JPH0792492A - Active matrix type liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide a novel thin-film transistor array substrate structure capable of improving the image quality of the active matrix type liquid crystal display element. CONSTITUTION:This active matrix type liquid crystal display element consists of a fist glass substrate 101 which is formed with plural scanning lines and plural signal lines, picture element electrodes 108 disposed in correspondence to the respective intersected points thereof and at least >=1 thin-film transistors(TFTs) connected to the respective picture element electrodes 108, a second glass substrate which is laminated with filters and transparent electrode films corresponding to the respective picture element electrodes 108 and a liquid crystal layer which is clamped between the first and second glass substrates. At least >=1 layers of insulating films 102 are formed between the first glass substrate 101 and the picture element electrodes 108 formed on the first glass substrate. As a result, the restriction in processes to the film thicknesses and refractive indices of the picture element electrodes 108 for suppressing the 'interference fringe'-like change in luminance is drastically relieved and the liquid crystal display having excellent productivity and high quality is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device which can be used as a display for OA equipment and the like.

[0002]

2. Description of the Related Art Presently, liquid crystal display devices have been used in various fields such as viewfinders for video cameras, pocket televisions, and high definition projection televisions, personal computers, workstations, information display terminals such as word processors. Are being actively developed and commercialized. Among them, the active matrix type liquid crystal display element is particularly attracting attention because it can realize colorization and high image quality. The active matrix type is a driving method of a liquid crystal display used in comparison with the conventional simple matrix type. Each pixel electrode arranged in a matrix is provided with a switching element, and each pixel electrode is connected through the switching element. This is a method of supplying a signal voltage for controlling the optical characteristics of liquid crystal molecules. A switching element using a thin film transistor (TFT) is the mainstream.

FIG. 3 shows a general structure of a conventional active matrix type color liquid crystal display device. In FIG. 3, reference numeral 301 denotes a light source (backlight). From the viewpoint of brightness and luminous efficiency, the backlight mainly has a red / green / blue emission line spectrum. 302 is a thin film transistor array substrate (TFT array substrate) in which a thin film transistor is formed on each pixel electrode, 303 is a liquid crystal layer, 304
Shows a counter glass substrate formed with a counter transparent electrode film 305 and a filter layer 306. Also, 307 is T
The polarizing plates arranged outside the FT array substrate 302 and the counter glass substrate 304 are shown.

Light from the backlight 301 is polarized by the polarizing plate 307 on the light source side, and only linearly polarized light is emitted from the TFT.
It is incident on the array substrate 302. Incident linearly polarized light is a TFT
The polarization state is changed according to the applied voltage of the liquid crystal layer 303 determined by the potential of each pixel electrode controlled by the above and the potential of the counter electrode 305, and the light intensity is modulated through the color filter layer 306 and the emission side polarization plate 307.

By the way, the liquid crystal display element has a multilayer film structure in which thin films such as a liquid crystal layer, pixel electrodes and TFTs are laminated. In the case of such a multi-layered thin film structure, it is known that multiple interference of light occurs and a phenomenon in which the transmittance periodically changes depending on the wavelength of incident light. Since the cycle of change in transmittance depending on the incident light wavelength fluctuates in response to a slight change in the gap thickness of the liquid crystal layer, when a light source having the above-mentioned emission line spectrum is used, a slight change in the liquid crystal layer There is a problem that "interference fringe" -like luminance change occurs due to multiple interference of light in response to such a change in the gap. As a method of suppressing this phenomenon, for example, as described in Proceedings of the 17th Liquid Crystal Symposium (1991), pages 182 to 183, the film thickness of the pixel electrode formed on the thin film transistor array is changed. Control methods are being studied.

[0006]

However, in the control by only the film thickness of the pixel electrode as in the conventional method, the above-mentioned luminance change is caused by the film electrode film thickness and the refractive index being slightly deviated from the optimum values. However, there is a problem in that the film thickness must be accurately formed when the pixel electrode is formed. The present invention solves the above problems, and an object thereof is to increase the variation margin of the film thickness and the refractive index of the pixel electrode with respect to the above-mentioned "interference fringe" -like luminance change.

[0007]

In order to solve the above-mentioned problems, an active matrix type liquid crystal display device of the present invention comprises a plurality of scanning lines (gate lines) and a plurality of signal lines (source lines), and their intersections. A pixel electrode provided corresponding to
A first glass substrate formed with at least one thin film transistor (TFT) connected to each pixel electrode, and a second glass substrate formed by laminating a filter and a transparent electrode film corresponding to each pixel electrode. And a liquid crystal layer sandwiched between the first and second glass substrates,
At least one insulating film is formed between the first glass substrate and the pixel electrode formed on the first glass substrate.

[0008]

By forming at least one insulating film between the first glass substrate and the pixel electrode, light reflection at the film interface is reduced, and the pixel electrode of the "interference fringe" -like change in luminance is reduced. The variation margin of the film thickness and the refractive index can be increased.

[0009]

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

FIG. 1 shows a sectional structure of a thin film transistor used in an active matrix type liquid crystal display device according to an embodiment of the present invention. In the figure, 101 is a first glass substrate, 102
Indicates the first insulating film. In this embodiment, silicon nitride (SiNx) is used as the first insulating film 102 and P-CV is used.
D was formed on the entire surface of the first glass substrate 101.
103 is a gate electrode. Aluminum was used as the gate electrode 103. Reference numeral 104 denotes a second insulating film selectively formed on the gate electrode 103, and silicon nitride (SiNx) is used in this embodiment. Reference numeral 105 denotes a semiconductor layer, which uses amorphous silicon. 106, 107
Shows a source electrode and a drain electrode, respectively, and has a two-layer structure of titanium / aluminum. Reference numeral 108 denotes a pixel electrode. In this embodiment, ITO (I
nOx-SnOx) was used.

Using the thin film transistor element having the above structure, the active matrix type liquid crystal display element is manufactured by changing the film thickness of the first insulating film 102 (SiNx) and the film thickness of the pixel electrode 108 (ITO). The change in luminance in the form of "interference fringe" due to the in-plane gap unevenness was evaluated. As a result, as shown in FIG.
When the film thickness is less than 50 (nm), the above "interference fringes"
It was revealed that the film thickness range of the pixel electrode 108 in which a uniform luminance change is not observed is very small. On the other hand, when the film thickness of the first insulating film 102 is in the range of 50 (nm) to 150 (nm), the film thickness range of the pixel electrode 108 in which the above "interference fringe" -like luminance change is not observed is 70 (nm). It was confirmed that it could be expanded significantly.

By changing the film forming conditions,
When the refractive index of the pixel electrode is changed, and the refractive index of the first insulating film is n, and those of the pixel electrode and the first glass substrate are n ₁ and n ₂ , respectively, the above formula is satisfied only when the following formula is satisfied. The thickness of the first insulating film 102 is from 50 (nm) to 150
In the range of (nm), the expansion of the film thickness range of the pixel electrode 108 was observed when the "interference fringe" -like luminance change was not observed.

N ₂ <n <n ₁

[0014]

As described above, according to the structure of the active matrix type liquid crystal display element of the present invention, the pixel required for suppressing the "interference fringe" -like luminance change which is a problem in image quality. The amount of change in film thickness (margin) of the electrode could be expanded to 70 (nm). As a result, it is possible to significantly reduce the process constraint on the film thickness of the pixel electrode, which has been conventionally required to achieve the above quality problem, and to manufacture a high-quality liquid crystal display with excellent productivity. It will be possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a thin film transistor array substrate of a liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is a graph showing a film thickness range in which the same “interference fringe” luminance change is not observed.

FIG. 3 is an exploded perspective view showing a schematic configuration of a conventional active matrix type liquid crystal display element.

[Explanation of symbols]

 101 first glass substrate 102 first insulating film 103 gate electrode 104 second insulating film 105 semiconductor layer 106 source electrode 107 drain electrode 108 pixel electrode 301 light source 302 thin film transistor array substrate 303 liquid crystal layer 304 counter glass substrate 305 counter transparent electrode layer 306 filter Layer 307 Polarizing plate

Claims (2)

[Claims] 1. A pixel electrode provided corresponding to each intersection of a plurality of scanning lines (gate lines) and a plurality of signal lines (source lines),
A first glass substrate formed with at least one thin film transistor (TFT) connected to each pixel electrode, and a second glass formed by laminating a filter and a transparent electrode film corresponding to each pixel electrode. An active matrix type liquid crystal display device comprising a substrate and a liquid crystal layer sandwiched between the first and second glass substrates, the first glass substrate and a pixel electrode formed on the first glass substrate. When at least one insulating film is formed between and, the refractive index of the insulating film is n, the refractive index of the pixel electrode is n ₁ , and the refractive index of the first glass substrate is n _2. , N ₂ <n <n ₁ is satisfied, an active matrix type liquid crystal display device. 2. The active matrix type liquid crystal according to claim 1, wherein the insulating film formed between the first glass substrate and the pixel electrode has a film thickness of 50 (nm) to 150 (nm). Display element.