JPH0815719A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device having a specified value of charge holding capacitor, an effect to prevent short circuit, and high transmittance. CONSTITUTION:When the area of a charge holding capacitor 7 is 30% of the area where light transmits, the film thickness of the insulating film 18 for the charge-holding capacitor comprising silicon nitride (having the refractive index about 1.9 and the dielectric const. about 7) is designed to be 0.29-0.31mum. In this range, the possibility of forming a short circuit between a pixel electrode 14 and a lower electrode 17 is very small, a charge holding capacitor with an enough volume is formed (<=0.4mum thickness), and the transmittance of the panel becomes the max.

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 mounted on equipment such as a portable television receiver, a wall-mounted television receiver, and a portable equipment having a display function.

[0002]

2. Description of the Related Art A liquid crystal panel of a liquid crystal display device usually has a liquid crystal material enclosed between two opposed substrates, and a voltage is partially applied to the liquid crystal material to display a desired image. It has become. Specifically, at least one of the two substrates is provided with pixel electrodes made of transparent conductive films arranged in a matrix, and a switching element such as a transistor for selectively applying a voltage to each pixel electrode. Is provided to control the transmittance of light from the backlight for each pixel. In recent years, there is an increasing demand for lower power consumption in liquid crystal display devices, and it is extremely important to reduce the power consumption of the backlight. In order to achieve low power consumption of the backlight, it is essential to further improve the light transmittance.

FIG. 9 is a plan view showing one pixel and its peripheral portion of a pixel transparent electrode of a conventional liquid crystal display device disclosed in JP-A-2-200704, and FIG.
FIG. 3 is a development view of a cross section taken along line XX of FIG. Reference numeral 8 in the drawing denotes a transparent insulating substrate, and a transparent lower electrode 17 is formed at a predetermined position (lower center in FIG. 9) on the insulating substrate 8. A charge holding capacitor insulating film 18 is formed on the entire surface of the lower electrode 17 except the position where the contact hole 19 is to be formed. In FIG. 9, the contact holes 19 are arranged side by side in the lateral direction, and the gate electrode lines 1 are formed in the lateral direction so as to cover these contact holes 19. Similarly, on the upper side of the thin film transistor 3 in FIG. 9, the gate electrode line 1 parallel to the lower side gate electrode line 1 is formed.

The gate electrode 4 of the thin film transistor 3 is provided at a predetermined position (upper part in FIG. 9) on the charge storage capacitor insulating film 18.
The gate electrode line 1 on the upper side is formed so as to extend toward the partition portion 9 located in the central portion of FIG. The pixel electrode 14 is formed in a region extending to the edge of the lower electrode 17 with a predetermined distance from the thin film transistor 3. The lower electrode 17, the pixel electrode 14, and the charge storage capacitor insulating film 18 are stacked to form the charge storage capacitor 7.
A transparent gate insulating film 12 is formed in a region of the pixel electrode 14 other than a portion where the contact hole 25 is formed.

A semiconductor film 13 is formed on the gate electrode 4 and on the peripheral portion of the gate insulating film 12, and a protective film is formed on the semiconductor film 13 except for the portions where the contact holes 23 and 24 are formed. 21 is formed. A phosphorus (P) -doped semiconductor film 22 is formed in the formation region of the thin film transistor 3 except the central portion of the gate electrode 4, the source electrode 5 is formed in the source region on the semiconductor film 22, and the drain electrode 6 is formed in the drain region. Are formed respectively. Figure 9
In, the source electrode lines 2 are formed in the vertical direction on the left and right sides of the partition portion 9, and the portion extending from this source electrode line 2 to the source region of the thin film transistor 3 in each partition is the source electrode 5. The entire surface is covered with a transparent protective film 26. Note that the charge storage capacitor insulating film 1
8, the gate insulating film 12 and the protective film 26 are not shown in FIG. In addition, the pixel portion having such a structure is formed in a matrix on the pixel transparent electrode.

FIG. 11 is a cross-sectional view of a liquid crystal panel of a conventional liquid crystal display device, focusing on a region through which light is transmitted.
The liquid crystal panel includes an alignment film 28 formed on the protective film 26 of the pixel transparent electrode shown in FIGS.
A structure in which the counter electrode 27 and the alignment film 28 are laminated on one surface side is made to face each other with the alignment film 28 inside and the liquid crystal 29 is filled between them. The thickness of the liquid crystal 29 is about 5 μm, and the thickness of the pixel transparent electrode excluding the insulating substrate 8 is about 1 μm. As can be seen from FIGS. 9, 10, and 11, the liquid crystal display device is composed of many thin films.

[0007]

The refractive index of each of these layers is 1.5 for the insulating substrate 8, the liquid crystal 29 and the alignment film 28, while the refractive index of the other thin films is 1.8 to 2.0. high. Therefore, light reflection and interference occur at the thin film interface. The degree of light reflection and interference varies depending on the thickness of the thin film, and in some cases the transmittance of the liquid crystal panel (hereinafter referred to as panel transmittance) may be significantly reduced. Therefore, the thickness of the thin film layer should be optimized. That is especially important.

In the conventional liquid crystal display device, the film thickness is determined, for example, from the viewpoint of prevention of short circuit between the pixel electrode 14 and the lower electrode 18 and the size of the charge retention capacity, and from the viewpoint of improving the panel transmittance. Hasn't been improved much. Above all, the film thickness of the charge storage capacitor insulating film 18 has a great influence on the panel transmittance, so that the advantage of the pixel electrode 14 made transparent for improving the panel transmittance may be impaired.

Further, Japanese Patent Laid-Open No. 4-248584 discloses a liquid crystal display device in which the panel transmittance is improved by improving the Si / N ratio of a protective film (silicon nitride film). Controlling this ratio is not easy.

The present invention has been made in view of such circumstances, and a predetermined charge holding capacity is ensured, and the lower electrode,
By setting the film thickness of the charge storage capacitor insulation film so that the possibility of short circuit between pixel electrodes is sufficiently low and the overall transmittance takes a maximum value, It is an object of the present invention to provide a liquid crystal display device capable of simultaneously obtaining high transmittance.

[0011]

In the liquid crystal display device according to the first and second aspects of the invention, the film thickness of the charge storage capacitor insulating film is the same as that of the entire laminated body including the one surface side electrode, the other surface side electrode and the liquid crystal. It is characterized in that the transmittance is set so as to take a substantially maximum value.

A liquid crystal display device according to a third invention is characterized in that, in the second invention, the charge storage capacitor insulating film is made of silicon nitride.

A liquid crystal display device according to a fourth invention is the liquid crystal display device according to the third invention, wherein the film thickness of the charge storage capacitor insulating film is 0.29 to 0.
It is characterized in that it is 31 μm.

A liquid crystal display device according to a fifth invention is characterized in that, in the second invention, the charge storage capacitor insulating film is made of tantalum oxide.

A liquid crystal display device according to a sixth invention is the liquid crystal display device according to the fifth invention, wherein the thickness of the charge storage capacitor insulating film is 0.36 to 0.
It is characterized in that it is 38 μm.

The liquid crystal display device according to the seventh invention is characterized in that, in the second invention, the gate insulating film and the protective film in a region through which light is transmitted are removed.

A liquid crystal display device according to an eighth invention is characterized in that, in the seventh invention, the charge storage capacitor insulating film is made of silicon nitride.

A liquid crystal display device according to a ninth invention is the liquid crystal display device according to the eighth invention, wherein the film thickness of the charge storage capacitor insulating film is 0.30 to 0.
It is characterized in that it is 33 μm.

A liquid crystal display device according to a tenth invention is the liquid crystal display device according to the seventh invention, characterized in that the charge retention capacitor insulating film is made of tantalum oxide.

A liquid crystal display device according to the eleventh invention is the tenth invention.
In the invention, the thickness of the charge storage capacitor insulating film is 0.37 to
It is characterized in that it is 0.40 μm.

[0021]

FIG. 12 shows the relationship between the film thickness of the charge storage capacitor insulating film and the transmittance of the entire laminate including the one-side electrode, the other-side electrode and the liquid crystal (hereinafter referred to as panel transmittance). The panel transmittance is uniquely determined by the material (refractive index) of the charge storage capacitor insulating film, and as shown in FIG. 12, it has a characteristic that a maximum value and a minimum value are repeated as the film thickness increases and decreases.
Therefore, in the present invention, the film thickness of the charge storage capacitor insulating film is set in consideration of the following two points which have been conventionally considered and the characteristics described above.

First, in order to prevent a short circuit between the lower electrode and the pixel electrode, it is necessary to set the film thickness to a certain value or more. Therefore, the lower limit of the film thickness is determined. And in order to secure a predetermined charge retention capacity, it is necessary to make the film thickness below a certain level,
For this reason, the upper limit of the film thickness is determined. A film thickness within the range defined by these lower and upper limits and at which the panel transmittance has a substantially maximum value shown in FIG. 12 is set as the film thickness of the charge storage capacitor insulating film. As a result, in addition to the predetermined charge holding capacity value and the short-circuit prevention effect, high transmittance can be obtained simultaneously.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. Example 1. FIG. 1 is a plan view showing one pixel and its peripheral portion of a pixel transparent electrode of a liquid crystal display device according to the present invention, and FIG. 2 is a sectional development view taken along line II-II of FIG. . In the figure, 8 is a transparent insulating substrate, and a transparent lower electrode 1 is provided at a predetermined position (lower center in FIG. 1) on the insulating substrate 8.
7 are formed. A charge holding capacitor insulating film 18 is formed on the entire surface of the lower electrode 17 except the position where the contact hole 19 is to be formed. In FIG. 1, the contact holes 19 are arranged side by side in the lateral direction, and the gate electrode lines 1 are formed in the lateral direction so as to cover these contact holes 19. Similarly, on the upper side of the thin film transistor 3 in FIG. 1, the gate electrode line 1 parallel to the lower gate electrode line 1 is also formed.
Are formed.

The gate electrode 4 of the thin film transistor 3 is provided at a predetermined position (upper part in FIG. 1) on the charge storage capacitor insulating film 18,
The gate electrode line 1 is formed so as to extend from the upper gate electrode line 1 toward the partition portion 9 located in the central portion of FIG. The pixel electrode 14 is formed in a region extending to the edge of the lower electrode 17 with a predetermined distance from the thin film transistor 3. The lower electrode 17, the pixel electrode 14, and the charge storage capacitor insulating film 18 are stacked to form the charge storage capacitor 7.
A transparent gate insulating film 12 is formed in a region of the pixel electrode 14 other than a portion where the contact hole 25 is formed.

A semiconductor film 13 is formed on the gate electrode 4 and on the gate insulating film 12 around the gate electrode 4, and a protective film is formed on a region of the semiconductor film 13 excluding portions where the contact holes 23 and 24 are formed. 21 is formed. A phosphorus (P) -doped semiconductor film 22 is formed in the formation region of the thin film transistor 3 except the central portion of the gate electrode 4, the source electrode 5 is formed in the source region on the semiconductor film 22, and the drain electrode 6 is formed in the drain region. Are formed respectively. FIG.
In, the source electrode lines 2 are formed in the vertical direction on the left and right sides of the partition portion 9, and the portion extending from this source electrode line 2 to the source region of the thin film transistor 3 in each partition is the source electrode 5. The entire surface is covered with a transparent protective film 26. Note that the charge storage capacitor insulating film 1
8, the gate insulating film 12 and the protective film 26 are not shown in FIG. In addition, the pixel portion having such a structure is formed in a matrix on the pixel transparent electrode. The above configuration is similar to that of the conventional liquid crystal display device shown in FIGS.

In the present invention, the charge storage capacitor insulating film 1
The film thickness of No. 8 is set so that the transmittance of the panel has a substantially maximum value. The relationship between the film thickness of the charge storage capacity insulating film 18 and the transmittance of the panel is uniquely determined by the material (refractive index) of the charge storage capacity insulating film 18. Therefore, in this relationship, there is a low possibility that the pixel electrode 14 and the lower electrode 17 are short-circuited, and there is a region in which a sufficiently large charge retention capacity can be formed, and the maximum transmittance of the panel is the charge retention capacity. The thickness of the insulating film 18 may be set.

A case where the charge storage capacitor insulating film 18 is made of silicon nitride (SiN) will be described. Silicon nitride has a refractive index of about 1.9 and a dielectric constant of about 7. FIG. 3 shows the relationship between the film thickness of the charge storage capacitor insulating film 18 and the panel transmittance when the charge storage capacitor 7 occupies 30% of the area of the portion through which light is transmitted. Considering that the film thickness for securing the necessary charge storage capacity is 0.4 μm or less, the optimum film thickness at which the panel transmittance is maximum is 0.29 to
It is 0.31 μm. With this film thickness, the possibility of short circuit between the pixel electrode 14 and the lower electrode 17 is sufficiently low.

Embodiment 2 FIG. Next, the case where the charge storage capacitor insulating film 18 shown in FIGS. 1 and 2 is made of tantalum oxide (Ta ₂ O ₅ ) will be described. The refractive index of tantalum oxide is about 2.2.
Is about 2.3 and the dielectric constant is about 21-25. FIG. 4 shows the relationship between the film thickness of the charge storage capacitor insulating film 18 made of tantalum oxide and the panel transmittance. Considering that the film thickness for ensuring the necessary charge storage capacity is 0.4 μm or less and that the short circuit between the pixel electrode 14 and the lower electrode 17 can be prevented, the optimum panel transmittance is obtained. The film thickness is 0.36 to 0.38 μm. Similar effects can be obtained in this embodiment as well.

Example 3. FIG. 5 is a sectional development view showing a pixel transparent electrode of the liquid crystal display device according to the present invention, and is a view corresponding to FIG. In the pixel transparent electrode shown in FIG. 2, the gate insulating film 12 and the protective film 26 are formed on the pixel electrode 14, but in the present embodiment, the pixel electrode 14 that allows light to pass therethrough.
Of the gate insulating film 12 of
The protective film 26 is removed by etching. Other configurations are the same as those shown in FIG. 1, and the same reference numerals are given and description thereof is omitted.

FIG. 6 is a sectional view of the liquid crystal panel of the liquid crystal display device shown in FIG. 5, focusing on the region through which light is transmitted. The region through which light passes is the gate insulating film 12 and the protective film 2.
6 is removed, the alignment film 2 is directly formed on the pixel electrode 14.
8 are formed. In the liquid crystal panel, the pixel electrode on which the alignment film 28 is formed and the one in which the counter electrode 27 and the alignment film 28 are laminated and formed on one surface side of the insulating substrate 8 face each other with the alignment film 28 inside. The liquid crystal 29 is filled between them.

FIG. 7 shows the relationship between the film thickness of the charge storage capacity insulating film 18 and the panel transmittance when the charge storage capacity insulating film 18 is made of silicon nitride in the pixel transparent electrode having such a structure. . From FIG. 7, the optimum film thickness with the maximum panel transmittance is 0.30 to 0.33 μm. Similar effects can be obtained in this embodiment as well.

Example 4. Next, the case where the charge storage capacitor insulating film 18 shown in FIG. 5 is made of tantalum oxide will be described.
FIG. 8 shows the relationship between the film thickness of the charge storage capacitor insulating film 18 made of tantalum oxide and the panel transmittance. From FIG. 8, the optimum film thickness with the maximum panel transmittance is 0.37 to 0.40 μm.
Is. Similar effects can be obtained in this embodiment as well.

[0033]

As described above, in the liquid crystal display device according to the present invention, a predetermined charge holding capacity is secured, a short circuit between the lower electrode and the pixel electrode is prevented, and the total transmittance has a maximum value. By setting the film thickness of the charge storage capacitor insulating film to
The present invention has excellent effects such that a high transmittance is simultaneously obtained in addition to a predetermined charge holding capacity value and a short-circuit prevention effect.

[Brief description of drawings]

FIG. 1 is a plan view showing a pixel transparent electrode of a liquid crystal display device according to the present invention.

FIG. 2 is a sectional development view of the liquid crystal display device shown in FIG. 1, taken along line II-II.

FIG. 3 is a graph showing the relationship between the film thickness of the charge storage capacitor insulating film made of silicon nitride and the panel transmittance in the structures shown in FIGS. 1 and 2.

FIG. 4 is a graph showing the relationship between the film thickness of the charge storage capacitor insulating film made of tantalum oxide and the panel transmittance in the structure shown in FIGS. 1 and 2.

FIG. 5 is a plan view showing another embodiment of the pixel transparent electrode of the liquid crystal display device according to the present invention.

6 is a cross-sectional view of the liquid crystal panel of the liquid crystal display device shown in FIG. 5, focusing on a region through which light is transmitted.

FIG. 7 is a graph showing the relationship between the film thickness of the charge storage capacitor insulating film made of silicon nitride and the panel transmittance in the structures shown in FIGS. 5 and 6.

8 is a graph showing the relationship between the film thickness of the charge storage capacitor insulating film made of tantalum oxide and the panel transmittance in the structure shown in FIGS. 5 and 6. FIG.

FIG. 9 is a plan view showing a pixel transparent electrode of a conventional liquid crystal display device.

10 is a sectional development view of the liquid crystal display device shown in FIG. 9, taken along line XX.

FIG. 11 is a cross-sectional view of a liquid crystal panel of the conventional liquid crystal display device, focusing on a region through which light is transmitted.

FIG. 12 is an explanatory diagram showing the relationship between the film thickness of the charge storage capacitor insulating film and the panel transmittance.

[Explanation of symbols]

1 Gate Electrode Line, 2 Source Electrode Line, 3 Thin Film Transistor, 4 Gate Electrode, 5 Source Electrode, 6 Drain Electrode, 7 Charge Retaining Capacitance, 8 Insulating Substrate, 9 Partition, 12 Gate Insulating Film, 13, 22 Semiconductor Film, 14
Pixel electrode, 17 lower electrode, 18 charge storage capacitor insulating film, 19, 23, 24, 25 contact hole, 2
1, 26 protective film, 27 counter electrode, 28 alignment film, 2
9 Liquid crystal.

Claims (11)

[Claims] 1. A liquid crystal display device in which a lower electrode, a charge retention capacitor insulating film, and a pixel electrode are laminated on the surface of an insulating substrate, and one surface side electrode and the other surface side electrode are opposed to each other with a liquid crystal interposed therebetween. The thickness of the charge storage capacitor insulating film is set so that the transmittance of the entire laminate including the one surface side electrode, the other surface side electrode and the liquid crystal has a substantially maximum value. apparatus. 2. A one-side electrode in which a lower electrode, a charge retention capacitor insulating film, a pixel electrode, a gate insulating film and a protective film are laminated on the surface of an insulating substrate and a multi-side electrode are opposed to each other with a liquid crystal interposed therebetween. In the liquid crystal display device, the film thickness of the charge storage capacitor insulating film is set so that the transmittance of the entire laminated body including the one surface side electrode, the other surface side electrode and the liquid crystal has a substantially maximum value. Liquid crystal display device characterized by. 3. The liquid crystal display device according to claim 2, wherein the charge storage capacitor insulating film is made of silicon nitride. 4. The film thickness of the charge storage capacitor insulating film is from 0.29 to
The liquid crystal display device according to claim 3, wherein the liquid crystal display device has a thickness of 0.31 μm. 5. The liquid crystal display device according to claim 2, wherein the charge storage capacitor insulating film is made of tantalum oxide. 6. The film thickness of the charge storage capacitor insulating film is 0.36 to
The liquid crystal display device according to claim 5, wherein the liquid crystal display device has a thickness of 0.38 μm. 7. The liquid crystal display device according to claim 2, wherein the gate insulating film and the protective film in a region where light is transmitted are removed. 8. The liquid crystal display device according to claim 7, wherein the charge storage capacitor insulating film is made of silicon nitride. 9. A film thickness of the charge storage capacitor insulating film is 0.30 to
9. The liquid crystal display device according to claim 8, wherein the liquid crystal display device has a thickness of 0.33 .mu.m. 10. The liquid crystal display device according to claim 7, wherein the charge storage capacitor insulating film is made of tantalum oxide. 11. The film thickness of the charge storage capacitor insulating film is 0.37.
11. The liquid crystal display device according to claim 10, wherein the liquid crystal display device has a thickness of 0.40 .mu.m.