JP2003084686A - Liquid crystal display device and organic el (electroluminescence) display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance driving capability and also to enlarge the aperture ratio by arranging optimally an asymmetric structure thin film transistor so that the current of the transistor becomes larger. SOLUTION: A liquid crystal display device whose driving capability is enhanced and whose luminance is improved, is obtained by electrically connecting an electrode whose width is larger in the source electrode and the drain electrode of a thin film transistor for driving a pixel to a pixel electrode, in a liquid crystal display device. Moreover, an organic EL (electroluminescence) display device which is capable of performing more correct display and whose aperture ratio is large, is obtained by arranging the polarity relation of the source electrode and the drain electrode of the asymmetric structure thin film transistor driving directly a pixel in the circuit of a display panel so that the current of the transistor becomes larger, in an organic EL display device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device.
The present invention relates to a liquid crystal display device having a high-speed response characteristic using OCB (optical compensation bend) mode and FSC (field sequential) drive, and an organic EL display device.

[0002]

2. Description of the Related Art Thin film transistors (TFT: Thin-Film-)
Active matrix type liquid crystal displays using Transistor) are thin, lightweight, and can be driven at low voltage. They have various advantages such as displays for camcorders, personal computers, and personal word processors. It is used in various fields and forms a large market.

In recent years, in particular, in addition to the conventional still image display on a personal computer or the like, the use for moving image display and TV application is spreading, and there is an increasing demand for a liquid crystal display device suitable for such moving image display. In response to this, as a liquid crystal element for improving high-speed response performance, a bend-aligned liquid crystal display element called an OCB mode has been proposed in JP-A-7-84254. The OCB mode liquid crystal cell has a fast response of the liquid crystal to a change in voltage and can realize a high-speed response, but on the other hand, it has a drawback that the liquid crystal capacity becomes large.
A drive called FSC (field sequential) drive has also been proposed. In this driving method, one frame period is divided into a plurality of subfields, and a plurality of light sources having different spectrums, for example, red, green, blue,
In the driving method, one frame period is divided into three sub-frames in synchronization with the three light sources and the signals corresponding to the respective colors are written in the pixel electrodes. In this driving method, since a plurality of light sources are used, a color filter is unnecessary. In addition, the three pixels corresponding to each of RGB, which are required in a normal liquid crystal panel, can be combined into one pixel, so that the number of IC drivers can be reduced and the cost can be reduced. In addition, organic EL displays are attracting attention as another flat display for displaying moving images and TV. Since the organic EL display is a self-luminous display device, various companies are currently rushing to develop it as a display with a wide viewing angle, a thin shape, and low power consumption. In particular, an active-matrix driven organic EL display displays an image by passing a current through an organic EL element through a thin film transistor and adjusting the brightness of each of the RGB organic EL elements according to the magnitude of the current. It is attracting attention because of its long life.

In order to display moving images and to support TV, OCB mode and FSC driving have been studied for liquid crystal panels. However, for OCB mode liquid crystal panels, there are differences in dielectric constant of liquid crystal materials and narrowing for speeding up. Due to the increase in liquid crystal capacity due to the cell gap, charging by the thin film transistor becomes strict. In addition, FSC driving requires high-speed writing that is three times or more faster than that of a normal liquid crystal panel, and thus requires a large charging capacity. Furthermore, in order to display a moving image more clearly, studies are being made to write a non-image signal other than an image signal, such as black insertion or white insertion, and charging is becoming more severe. In the case of an organic EL panel, a current is constantly passed through the organic EL element to cause it to emit light, and therefore a driving capacity larger than that of a thin film transistor used for a pixel of a liquid crystal panel is required. Therefore, it is indispensable to increase the size of the thin film transistor, which causes a demerit of reducing the aperture ratio. Therefore, how to increase the amount of current while suppressing the area occupied by the thin film transistor has been studied, and it is possible to increase the effective channel width and increase the amount of current per area occupied by the thin film transistor by a structure such as a bending structure or a bend. Being tried.

[0005]

However, in the bent structure or the bent structure, a thin film transistor having a structure which is asymmetric with each other when viewed from the source electrode and the drain electrode is produced. In such a thin film transistor, we predict that current-voltage characteristics will be asymmetric due to the asymmetric structure, and we have investigated the current-voltage characteristics of thin-film transistors with an asymmetric structure and found that the current-voltage characteristics are asymmetric. It was FIG. 9 shows current-voltage characteristics of the n-channel thin film transistor having the structure of FIG. 1, and has different characteristics depending on which of the source electrode and the drain electrode has the positive polarity. That is, a large current value is shown for a certain source / drain polarity. This is due to carrier distribution and parasitic resistance,
This is a behavior peculiar to the asymmetric structure. When the electrode having a shorter width has a positive polarity (A in FIG. 9), the current becomes larger than that in the opposite case. On the contrary, in the p-channel type thin film transistor, when the wider electrode has a positive polarity, the current becomes larger.

In the liquid crystal panel, positive voltage and negative voltage are alternately written into the pixel electrode for each frame with the counter voltage Vcom as a reference, which is so-called AC driving. This is to prevent burn-in of the liquid crystal. In writing from positive to negative and from negative to positive, the pixel electrode side has a positive polarity and a negative polarity, respectively. That is, the polarities of the source and the drain are switched every frame. When the thin film transistor used for the pixel is an N channel, the pixel electrode side becomes positive when writing to change the pixel voltage from positive to negative, and the pixel electrode side becomes negative when writing to change from negative to positive. . When the pixel electrode side has a writing polarity that changes from negative to positive, the bias value between the gate and the drain (that is, the pixel electrode) decreases during writing, and the current value decreases. Therefore, writing is severe when the pixel electrode changes from negative to positive. In the case where the thin film transistor is a P type, conversely, for the same reason, when the pixel electrode side has a writing polarity that changes from positive to negative, charging becomes severe.

FIG. 2 shows a conventional structure. As shown in the figure, in order to reduce the capacitance Cgd between the gate and the drain, the shorter electrode is connected to the pixel electrode. This is to reduce recharge (so-called punch-through voltage). However, when considering the asymmetry of the current-voltage characteristics that we found, the conventional structure has a thin film transistor arrangement in which the current decreases when writing in a polarity with severe charging, and the driving capability of the thin film transistor originally possessed is I have not been able to fully demonstrate.

The present invention has been made in view of the above problems, and increases the charging ability with respect to a strict polarity of charging, increases the charging ability, enables high-speed writing, and increases the aperture ratio. The purpose is to increase the brightness and improve the brightness.

[0009]

To achieve the above object, a liquid crystal display device and an organic EL display device of the present invention have the following configurations.

In the liquid crystal display device of the present invention, an n-channel thin film transistor in which the source electrode and the drain electrode have different widths is used, and the electrode having the larger width is electrically connected to the pixel electrode. By doing so, when writing is performed with a strict polarity of charging, that is, when the pixel electrode has a negative polarity with respect to the source electrode, the current becomes larger and the charging capability can be increased. Therefore, it is possible to drive at high speed, and it is possible to improve brightness by increasing the aperture ratio.

Further, in the present invention, the above-mentioned thin film transistors are arranged on a panel of a field sequential drive (FSC) drive system for performing high-speed writing which is three times as high as that of a normal liquid crystal display. by this,
The driving capability is improved, and the brightness can be improved.
When writing a non-image signal such as black insertion or white insertion in order to improve image quality, higher-speed writing is required, and the improvement of the driving capability according to the present invention is effective.

According to the present invention, a thin film transistor having an asymmetric structure is arranged in an OCB mode liquid crystal display device so that the current becomes large when writing is performed in a polarity with severe charging. By increasing the driving ability according to the present invention, high-speed driving can be performed and an aperture ratio can be increased even in an OCB mode liquid crystal panel having a large liquid crystal capacity. Further, if the cell gap is made small in order to improve the response speed, the liquid crystal capacitance becomes even larger, and the effectiveness of the present invention becomes greater.

Further, in the present invention, the above-mentioned asymmetric thin film transistor is arranged in the liquid crystal panel of OCB mode and FSC drive. The OCB mode requires a larger drive capacity than the normal TN mode FSC drive. The drive capacity improvement of the present invention enables high-speed writing, and the increase in aperture ratio improves brightness. be able to.

Further, in the present invention, the capacitance between the gate electrode and the drain electrode is increased as the distance from the gate signal input side increases. When the structure according to the present invention is adopted, the capacitance Cgd between the gate and the drain becomes larger than that in the case of the reverse arrangement, which causes a large recharge when the gate signal changes from on to off. Because,
There is concern about flicker. The recharge increases as the distance from the gate signal input side increases. This is because the waveform of the gate signal becomes blunt as it goes away from the input side of the gate signal. If Cgd is increased as the distance from the gate signal input side increases, the punch-through voltage due to capacitive coupling increases, so that the effect of gate waveform blunting can be canceled, and flicker can be prevented while improving drive capability.

Further, in the present invention, the drain electrode is composed of a plurality of electrodes. By configuring with a plurality of electrodes, it is possible to suppress the overlap with the gate electrode while suppressing the increase in the driving ability and suppress the increase in Cgd.

Furthermore, in the present invention, the width of the drain electrode electrically connected to the pixel electrode is 1.2 to 2.5 times the width of the source electrode electrically connected to the source signal line. There is. In the case of a bent structure or a structure in which the drain electrode is composed of a plurality of electrodes, a structure in which the charging capacity per unit area is increased can be realized by setting the ratio of the source electrode and the drain electrode as described above. As a result, the charging capacity can be increased without lowering the aperture ratio, and high-speed writing is possible.

In the organic EL display device of the present invention, a thin film transistor in which the source electrode and the drain electrode have different widths is electrically connected to the organic EL element, and each of the regions where the drain electrode and the source electrode face each other. If the widths are W1 and W2, then W1> W2, and if the thin film transistor is an n-channel type, the drain electrode has a negative polarity with respect to the source electrode, and if it is a p-channel type, the drain electrode is the source. It is electrically connected to the organic EL element so as to have a positive polarity with respect to the electrode. As a result, the amount of current flowing through the organic EL element is increased and the brightness is improved.

Further, in the present invention, at least one of the source electrode and the drain electrode has a bent structure. As a result, the effective channel width per unit area can be increased, and the amount of current per unit area can be increased. That is, the driving ability can be increased.

In the present invention, the semiconductor film is polycrystalline silicon. Polycrystalline silicon has a high mobility and a large current can be obtained. Further, with the structure of the present invention, a larger current can be obtained and the driving ability can be improved.

Further, in the present invention, the semiconductor film is made of amorphous silicon. Amorphous silicon has a lower mobility than polycrystalline silicon, but since it can be directly deposited, it can be manufactured by a smaller number of steps than polycrystalline silicon. Therefore, it can be manufactured more easily and at a lower cost than polycrystalline silicon. With the structure as described above, the amount of current can be increased and the driving capability can be increased.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The liquid crystal display device of the present invention will be described more specifically with reference to the drawings.

(Embodiment 1) FIG. 1 is a plan view showing an electrode configuration of one pixel on an array substrate in a liquid crystal display device of Embodiment 1. The amount of current of the thin film transistor increases in proportion to the channel width, but in the bent structure, the definition of the channel width is complicated. But almost
It is determined by the effective channel width of each of the source electrode 20 and the drain electrode 60. The effective channel width is a region where the gate electrode 10 and the semiconductor film 30 overlap each other.
It is the width of the portion where the source electrode and the drain electrode face each other. In the structure of FIG. 1, the effective channel width of the source _{electrode, W 2 - 1 × 2 +} W 2 - 2, becomes the effective channel width of the drain _{electrode, W 1-1 × 2 + W 1} - 2, and becomes. In a thin film transistor in which both electrodes have different effective channel widths, the current differs depending on which electrode has the positive polarity. FIG. 9 shows current-voltage characteristics of the thin film transistor having the structure of FIG.
Shown in. The characteristic A is the current-voltage characteristic when the effective channel width is shorter, that is, when the source electrode 20 of FIG. 1 has a positive polarity. In this case, it is an N-type thin film transistor, the source electrode 20 is 12V, the drain electrode 60 is grounded, and the voltage of the gate electrode 10 is changed from 0V to 20V. Conversely, the characteristic of B is that the source electrode 20 is grounded, the drain electrode 60 is set to 12 V, and the gate electrode 10 is
It is the characteristic when the voltage of is changed from 0V to 20V. When a large number of thin film transistors having the structure shown in FIG. 1 were measured, the size was different due to processing variations, but the difference between the two characteristics was about 20 to 40%. That is, the current changes from 20% to 40% depending on which one has the positive polarity. This is due to changes in parasitic resistance and carrier distribution. This behavior is peculiar to a thin film transistor having an asymmetric structure with different effective channel widths.

FIG. 2 shows a conventional structure proposed in Japanese Patent Laid-Open No. 3-233431. This has a structure in which the source electrode and the drain electrode are interchanged in the thin film transistor having the structure of FIG. The reason for this structure is simply to reduce the Cgd, but since the liquid crystal is charged by alternately rewriting positive and negative polarities, the pixel electrode side has a positive polarity for each writing. Or becomes negative. When the pixel electrode side has a positive polarity and the source signal line side has a negative polarity, the source potential during writing is constant and the drain potential is always smaller than the source potential, so charging is sufficiently performed. When the electrode side has a negative polarity, the potential difference between the gate and the drain (pixel electrode) becomes smaller with charging, and thus charging becomes more severe. That is, the driving ability of the liquid crystal display device is determined by the charging ability when the pixel electrode side has negative characteristics. From this point of view, when the conventional structure of FIG. 2 is viewed, the current is reduced when writing is performed in a polarity with severe charging. In the present invention, the structure as shown in FIG. 1 is adopted in view of the asymmetric current-voltage characteristics of the thin film transistor having an asymmetric structure found by us.
As a result, the current becomes larger when the pixel electrode side is negatively charged, and the driving capability is increased. When the pixel side becomes the positive electrode, charging is much easier as compared with the opposite case as described above, and thus the driving ability is not lowered. In addition, Cgd is increased by changing from the arrangement of FIG. 2 to the arrangement of FIG.
Influences not only the area of the region where the drain electrode and the gate electrode overlap, but also the area of the semiconductor film. Therefore, depending on the bias of the source electrode, when the structure of FIG. The increase in Cgd is slight. further,
In a general liquid crystal display device, Cgd accounts for about a few percent of the charged capacity, so an increase in current has a greater effect than a slight increase in Cgd, resulting in an improvement in drive capability. .

Up to now, the case of the n-channel type thin film transistor has been described, but even when the p-channel type thin film transistor is used, the same effect can be obtained by using the structure in which the drain is elongated as shown in FIG. Firstly, in the case of the p-channel type, the asymmetric characteristic corresponding to FIG. 9 shows that the current becomes large when the longer one of the source and the drain has the positive polarity, as opposed to the n-channel type (see FIG. 9 A characteristics). This is because the causes of the asymmetric characteristics are the distribution of carriers (holes) and the parasitic resistance. On the other hand, when a p-channel thin film transistor is used for pixel charging, in an operation in which the pixel electrode side changes from positive polarity to negative polarity, the potential difference between the gate and the drain (pixel electrode) becomes smaller with charging, and thus the charging becomes more severe. . Therefore, after all, even in the case of a p-channel thin film transistor, it is preferable to connect the longer one of the source and the drain of the transistor to the pixel electrode.

In this embodiment, the structure shown in FIG. 1 has been described, but the invention can be similarly applied to a thin film transistor having another asymmetric structure. The point is that the electrode having the larger effective channel width, of the source electrode and the drain electrode, is brought to the pixel side. Structures of thin film transistors having other asymmetric structures are shown in FIGS. FIG. 3 is similar to the structure of FIG. 1, but has a structure that is simply repeated periodically. Compared with the structure of FIG. 1, the current amount can be tripled. Figure 4
The structure of is similar to the structure obtained by dividing the structure of FIG. 1, and the effective channel width at this time is W _4-1 + W _4-2 on the source electrode side and W _3-1 + W _3-2 on the drain electrode side. ,become. The structure of FIG. 5 is an example in which the drain electrode is composed of a plurality of electrodes, and the effective channel width on the drain electrode side is W ₅ × 2.
And the effective channel width on the source electrode side is W ₆ × 2. Various other structures can be adopted, but in a thin film transistor having an asymmetric structure in which the effective channel widths of the source electrode and the drain electrode are different, the electrode with the larger effective channel width length is brought to the pixel side. The effects of the present invention can be obtained.

In order to increase the charging capacity per unit area, a bending (bending) structure as shown in FIGS. 1, 3 and 4 is used, or an electrode is composed of a plurality of electrodes as shown in FIG. It is necessary to. Various modifications are conceivable in both structures. Of the source electrode and drain electrode, the electrode with the larger effective channel width is 1.2 to 2.5 times the width of the electrode with the smaller effective channel width. By adopting the above, it is possible to obtain an optimum structure for increasing the amount of current per unit area.

Further, when a liquid crystal material having an OCB mode is used as the liquid crystal material, the structure of the present invention is more effective because the liquid crystal capacity becomes large, and when non-image signal insertion such as black insertion is performed. Is even more effective.

(Embodiment 2) The effect of the present invention is an improvement in driving ability, and is particularly effective for a display device and a driving method that require high-speed writing. As one of such liquid crystal display devices, there is a liquid crystal display device using field sequential drive (FSC) drive. Figure 7 shows an example of the FSC drive waveform. In an ordinary liquid crystal display device, backlight light (white light) is converted into RGB 3 by a color filter.
Full-color display is realized by dividing each color and writing each RGB signal to the pixel corresponding to each RGB. On the other hand, in the FSC drive system, one pixel displays RGB three colors. One frame period is divided into RGB sub-frames, and a light source having RGB spectral spectra is turned on in synchronization with the sub-frames to display RGB three colors with one pixel. This eliminates the need for color filters and reduces the driver ICs by reducing the number of pixels to one-third, which has the advantage of reducing costs. Further, by writing a non-image signal such as black insertion or white insertion, a display more suitable for a moving image can be realized.

When the FSC drive is used, it is necessary to write RGB signals in one frame period, and therefore, it is necessary to perform high-speed writing three times or more as compared with a normal liquid crystal display device. Therefore, how to increase the current of the thin film transistor becomes important, and the present invention is effective. The FSC-driven liquid crystal display device has only one-third of the pixels as an array configuration, and there is no substantial difference from a normal liquid crystal display device. Therefore, in the same manner as in Example 1,
With the structure and arrangement shown in FIG. 1 and FIGS. 3 to 5, the amount of current can be increased and high-speed writing can be performed. That is, FSC drive becomes possible.

In FSC driving, when displaying a moving image, a liquid crystal material / mode having a faster response speed is suitable, and an OCB mode or the like is used. In this case, since the liquid crystal capacity becomes large, a larger driving capacity is required, and the effect of the present invention becomes large.

(Third Embodiment) FIG. 6 is a diagram showing a pixel structure in a liquid crystal display device according to a third embodiment.

In the present invention, the electrode having the larger effective channel width is electrically connected to the pixel electrode, thereby improving the writing ability of the polarity having the severer charging. At this time, as described above, Cgd becomes large and recharge becomes large. As mentioned above, the effect of increasing Cgd is small, but depending on the specifications such as size and resolution, it may not be negligible. For example, the panel size is large,
This is the case when the resolution is high. As the panel size increases, the rounding of the gate signal waveform increases, the amount of recharge when the gate signal turns off increases, and flicker occurs. The dullness of the gate waveform increases as the distance from the gate signal input side increases, and the recharge amount also increases accordingly. Flicker occurs due to the difference in the recharge amount. In this case,
By adopting the Cgd inclined structure together with the structure and arrangement of the present invention, the amount of recharge can be made uniform and flicker can be prevented. FIG. 6 shows an example in which the Cgd tilt is adopted.
As shown in the figure, the region where the drain electrode overlaps with the gate electrode is made larger as it is farther from the gate signal input side (from left to right in FIG. 6), so that the recharge amount can be made uniform. it can. In this embodiment, it is realized by changing a part of the region where the drain electrode and the gate electrode overlap (regions indicated by WX1, WXi, WXn in the figure). Of course, other regions may be changed as long as the drain electrode and the gate electrode overlap each other. Further, when the gate signal is input from one of the left and right sides, Cgd may be increased as the distance from the signal input side increases. You should increase Cgd.

(Fourth Embodiment) FIG. 8 is a circuit diagram showing a circuit configuration of an organic EL display device according to a fourth embodiment. The circuit configuration is an example. The circuit operation is as follows.

The organic EL display device comprises an X-direction signal line 70a,
70b, ..., Y direction signal lines 80a, 80b, ...
.., power supply lines 90a, 90b, .., switch thin film transistors 100a, 100b, .., current control thin film transistors 110a, 110b ,.
Elements 120a, 120b, ..., Capacitor 130
a. 130b, ..., X-direction peripheral drive circuit 140, Y
The direction peripheral drive circuit 150 and the like are used.

A pixel is specified by the X-direction signal line 70 and the Y-direction signal line 80, and the switching thin film transistor 100 is turned on in the pixel. As a result, the current controlling thin film transistor 110 is turned on, and the current supplied from the power supply line 90 causes a current to flow through the organic EL element 120, causing the organic EL element to emit light.

For example, when a signal corresponding to image data is output to the X-direction signal line 70a and a Y-direction scanning signal is output to the Y-direction signal line 80a, the switching thin film transistor 100a of the pixel specified by this is turned on. Then, the current control thin film transistor 110a is rendered conductive by a signal corresponding to the image data, a current corresponding to the image flows through the organic EL element 120a, and the organic EL element emits light. In this way, the image signal is written in all the pixels and the image is displayed. What is important in the present invention is the thin film transistor 110 which sends an image signal directly to the organic EL element, and in the circuit shown in FIG.
When the thin film transistor is an n-channel type, the electrode with the larger effective channel width of the source electrode and the drain electrode is connected to the organic EL element side, and when the thin film transistor is the n-channel type, the one with the smaller effective channel width is connected. The electrodes are electrically connected to the organic EL element side. As a result, the polarity relationship between the source and drain of the thin film transistor is set so that a larger current flows, and a large current flows through the organic EL element, so that the display information can be rewritten faster and more accurate display can be performed. It will be. Further, since the amount of current per unit area can be increased, the shape of the thin film transistor can be reduced, and the area of the organic EL element can be increased accordingly (improvement of aperture ratio).

This embodiment shows an example of an organic EL display device, and the organic EL display device can have various circuit configurations. The point of the present invention is organic EL
In an arrangement of a thin film transistor having an asymmetric structure that is directly electrically connected to an element, in the case of an n-channel thin film transistor, one of the source electrode and the drain electrode of the thin film transistor having a larger effective channel width has a negative polarity. In the case of a p-channel thin film transistor, the circuit may be configured so that the electrode having the smaller effective channel width has a negative polarity. The reason for this is Embodiment 1
This is because it is the same as that described for the liquid crystal element in, and the driving capability of the thin film transistor can be increased by setting the source electrode and the drain electrode of the thin film transistor in the above-described polar relationship. What is different from the case of the liquid crystal element is that the polarity relationship between the source and the drain of the pixel driving thin film transistor does not change during the driving operation. The thin film transistor having an asymmetric structure can have various structures as shown in FIG. 1 and FIGS. 3 to 5. It may have a bent structure or may be composed of a plurality of electrodes. Moreover, the combination may be sufficient. In addition, the source electrode or the drain electrode having the larger effective channel width is made 1.2 times to 2.5 times as wide as the electrode having the smaller effective channel width, so that the current per unit area is increased. It is possible to have an optimal structure for increasing the amount.

The asymmetry of the current-voltage characteristics of the asymmetric structure thin film transistor, which is the main point of the present invention, depends on the parasitic resistance and the carrier distribution, so that the semiconductor film may be amorphous silicon or polycrystalline silicon, or the top gate. The effect is the same whether it is a bottom type or a bottom gate type. When relatively low speed driving is performed, it is sufficient to arrange a thin film transistor using an amorphous silicon film that can be formed in a small number of steps as a semiconductor film as in the present invention, and when performing high speed driving such as FSC driving, When a large current is required to emit light such as an organic EL display device, a semiconductor film having a high mobility such as polycrystalline silicon may be used.

[0039]

As described above, according to the present invention, the driving ability can be improved by optimizing the arrangement of the thin film transistors having an asymmetric structure, high speed driving is possible, and the aperture ratio is increased. This improves the brightness.

[Brief description of drawings]

FIG. 1 is a plan view showing a pixel configuration in a liquid crystal display device according to a first embodiment.

FIG. 2 is a plan view showing a pixel configuration of a conventional liquid crystal display device.

FIG. 3 is a diagram showing a structural example of a thin film transistor having an asymmetric structure.

FIG. 4 is a diagram showing a structural example of a thin film transistor having an asymmetric structure.

FIG. 5 is a diagram showing a structural example of a thin film transistor having an asymmetric structure.

FIG. 6 is a plan view showing a pixel configuration of a liquid crystal display device having a Cgd capacitance gradient.

FIG. 7 is a waveform diagram of field sequential drive.

FIG. 8 is a circuit diagram showing a pixel configuration of an organic EL display device.

FIG. 9 is a diagram showing current-voltage characteristics of a thin film transistor having an asymmetric structure.

[Explanation of symbols]

10 Gate electrode 20 Source electrode 30 Semiconductor film 40 pixel electrodes 50 Contact area between drain electrode and pixel electrode 60 drain electrode 70 X direction signal line 80 Y direction signal line 90 power line 100 switch thin film transistor 110 Current Control Thin Film Transistor 120 Organic EL device 130 capacitors 140 X direction peripheral drive circuit 150 Y direction peripheral drive circuit

Front page continuation (51) Int.Cl. ⁷ identification code FI theme code (reference) G09F 9/35 G09F 9/35 5C080 H01L 29/786 H05B 33/14 A 5C094 H05B 33/14 G09G 3/20 641E 5F110 / / G09G 3/20 641 3/30 Z 3/30 3/34 J 3/34 3/36 3/36 H01L 29/78 616T F term (reference) 2H088 GA02 HA06 HA08 HA28 JA04 MA06 MA10 2H092 JA24 JA32 JA38 JA42 KA05 KA07 NA01 NA07 PA06 PA13 QA06 2H093 NA65 NC34 NC43 NC44 ND08 ND17 ND32. AA10 AA13 AA21 AA48 AA53 AA56 BA03 BA27 BA43 CA19 DA09 DA13 DB01 DB04 EA04 FA01 FB01 FB02 FB12 FB14 FB15 FB20 JA01 5F110 AA02 AA07 AA30 GG02 GG13 GG15 HM04 HM12 HM13

Claims (15)

[Claims] 1. A thin film transistor having a drain electrode and a source electrode is formed in a region where a semiconductor film and a gate electrode overlap each other, and the widths of the regions where the drain electrode and the source electrode face each other are W1 and W2, respectively. Then, W1> W2, and the drain electrode is electrically connected to the pixel electrode. 2. A thin film transistor having a drain electrode and a source electrode is formed in a region where a semiconductor film and a gate electrode overlap each other, and widths of the regions where the drain electrode and the source electrode face each other are W1 and W2, respectively. Then, W1> W2 and the thin film transistor is n
In the case of the channel type, the drain electrode has a negative polarity with respect to the source electrode, and in the case of the p channel type, the drain electrode has a positive polarity with respect to the source electrode.
An organic EL display device, which is electrically connected to an L element. 3. A thin film transistor having a drain electrode and a source electrode is formed in a region where a semiconductor film and a gate electrode overlap with each other, and widths of regions where the drain electrode and the source electrode face each other are W1, W2,
Then, W1> W2, the drain electrode is electrically connected to the pixel electrode, and one frame period is divided into a plurality of subframes in synchronization with the light emission of a plurality of light sources having different spectrums. A liquid crystal display device, wherein a signal is written to the pixel electrode. 4. The zero voltage orientation state is splay orientation,
The liquid crystal display device according to claim 1 or 3, wherein the display alignment state is bend alignment. 5. The capacitance between the gate electrode and the drain electrode is formed such that the capacitance increases with increasing distance from the gate signal input side.
The liquid crystal display device according to claim 3. 6. The liquid crystal display device according to claim 1 or claim 3, wherein the drain electrode is composed of a plurality of electrodes. 7. The organic EL display device according to claim 2, wherein the wider electrode of the source and drain electrodes is composed of a plurality of electrodes. 8. The method according to claim 1, wherein W1 is 1.2 times to 2.5 times as large as W2.
7. The liquid crystal display device according to claim 6. 9. The organic EL display device according to claim 2 or 7, wherein W1 is 1.2 times to 2.5 times as large as W2. 10. The source electrode and the drain electrode are separated from each other by a certain distance and are bent and face each other, or any one of claims 3 to 6 and claim 8. The described liquid crystal display device. 11. The organic EL display device according to claim 2, wherein the source electrode and the drain electrode are separated from each other at a constant distance and are bent and face each other. 12. The liquid crystal display device according to claim 1, wherein the semiconductor film is polycrystalline silicon, or claim 3 or claim 6 or claim 8 or claim 10. 13. The organic EL display device according to claim 2, wherein the semiconductor film is polycrystalline silicon. 14. The semiconductor film is amorphous silicon, and the semiconductor film is formed of amorphous silicon.
Alternatively, the liquid crystal display device according to claim 8. 15. The organic EL display device according to claim 2, wherein the semiconductor film is amorphous silicon.