JPH0713190A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device which prevents the deterioration in image quality by a fluctuation in pixel potentials by effectively suppressing the light leak current of thin-film transistors(TFTs) constituted as switching elements for pixels. CONSTITUTION:One pixel in a display panel is composed of a liquid crystal cell, storage capacitance and the TFT 23. This liquid crystal cell is composed of a pixel electrode formed on an array substrate, a counter electrode formed on a counter substrate and a liquid crystal layer clamped therebetween. The minority carriers which determine the magnitude of the light leak current and which are shorter in their diffusion length than the diffusion length of the minority carrier of the other TFT 28 used for a driving circuit existing in a position not affected by incident light are used for the TFT 23. The light leak current of the TFT 23 is thus effectively utilized.

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 used for a light valve of a projection display.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have come to be widely used in various fields such as television displays and office automation displays because of their light weight and low power consumption. A projection display is one that utilizes such a liquid crystal display device.

Here, regarding the projection display for projecting a color image, "S. Morozumi et.a.
l. SID '86 DIGEST, 357 (1986) ".
This document describes a projection display that combines three colors of red (R), green (G) and blue (B) to project a color image, and based on a video signal,
A liquid crystal display device is used in which a light valve is used as an electric / optical conversion unit that converts light from a light source into a projection light signal. This liquid crystal display device is inserted between a color separation optical system and a color synthesis optical system, and converts the light source light separated into each color of R, G, and B into projection light corresponding to a video signal for each color. In this case, the light source is installed on the counter substrate side, which is the substrate on which the counter electrode facing the pixel electrode of each pixel of the liquid crystal display device is formed, and the source light is emitted from the counter substrate side.

As is well known, the liquid crystal display device has an array substrate serving as a first electrode substrate configured as an array substrate and a counter substrate serving as a second electrode substrate configured as a counter substrate. A liquid crystal layer is sandwiched between a substrate and a counter substrate. A plurality of signal lines and scanning lines are arranged in a matrix on the array substrate, and pixel electrodes made of a transparent material are respectively provided at the intersections of the signal lines and the scanning lines. Are connected to corresponding ones of the signal lines and the scanning lines via thin film transistors which respectively function as pixel switching elements. In addition, a counter electrode facing the pixel electrode is provided on the counter substrate.

Here, since the counter substrate receives the irradiation light from the light source as described above, a black matrix is formed on the counter substrate so that the light source light is incident on the thin film transistors forming the pixel switching elements. Prevent
Generation of a light leak current due to the light from the light source and fluctuation of the pixel potential accompanying it are suppressed.

However, even if the black matrix is arranged on the counter substrate side, the light incident on the thin film transistor cannot be sufficiently suppressed because of reflection from the projection optical system on the back surface of the substrate or the emission side. That is, light is also incident from the projection optical system side. Since the reflected light intensity is proportional to the incident light intensity, the influence of the reflected light becomes more remarkable as the incident light intensity increases. Further, the fluctuation of the pixel potential causes deterioration of the image quality, but the fluctuation of the pixel potential is
Since it is determined by the amount of light leakage current with respect to the storage capacitance,
The smaller the pixel capacity, the more remarkable. Therefore, in a liquid crystal display device having a small pixel size for high definition, the fluctuation of the pixel potential due to the light leak current becomes more problematic.

As a method of suppressing such a light leakage current, for example, as disclosed in Japanese Patent Laid-Open No. 62-262026, a light-shielding layer is provided on the substrate side of the active region of a thin film transistor, and a light projection layer from a projection optical system to the thin film transistor is provided. It is known to suppress the incidence of light. However, since a high temperature process of about 1000 ° C. is required to form a thin film transistor, a material for the light shielding layer formed under the thin film transistor is required to have a property capable of withstanding a high temperature process of 1000 ° C. or higher. As there is no suitable one, it is not realistic.

By the way, as described above, a plurality of signal lines and scanning lines are arranged in a matrix on the array substrate,
At each intersection of these signal lines and scanning lines, a thin film transistor is provided as a pixel switching element that connects with the corresponding pixel electrode. In addition to this, a driving circuit for supplying an image signal to the signal line and a scanning signal to the scanning line at predetermined timings is provided at the peripheral portion of the display unit provided with the matrix wiring. When this drive circuit is configured by thin film transistors, the thin film transistors for this drive circuit are required to have higher performance than thin film transistors as pixel switching elements.

Due to such differences in characteristics, it is possible to use an amorphous silicon thin film transistor having a low transistor performance as the pixel switching element. In this case, since the amorphous silicon thin film transistor cannot be applied to the drive circuit that requires higher performance, the drive circuit cannot be molded at the same time, and only the pixel switching element is formed on the array substrate to form the drive circuit. Will use a higher performance external IC.

However, since providing such an external IC as a drive circuit requires many steps from the viewpoint of manufacturing, the drive circuit can be formed at the same time when the pixel switching element is formed. desirable.

This can be achieved by using a polycrystalline silicon thin film transistor having better transistor characteristics than amorphous silicon. In this case,
Various types of processing for improving transistor characteristics are performed on thin film transistors included in a driver circuit.
For example, JP-A-58-4180 or JP-A-64-4
Japanese Patent Laid-Open No. 45162/1992 discloses a structure in which only a portion of a semiconductor thin film formed on a substrate corresponding to a drive circuit is annealed to increase its mobility so that performance required as a drive circuit is satisfied. Is listed. Further, in Japanese Patent Application Laid-Open No. 1-194351, a structure is improved in which the transistor characteristics of a thin film transistor forming a drive circuit are improved by increasing the film thickness of a portion corresponding to the drive circuit in a semiconductor thin film formed on a substrate. Is listed.

These JP-A-58-4180, JP-A-64-45162 or JP-A-1-194435.
The method disclosed in the known example of Japanese Patent Publication No. 1 is a means for providing thin film transistors formed on the same substrate with performances suitable for respective purposes such as pixel switching or drive circuits. It is not sufficient as a measure against leak current.

[0013] Here, Japanese Patent Application Laid-Open No. 58-4180 discloses that mobility is reduced to reduce light leakage current, but mobility is not a direct physical quantity for light leakage. Therefore, it is difficult to properly control to a desired value, and it is not very effective as a light leak reduction measure.
Further, changing the film thickness disclosed in JP-A-1-194351 is effective as one of means for reducing the light leak current, but there is a limit in changing the film thickness, and it is fine. Control is difficult.

[0014]

As described above, when light from the outside, such as reflected light from the projection optical system, is incident, a light leak current is generated in the thin film transistor configured as a pixel switching element, and the pixel leaks. There is a problem that causes deterioration of image quality due to fluctuations in potential.

An object of the present invention is to provide a liquid crystal display device which effectively suppresses a light leak current of a thin film transistor configured as a pixel switching element and prevents deterioration of image quality due to fluctuations in pixel potential. .

[0016]

In the liquid crystal display device of the present invention, a plurality of signal lines and scanning lines arranged in a matrix are provided for each pixel, and the signal is provided through a pixel switching element formed of a thin film transistor. A pixel electrode connected to the scan line and the scan line, and a drive circuit configured by a thin film transistor for supplying an image signal and a scan signal to a corresponding one of the signal line and the scan line
Of the first electrode substrate and a second electrode substrate having a counter electrode facing the pixel electrode with a gap facing the first electrode substrate, and the first electrode substrate and the second electrode substrate. A thin film transistor having a liquid crystal layer sandwiched in a gap and used as a thin film transistor forming the pixel switching element, wherein the diffusion length of minority carriers is shorter than the diffusion length of the minority carriers of the thin film transistors forming the drive circuit. is there.

[0017]

The present invention is used as a thin film transistor which constitutes a pixel switching element in a driving circuit or the like in which the diffusion length of minority carriers that determines the magnitude of light leakage current is not affected by incident light. Since a thin film transistor whose length is shorter than the diffusion length of the minority carrier is used,
It is possible to effectively suppress the light leakage current of the thin film transistor that constitutes the pixel switching element.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the liquid crystal display device of the present invention will be described below with reference to the drawings.

First, the principle will be described.

The photo-leakage current is generated when minority carriers generated near the drain junction due to incident light flow over the drain junction when the thin film transistor is in the off state. This phenomenon will be specifically described with reference to FIG. 7 showing the cross-sectional shape of the thin film transistor.

In FIG. 7, 11 is an active layer of the thin film transistor, the right side of the active layer 11 in the figure is a drain region, and the left side is a source region. A gate insulating film 12 is formed on the upper surface of the active layer 11, and a gate electrode 13 is integrally formed via the gate insulating film 12. Further, the drain region of the active layer 11 is connected to the positive potential 14 as shown, and the gate electrode 13 and the source region of the active layer 11 are each connected to the ground potential 15. Further, a depletion layer 16 is formed near the drain region of the active layer 11.

In the above structure, the minority carriers contributing to the photo-leakage current are in the depletion layer 16 at the drain junction and in the vicinity of the depletion layer 16, that is, in the hatched region inside the depletion layer 16 and about the diffusion length. Limited to minority carriers generated in 17. This is because, since there is no potential gradient in the semiconductor outside the depletion layer 16, the minority carriers flow as a diffusion current, but at that time, recombination occurs and the current decreases exponentially with respect to the distance.

Here, comparing the width of the depletion layer 16 with the diffusion length, that is, the width of the region 17 in the shaded area in the figure
Since the width of 16 is sufficiently smaller than the diffusion length, the magnitude of the light leak current is determined by the diffusion length. Therefore, the longer the diffusion length, the larger the light leak current.

The light leak characteristics of various polycrystalline silicon thin film transistors were measured, and it was found that there was a large difference in the light leak characteristics depending on the manufacturing method of the transistor. An example of this measurement result is shown in FIG.

In FIG. 8, an amorphous silicon film is deposited by a LPCVD method using disilane gas as a raw material, and a polycrystalline silicon film obtained by solid-phase growing this amorphous silicon in a constant temperature bath at 600 ° C. is used as an active phase. The measurement result of the leak current by the light irradiation when the Green light of the thin film transistor is made incident from the side opposite to the gate electrode is shown. And, in the figure, the solid line shows the results of the characteristics of the sample not subjected to the hydrogenation treatment, and the broken line shows the results of the characteristics of the sample subjected to the hydrogenation treatment. Further, in FIG. 8, the horizontal axis represents the film thickness of the active layer of the thin film transistor.

Here, as described above, the place where the light leakage current is generated is the depletion layer 16 at the drain junction and the depletion layer 16
Since it is the region 17 on both sides of which the diffusion length is approximately the same, the light leakage current indicated by the vertical axis increases as the thickness of the active layer increases. Here, the difference in light leakage current between the characteristic indicated by the solid line and the characteristic indicated by the broken line at the same film thickness is based on the difference in the diffusion length of minority carriers in the film. That is, in the film having the characteristic indicated by the broken line, since the hydrogenation treatment is performed as described above, the localized level in the film is removed and the recombination level is reduced, so that the diffusion length is increased. Therefore, the number of minority carriers that can reach the high electric field region of the drain junction increases, and the light leak current increases.

Therefore, in order to reduce the light leakage current, the diffusion length may be shortened as shown by the solid line. However, when the diffusion length is shortened as shown by the solid line, this diffusion length is short. As a result, the characteristics of the thin film transistor deteriorate. In the above example, since the localized level increases, the threshold voltage rises and the leak current at the time of reverse biasing the gate increases. However, the thin film transistor forming the pixel switching element as described above is not required to have high performance, unlike the thin film transistor forming the driving circuit. Also,
Although the width varies considerably depending on the circuit configuration and driving method, for example, when the liquid crystal display device is a light valve for HDTV, the thin film transistor forming the driving circuit has a mobility of 100 (cm ² / Vsec) or more. Threshold voltage ± 2
Performance of about V is desired. On the other hand, the thin film transistor forming the pixel switching element is not required to have the characteristics of the thin film transistor for the drive circuit described above, and has a mobility of about 1 to 10 (cm ² / Vsec) and a threshold voltage of ± 5.
It can be used even at V level. However, the thin film transistor that constitutes the pixel switching element needs to have a sufficiently small light leak current.

As described above, since the thin film transistor which constitutes the pixel switching element has a relatively large margin in terms of performance, a certain increase in the threshold voltage may affect the characteristics of the entire liquid crystal device within the standard. There is no. Also, the leak current at the time of reverse bias of the gate can be suppressed within the standard by relaxing the electric field in the drain portion using the LDD structure and reducing the thickness of the active layer, which affects the characteristics of the entire liquid crystal device. There is no such thing.

The characteristics are summarized as follows.

(1) The light leak current is determined by the diffusion length of minority carriers in a thin film transistor having the same structure such as size and film thickness.

(2) When the diffusion length of the minority carriers is shortened, the light leak current is reduced but the transistor characteristics are slightly deteriorated.

(3) The required performance of the thin film transistor in the pixel portion, which causes a problem of light leakage current, is lower than that of the thin film transistor forming the driving circuit.

From these (1) to (3), the thin film transistor in the pixel portion can reduce the light leak current by (1), and as a result, even if the influence of (2) appears, it is required. The performance can be satisfied.

Therefore, by making the diffusion length of the thin film transistor constituting the pixel switching element smaller than the diffusion length of other thin film transistors for the drive circuit or the like, the other characteristics of the liquid crystal display device are not affected. The light leakage current of the pixel switching element is reduced. That is, the carrier diffusion length is a direct physical quantity for light leakage, so it is easy to control to a desired value, and the control range is wider and finer control is possible than when changing the film thickness. Therefore, the light leak current with respect to the incident light can be surely reduced. as a result,
It is possible to prevent the deterioration of the image quality due to the fluctuation of the pixel potential due to the light leak current, and to obtain the good image quality.

A liquid crystal display device having such characteristics will be described below.

First, an equivalent circuit of the liquid crystal display device will be described with reference to FIG.

In FIG. 2, one pixel in the display panel is composed of a liquid crystal cell 21, a storage capacitor 22, and a thin film transistor 23 as a pixel switching element. The liquid crystal cell 21 is composed of a pixel electrode provided on the array substrate, a counter electrode provided on the counter substrate, and a liquid crystal layer sandwiched between the array substrate and the counter substrate.

The thin film transistor 23 is formed on the array substrate and is connected to the signal lines 24 and the scanning lines 25 corresponding to the matrix wiring on the array substrate, respectively. The drive circuit 26 for driving the matrix wiring is a thin film transistor 27 as a Y direction shift register connected to the scanning line 25, and an X direction shift connected to the signal line 24 via a thin film transistor 28 as a switching element for image signals. It is composed of a thin film transistor 29 as a register. Further, the thin film transistor 28 sends the image signal 30 to the corresponding signal line 24 by the shift signal of the thin film transistor 29. In addition,
The image display operation by the thin film transistor 27, the thin film transistor 29 and the like is the same as the conventional one, and the description thereof will be omitted.

Of these, the thin film transistor 23 is
Thin film transistors 27, 28, 29 for other drive circuits 26
It is configured so that the diffusion length is shorter than that of.

Next, the sectional structure of the thin film transistor will be described with reference to FIG.

Incidentally, FIG. 1A shows a thin film transistor 28 for a driving circuit, and FIG. 1B shows a thin film transistor 23. Further, the structures of the thin film transistor 28 and the thin film transistor 23 are basically the same, and the same reference numerals are given to the respective parts for description.

First, 32 is an active layer made of a polycrystalline silicon film, and this active layer 32 is formed on a quartz substrate 33, and a gate electrode 35 is formed on the upper surface of the quartz substrate 33 via a gate insulating film 34.
Are formed. Further, an interlayer insulating film 36 is formed on the upper surfaces of these, and in the source / drain regions of the active layer 32, contact holes are provided in the interlayer insulating film 36 and the gate insulating film 34 as shown in the figure, and metal is formed in the contact holes. By depositing the film 37, external connection is possible. Regarding the thin film transistor 23, one of the source / drain regions of the active layer 32 is connected to the transparent conductive film 38 which is a pixel electrode.

A method of reducing the diffusion length of the thin film transistor having the above structure will be described below.

As a first method, as described above, when the hydrogenation process is performed to improve the performance of the thin film transistor, only the thin film transistor 23 is not selectively subjected to the hydrogenation process.

Here, the hydrogenation treatment is performed by introducing hydrogen into a chamber of a plasma CVD apparatus or the like and applying a high frequency to generate plasma. In this case, if the surface of the substrate including the thin film transistor is covered with, for example, a silicon nitride film having a small hydrogen diffusion coefficient in the film, the hydrogenation process is not performed on the covered portion. Therefore, prior to the hydrogenation treatment, a silicon nitride film is deposited on the entire surface of the substrate on which each thin film transistor is formed, and thereafter, the silicon nitride film is left only on the pixel switching element portion not subjected to the hydrogenation treatment by photolithography. . Then, in this state, the entire substrate is hydrogenated, so that a partial hydrogenation is performed except for the pixel switching elements.

FIG. 3 shows the hydrogenation process.
A silicon nitride film 40 is formed on the thin film transistor 23 shown in FIG.
Covered with. In this state, hydrogen 41 is introduced as described above, a high frequency is applied, and plasma is generated to perform hydrogenation treatment. Further, since hydrogen diffuses little in the nitride film 40, by adjusting the hydrogenation time,
The thin film transistor 28 for the drive circuit shown in FIG. 3A is subjected to hydrogenation treatment, and the thin film transistor 23 shown in FIG. 3B is not subjected to hydrogenation treatment.

Here, the thin film transistor 23 in the portion where hydrogenation is not performed has many localized levels, and these localized levels act as recombination levels, so that the diffusion length becomes short and the light leakage is reduced. The current is low. In addition, comparing the optical leakage currents of the NMOS and the PMOS, the PMOS has the N
It is about ½ to ⅓ of that of the MOS, and the use of the PMOS is slightly advantageous for suppressing the light leak current.

Next, a second method for shortening the diffusion length will be described. This method is a method of deteriorating the crystallinity of the active layer of the thin film transistor, which is intended to shorten the diffusion length, specifically, a method of reducing the crystal grain size. This can be achieved by putting a substance that inhibits solid phase growth in the film before solid phase growth. Oxygen, hydrogen, or a rare gas element is known as a material that inhibits this solid-phase growth.

FIG. 4 shows an ion implantation step before solid phase growth which is the second method. In FIG. 4, the quartz substrate 33
A polycrystalline silicon film 32a to be the active layer 32 shown in FIG. 3 is deposited on the entire upper surface. After this, apply photoresist to the entire surface
As shown in FIG. 4A, 42 is applied, and a photoresist 42 is left in a portion which becomes an active layer of the thin film transistor 28 for the driving circuit as shown in FIG. 4A, and the thin film transistor 23 shown in FIG. Photoresist only on layer
Remove 42. In this state, oxygen 43 is injected by ion implantation from above the substrate as shown in the figure, and after this injection is completed, the resist is peeled off and solid phase growth is performed.

In the case of oxygen implantation, the dose amount is 10
By setting it to about ¹⁸ to 10 ²⁰ (cm ⁻³ ), the crystal grain size during solid phase growth can be reduced.

In the thin film transistor formed in the portion where the crystal grain size is reduced due to the solid-phase growth hindered by the above-mentioned ion implantation, since the crystal grain size of the active layer is small, the volume occupied by the grain boundaries per unit volume is small. growing. Since the localized level density is high at the crystal grain boundaries, the thin film transistor formed in this portion has a short diffusion length and a small light leak current.

Next, another embodiment of the above-mentioned second method will be described with reference to FIG. First, the portion which becomes the active layer 32 of the thin film transistor 28 for the drive circuit shown in FIG. 5A is exactly the same as in FIG. 4, and the entire surface is covered with the photoresist 42 so that oxygen 43 is not implanted. . On the other hand, the portion which becomes the active layer 32 of the thin film transistor 23 shown in FIG.
Instead of removing from the entire surface that becomes the active layer as in (b), the source / source in the active layer 32 of the thin film transistor 23 is not removed.
Resist on the part that becomes the junction between the drain and the channel.
Leave 42a and 42b. After that, as in the case of FIG. 4, oxygen 43 is implanted from above the substrate by an ion implantation method, and after this implantation is completed, the resist is peeled off and solid phase growth is performed.

In this way, the grain size of the drain junction covered with the resists 42a and 42b becomes larger than that of the other portions, and the localized level density is lowered. This localized level is a source of generation of a leak current in the dark at a drain junction portion to which a strong electric field is applied. As described above, the crystal grain size of this portion is increased to increase the localized level density. By keeping it low, the leak current in the dark does not increase. Further, since the crystal grain size is small in the other portions, the diffusion length is shortened, so that the light leak current is reduced as in the case of FIG.

Further, another embodiment of the second method will be described. In any of the above examples, in order to reduce the crystal grain size of the active phase, oxygen, hydrogen, or a rare gas element that inhibits solid phase growth is injected into the film before solid phase growth. Is a material that becomes microcrystalline or amorphous by implanting silicon into the crystallized active layer. Even in this case, the crystal grain size of the active layer can be made small, so that the diffusion length becomes short and the light leak current becomes small.

Next, a third method for shortening the diffusion length will be described. This method is a method in which an element serving as a recombination center is put in the active layer 32 of the thin film transistor 23 whose diffusion length should be shortened. Here, since the probability of recombination rapidly increases as the energy level approaches the center of the band, an element that forms an energy level near the band center in silicon is convenient as the recombination center. Heavy metals such as gold and iron are suitable as such elements.

Further, as a method for introducing such an element into the active layer, an ion implantation method is used which can easily control the introduction position and the introduction amount. This ion implantation is the second
Similar to the above method, there are a method performed before solid phase growth and a method performed when implanting impurities into the source / drain. The method performed before solid phase growth is to form a resist mask similar to the second method, and to introduce a heavy metal forming a recombination center into the active layer 32 of the thin film transistor 23 by ion implantation. Good.

On the other hand, the method for implanting impurities into the source / drain is as shown in FIG. Here, the impurity is implanted into the source / drain by using the gate electrode 35 as a mask, but the heavy metal 44 serving as the recombination center is also ion-implanted by using the gate electrode 35 as a mask. Therefore, with respect to the thin film transistor 28 portion for the drive circuit which does not require the introduction of the heavy metal 44, the upper surface is covered with the resist mask 45 after the impurity is injected into the source / drain to prevent the recombination center from being formed in the active layer 32. I'm out.

Usually, after the source / drain ion implantation, a high temperature treatment step is performed to electrically activate the impurities. At this time, the heavy metal element forming the recombination center is also subjected to high temperature treatment at the same time. However, since the thermal diffusion distance of this heavy metal element is smaller than the thermal diffusion distance of the source / drain impurities, it depends on the thermal diffusion distance of the source / drain impurities. The heavy metal element does not reach the determined source / drain junction. Therefore, the localized level density of the source / drain junction can be lowered, the leak current in the dark does not increase, and the diffusion length of other portions is short, so that the light leak current can be effectively suppressed. You can

By each of the above-mentioned methods, the diffusion length of the minority carriers of any thin film transistor among a large number of thin film transistors can be shortened, so that a driving circuit section of high performance thin film transistors and a high performance thin film transistor can be formed on a common array substrate.
It is possible to integrally form a pixel switching element including a thin film transistor having a small light leak current.
For this reason, it is significantly advantageous in the manufacturing process as compared with the one using the drive circuit by the external IC. Further, since the pixel switching element has a small light leak current, high display quality can be obtained, and the driving circuit can maintain high driving performance.

[0060]

According to the liquid crystal display device of the present invention, as a thin film transistor which constitutes a pixel switching element,
The minority carrier diffusion length, which determines the magnitude of light leakage current, is shorter than the minority carrier diffusion length of other thin film transistors used in drive circuits, etc. that are not affected by incident light. Since the light leak current of the switching element and the fluctuation of the pixel potential due to the light leak current can be effectively suppressed, the deterioration of the image quality due to the fluctuation of the pixel potential is prevented, and the liquid crystal display device of high image quality and high performance is provided. Can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a thin film transistor used in an embodiment of a liquid crystal display device of the present invention. (A) is a part where the diffusion length is not short (b) is a part where the diffusion length is short

FIG. 2 is an equivalent circuit diagram of the above liquid crystal display device.

FIG. 3 is an explanatory diagram showing a first method for shortening the diffusion length of minority carriers in the same thin film transistor. (A) When the diffusion length is not shortened (b) When the diffusion length is shortened

FIG. 4 is an explanatory diagram showing a second method for shortening the diffusion length of minority carriers in the same thin film transistor. (A) When the diffusion length is not shortened (b) When the diffusion length is shortened

FIG. 5 is an explanatory view showing another second method for shortening the diffusion length of minority carriers of the same thin film transistor. (A) When the diffusion length is not shortened (b) When the diffusion length is shortened

FIG. 6 is an explanatory diagram showing a third method for reducing the diffusion length of minority carriers in the same thin film transistor. (A) When the diffusion length is not shortened (b) When the diffusion length is shortened

FIG. 7 is an explanatory diagram of a mechanism of light leakage current generation in a thin film transistor.

FIG. 8 is a diagram showing measurement results of a light leak current of a thin film transistor, with and without hydrogenation treatment.

[Explanation of symbols]

23 Thin film transistor as switching element for pixel 24 Signal line 25 Scan line 26 Drive circuit 38 Transparent conductive film as pixel electrode

Claims (1)

[Claims] 1. A plurality of signal lines and scanning lines arranged in a matrix, pixel electrodes provided for each pixel and connected to the signal lines and scanning lines via pixel switching elements each formed of a thin film transistor, and an image. A first electrode substrate having a driving circuit configured by a thin film transistor for supplying a signal and a scanning signal to corresponding ones of the signal line and the scanning line, and a gap facing the first electrode substrate and facing the pixel electrode A thin film transistor which comprises a second electrode substrate having counter electrodes arranged in parallel and a liquid crystal layer sandwiched between the first electrode substrate and the second electrode substrate, and which constitutes the pixel switching element. , That the diffusion length of the minority carrier is shorter than the diffusion length of the minority carrier of the thin film transistor that constitutes the driving circuit. A liquid crystal display device according to symptoms.