a cross-sectional view illustrating a display device. [Figure 14] FIG. 1 is a cross-sectional view illustrating a display device. [Figure 15] 4 is a timing chart illustrating waveforms of a display device. [Figure 16] 1A to 1C are diagrams illustrating electronic devices. [Figure 17] 1A to 1C are diagrams illustrating electronic devices. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment will be described with reference to the drawings. In the drawings, the same reference numerals are used to indicate the same objects, and the same parts or the same components are shown in different drawings. Detailed description of the parts having various functions will be omitted.

[0015] (Embodiment 1) In this embodiment, a transistor having an oxide semiconductor, particularly a transistor having an oxide semiconductor in an active layer, A device (semiconductor device, display device, or light-emitting device) configured using a transistor having the above structure An example of the transistor having an oxide semiconductor is described with reference to the drawings. Since the current is low, the off-state current generated in a semiconductor device including an oxide semiconductor is low. In addition, a transistor including an oxide semiconductor can be insulating. High voltage resistance. Therefore, it operates normally even when high voltage is applied. The off-state current when switching on can also be reduced, reducing defects caused by the off-state current. It is possible to do so.

[0016] FIG. 1 shows a configuration example of a device according to the present embodiment. 01 and circuit 111.

[0017] In the pixel section 101, a plurality of pixels are arranged in a matrix. "Arranged in a square" means that the pixels are arranged in a straight line in the vertical or horizontal direction. This includes cases where the elements are arranged in a zigzag pattern or in a jagged line. For example, the pixel 102a and the pixel 102b are arranged side by side in the horizontal direction. The pixel 102c and the pixel 102d are arranged side by side in the horizontal direction. Pixels 102a and 102c are arranged vertically side by side. The pixels 102a and 102b are arranged in a vertical line. The vertically arranged pixels are connected to each other by wiring that runs vertically. The pixels that are connected and arranged in the horizontal direction are connected by wiring that extends in the left-right direction. For example, pixel 102a and pixel 102b are connected by a wiring 104a. Similarly, the pixel 102c and the pixel 102d are connected by a wiring 104b. Similarly, the pixel 102a and the pixel 102c are connected by a wiring 103a. The pixel 102b and the pixel 102d are connected to each other by a wiring 103b. In addition, other wiring, such as wiring to which all pixels are connected (common wiring, power supply line, etc.), Therefore, the pixels can be connected. The same can be said for the other pixels. and are similarly connected.

[0018] Here, the wirings arranged extending in the left-right direction, such as the wiring 104a and the wiring 104b, are The wiring 104a may be connected to the gate of a transistor included in the pixel. Wires extending in the left-right direction, such as the wire 104b, are gate signal lines (gate wiring Alternatively, the wiring 104a, the wiring 104b, etc. As shown in the figure, the wiring extending in the left and right direction is supplied with signals to select one row at a time. Therefore, the signal such as the wiring 104a and the wiring 104b may be scanned. The wiring extending in the left and right direction is the scan signal line (scan wiring, scan line It can have functions such as).

[0019] Alternatively, the wiring 103a, the wiring 103b, the wiring 103c, the wiring 103d, the wiring 103e, Wire 103f, wire 103g, wire 103h, wire 103i, wire 103j, wire 103k , like the wiring 103L (the wiring 103a to the wiring 103L), The wiring may be connected to the source or drain of a transistor in each pixel. Therefore, wirings arranged to extend in the vertical direction, such as the wirings 103a to 103L, The line can have the function of a source signal line (source wiring, source line, etc.); or In the wirings arranged to extend in the vertical direction, such as the wirings 103a to 103L, data is A data signal, a video signal, a source signal, etc. may be supplied. The wirings extending in the vertical direction, such as the wirings 103a to 103L, are data signal lines (data The semiconductor device may have the functions of a photodiode (e.g., photodiode wiring, data line, etc.).

[0020] Next, the circuit 111 is arranged to extend in the vertical direction like the wirings 103a to 103L. The circuit 111 is connected to the pixel portion 101 or each pixel through a wiring. It can be configured as a circuit with various functions.

[0021] An example of a circuit configuration of the circuit 111 is shown in detail in FIG. For example, it may have the function of a precharge circuit, or the function of a check circuit. Alternatively, the circuit 111 may have the functions of a precharge circuit and a check circuit. However, one aspect of the embodiment of the present invention is that Not limited to:

[0022] The circuit 111 includes a transistor 201a, a transistor 201b, a transistor 201c, Transistor 201d, transistor 201e, transistor 201f, transistor 2 01g, transistor 201h, transistor 201i, transistor 201j, Transistor 201k, transistor 201L (transistors 201a to 201 The wirings 103a to 103L are connected to the wiring 202 and the transistor 20 1a to 201L are connected to each other. One of the source and drain of each of the transistors 201a to 201L is connected to a wiring 202. The other of the sources or drains of the transistors 201a to 201L is are connected to the wirings 103a to 103L, respectively. is connected to the gates of the transistors 201a to 201L. Therefore, the gates of the transistors 201a to 201L are connected to each other. do.

[0023] In this specification, a transistor includes a gate, a drain, and a source. The drain terminal is a diode that has at least three terminals. Between the drain region or drain electrode and the source (source terminal, source region or source electrode) A current flows through the drain, the channel region, and the source. This is what is possible.

[0024] In this specification and the like, an example of a transistor is a multi-gate transistor having two or more gate electrodes. A multi-gate transistor can be used. Since the panel regions are connected in series, a structure in which multiple transistors are connected in series is obtained. Therefore, the multi-gate structure reduces the off-current and improves the breakdown voltage of the transistor (reliability). Or, by using a multi-gate structure, it is possible to improve the efficiency when operating in the saturation region. Even if the voltage between the drain and source changes, the current between the drain and source does not change much. The voltage-current characteristic does not change and has a flat slope. By using certain voltage-current characteristics, it is possible to create an ideal current source circuit or a circuit with a very high resistance. As a result, a differential circuit or a current mirror circuit with good characteristics can be realized. It is possible to achieve the following:

[0025] An example of a transistor is a transistor having a structure in which gate electrodes are arranged above and below a channel. A transistor with a structure in which gate electrodes are arranged above and below the channel can be applied. By using this structure, the circuit configuration becomes like multiple transistors connected in parallel. This increases the channel area, which increases the current value. By using a structure in which gate electrodes are arranged above and below the Therefore, the subthreshold swing value (S value) can be improved.

[0026] The circuit configuration of the circuit 111 is not limited to that shown in FIG. 2, and may have various circuit configurations. An example of the circuit 111 in this case is shown in FIG. 3. Therefore, in FIG. The contents described with respect to can also be applied to FIG.

[0027] FIG. 3 shows an example in which a plurality of wirings 202 are provided as shown in FIG. 2. Although the case where 202 is three pieces has been described, one aspect of the embodiment of the present invention is not limited to this. The number of wirings 103a to 103L can be two, four or more. Any one of the wiring 202a, the wiring 202b, and the wiring 202c and the transistor 201 a to transistor 201L. One of the sources or drains of the transistors 201a to 201L is connected to a wiring 202a, 202b or 202c. The other of the source and drain of the transistor 201L is connected to the wiring 103a to the wiring 103b. The wiring 203 is connected to the transistors 201a to Therefore, the gates of the transistors 201a to 201L are connected to the gates of the transistors 201a to 201L. The gates of the transistors 201L are connected to each other.

[0028] In addition, when performing color display, each color of the pixel to be displayed, wiring 202a, wiring 202b, For the wiring 202c, each color is connected to the wiring 202a, the wiring 202b, or the wiring 202c. For example, the wiring 202a may correspond to any one of the transistors c. The wiring connected through the filter is connected to the red pixel. are connected to the wiring 103a, the wiring 103d, the wiring 103g, and the wiring 103h through transistors, respectively. Similarly, the wiring connected to the wiring 202b through a transistor is , and are connected to blue pixels. 103b, 103e, 103h, and 103k are connected to the wiring 103b, 103e, 103h, and 103k. The wiring connected to the wiring 202c via a transistor is connected to a green pixel. Therefore, the wiring 202c is connected to the wiring 103c and the wiring 103c through the transistors. 3f, wiring 103i, and wiring 103L. The colors are not limited to red, blue, and green. For example, you could add white to make four colors, or use multiple slightly different reds (or blues or greens). It is also possible to use the color filter, which allows color control.

[0029] Next, another example of the circuit configuration of the circuit 111 is shown in FIG. 4. Therefore, FIGS. The above description can also be applied to FIG.

[0030] FIG. 4 shows an example in which a plurality of wirings 203 are provided as shown in FIG. Although the case where 203 is three is shown, one aspect of the embodiment of the present invention is not limited to this. The number of wirings 103a to 103L can be two, four or more. The wiring 202 is connected to the transistors 201a to 201L. Therefore, the sources or drains of the transistors 201a to 201L One of the inputs is connected to a wiring 202, and the other of the inputs is connected to the transistors 201a to 201L. The other of the sources or drains of the transistors 103a to 103L are connected to the wirings 103a to 103L, respectively. Then, any one of the wiring 203a, the wiring 203b, and the wiring 203c is connected to the gates of the transistors 201a to 201L. Therefore, some of the transistors 201a to 201L (for example, For the gates of the transistors 201a, 201d, 201g, and 201j, the gates are connected to each other. , and are connected to the wiring 203a. Similarly, the transistors 201a to 20 Another part of 1L (e.g., transistors 201b, 201e, 201h, 201k ), the gates are connected to each other and to the wiring 203b. Further parts of the transistors 201a to 201L (for example, For transistors 201c, 201f, 201i, and 201L, the gates are connected together. and is connected to a wiring 203c.

[0031] In addition, when performing color display, each color of the pixel to be displayed, wiring 203a, wiring 203b, For the wiring 203c, each color is connected to the wiring 203a, the wiring 203b, or the wiring 203c. For example, the wiring 203a and the gate are connected to each other. The wiring connected to the wiring 202 through the transistor connected to the Therefore, the wiring 202 is connected to the wiring 203a and each transistor whose gate is connected. Connected to wiring 103a, wiring 103d, wiring 103g, and wiring 103j via transistors Similarly, the wiring 203b is connected to the transistor having the gate. The wiring connected to 202 is connected to the blue pixel. Therefore, the wiring 202 is The wiring 103b and the wiring 203b are connected to each transistor having a gate connected thereto. The wire 203c is connected to the gate 103e, the gate 103h, and the gate 103k. The wiring connected to the wiring 202 through the transistor to which the port is connected is a green pixel. Therefore, the wiring 202 is connected to the wiring 203c. Through each transistor, the wiring 103c, the wiring 103f, the wiring 103i, the wiring 103 The colors are not limited to red, blue, and green. For example, white can be added to make four colors. It is also possible to use multiple slightly different reds (or blues or greens). This allows for color control.

[0032] Next, another example of the circuit configuration of the circuit 111 is shown in FIG. 5. Therefore, FIG. 5. Also, the contents described with respect to FIG. 4 can be applied to FIG.

[0033] FIG. 5 shows an example in which a plurality of wirings 202 and wirings 203 are provided. 5 shows a case where the wiring 203 in FIG. 3 is multiple, or the wiring 203 in FIG. This also corresponds to the case where a plurality of wires 202 are provided. Note that in FIG. 5, the wiring 202 and the wiring 203 Although the above is a case where each of the three wires is used, one aspect of the embodiment of the present invention is not limited to this. The number of wirings 103a to 103L can be two or four or more. , any one of the wiring 202a, the wiring 202b, and the wiring 202c and the transistor 2 01a to 201L. The source or drain of each of the transistors 201a to 201L is connected to a wiring 202a. The transistor 201a is connected to either the wiring 202b or the wiring 202c. The other of the source and drain of each of the transistors 201 to 201L is connected to the wiring 103. a to 103L. Any one of the lines 203c is connected to the gates of the transistors 201a to 201L. Therefore, among the transistors 201a to 201L, For some of the transistors (e.g., transistors 201a, 201d, 201g, and 201j), The gates of the transistors 20 are connected to each other and to the wiring 203a. Another part of the transistors 201a to 201L (for example, the transistors 201b, 1e, 201h, 201k), the gates are connected to each other and to the wiring 203b. Similarly, among the transistors 201a to 201L, As for another part (e.g., transistors 201c, 201f, 201i, and 201L), , the gates are connected to each other and to a wiring 203c.

[0034] In addition, when performing color display, each color of the pixel to be displayed and the wiring 20 are connected in the same manner as in FIG. 2 to FIG. 3a, wiring 203b, or wiring 203c, wiring 202a, wiring 202b, or wiring For 202c, each color and either wiring 203a, wiring 203b, or wiring 203c Alternatively, the wiring 202a, the wiring 202b, or the wiring 202c may be arranged to correspond to one of the wirings 202a, 202b, or 202c. It is possible to match one of them. This allows you to control the color. do.

[0035] (Embodiment 2) In this embodiment, an example of the operation of the circuit 111 shown in FIGS. 2 to 5 will be described.

[0036] The circuit 111 can have various functions depending on how it operates. The circuit 111 can have the function of a check circuit and / or a precharge circuit. However, one aspect of the embodiment of the present invention is not limited to this, and may have further other functions. It is.

[0037] First, a method of operation when the circuit 111 is operated as a precharge circuit will be described. The waveform when precharging is performed is shown in FIG. The waveform of the supplied signal is shown in FIG. 6(A). Signal 901 is a waveform having a period 902. For example, the period 902 corresponds to one frame period or one subframe period. In most cases, the signal 901 is an H signal only during a period 903 in a cycle 902. In the other periods, the signal is L. In many cases, this corresponds to the selection period or 1H period. Figure 6(B) shows a detailed view of one gate selection period. The waveforms shown in FIG. 1 are the first half 904 and the second half 905 of one gate selection period. In the first half period 904, a predetermined voltage is applied in advance. In this way, a predetermined voltage can be supplied to the wiring 103a through the wiring 103L. Therefore, the first half period 904 corresponds to the precharge period. In the latter period 905, a video signal is supplied. Therefore, it can also be said that the latter period 905 is a signal input period. For example, the signal 908 is supplied to one of the wirings 103a to 103L. The signal 908 is approximately equal to the potential 906 during the first half of the period 904. Here, the potential 906 can be said to be a reference potential, and as an example The potential is approximately equal to the common potential or counter potential supplied to a display element, for example, a liquid crystal element. Alternatively, the potential may be approximately the middle of the amplitude of the potential of the video signal. In the latter period 905, the signal 908 has a potential according to the video signal. Therefore, the potential of the signal 908 in the latter period 905 is a video signal or The value varies depending on the polarity of the signal supplied to the liquid crystal element. By supplying a constant voltage to the wirings 103a to 103L, the signal can be supplied quickly. Therefore, the signal writing speed is increased, and the signal writing time is shortened. will be shorter.

[0038] In the case of the circuit of FIG. 2, a signal such as signal 907 is provided on wiring 203. Signal 907 is During the first period 904, the transistors 201a to 201L are in a conductive state. A potential 906 is supplied to the wiring 202. As a result, in the first period 904, precharge is applied to the wirings 103a to 103L. It is possible to perform this.

[0039] At this time, the potential of each wiring is controlled using a transistor including an oxide semiconductor. This reduces the effect of the off-state current of the transistor, thereby reducing voltage and noise leakage. Therefore, a precise voltage can be supplied to the wiring. By using transistors that can perform accurate display.

[0040] In this manner, the transistors 201a to 201L are turned on by the gate signals. Therefore, the transistors 201a to 201c have a function of controlling the on and off of the transistors 201a to 201c. The star 201L may have a switch function.

[0041] In the case of the circuit in FIG. 3, a plurality of wirings such as the wirings 202a to 202c are provided. Therefore, in the first period 904, different Therefore, for example, in the first half period 904, It is possible to supply different potentials to the wirings 103a to 103L depending on the This allows for optimal operation in expressing a wide range of colors.

[0042] Alternatively, in the case of the circuit in FIG. 4, a plurality of wirings such as wirings 203a to 203c may be provided. Therefore, by further dividing the first half period 904 into multiple periods, Only one of the transistors 201a to 201L is turned on. In this case, the signal waveforms supplied to the wirings 203a to 203c can be 7. Signal 907a indicates a signal supplied to wiring 203a, and signal 907b indicates a signal supplied to wiring 203b. A signal 907c indicates a signal supplied to the wiring 203c. The signal 907a is an H signal only during the first half of the first half period 904. Signal 907b is an H signal only during the middle period of the first half period 904. The signal becomes H signal only in the latter half of the half period 904. In this way, the first half period 904 is By further dividing the period into a plurality of periods, in each of the plurality of periods, the wiring 202 By making the potentials supplied to the wirings 103a to 103L different from each other, Therefore, in the first half period 904, the potentials of the colors can be different. Accordingly, different potentials can be supplied to the wirings 103a to 103L, respectively. This allows the system to perform the most appropriate operation according to the color.

[0043] Alternatively, in the case of the circuit in FIG. 5, a plurality of wirings such as wirings 202a to 202c may be provided. Therefore, in the first period 904, different In addition, a plurality of wirings such as the wirings 203a to 203c can be provided. Therefore, the first half period 904 is divided into multiple periods as shown in FIG. By this, only one of the transistors 201a to 201L In this way, the first half period 904 can be By further dividing the period into a plurality of periods, in each of the plurality of periods, the wiring 202 By making different potentials supplied to the wirings 103a to 202c, The potentials supplied to the line 103L can be different. In step 04, different potentials are supplied to the wirings 103a to 103L depending on the color. This makes it possible to perform optimal operations according to the color.

[0044] Next, a method of operating the circuit 111 as a test circuit will be described. We consider case 2.

[0045] First, a signal is supplied to the pixel by some means. For example, the wirings 103a to 103c are connected to the pixel. A signal line driver circuit connected to the wiring 103L supplies signals to the wirings 103a to 103L. More preferably, the signal is supplied to one of the wirings 103a to 103L. Alternatively, the transistors 201a to 201L are turned on to supply current through the wiring 202. In addition, the wirings 103a to 103L, more preferably the wirings 103a to 103L Alternatively, a signal is supplied to one of the wirings 103a to 103L. Alternatively, a needle for supplying a signal may be brought into contact with one of the wirings 103a to 103L. Then, a signal is supplied to one of the gate lines, such as the wiring 104a or the wiring 104b. If an H signal is supplied to one of the transistors, the pixel will In this case, a signal is supplied to the pixel. Then, an L signal is supplied to the gate line. , a signal is maintained within the pixel.

[0046] Next, a high signal is applied to the gate line. Then, the signal held in the pixel is At that time, a H signal is supplied to the wiring 203. The transistors 201a to 201L are turned on. The signal stored in the memory cell can be read out via the wiring 202.

[0047] At this time, if there is a defect in the transistor in the pixel, the signal cannot be read out properly. Therefore, depending on whether it is good or bad, it is possible to inspect whether the transistor is normal or not. .

[0048] In addition, when a signal is supplied to one of the wirings 103a to 103L, A signal is supplied to one of the gate lines, and the same operation is repeated. Then, this operation is repeated for all gate lines. This allows all pixels to be inspected. Note that one gate line is selected. In a situation where a gate line is connected to the same pixel, only one pixel is connected to the same pixel. By supplying and reading out signals, it is possible to inspect each pixel accurately. Alternatively, a signal may be supplied to and read out from some or all of the pixels. This allows for rough inspection of pixels.

[0049] In the case of FIG. 3, a plurality of wirings such as wirings 202a to 202c are arranged. Therefore, the signals held in the plurality of pixels are transmitted through the wirings 202a to 202c. Therefore, in the case of Figure 3, three wires are arranged. Therefore, when a signal is first supplied to a pixel, the signal is supplied to three pixels at the same time and read out. When reading out, three pixels can be read out at the same time. This allows for quick inspection. Therefore, the process time for manufacturing semiconductor devices can be shortened, and the cost can be reduced. It is possible to reduce it.

[0050] In the case of FIG. 4, a plurality of wirings such as wirings 203a to 203c are arranged. Therefore, when the signal held in the pixel is read out through the wiring 202, By sequentially changing the signals supplied to the wirings 203a to 203c to H signals, Therefore, when a signal is first supplied to the pixel, When signals are supplied to multiple pixels and read out, the pixels can be read out sequentially one by one. Therefore, the inspection can be performed quickly. This shortens the testing period and reduces costs.

[0051] In the case of FIG. 5, a plurality of wirings such as wirings 202a to 202c are arranged. Therefore, the signals held in the plurality of pixels are transmitted through the wirings 202a to 202c. Further, the signals can be simultaneously read out through the wirings 203a to 203c. Therefore, the signal held in the pixel is transmitted to the wiring 202. When reading out the signals through the wirings 203a to 203c, the signals are sequentially supplied as H signals. By changing the setting, the signals can be read out one by one. Therefore, the test can be performed quickly. Therefore, the process time for manufacturing a semiconductor device or the like can be shortened. , and costs can be reduced.

[0052] Such inspections are carried out as part of the process of manufacturing semiconductor devices, etc. After the semiconductor device is assembled and shipped, the inspection circuit will not operate. .

[0053] In addition, when the off-state current of the transistors 201a to 201L is large, the current As a result, noise is introduced into the wirings 103a to 103L. Here, the transistors including an oxide semiconductor are transistors 201a to 201c. By using it as 01L, the off current can be reduced, and noise can be reduced. .

[0054] In this way, the circuit 111 can achieve various functions by changing the operation method. Therefore, the circuit 111 functions as a precharge circuit and as a check circuit. By having both functions, multiple circuits can be used. Since many functions can be realized, it is possible to realize low costs and low power consumption.

[0055] (Embodiment 3) In this embodiment mode, an example of a circuit surrounding the circuit 111 will be described.

[0056] FIG. 8 shows an example of the circuit 111, the pixel portion 101, and the peripheral circuits thereof. A circuit 111 and a pixel portion 101 are arranged on the substrate 1. The transistors and wirings in the pixel portion 101 are the same as those in the pixel portion 101. The film is deposited on the substrate, etched, and patterned at the same time. The pixel portion 101 and the pixel portion 102 are formed at the same time through the same process steps and on the same substrate. Therefore, the materials of the transistors and the wirings are the same as those of the circuit 111 and the pixel portion 112. Therefore, the transistor in the pixel portion 101 has an oxide semiconductor. In this case, the transistors in the circuit 111 also include an oxide semiconductor.

[0057] In this specification and the like, a transistor can be formed using various substrates. The type of substrate is not limited to a specific one. An example of the substrate is a semiconductor substrate. Solid substrates (e.g., single crystal substrates or silicon substrates), SOI substrates, glass substrates, quartz substrates, Flexible substrates include polyethylene terephthalate (PET) ), plastics such as polyethylene naphthalate (PEN), or acrylic, etc. Examples include flexible synthetic resins.

[0058] Note that a transistor is formed using a certain substrate and then transferred to another substrate. Alternatively, the transistors may be disposed on a separate substrate.

[0059] In addition, all of the circuits required to realize a given function are formed on the same substrate. This allows for cost reduction by reducing the number of components, or the number of connection points with circuit components. The reduction in number of components can improve reliability.

[0060] In FIG. 8A, a circuit 501, a circuit 502, a circuit 503, and a circuit 504 are disposed on a substrate 51. 1. Therefore, for example, the circuit 501 and the circuit 502 are provided on a different substrate. The circuit 503 or the circuit 504 is an IC chip using a single crystal substrate or an SOI substrate. However, the circuit 501, the circuit 502, the circuit 503, and / or the circuit The circuit 504 is mounted on a substrate 511 using COG (chip on glass) mounting. There may be cases where this occurs.

[0061] Here, the circuit 501 controls the circuit 111, supplies signals and voltages to the circuit 111, or The circuit 501 has a function of reading a signal from the circuit 111. For example, the circuit 111 has a function corresponding to the function of the preamplifier 1. When the circuit 501 has a function of a charge circuit, the circuit 501 has a function of controlling the precharge operation. Similarly, if the circuit 111 has the function of a check circuit, the circuit 501 has the function of a check circuit. Similarly, the circuit 111 functions as a precharge circuit and a check circuit. If the circuit has the function, the circuit 501 has a function of controlling the precharge and test operations. It has.

[0062] The circuit 502 has a function of supplying signals to the wiring 104a, the wiring 104b, and the like. Therefore, the circuit 502 has a function as a gate line driving circuit (scan driver). The circuit 503 has a function of supplying signals to the wirings 103a to 103L. Therefore, the circuit 503 functions as a signal line driver circuit (data driver). The circuit 504 has a function of controlling the circuit 502 or the circuit 503. Thus, the circuit 504 includes a controller, a pulse generator, a clock signal, signal generation circuit, common voltage generation circuit, timing generator circuit, image processing circuit, or It can have functions such as a power supply circuit.

[0063] In FIG. 8B, the configuration in FIG. 8A does not include the circuit 501. If the circuit 501 functions as a test circuit, the circuit 501 is required when the test is being performed. However, after the test is completed, the circuit 501 is no longer necessary. Therefore, during the test, The circuit 501 is provided as shown in FIG. 1, and after the test is completed, the circuit 501 can be removed. When the circuit 501 is removed as in FIG. 8(B), the wiring 202 and the wiring 203 are The device enters a pinging state.

[0064] In FIG. 8, the circuit 501, the circuit 502, the circuit 503, and the circuit 504 are connected to the substrate 51. 1, but one aspect of the embodiment of the present invention is not limited to this. For example, some of these circuits may be provided on the substrate 511. FIG. 9 shows an example in which the circuit 502 is provided over a substrate 511. 8A shows a configuration having a circuit 501, and FIG. 9B shows a configuration having a circuit 501 similar to FIG. 9, the circuit 111 and the pixel portion 10 are not included. 1 and the circuit 502 are formed on the same substrate through the same process steps. When the transistor in the pixel portion 101 includes an oxide semiconductor, the transistor in the circuit 111 The transistors in the transistor and the circuit 502 also contain an oxide semiconductor. When the circuit 501 is removed as shown in FIG. 1, the wiring 202 and the wiring 203 are floating. The device will be in a gagged state.

[0065] In this way, by forming the circuit 502 on the same substrate as the pixel portion 101, the cost can be reduced. It is possible to make it easier.

[0066] As an example different from that shown in FIG. 9, the circuit 503 or a part of the circuit 503 is also mounted on the substrate 511. As an example of a part of the circuit 503, the wirings 103a to 103b are provided. An analog switch (transfer gate) can be connected to the line 103L. Similarly, the circuit 504 or a part of the circuit 504 may also be provided on the substrate 511 .

[0067] (Embodiment 4) In this embodiment, an example of a pixel included in the pixel portion 101 will be described.

[0068] FIG. 10A illustrates an example of a circuit of a pixel 102a. A transistor 80 is connected to a wiring 104a. A first terminal of the transistor 801 is connected to the gate of the wiring 103a. A second terminal of the transistor 801 is connected to a first terminal of the display element 802. A second terminal of the display element 802 is connected to the wiring 803. A first terminal of the capacitance element 804 is , and the second terminal of the capacitor 804 is connected to a wiring 805. and is connected.

[0069] Here, the wiring 803 can be connected to each other in all pixels. A predetermined voltage is supplied to the wiring 803. Therefore, the wiring 803 is a common wiring. , a counter electrode, etc.

[0070] Here, the wiring 805 is connected to other pixels, for example, the left and right pixels. It is possible to supply a predetermined voltage to the wiring 805. It is possible for the wiring to have functions such as wiring and capacitance wiring.

[0071] Note that the transistor 801 supplies a signal to the display element 802 or the capacitor 804. Therefore, the transistor 801 can have the function of selecting whether Alternatively, the transistor 801 may function as a switching transistor. It can function as a switching transistor and a selection transistor. It is possible.

[0072] It is also possible to improve the aperture ratio by omitting the capacitor 804. 10B. The transistor 801 is a transistor with low off-state current, for example For example, when a transistor including an oxide semiconductor is used, the capacitor 804 can be omitted. , the voltage applied to the display element 802 can be maintained.

[0073] It should be noted that the example of the pixel circuit is not limited to the circuit shown in FIG. 10. An example is shown. A gate of a transistor 1301 is connected to a wiring 104a. A first terminal of the transistor 1301 is connected to the wiring 103a, and a second terminal of the transistor 1301 is connected to the wiring 103b. is connected to the gate of the transistor 1311. The second terminal of the transistor 1311 is connected to the first terminal of the display element 802. The second terminal of the display element 802 is connected to the wiring 1303. A first terminal of the capacitor 1304 is connected to a second terminal of the transistor 1301. A second terminal of the transistor 1304 is connected to a second terminal of the transistor 1311 .

[0074] Note that the wiring or terminal to which the second terminal of the capacitor 1304 is connected is not limited to that shown in FIG. 1305. Instead, it can be connected to another wire, for example wire 1305.

[0075] Here, the wiring 1303 can be connected to each other in all pixels. A predetermined voltage is supplied to the wiring 1303. , a cathode wiring, a cathode line, etc.

[0076] Here, the wiring 1305 is connected to other pixels, for example, pixels on the left and right or pixels above and below. The power supply 10 can be connected to the power supply 12 and a predetermined voltage is supplied to the power supply 12. The wiring 1305 has functions such as a common wiring, a capacitance wiring, a power supply line, a current supply line, and an anode line. It is possible to do so.

[0077] The transistor 1301 transmits a signal to the transistor 1311 or the capacitor 1304. Therefore, it is possible to select whether or not to supply the transistor The transistor 1301 can have a switching function. It is possible for the transistor to function as a switching transistor and a selection transistor.

[0078] Note that the transistor 1311 supplies a signal, a voltage, or a current to the display element 802. It has a switch function to select whether to switch on or off, and a current source function to control the magnitude of these. Alternatively, the transistor 1311 can be used as a drive transistor. It is possible for the device to have all of the above functions.

[0079] It is possible to improve the aperture ratio by omitting the capacitor 1304. The diagram is shown in FIG. 11B. For example, a transistor having an oxide semiconductor is used to form a capacitor element 1. Even if 304 is omitted, the voltage applied to the display element 802 can be maintained.

[0080] Note that the display element 802 can be made of various elements and functions as a light-emitting element. It is also possible to use the light emitting element 802a as a display element. is shown in Figure 11(B).

[0081] An example of the display element is an EL (electroluminescence) element (organic and EL elements containing inorganic substances, organic EL elements, inorganic EL elements), LEDs (white LEDs, red LEDs D, green LED, blue LED, etc.), liquid crystal elements, electronic ink, electrophoretic elements, carbon nanotubes The contrast, brightness, reflectance, transmittance, etc. are controlled by electromagnetic effects such as the use of nanotubes. One example of a display device using liquid crystal elements is a liquid crystal Examples of display devices using electronic ink or electrophoretic elements include , electronic paper, etc.

[0082] An example of an EL element is a device that includes an anode, a cathode, and an EL layer sandwiched between the anode and the cathode. One example of an EL layer is a device that uses light emission (fluorescence) from singlet excitons. Those that utilize emission from triplet excitons (phosphorescence), and those that utilize emission from singlet excitons ( those that utilize fluorescence and those that utilize emission from triplet excitons (phosphorescence), Those formed by organic matter, those formed by inorganic matter, those formed by organic matter Those made of polymeric materials, those made of low molecular weight materials, those made of inorganic materials, Some contain polymeric materials, while others contain polymeric and low molecular weight materials. However, the present invention is not limited to this, and various EL elements can be used.

[0083] An example of a liquid crystal element is a liquid crystal device that controls the transmission or non-transmission of light by the optical modulation action of liquid crystal. The element can be constructed by a pair of electrodes and a liquid crystal layer. The optical modulation of the liquid crystal is achieved by applying an electric field (horizontal electric field, vertical electric field or oblique electric field) to the liquid crystal. The liquid crystal is controlled by a twisted-negative (TN) electric field. ed Nematic) mode, STN (Super Twisted Nematic ) mode, IPS (In-Plane-Switching) mode, FFS (Frin ge Field Switching) mode, MVA (Multi-domain Vertical Alignment) mode, PVA(Patterned Ver. tical Alignment) mode, ASV (Advanced Super V) iew) mode, ASM(Axially Symmetric aligned Mi cro-cell mode, OCB (Optically Compensated B irefringence mode, ECB (Electrically Controlled lled Birefringence mode, FLC (Ferroelectric Liquid Crystal mode, AFLC (AntiFerroelectr ic Liquid Crystal) mode, PDLC (Polymer Dispe rsed Liquid Crystal) mode, PNLC (Polymer Net work Liquid Crystal) mode, guest host mode, blue phase (B However, it is not limited to these, and liquid crystal elements and A variety of drive systems can be used.

[0084] The transistors included in the circuit 111 have few limitations on the layout of the transistors. Therefore, the transistors included in the circuit 111 (transistors 201a to 201 The channel width (or gate width) W of the transistor (transistor, etc.) of the pixel is The channel width (or The gate width (W) can be made larger than the gate width (W). Since the off-current of the MOSFET is small, even if the channel width (or gate width) W is increased, there is no adverse effect. The channel width (or gate width) of the transistor in the circuit 111 is small. By increasing W, precharge and inspection can be performed quickly. The transistors included in the circuit 111 (transistors 201a to 201L) The channel length (or gate length) L of the transistor (transistor) in the pixel is The channel length (or The gate length L can be made larger.

[0085] (Embodiment 5) In this embodiment, the transistors 201a to 201L The transistors 801, 1301, and 1311 are formed in the channel forming region. In the present invention, a transistor in which a region is formed using an oxide semiconductor is used.

[0086] As for oxide semiconductors, the In-Sn-Ga-Zn-O oxide semiconductor, which is a quaternary metal oxide, is used. Conductors, ternary metal oxides such as In-Ga-Zn-O oxide semiconductors, In-Sn-Zn -O-based oxide semiconductors, In-Al-Zn-O-based oxide semiconductors, Sn-Ga-Zn-O-based oxide semiconductors Semiconductors made of Al-Ga-Zn-O oxides, or Sn-Al-Zn-O oxides In-Zn-O-based oxide semiconductors, which are binary metal oxides, and Sn-Zn- O-based oxide semiconductors, Al-Zn-O-based oxide semiconductors, Zn-Mg-O-based oxide semiconductors, S n-Mg-O oxide semiconductor, In-Mg-O oxide semiconductor, In-O oxide semiconductor The oxide semiconductors used are Sn-O-based oxide semiconductors or Zn-O-based oxide semiconductors. In addition, the oxide semiconductor may be an oxide semiconductor in which SiO2 is added to the above oxide semiconductor.

[0087] In addition, the oxide semiconductor is InMO3(ZnO) m Use materials expressed as (m>0) Here, M is one or more selected from Ga, Al, Mn and Co. Metal element. For example, M is Ga, Ga and Al, Ga and Mn, or Ga and Co, etc. InMO3(ZnO) m (m>0) Among them, the oxide semiconductor having a structure containing Ga as M is the In-Ga-Zn-O oxide described above. The thin film is also called an In-Ga-Zn-O semiconductor.

[0088] One embodiment of a method for manufacturing a transistor in which a channel formation region is formed using an oxide semiconductor is described. This will be explained with reference to FIG.

[0089] 12A to 12D are diagrams illustrating an example of a cross-sectional structure of a transistor. The transistor 410 shown in A) to D) is a bottom gate type called a channel etch type. It is one of the structures.

[0090] Although a transistor having a single gate structure is shown in FIG. If necessary, a transistor having a multi-gate structure having a plurality of channel formation regions may be formed. can be done.

[0091] Hereinafter, a transistor 410 is fabricated on a substrate 400 using FIGS. The process will be explained.

[0092] First, a conductive film is formed on a substrate 400 having an insulating surface, and then a first photolithography process is performed. A gate electrode layer 411 is formed by a deposition process.

[0093] There is no significant limitation on the substrate that can be used for the substrate 400 having an insulating surface, but at least At the very least, it is necessary for the material to have heat resistance sufficient to withstand subsequent heat treatment. For example, Glass substrates such as barium borosilicate glass and aluminoborosilicate glass can be used. In addition, if the temperature of the subsequent heat treatment is high, the glass substrate has a distortion point of 730°C or higher. It is recommended to use.

[0094] An insulating film serving as a base film may be provided between the substrate 400 and the gate electrode layer 411. The silicon nitride film, the silicon oxide film, and the like have a function of preventing the diffusion of impurity elements from the substrate 400. The insulating layer is made of one or more films selected from a silicon oxide film, a silicon nitride film, and a silicon oxynitride film. The insulating film can be formed by a laminate structure.

[0095] The material of the gate electrode layer 411 is selected from the group consisting of molybdenum, titanium, chromium, tantalum, and tungsten. Metallic materials such as stainless steel, aluminum, copper, neodymium, scandium, etc., or materials that contain these as their main components The insulating film 10 can be formed as a single layer or a laminated layer using an alloy material.

[0096] Next, the gate insulating layer 402 is formed over the gate electrode layer 411 .

[0097] The gate insulating layer 402 is formed by depositing silicon oxide using a plasma CVD method, a sputtering method, or the like. A silicon layer, a silicon nitride layer, a silicon oxynitride layer, a silicon oxynitride layer, or an aluminum oxide layer. The aluminum layer can be formed as a single layer or a stacked layer. Use of high-k materials such as hafnium (HfOx) and tantalum oxide (TaOx) The thickness of the gate insulating layer 402 is set to 100 nm or more and 500 nm or less. In this case, for example, a first gate insulating layer having a film thickness of 50 nm to 200 nm and a first gate A second gate insulating layer having a thickness of 5 nm to 300 nm is laminated on the insulating layer.

[0098] In this embodiment, the gate insulating layer 402 is formed to a thickness of 100 nm by plasma CVD. The following silicon oxynitride layers are formed:

[0099] In addition, a silicon oxynitride film is formed as the gate insulating layer 402 by using a high density plasma device. Here, the high-density plasma device may be 1×1011 / cm 3 More than 100% plasma density For example, a microwave power of 3kW to 6kW can be applied to Plasma is generated to form an insulating film. The insulating film obtained by the high-density plasma device It is excellent in step coverage because it can form a film of a constant thickness. The insulating film obtained by this device can be precisely controlled to a thin film thickness.

[0100] The insulating film obtained by the high-density plasma device is different from that obtained by the conventional parallel plate type PCVD device. The etching rates are significantly different from those of the insulating films used in the past, and the etching rates were compared using the same etchant. In the case of a parallel plate PCVD device, the insulation film obtained is 10% or more or 20% The insulating film obtained by the high-density plasma device is a dense film.

[0101] Note that the oxide semiconductor (highly purified oxide) to be made i-type or substantially i-type in a later process Since the semiconductor (compound semiconductor) is extremely sensitive to interface states and interface charges, Therefore, the gate insulating layer (GI) in contact with the highly purified oxide semiconductor is High quality is required. Therefore, high density plasma CVD using μ-wave (2.45GHz) is This is preferable because it allows the formation of a high-quality insulating film that is dense and has a high dielectric strength. The close contact between the semiconductor and the high-quality gate insulating layer reduces the interface state and improves the interface characteristics. The reason is that the film quality of the gate insulating layer is good. Of course, it is important to reduce the interface state density with the oxide semiconductor and form a good interface. It is essential.

[0102] Next, an oxide semiconductor film 4 with a thickness of 2 nm to 200 nm is formed on the gate insulating layer 402. The oxide semiconductor film 430 is formed of an In-Ga-Zn-O system or an In-Zn-O system. In this embodiment, the oxide semiconductor film 430 is formed of an oxide semiconductor film such as In. The film is formed by sputtering using a Ga-Zn-O-based oxide semiconductor target. The cross-sectional view at the step corresponds to FIG. 12A. In an atmosphere of noble gas (typically argon), in an atmosphere of oxygen, or in an atmosphere of noble gas (typically argon) and oxygen The film can be formed by a sputtering method in a mixed atmosphere.

[0103] Here, a metal oxide target containing In, Ga, and Zn (In2O3:Ga2O 3:ZnO=1:1:1 [molar ratio]) was used, and the distance between the substrate and the target was set at 1 00mm, pressure 0.2Pa, direct current (DC) power supply 0.5kW, argon and oxygen (argon The film is formed in an atmosphere of oxygen (oxygen flow rate: 30sccm:20sccm, oxygen flow rate ratio: 40%). By using a pulsed direct current (DC) power supply, the amount of powdery material generated during film formation can be reduced, and the film thickness distribution can be improved. The thickness of the In-Ga-Zn-O film is preferably 5 nm or more and 200 nm or less. In this embodiment, the oxide semiconductor film is formed using an In-Ga-Zn-O based metal A 20 nm thick In-Ga-Zn-O film was formed by sputtering using an oxide target. Next, the oxide semiconductor film 430 is formed into an island-like The film is processed into an oxide semiconductor layer.

[0104] Next, the oxide semiconductor layer is dehydrated or dehydrogenated. The temperature of the heat treatment in step 1 is 400° C. or higher and 750° C. or lower, preferably 400° C. or higher to prevent distortion of the substrate. Here, the substrate is introduced into an electric furnace, which is a type of heat treatment device, and an oxide semiconductor is The layer was heated at 450°C for 1 hour in a nitrogen atmosphere, and then exposed to air. Therefore, water or hydrogen is prevented from being recontaminated into the oxide semiconductor layer, and the oxide semiconductor layer 431 is obtained. See Figure 12(B).

[0105] The heat treatment device is not limited to an electric furnace, and may be a heat treatment device using heat conduction from a heating element such as a resistance heating element or the like. The apparatus may be equipped with a device for heating the object to be treated by thermal radiation. For example, the GRTA (Ga s Rapid Thermal Anneal) equipment, LRTA (Lamp Rapi) d Thermal Anneal (RTA) equipment The LRTA device can be equipped with halogen lamps, metal halide lamps, etc. Iridium lamps, xenon arc lamps, carbon arc lamps, high pressure sodium lamps, This is a device that heats the workpiece by radiating light (electromagnetic waves) emitted from a lamp such as a pressure mercury lamp. The GRTA device is a device that uses high-temperature gas for heat treatment. Inert gases such as argon or nitrogen that do not react with the workpiece during heat treatment An active gas is used.

[0106] For example, the first heat treatment is performed in an inert gas heated to a high temperature of 650°C to 700°C. The substrate is moved in and heated for a few minutes, then the substrate is moved out and heated to a high temperature inert gas. You can also use GRTA, which is a method of removing the food from inside the container. Using GRTA, high-temperature heat treatment can be performed in a short time. It becomes.

[0107] The atmosphere of the first heat treatment is nitrogen, helium, neon, or argon. It is preferable that the rare gas, dry air, etc., does not contain water, hydrogen, etc. The purity of the nitrogen or rare gases such as helium, neon, and argon introduced into the device is 6N (9 9.9999%) or more, preferably 7N (99.99999%) or more (i.e. impurity concentration It is preferable to set the content of the EDTA to 1 ppm or less, and preferably 0.1 ppm or less.

[0108] In addition, the first heat treatment of the oxide semiconductor layer is performed after the oxide semiconductor layer is processed into an island-shaped oxide semiconductor layer. It is also possible to perform the same on the semiconductor film 430. In that case, after the first heat treatment, The substrate is removed from the apparatus and a second photolithography process is performed.

[0109] In addition, in the case where an opening is formed in the gate insulating layer 402, the process is performed after the oxide semiconductor film 430 This may be carried out before or after the dehydration or dehydrogenation treatment.

[0110] Note that the etching of the oxide semiconductor film 430 here is not limited to wet etching. Alternatively, dry etching may be used.

[0111] The etching gas for the oxide semiconductor film 430 used in the dry etching is an etching gas containing chlorine. Gases containing fluorine (e.g., chlorine (Cl2), boron chloride (BCl3), etc.) are preferred.

[0112] The etching solution for the oxide semiconductor film 430 used in the wet etching is a mixture of phosphoric acid and acetic acid. A solution of acid and nitric acid or ITO07N (manufactured by Kanto Chemical Co., Ltd.) can be used.

[0113] Next, a metal conductive film is formed over the gate insulating layer 402 and the oxide semiconductor layer 431. The metal conductive film may be formed by sputtering or vacuum deposition. Aluminum (Al), Chromium (Cr), Copper (Cu), Tantalum (Ta), Titanium (Ti ), Molybdenum (Mo), Tungsten (W), Neodymium (Nd), Scandium (Sc ), an alloy containing the above elements, or a combination of the above elements In addition, a nitride film of the above-mentioned elements may be used. n), magnesium (Mg), zirconium (Zr), beryllium (Be), yttrium The material may be selected from one or more of the following materials: The insulating film may have a single-layer structure or a laminated structure of two or more layers. For example, A single-layer structure of titanium film, a two-layer structure of titanium film on aluminum film, and a titanium film on aluminum film Examples include a three-layer structure in which a titanium film is laminated on top of an aluminum film, and then a titanium film is laminated on top of an aluminum film. can be done.

[0114] When a heat treatment is performed after forming the metal conductive film, the metal conductive film must have heat resistance to withstand this heat treatment. It is preferable to have it.

[0115] A resist mask is formed on the metal conductive film by a third photolithography process. After etching the source electrode layer 415a and the drain electrode layer 415b, Remove the dystomask (see Figure 12(C)).

[0116] In this embodiment, a titanium film is used as the metal conductive film, and an I Using n-Ga-Zn-O oxide, ammonia hydrogen peroxide ( A mixture of 31% by weight hydrogen peroxide, 28% by weight ammonia water, and water (5:2:2) is used.

[0117] Note that in the third photolithography step, the oxide semiconductor layer 431 is only partly etched. In some cases, the oxide semiconductor layer is subjected to etching to have a groove (a recess).

[0118] In addition, in order to reduce the number of photomasks and steps used in the photolithography process, Resist formed using a multi-tone mask, an exposure mask that allows light to pass through in multiple intensities The etching process may be performed using a mask. The mask has a shape with multiple film thicknesses, and the shape is further deformed by ashing. Therefore, it can be used in multiple etching processes to process different patterns. Therefore, one multi-tone mask can be used to produce at least two different patterns. Therefore, the number of exposure masks can be reduced. This also eliminates the need for a corresponding photolithography process, making it possible to simplify the process.

[0119] Then, gases such as nitrous oxide (NO), nitrogen (N2), or argon (Ar) are added to The plasma treatment is performed using a fluorine atom. Water adsorbed on the surface is removed. In addition, a mixture of oxygen and argon gas is used to create a plasma. Processing may be carried out.

[0120] After the plasma treatment, a protective film is placed in contact with a part of the oxide semiconductor layer without being exposed to the air. An oxide insulating layer 416 which serves as an insulating film is formed.

[0121] The oxide insulating layer 416 has a thickness of at least 1 nm and is formed by an oxide insulating method such as a sputtering method. The edge layer 416 can be formed by using an appropriate method that does not allow impurities such as water and hydrogen to be mixed into the edge layer 416. When hydrogen is contained in the oxide insulating layer 416, the hydrogen enters the oxide semiconductor layer, and the oxide insulating layer 416 is oxidized. The back channel of the compound semiconductor layer 431 becomes low resistance (N-type), and the parasitic channel Therefore, the oxide insulating layer 416 is formed so as to contain as little hydrogen as possible. It is important that the deposition process does not involve hydrogen.

[0122] In this embodiment, a silicon oxide film having a thickness of 200 nm is used as the oxide insulating layer 416. The substrate temperature during film formation should be between room temperature and 300°C. In the embodiment, the temperature is set to 100° C. The silicon oxide film is formed by sputtering using a rare gas (typically In the case of argon, oxygen, or rare gas (typically argon) and oxygen The target may be a silicon oxide target or a mixture of silicon and oxygen. Alternatively, a silicon target can be used. For example, a silicon target can be used to A silicon oxide film can be formed by a sputtering method in an oxygen and nitrogen atmosphere.

[0123] The second heating is then carried out under an inert gas atmosphere, a dry air atmosphere, or an oxygen gas atmosphere. Heat treatment (preferably at 200°C or higher and 400°C or lower, for example at 250°C or higher and 350°C or lower) is performed. For example, the second heat treatment is performed at 250° C. for 1 hour in a nitrogen atmosphere. As a result, part of the oxide semiconductor layer (a channel formation region) is in contact with the oxide insulating layer 416. As a result, oxygen is supplied to a part (channel formation region) of the oxide semiconductor layer. In addition, at the boundary between the source electrode layer 415a or the drain electrode layer 415b and the oxide semiconductor layer, In the vicinity of the surface, oxygen diffuses into the source electrode layer 415a or the drain electrode layer 415b. As a result, a source region 414a and a drain region 414b are formed.

[0124] Through the above steps, the oxide semiconductor layer is dehydrated or dehydrogenated. After the heat treatment, a part of the oxide semiconductor layer (a channel formation region) is selectively treated with an oxygen excess. Note that a part of the oxide semiconductor layer in an oxygen-excess state is designated as a region 413 in the drawing. Through the above steps, a transistor 410 is formed.

[0125] Furthermore, heat treatment is performed in air at 100°C to 200°C for 1 hour to 30 hours. In this embodiment, heat treatment is performed at 150° C. for 10 hours. The heating temperature may be maintained at 100°C or 200°C. The heating and cooling from the heating temperature to room temperature may be repeated several times.

[0126] A protective insulating layer may be further formed on the oxide insulating layer 416. For example, the protective insulating layer may be formed by RF sputtering. The RF sputtering method is suitable for mass production, so it is suitable for forming a protective insulating layer. It is preferable as a membrane method. The protective insulating layer is formed by removing moisture, hydrogen ions, and OH - Contains impurities such as First, inorganic insulating films are used to block these substances from entering from the outside, and silicon nitride films and nitride films are used. An aluminum nitride film, a silicon nitride oxide film, an aluminum oxynitride film, or the like is used. In this example, a protective insulating layer 403 is formed using a silicon nitride film (FIG. 12(D)). )reference).

[0127] In this embodiment, the oxide semiconductor layer of the transistor 410 is formed using hydrogen as an n-type impurity. from the oxide semiconductor, and impurities other than the main components of the oxide semiconductor are minimized. It is made into true (i-type) or substantially true type by high purification. In other words, instead of adding impurities to make it i-type, impurities such as hydrogen and water were removed as much as possible. It is characterized by being able to produce a highly purified i-type (intrinsic semiconductor) or something close to it. By doing so, the Fermi level (Ef) is brought to the same level as the intrinsic Fermi level (Ei). can be done.

[0128] The band gap (Eg) of the oxide semiconductor is 3.15 eV and the electron affinity (χ) is 4 The titanium (T The work function of i) is almost equal to the electron affinity (χ) of the oxide semiconductor. In this case, At the interface of the nitride semiconductor, no Schottky barrier is formed for electrons.

[0129] For example, if the channel width W of a transistor is 1×10 4 μm and channel length L is 3 μm Even if the off-current is 10 -13 A or less, and the S value is 0.1V / de cade (gate insulating layer thickness 100 nm).

[0130] In this way, the oxide semiconductor is highly purified so that impurities other than the main component are not included as much as possible. This allows the transistor 410 to operate satisfactorily.

[0131] In order to suppress fluctuations in electrical characteristics, the oxide semiconductor described above is designed to be free of hydrogen and moisture, which are factors that cause fluctuations. Intentionally eliminate impurities such as hydroxyl groups or hydrides (also called hydrogen compounds) and The oxide semiconductor's main component, oxide, is reduced during the process of removing the oxide. Since the element is supplied, it is a highly purified and electrically i-type (intrinsic) oxide semiconductor.

[0132] Therefore, the less hydrogen there is in the oxide semiconductor, the better. There are very few carriers in semiconductors (close to zero), with a carrier density of 1×10 12 / cm 3 Less than 1 x 10 11 / cm 3 That is, the capacitance of the oxide semiconductor layer is less than The rear density is close to zero because there are very few carriers in the oxide semiconductor layer. The lower the off-current, the better. The transistor has a current value of 100 aA / μm per 1 μm of channel width (w). less than 10zA (zeptoamperes) / μm, preferably less than 1zA / μm Furthermore, since there is no pn junction and no hot carrier degradation, The electrical characteristics of the resistor are not affected.

[0133] In this way, the hydrogen contained in the oxide semiconductor layer is thoroughly removed, resulting in a highly purified oxide semiconductor layer. A transistor that uses an oxide semiconductor for a channel formation region has an extremely low off-state current. That is, when the transistor is off, the oxide semiconductor layer acts as an insulator. On the other hand, the oxide semiconductor layer can be regarded as a conductor for transistors. In the on-state, it is expected to have a higher current supply capacity than a semiconductor layer made of amorphous silicon. It is possible to do so.

[0134] In addition, thin film transistors having low-temperature polysilicon are manufactured using oxide semiconductors. The off-state current is estimated to be about 10,000 times larger than that of the previously developed transistor. Therefore, for transistors having oxide semiconductors, When the storage capacitance is the same (about 0.1 pF) as that of a thin-film transistor equipped with a The voltage retention period can be extended by about 10,000 times. When performing at 60 frames per second, the retention period for one signal write is increased by 10,000 times to 16. Even with a small number of image signal writes, the display Still images can be displayed.

[0135] (Embodiment 6) In this embodiment, an example of a pixel and a method of driving the pixel will be described. An example of a pixel including a display element having such a property and an example of a method of driving the pixel will be described.

[0136] FIG. 13A shows an example of a circuit diagram of a pixel. The pixel 5450 includes a transistor 5451, The transistor 5451 includes a capacitor 5452 and a display element 5453. The second terminal of the transistor 5451 is connected to the wiring 5461. One electrode of the display element 5453 (also called a pixel electrode) is connected to the other electrode of the display element 5453. The gate of the transistor 5451 is connected to a wiring 5462. The electrode is connected to a wiring 5463. The other electrode of the display element 5453 is an electrode 5454 ( It is connected to a common electrode (common electrode), counter electrode, cathode electrode, etc.

[0137] Note that one electrode of the display element 5453 is indicated as an electrode 5455 .

[0138] Here, when FIG. 13(A) corresponds to FIG. 10(A), the transistor 5451 is a transistor The display element 5453 corresponds to the display element 802, and the capacitor element 5452 corresponds to the display element 803. corresponds to the capacitor element 804, the wiring 5462 corresponds to the wiring 104a, and the wiring 5461 corresponds to the wiring Corresponds to 103a.

[0139] Note that the display element 5453 preferably has a memory property. The driving method of the display element 5453 is a microcapsule type electrophoresis method, a microcapsule Type electrophoresis, horizontal migration type electrophoresis, vertical migration type electrophoresis, twist ball type type, powder movement type, electronic powder liquid type, cholesteric liquid crystal element, chiral nematic These include ferromatic liquid crystal, antiferroelectric liquid crystal, and polymer dispersed liquid crystal.

[0140] The voltage applied to such a display element 5453 is very high. The transistors that drive the transistors must have high breakdown voltage. Even when a large current is applied, the off-state current must be low. By using a transistor including an oxide semiconductor as a transistor, the withstand voltage can be high. A transistor with a small off-state current can be realized.

[0141] Figure 13(B) shows a cross-sectional view of a pixel using a microcapsule type electrophoretic method. A plurality of microcapsules 5480 are disposed between 5454 and the electrode 5455. The microcapsules 5480 are fixed by a resin 5481. The resin 5481 is a bilayer. The resin 5481 preferably has a light-transmitting property. The space formed by 54, the electrode 5455, and the microcapsule 5480 contains air or The electrode 5454 may be filled with a gas, such as an inert gas. A layer containing an adhesive or a bonding agent is formed on one or both of the electrode 5455 and the micro The capsule 5480 may be secured in place.

[0142] The microcapsule 5480 includes a membrane 5482, a liquid 5483, particles 5484, and a particle 5485. The liquid 5483, the particles 5484, and the particles 5485 are formed on the film 5482. The film 5482 is transparent. The liquid 5483 is a dispersion liquid. The liquid 5483 separates the particles 5484 and the particles 5485 into the membrane 5482. It is preferable that the liquid 5483 is transparent and colorless. The particles 5484 and 5485 are different in color. One of the particles 5484 and 5485 is black, and the other of the particles 5484 and 5485 is white. The particles 5484 and 5485 are arranged so that their charge densities and polarities are different from each other. For example, one of the particles 5484 and 5485 is positively charged. The other of the particles 5484 and 5485 may be negatively charged. When a potential difference occurs between 454 and electrode 5455, particles 5484 and 5485 are electrically In this way, the reflectance of the display element 5453 changes, The gradation can be controlled. However, the structure of the microcapsule 5480 is the same as that described above. For example, the liquid 5483 can be colored. Thus, the particles encapsulated in membrane 5482 can be of one type. Or, three types. As another example, particles 5484 and particles 5485 can be white. Not only black, but also red, green, blue, cyan, magenta, yellow, emerald green You can choose from a range of colours including black, red, and vermilion.

[0143] The film 5482 is made of a material having light-transmitting properties (for example, acrylic resin (for example, polymethacrylic Polymethyl acrylate, polyethyl methacrylate, etc.), polymer resins such as urea resin or gum arabic The membrane 5482 may be gelatinous. This provides flexibility, It is possible to improve bending strength and mechanical strength, and therefore improve flexibility. Alternatively, the microcapsules 5480 can be uniformly packed into the film without gaps. The substrate may be disposed on a substrate such as a substrate.

[0144] The liquid 5483 may be a light-transmitting oily liquid. 483 includes alcohol solvents (e.g., methanol, ethanol, etc.), esters ( ethyl acetate or butyl acetate, aliphatic hydrocarbons (e.g. acetone, methyl Ketones such as methyl ketone, methyl isobutyl ketone, pentane, hexane, or octane, etc. ), alicyclic hydrocarbons (e.g., cyclohexane or methylcyclohexane), long-chain alkane Aromatic hydrocarbons such as benzenes having alkyl groups (e.g., benzene, toluene, xylene, etc.), halogenated hydrocarbons (e.g. methylene chloride, chloroform, etc.), carboxylates , water, or other oils, or at least two of these materials. or mixtures of these materials or at least two of these materials. The mixture may also contain surfactants.

[0145] The particles 5484 and the particles 5485 are each made of a pigment. The pigments that make up particle 5485 are preferably different colors. The particles 84 are made of black pigment, and the particles 5485 are made of white pigment. Black pigments include aniline black and carbon black. Examples of materials include titanium dioxide, zinc oxide, and antimony trioxide. These pigments may contain charge control agents (e.g. electrolytes, surfactants, metal soaps, resins, rubbers, Oil, varnish or compound, etc.), dispersing agent (e.g. titanium-based coupling agent, aluminum Addition of a lubricant or stabilizer, etc. It is possible to add

[0146] FIG. 14A shows an image in which a twist ball method is used as the method of the display element 5453. The cross-sectional view of the element is shown. The twist ball method changes the reflectance by rotating the display element. The difference from FIG. 13B is the difference between the electrode 5454 and the electrode 5455. In between, instead of the microcapsules 5480, a twist ball 5486 is placed. The twist ball 5486 is formed around the particle 5487. The particle 5487 has a hemispherical surface and a cavity 5488. The particle 5487 is a spherical particle painted in one color and another color different from the one color. The hemispheres are painted white and black. A charge density and polarity difference are provided. Therefore, a potential between the electrodes 5454 and 5455 is By creating a difference, the particle 5487 can be caused to rotate according to the electric field direction. Cavity 5488 is filled with a liquid, similar to liquid 5483. However, the twist ball 5486 is limited to the structure shown in FIG. For example, the structure of the twist ball 5486 may be cylindrical or elliptical, etc. It is possible.

[0147] FIG. 14B shows a display device using a microcup type electrophoretic system. The cross-sectional view of a pixel when the microcup array is formed is shown in Fig. 1. The microcup array is made of UV-curable resin and has multiple A microcup 5491 having a recess is filled with charged pigment particles dispersed in a dielectric solvent 5492. The sealing layer 5494 is then filled with a filler 5493 and sealed with a sealing layer 5494. An adhesive layer 5495 may be formed between the dielectric solvent 5492 and the electrode 5455. For this purpose, it is possible to use a non-colored solvent, or a colored solvent such as red or blue. Here, the case where there is one type of charged pigment particles is illustrated, but it is also possible to use two types of charged pigment particles. Since the microcups have a wall structure that separates the cells, they are resistant to shocks and It is also able to withstand pressure. The contents of the microcups are sealed, The effects of environmental changes can be reduced.

[0148] FIG. 14C shows a display device using an electronic liquid powder (registered trademark) method. The cross-sectional view of a pixel in this case is shown. Electronic Liquid Powder (registered trademark) exhibits fluidity and has the characteristics of fluid and particles. In this method, the cells are separated by partitions 5504, and electronic powder is placed in the cells. Fluid (registered trademark) 5502 and electronic liquid powder (registered trademark) 5503 are placed. (registered trademark) 5502 and electronic liquid powder (registered trademark) 5503, white particles and black particles However, Electronic Liquid Powder (registered trademark) 5502 and Electronic Liquid Powder (registered trademark) The type of the liquid powder 5503 is not limited to this. For example, the liquid powder 5502 and For electronic powder (registered trademark) 5503, colored particles of two colors other than white and black are used. As another example, Electronic Liquid Powder (registered trademark) 5502 and Electronic Liquid Powder (registered trademark) It is possible to omit either the mark 5503 or the mark 5504.

[0149] As shown in FIG. 13A, a signal is input to the wiring 5461. A signal (for example, a video signal) for controlling the gray scale of the display element 5453 is applied to the line 5461. In this way, the wiring 5461 is a signal line or a source signal line (video The wiring 5462 has a function as a signal line or a source line. In particular, a signal indicating whether the transistor 5451 is in a conducting state or not is input to the wiring 5462. A signal (e.g., gate signal, scanning signal, selection signal, etc.) for controlling the In this way, the wiring 5462 is a signal line or a gate signal line (a scanning signal line or a gate The wiring 5463 is supplied with a predetermined voltage. The wiring 5463 is connected to the capacitor 5452. The electrode 5463 functions as a power supply line or a capacitance line. A constant voltage is supplied to the electrodes 5454 between a plurality of pixels or between all pixels. Therefore, the electrode 5454 is a common electrode (common electrode, opposite It is assumed that the electrode has a function as an electrode (e.g., a counter electrode or a cathode electrode).

[0150] Note that signals input to the wiring 5461, the wiring 5462, the wiring 5463, and the electrode 5454 The voltage is not limited to the above, and various other signals or voltages may be input. For example, a signal can be input to the wiring 5463. Since the potential of the electrode 5455 can be controlled by this, the signal input to the wiring 5461 Therefore, the wiring 5463 can function as a signal line. As another example, the voltage supplied to the electrode 5454 can be changed. In this way, the voltage applied to the display element 5453 can be adjusted. The amplitude voltage of the signal input to the line 5461 can be reduced.

[0151] The transistor 5451 has a function of controlling the conduction state between the wiring 5461 and the electrode 5455. Alternatively, the transistor 5451 supplies a potential of the wiring 5461 to the electrode 5455. Alternatively, the transistor 5451 has a function of controlling the timing of supplying the pixel 54 50. In this way, the transistor 5451 The transistor has a function as a switch or a selection transistor. The transistor 5451 is an N-channel type. When an H signal is input to wiring 5462, it turns on, and when an L signal is input to wiring 5463, it turns off. However, the polarity of the transistor 5451 is not limited to an N-channel type. Transistor 5451 can be a P-channel type. 451 is turned on when an L signal is input to wiring 5462, and turned on when an H signal is input to wiring 5462. The capacitor 5452 is connected to an electrode 5455 and a wiring 5463. The capacitor 5452 has a function of holding a potential difference between the electrode 5455 and the This function keeps the potential at a predetermined value. This turns off the transistor 5451. Even if the voltage is applied to the display element 5453, the voltage can be continuously applied to the display element 5453. The transistor 5451 and the transistor 452 function as a storage capacitor. The functions of the capacitor 5452 are not limited to those described above, and may have various other functions. It is possible to do so.

[0152] Next, an outline of the operation of the pixel of this embodiment will be described. The control is performed by applying a voltage to the display element 5453 to generate an electric field in the display element 5453. The voltage applied to the display element 5453 is controlled by the potential of the electrode 5454 and the This is done by controlling the potential of the electrode 5455. Specifically, the control of the potential of the electrode 5454 This is performed by controlling the voltage supplied to the electrode 5454. The control is performed by controlling a signal input to the wiring 5461. The signal input to 61 is input to the electrode 5455 by turning on the transistor 5451. are supplied to.

[0153] The strength of the electric field applied to the display element 5453, the direction of the electric field applied to the display element 5453, and The display element 5453 is controlled by controlling one or more of the time when an electric field is applied to the display element 5453. The gradation of the electrode 5453 can be controlled. By not generating a potential difference, the gray scale of the display element 5453 can be maintained.

[0154] Next, an example of the operation of the pixel of this embodiment will be described. The diagram shows a period T having a selected period and a non-selected period. The selected period refers to the period between the start time of one selection period and the start time of the next selection period.

[0155] During the selection period, an H signal is input to the wiring 5462, so that the potential of the wiring 5462 (potential V5 The input terminal 462 is at H level. Therefore, the transistor 5451 is turned on. Then, the wiring 5461 and the electrode 5455 are brought into a conductive state. The signal to be output is supplied to the electrode 5455 via the transistor 5451. The potential of 5455 (shown as potential V5455) is equal to the value of the signal input to the wiring 5461. At this time, the capacitor 5452 has a potential difference between the electrode 5455 and the wiring 5463. During the non-selection period, an L signal is input to the wiring 5462, so that The potential becomes L level. Therefore, the transistor 5451 is turned off, and the wiring 54 61 and the electrode 5455 are in a non-conductive state. Then, the electrode 5455 is in a floating state. In this case, the capacitor 5452 is connected between the electrode 5455 and the wiring 5463 during the selection period. Therefore, the potential of the electrode 5455 is the same as that of the wiring 546 during the selection period. The signal remains equal to the signal input to transistor 1 during the non-selection period. Even if the switch 5451 is turned off, a voltage can continue to be applied to the display element 5453. As described above, by controlling the signal input to the wiring 5461 during the selection period, It is possible to control the voltage applied to the display element 5453. The gradation is controlled by controlling a signal input to the wiring 5461 during the selection period. It can be done.

[0156] Note that the potential of the electrode 5455 in the non-selection period is determined by the off-state current of the transistor 5451, the Feedthrough of transistor 5451 and charge injection of transistor 5451 The signal input to the wiring 5461 during the selection period is affected by one or more of the following: may differ.

[0157] As shown in FIG. 15B, in a part of the selection period, the potential of the electrode 5455 is changed to This can be set equal to pole 5454, which selects pixel 5450. Even if the same signal continues to be input to the pixel 5450, the electrode 545 By changing the potential of the display element 5453, the electric field strength of the display element 5453 can be changed. Therefore, it is possible to reduce afterimages or to speed up the response speed. Alternatively, the variation in response speed between pixels can be reduced, and unevenness or residual images can be prevented. In order to realize such a driving method, the selection period is divided into a period T1 and a period In the period T1, the signal input to the wiring 5461 is In the period T2, the input to the wiring 5461 is The input signal may have various values ​​to control the gray scale of the display element 5453. If the time of period T1 is too long, the time to write a signal for controlling the gradation of the display element 5453 to the pixel 5 450 becomes short. Therefore, it is preferable that the period T1 is shorter than the period T2. In particular, it is preferable that the period T1 is 1% or more and 20% or less of the selection period. More preferably, it is 3% or more and 15% or less. Even more preferably, it is 5% or more and 10% or less.

[0158] Next, an example of the operation of the pixel of the present embodiment for controlling the gradation of the display element 5453 by the time of applying a voltage to the display element 5453 will be described. The timing chart shown in FIG. 15(C) has a period Ta and a period Tb. And the period Ta has N (N is a natural number) periods T. The N periods T are each the same as the period T shown in FIGS. 15(A) to (B). The period Ta is a period for changing the gradation of the display element 5453 (for example, an address period, a writing period, an image rewriting period, etc.). The period Tb is a period (holding period) for holding the gradation of the display element 5453 in the period Ta.

[0159] It is assumed that a voltage V0 is supplied to the electrode 5454. Therefore, the potential of the electrode 5454 is V0. It is assumed that a signal having at least three values is input to the wiring 5461. The potentials of the three values of the signal are the potential VH (VH > V0), the potential V0, and the potential VL (VL < V0), respectively. Therefore, it is assumed that the potential VH, the potential V0, and the potential VL are applied to the electrode 5455.

[0160] By controlling the potential applied to the electrode 5455 in each of the N periods T included in the period Ta, the voltage applied to the display element 5453 can be controlled. For example, electrode 5 ​​​​​​​​​​​​​ By applying a potential VH to 455, the potential difference between the electrodes 5454 and 5455 is VH-VL. This allows a positive voltage to be applied to the display element 5453. By applying a potential V0 to the electrode 5455, the potential between the electrodes 5454 and 5455 is The potential difference becomes zero. This allows a voltage of zero to be applied to the display element 5453. When a potential VL is applied to the electrode 5455, the electrodes 5454 and 5455 The potential difference is VL-VH. By this, a negative voltage is applied to the display element 5453. As described above, during the period Ta, the display element 5453 is applied with a positive voltage (VH-VL ), negative voltage (VL-VH), and zero can be applied in various orders. In this way, the gray scale of the display element 5453 can be finely controlled. Alternatively, afterimages can be reduced. Or, the response speed can be increased.

[0161] In this embodiment, when a positive voltage is applied to the display element 5453, the display element 545 The third gradation is closer to black (also called the first gradation). When pressure is applied, the gray scale of the display element 5453 approaches white (also called the second gray scale). When zero voltage is applied to the display element 5453, the grayscale of the display element 5453 is maintained. This shall be done.

[0162] During the period Tb, the signal input to the wiring 5461 is not written to the pixel 5450. Therefore, in the period Tb, the voltage applied to the electrode 5455 in the N-th period T of the period Ta is In particular, in the period Tb, the potential of the display element 5453 continues to be applied to the electrode 5455. It is preferable that the gray scale of the display element 5453 be maintained by not generating an electric field therein. For this purpose, in the N-th period T of the period Ta, a potential V0 is applied to the electrode 5455. As a result, the potential V0 is applied to the electrode 5455 even during the period Tb. Therefore, zero voltage is applied to the display element 5453. The gradation can be maintained.

[0163] Note that the closer the gradation level that the display element 5453 next displays to the first gradation level, the In this case, the time during which the potential VH is applied to the electrode 5455 may be increased. It is preferable to increase the number of times that the potential VH is applied to the electrode 5455. Among them, the potential VH is applied to the electrode 5455 from the time when the potential VL is applied to the electrode 5455. Alternatively, during the N periods T, the potential VH is at the electrode 5 The number of times that potential VL is applied to electrode 5455 minus the number of times that potential VL is applied to electrode 5455 is More is better.

[0164] Note that the closer the gradation level that the display element 5453 next displays to the second gradation level, the In this case, the time during which the potential VL is applied to the electrode 5455 may be increased. It is preferable to increase the number of times that the potential VL is applied to the electrode 5455. Among them, the potential VL is applied to the electrode 5455 from the time when the potential VH is applied to the electrode 5455. Alternatively, during the N periods T, the potential VL is at the electrode 5 The number of times that potential VH is applied to electrode 5455 minus the number of times that potential VH is applied to electrode 5455 is More is better.

[0165] During the period Ta, the potentials applied to the electrode 5455 (potential VH, potential V0, potential V L) depends not only on the gray scale that the display element 5453 will next display, but also on the display It is possible to depend on the gray level already displayed by element 5453. Even if the gray scale to be displayed by the element 5453 is the same, the gray scale to be displayed by the display element 5453 may be changed. Different combinations of potentials may be applied to the electrodes 5455.

[0166] For example, in the period Ta for displaying the gradation already displayed by the display element 5453, The longer the time that the potential VH is applied to the electrode 5455, the The longer the time that the potential VL is applied to the electrode 5455 minus the time that the potential VL is applied to the electrode 5455, the The more times the potential VH is applied to the electrode 5455 during the period T, or the more times the potential VH is applied to the electrode 5455 during the period T, the greater the number of times the potential VH is applied to the electrode 5455 during the period T. T, the number of times that the potential VH is applied to the electrode 5455 is reduced by the number of times that the potential VL is applied to the electrode 5455. The greater the value obtained by subtracting the number of times the potential VL is applied to the electrode 5455 during the period Ta, the greater the Alternatively, the potential VL may be applied to the electrode 5455 during the N periods T. Alternatively, during the period Ta, the potential VL is applied to the electrode 5455. It is preferable to lengthen the time obtained by subtracting the time during which the potential VH is applied to the electrode 5455 from the time during which the potential VH is applied to the electrode 5455. Or, the number of times that the potential VL is applied to the electrode 5455 during the N periods T is determined as the potential VH It is advisable to increase the number of times that the number of times that the electrode 5455 is applied is subtracted from the number of times that the electrode 5455 is applied. can be reduced.

[0167] As another example, the gradation already displayed by the display element 5453 may be changed during the period Ta for display. In this case, the longer the time that the potential VL is applied to the electrode 5455, the The longer the time that the potential VH is applied to the electrode 5455 minus the time that the potential VH is applied to the electrode 5455, the The more times the potential VL is applied to the electrode 5455 among the N periods T, or After the period T, the potential VH is applied to the electrode 5455 based on the number of times the potential VL is applied to the electrode 5455. The greater the value obtained by subtracting the number of times the potential VH is applied to the electrode 5455 during the period Ta, the greater the potential VH is applied to the electrode 5455 during the period Ta. Alternatively, during the N periods T, the potential VH may be applied to the electrode 5455. Alternatively, during the period Ta, the potential VH is applied to the electrode 5455. If we extend the time that the potential VL is applied to the electrode 5455 minus the time that the potential VL is applied to the electrode 5455, Alternatively, the potential VH may be determined based on the number of times that the potential VH is applied to the electrode 5455 during the N periods T. It is advisable to increase the number of times VL is applied to the electrode 5455 minus the number of times VL is applied to the electrode 5455. The image can be reduced.

[0168] It is assumed that the N periods T are of equal length. However, the length of the N periods T is For example, at least two of the N periods T are different from each other. In particular, it is advisable to weight the length of the N periods T. For example, For example, if N=4, and the length of the first period T is time h, then the length of the second period T is time h. The length of the third period T should be time h x 4. The fourth period T should be time h x 4. The length of the period T should be time h × 8. In this way, the length of the N periods T is weighted. By performing the above, the number of times that the pixel 5450 is selected can be reduced, and the display element 54 The time for which the voltage is applied to the transistor 53 can be precisely controlled. This allows the power consumption to be reduced. It is possible.

[0169] It is possible to selectively apply a potential VH or a potential VL to the electrode 5454. In this case, it is preferable to selectively apply the potential VH and the potential VL to the electrode 5455. For example, when a potential VH is applied to the electrode 5454, when a potential VH is applied to the electrode 5455, When a potential VL is applied to the electrode 5455, A negative voltage is applied to the display element 5453. On the other hand, a potential VL is applied to the electrode 5454. In this case, when a potential VH is applied to the electrode 5455, a positive voltage is applied to the display element 5453. When a potential VL is applied to the electrode 5455, the display element 5453 has zero voltage. In this way, the signal input to the wiring 5461 is converted into a binary (digital signal). Therefore, the circuit for outputting a signal to the wiring 5461 can be simplified. Cut.

[0170] Note that during the period Tb or part of the period Tb, the wiring 5461 and the wiring 5462 are connected to a signal In other words, it is possible to make the wiring 5461 and the wiring 5462 in a floating state. Note that during the period Tb or part of the period Tb, the wiring 5463 It is possible to input no signal. In other words, it is possible to put the wiring 5463 in a floating state. In addition, during the period Tb or a part of the period Tb, a voltage is supplied to the electrode 5454. That is, the electrode 5454 can be floating.

[0171] (Embodiment 7) In this embodiment, an example of an electronic device will be described.

[0172] 16(A) to 16(H) and 17(A) to 17(D) are diagrams showing electronic devices. These electronic devices include a housing 5000, a display unit 5001, a speaker 5003, and an LED. A lamp 5004, an operation key 5005 (including a power switch or an operation switch), a connection terminal Child 5006, sensor 5007 (force, displacement, position, velocity, acceleration, angular velocity, number of rotations, distance, Light, liquid, magnetism, temperature, chemicals, sound, time, hardness, electric field, current, voltage, power, radiation, (including functions for measuring flow rate, humidity, gradient, vibration, odor, or infrared rays), 5008, etc.

[0173] FIG. 16A shows a mobile computer, which includes, in addition to the above, a switch 5009, The portable terminal 5010 may have an infrared port 5010. FIG. A type of image reproducing device (for example, a DVD reproducing device) that, in addition to the above, also has a second display 16C shows a goog In addition to the above, the display includes a second display unit 5002, a support unit 5012, The game machine may have earphones 5013, etc. FIG. 16(D) shows a portable game machine. In addition to the above, the device may have a recording medium reading unit 5011, etc. In addition to the above, the projector includes a light source 5033, a projection lens 5034, etc. FIG. 16(F) shows a portable gaming machine, which, in addition to the above, has a second display unit. 16G shows a television receiver 5002, a recording medium reading unit 5011, etc. In addition to the above, the image sensor may also include a tuner, an image processor, etc. 16(H) is a portable television receiver, capable of transmitting and receiving signals in addition to the above. FIG. 17(A) shows a display, and the above-mentioned In addition to the above, a support stand 5018 and the like can be provided. FIG. 17(B) shows a camera. In addition to the above, an external connection port 5019, a shutter button 5015, an image receiving unit 5016, etc. FIG. 17(C) is a computer, In addition, there is a pointing device 5020, an external connection port 5019, a reader / writer 5 021, etc. FIG. 17(D) shows a mobile phone, which can have the above-mentioned In addition, an antenna 5014, a 1-segment partial reception service tuner for mobile phones and mobile terminals It may have a nozzle, etc.

[0174] The electronic devices shown in FIGS. 16(A) to 16(H) and 17(A) to 17(D) are It can have such functions.

[0175] The electronic device described in this embodiment has a display unit for displaying some information. It is characterized by:

[0176] Next, application examples of the semiconductor device will be described.

[0177] FIG. 17(E) shows an example in which a semiconductor device is integrated with a building. ) includes a housing 5022, a display unit 5023, a remote control device 5024 as an operation unit, and a speaker 5025. The semiconductor device is a wall-mounted type that is integrated with the building and requires a large space to install. It can be installed without requiring a large space.

[0178] FIG. 17(F) shows another example in which a semiconductor device is provided inside a building as an integral part of the building. The display panel 5026 is attached to the unit bath 5027 and is The display panel 5026 becomes viewable.

[0179] In this embodiment, a wall and a unit bath are used as examples of structures. The manner in which the semiconductor device is installed is not limited to this, and the semiconductor device can be installed in various structures.

[0180] Next, an example in which the semiconductor device is integrated with a moving object will be described.

[0181] FIG. 17G is a diagram showing an example in which the semiconductor device is provided in an automobile. 5028 is attached to a vehicle body 5029 of a vehicle, and is configured to detect the movement of the vehicle body or the inside and outside of the vehicle. The information entered can be displayed on demand. It is okay to do so.

[0182] FIG. 17(H) is a diagram showing an example in which a semiconductor device is integrated with a passenger airplane. FIG. 17(H) shows a passenger plane with a display panel 5031 mounted on a ceiling 5030 above the seats. The display panel 5031 is attached to the ceiling 50. 30 and the hinge portion 5032. This allows passengers to view the display panel 5031. The display panel 5031 is operated by passengers. It has the function of displaying information by

[0183] In this embodiment, an automobile body and an airplane body are exemplified as moving bodies. However, this is not limited to motorcycles, four-wheeled vehicles (including cars, buses, etc.), trains (monorail, etc.) They can be installed on a variety of things, including buildings, railways, ships, etc.

[0184] In such electronic devices, a transistor including an oxide semiconductor having low off-state current is used. By configuring the circuit in this way, it is possible to prevent unnecessary current from leaking in. This makes it easier for the circuit to operate normally. This allows accurate display. come. [Explanation of symbols]

[0185] 101 Pixel section 102a pixels 102b pixels 102c pixels 102d pixels 103a, 103b, 103c, 103d, 103e, 103f, 103g, 103h, 103i, 103j, 103k, 103L wiring 104a Wiring 104b Wiring 111 Circuit 201a, 201b, 201c, 201d, 201e, 201f, 201g, 201h, 201i, 201j, 201k, 201L transistors 202a Wiring 202b Wiring 202c Wiring 203a Wiring 203b Wiring 203c Wiring 400 Substrates 402 Gate insulating layer 403 Protective insulation layer 410 Transistor 411 Gate electrode layer 414a Source Region 414b Drain region 415a Source electrode layer 415b Drain electrode layer 416 Oxide insulating layer 430 Oxide Semiconductor Film 431 Oxide Semiconductor Layer 501 Circuit 502 Circuit 503 Circuit 504 Circuit 511 Substrate 801 Transistors 802 Display element 802a Light emitting element 803 Wiring 804 Capacitive element 805 Wiring 901 signal 902 cycles 903 period 904 period 905 period 906 Potential 907 signal 907a signal 907b signal 907c signal 908 signal 1301 Transistor 1303 Wiring 1304 Capacitive element 1305 Wiring 1311 Transistor

Claims

[Claim 1] A pixel unit including a plurality of pixels and a precharge circuit, the precharge circuit includes a plurality of first transistors; Each of the plurality of pixels includes a second transistor and a liquid crystal element, The liquid crystal display device, wherein the first transistor and the second transistor each include an oxide semiconductor.

Images