JP2003229574A - Thin film transistor array substrate and liquid crystal image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film transistor in which degradation by heat generation is prevented by suppressing the temperature rise of the thin film transistor and to improve the reliability of a liquid crystal image display device by forming an array substrate by using it. <P>SOLUTION: By removing an insulating film on the gate electrode, source electrode and drain electrode of the thin film transistor (TFT) or superimposing a transparent electrode on it, the effect of heat conducting paths from the electrodes to a liquid crystal layer is improved, the temperature rise of the TFT is suppressed and the TFT with excellent reliability is obtained. Also, by the TFT forming a driving circuit part of the array substrate with, a liquid crystal display device with excellent reliability is obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor array substrate and a liquid crystal image display device using the same.

[0002]

2. Description of the Related Art In recent years, a polycrystalline silicon thin film transistor having a semiconductor layer of polycrystalline silicon having a mobility higher than that of amorphous silicon has been actively developed. By using this polycrystalline silicon thin film transistor, not only the liquid crystal switching pixel transistor but also a drive circuit for driving the pixel transistor can be formed on the glass substrate. Taking advantage of this feature, a liquid crystal display device with added value such as compactness, cost reduction, high reliability, etc. has been developed. Currently, digital still cameras, digital video cameras, car navigation systems, laptop computers, etc. Widely used in.

In addition, the polycrystalline silicon thin film transistor is
Since we get a much higher mobility, as mentioned above,
Taking advantage of the characteristics, a polycrystalline silicon thin film transistor array is formed on an insulating substrate such as a glass substrate, and a liquid crystal display device or an organic EL display device is being developed.

As described above, the polycrystalline silicon thin film transistor can be formed on an insulating substrate such as an inexpensive glass substrate and has various applications. On the other hand, the reliability is lower than that of a MOS transistor formed on a silicon substrate. In addition, there is a problem that the characteristic variation is large.

One of the major reliability problems is self-heating deterioration. The self-heating deterioration is a phenomenon in which the temperature of the thin film transistor rises due to Joule heat and the transistor characteristics are deteriorated due to heat. As shown in FIG. 6, S value deterioration and Vth shift occur. Such a characteristic change naturally causes image deterioration of the liquid crystal display device. This deterioration is caused in a thin film transistor having a large amount of current, so that it is particularly observed in a thin film transistor forming a drive circuit in a liquid crystal display device. Among them, a transistor that forms a buffer that outputs a signal to a source signal line or a gate signal line needs to flow a large current, so that the size is large and the transistor reaches a high temperature, so that self-heating deterioration is large.

As a precedent of measures for suppressing the temperature rise, a heat dissipation layer having a high thermal conductivity, such as that disclosed in Japanese Patent Laid-Open No. 5-206468 and Japanese Patent Laid-Open No. 6-177386, is newly provided above and below the polycrystalline silicon film. Although a method has been proposed in which the heat generated in the channel part is released to suppress the temperature rise by forming the film, the formation of a new film with good thermal conductivity increases the number of steps and also leads to cost increase. . In addition, the transistor characteristics may change depending on the newly formed film, which is not suitable for practical use.

As another example of measures for suppressing the temperature rise, in Japanese Patent Laid-Open No. 10-116990, an electrode film having a high thermal conductivity among the constituent elements of the thin film transistor is expanded to form a heat dissipation expansion part. Is proposed. However, since an insulating film such as SiNx or SiOx is formed on top of this, there is a problem that heat is difficult to escape.

[0008]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a thin film transistor that suppresses the temperature rise of the thin film transistor due to Joule heat as much as possible without changing the number of steps and only by changing the mask pattern and does not cause self-heating deterioration. Another object of the present invention is to provide a liquid crystal display device using the thin film transistor, which does not cause image deterioration.

[0009]

The present invention provides a thin film transistor array substrate including a semiconductor film, a gate insulating film, an interlayer insulating film, a source electrode, a drain electrode, and a protective insulating film as constituent elements. It is a thin film transistor array substrate characterized in that the above-mentioned constituent elements are not present on at least one of the drain electrodes. By configuring in this way,
The heat generated in the channel portion of the thin film transistor is transferred to the liquid crystal layer in contact with the substrate and is efficiently radiated by the convection of heat in the liquid crystal layer, so that the temperature rise of the thin film transistor can be suppressed and the deterioration of the TFT can be prevented. it can.

Further, the thin film transistor array substrate of the present invention further comprises a transparent electrode, and the transparent electrode is connected to at least one of the gate electrode, the source electrode and the drain electrode, thereby enhancing the heat dissipation efficiency of the thin film transistor. You can

The liquid crystal image display device of the present invention is characterized by using the above-mentioned thin film transistor array substrate of the present invention. As a result, there is no deterioration of TFT characteristics,
Therefore, a display device having excellent display performance reliability can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention shown in FIGS. 1 to 4 will be described below in comparison with a conventional example shown in FIG.

First, a conventional thin film transistor (TF)
The structure of T) will be briefly described. FIG. 7A is a TFT structure of a pixel portion of a conventional p-Si TFT array, and FIG.
(B) shows the structure of the TFT in the drive circuit portion. The drive circuit TFT of FIG. 7B will be described.
The pixel portion TFT in FIG. 7A is a driving circuit portion TFT.
The ITO transparent electrode 110 is only added to. On the glass substrate 60, islands 10a and 10b of p-Si semiconductor, gate insulating film 80, gate electrode 50, interlayer insulating film 90, source electrode 30 and drain electrode 40, protective insulating film 10
0, the alignment film 130 is laminated. The gate insulating film, the interlayer insulating film, etc. are usually formed by using an insulating material such as SiOx or SiNx. The semiconductor island is usually composed of a low-resistance region 10b serving as a source and a drain doped with impurities using the gate electrode as a mask and a non-doped channel region 10a. Source electrode 30, drain electrode 40
Is a low resistance region 10b which is a semiconductor island through a contact hole formed in the gate insulating film 80 and the interlayer insulating film 90.
Is electrically connected to. The upper surface of the TFT array substrate is in contact with the liquid crystal layer (not shown).

(Embodiment 1) Next, FIGS. 1A to 1D show a TFT structure of a drive circuit portion of the present embodiment 1.
Since heat generation is a problem in the TFT of the drive circuit,
The following description is all about the TFT of the drive circuit section. That is, it is an improvement over the conventional example shown in FIG. Since the first embodiment and the conventional example have the same components, the same components are designated by the same reference numerals.

FIG. 1A shows a first embodiment, which is an interlayer insulating film 90 on the gate electrode 50 and a protective insulating film 100.
Is characterized by being removed. The heat generated in the semiconductor part of the TFT is first transferred to the metal part having high thermal conductivity. If the insulating layer on the gate electrode 50 is removed,
The heat is easily transferred to the liquid crystal layer thereabove, and the heat is efficiently diffused in the liquid crystal layer by the convection of the heat, so that the heat generation of the TFT can be suppressed by this configuration. In this way, the heat conduction is improved by removing the interlayer insulating film and the protective insulating film which hinder the heat conduction. Since the alignment film 130 is usually extremely thin, it does not hinder heat conduction.

In the second embodiment shown in FIG. 1B, the protective insulating film 1 on the source electrode 30 and the drain electrode 40 is formed.
00 has been removed. This also enables the same improvement in heat conduction.

Further, FIG. 1C shows a third embodiment,
The interlayer insulating film 90 on the gate electrode 50 is removed, electrodes at the same level as the source and drain electrodes are formed there, and the protective insulating film 100 is partially removed. This configuration also enables similar improvement in heat conduction. Further, this structure also has an effect of reducing the wiring resistance of the gate electrode and the gate scanning line connected to the gate electrode to prevent signal deterioration.

Further, as shown in FIG. 1D, if the protective insulating film is removed from all over the gate electrode 50, the source electrode 30, and the drain electrode 40, the heat radiation can be further improved.

(Second Embodiment) FIGS. 2A to 2C show the structure of a drive circuit TFT according to a second embodiment of the present invention. In the example of FIG. 2A, the source electrode 3
0 and the protective insulating film 100 on the drain electrode 40 are removed, and the transparent electrode 110 made of ITO is formed there. By thus increasing the heat radiation area by the transparent electrode, the temperature rise of the TFT can be suppressed.
Further, FIG. 2B shows a structure in which the interlayer insulating film 90 and the protective insulating film 100 on the gate electrode 50 are removed and the transparent electrode 110 made of ITO is formed there. Thereby, the same heat radiation effect can be obtained. Further, in FIG. 2C, the interlayer insulating film 90 on the gate electrode 50 is removed and an electrode at the same level as the source / drain electrodes is formed thereon.
Further, a transparent electrode 110 made of ITO is formed on it. As described above, in the second embodiment, the heat dissipation effect of the TFT is enhanced by utilizing the transparent electrode which is not originally necessary.

(Embodiment 3) FIGS. 3A, 3B and 4 show the structure of a drive circuit TFT according to a third embodiment of the present invention. In the third embodiment, the present invention is applied to the case where the planarization film 120 is present in addition to the constituent elements described above.
The flattening film 120 is originally used to flatten the unevenness of the substrate surface in the pixel region and to increase the aperture ratio. Also, a resin type color filter layer may be used as the flattening film to form a color filter on array structure.

FIG. 3A shows the flattening film 120 removed in the area of the drive circuit TFT. Since the flattening film or the color filter layer is formed thicker than the other films, it becomes a major factor of obstructing the heat conduction path from the TFT to the liquid crystal layer. By removing this, the heat dissipation effect of the TFT can be enhanced. Further, as shown in FIG. 3B, the protective insulating film 10 further on the source electrode 30, the drain electrode 40, and the gate electrode 50.
The heat dissipation effect can be further enhanced by removing 0 and the interlayer insulating film 90.

Further, as shown in FIG.
By removing the inter-layer insulating film 90 and the protective insulating film 100 above 0 and forming the ITO transparent electrode 110 wide, the heat dissipation area can be expanded, so that the heat dissipation effect of the TFT can be enhanced.

(Fourth Embodiment) FIG. 5 is a plan view of a TFT array substrate of a liquid crystal display device according to a fourth embodiment of the present invention.

A polycrystalline silicon thin film transistor is formed on a glass substrate 60, and an X driver, a Y driver, and an image display section are formed. The X driver and the Y driver are composed of a logic circuit section that creates a signal waveform and a buffer that amplifies the signal. Generally, a signal output from the X driver is input to the gate line 180, a thin film transistor for writing a video signal is selected, a video signal output from the Y driver is input to the source line 200, and a video signal is formed in a pixel. Data is written in the liquid crystal cell 160 through the thin film transistor 150. By performing this for all the gate lines and the source lines, the video signal is written in the entire image display section.

The thin film transistor forming the driver is
Of course, it varies depending on the driving method, but when viewed as individual transistors, some transistors have high power and some have low power. Among them, in a transistor with high power, of course, the temperature rises due to heat generation due to Joule heat, self-heating deterioration is caused, a correct signal waveform cannot be formed, and as a result, a good image cannot be displayed. Therefore, by using a transistor having a large power as the transistor having the structure of suppressing the temperature rise according to the present invention described in the first to third embodiments, the self-heating deterioration is suppressed, the deterioration of the signal waveform is prevented, and a good image is obtained. Can be displayed.

The temperature rise due to Joule heat greatly changes depending on the size of the transistor, and the ultimate temperature increases as the size increases. In that sense, since a larger-sized transistor is used in the buffer section than in the logic circuit, the buffer section is more concerned about self-heating deterioration than the logic circuit section. The reason why the size of the transistor forming the buffer portion is large is that the buffer must amplify the signal waveform formed in the logic circuit portion and output the amplified signal waveform to the gate line or the source line.
Although various designs are possible depending on the panel, a transistor having a size (channel width W) forming the inverter 140 of the buffer section may be several hundreds μm. With such a large size, the heat is particularly large, and the temperature rise due to Joule heat is so large that self-heating deterioration occurs, and correct output cannot be obtained, and as a result, good image display cannot be performed. . Therefore, by using the thin film transistor forming the buffer portion having a particularly large size as the thin film transistor having the structure for suppressing the temperature increase described in Embodiments 1 to 3, self-heating deterioration can be prevented and favorable image display can be obtained. .

Although the present invention has been described by taking a polycrystalline silicon thin film transistor as an example, Joule heat is not generated even when the semiconductor film is single crystal silicon or microcrystalline silicon, or germanium or another semiconductor film or compound semiconductor film. Since it occurs in the same manner, it is possible to suppress heat generation with exactly the same structure. Further, since the SOI is formed on the insulating film, the temperature rise due to Joule heat is larger than that of the MOS transistor on the silicon substrate, and the characteristic change due to heat generation poses a problem. Can be similarly applied.

[0028]

As described above, according to the present invention, it is possible to suppress the temperature rise of the thin film transistor due to self-heating, prevent the deterioration due to self-heating, and obtain a highly reliable thin film transistor. By forming a driver circuit and a pixel transistor using the thin film transistor of the present invention, an advantageous effect that reliability of a liquid crystal display device is improved can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a TFT showing a first embodiment according to the present invention.

FIG. 2 is a sectional view of a TFT showing a second embodiment according to the present invention.

FIG. 3 is a sectional view of a TFT showing a third embodiment according to the present invention.

FIG. 4 is a cross-sectional view of a TFT showing a third embodiment according to the present invention.

FIG. 5 is a plan view of a TFT array substrate for a liquid crystal display device showing a fourth embodiment according to the present invention.

FIG. 6 is a TFT characteristic diagram showing an example of self-heating deterioration.

FIG. 7 is a sectional view showing the structure of a conventional TFT.

[Explanation of symbols]

10 Semiconductor film 10a channel region 10b Low resistance region 30 source electrode 40 drain electrode 50 gate electrode 60 glass substrate 80 Gate insulation film 90 Interlayer insulation film 100 Protective insulation film 110 ITO transparent electrode 120 Flattening film (color filter layer) 130 Alignment film 140 inverter Thin film transistor for 150 pixels 160 liquid crystal cell 180 gate line 200 source line

Claims (15)

[Claims] 1. A thin film transistor array substrate formed on an insulating substrate, comprising a semiconductor film, a gate insulating film, an interlayer insulating film, a source electrode, a drain electrode and a protective insulating film as constituent elements, wherein the gate electrode and the source electrode are provided. And the thin film transistor array substrate, wherein the constituent element does not exist on at least one of the drain electrodes. 2. A thin film transistor array substrate formed on an insulating substrate, comprising a semiconductor film, a gate insulating film, an interlayer insulating film, a source electrode, a drain electrode, a protective insulating film, and a transparent electrode as constituent elements, wherein the transparent electrode is A thin film transistor array substrate, which is connected to at least one of the gate electrode, the source electrode, and the drain electrode and has a function of improving heat dissipation efficiency. 3. A thin film transistor array substrate formed on an insulating substrate, comprising a semiconductor film, a gate insulating film, an interlayer insulating film, a source electrode, a drain electrode, a protective insulating film, and an organic film as constituent elements, the semiconductor film comprising: A thin film transistor array substrate, wherein the organic film is not present on the gate electrode, the source electrode and the drain electrode. 4. The thin film transistor array substrate according to claim 3, wherein the organic film has a function of alleviating a step of the underlying layer. 5. The thin film transistor array substrate according to claim 3, wherein the organic film functions as a color filter. 6. The thin film transistor array substrate according to claim 3, wherein the organic film functions as a color filter and a function of alleviating a step on the base. 7. A thin film transistor array substrate formed on an insulating substrate, comprising a semiconductor film, a gate insulating film, an interlayer insulating film, a source electrode, a drain electrode, a protective insulating film, and an organic film as components, A thin film transistor array substrate, wherein the constituent element is not present on at least one of the source electrode and the drain electrode. 8. The thin film transistor array substrate according to claim 7, wherein the organic film has a function of reducing a stepped portion of a base. 9. The thin film transistor array substrate according to claim 7, wherein the organic film functions as a color filter. 10. The thin film transistor array substrate according to claim 7, wherein the organic film functions as a color filter and a function of alleviating a step difference of a base. 11. A thin film transistor array substrate formed on an insulating substrate, comprising a semiconductor film, a gate insulating film, an interlayer insulating film, a source electrode, a drain electrode, a protective insulating film, an organic film and a transparent electrode as constituent elements. A thin film transistor array substrate, wherein a transparent electrode is connected to at least one of the gate electrode, the source electrode, and the drain electrode, and functions to improve heat dissipation efficiency. 12. The thin film transistor array substrate according to claim 11, wherein the organic film has a function of reducing a stepped portion of a base. 13. The thin film transistor array substrate according to claim 11, wherein the organic film functions as a color filter. 14. The thin film transistor array substrate according to claim 11, wherein the organic film functions as a color filter and a function of alleviating a level difference of a base. 15. A liquid crystal image display device using the thin film transistor array substrate according to claim 1. Description: