JPS63246729A - Two terminal type active matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To minimize a decrease in the opening rate of picture elements even if the picture elements are formed to high accuracy by constituting both upper and lower electrodes of transparent conductive films. CONSTITUTION:The transparent conductive films are used for both the two electrodes; the upper and lower electrodes 4, 2 of an additive capacity 23 of an active matrix liquid crystal display device using a two-element terminal having the additive capacity formed of the lower electrode, insulator layer and upper electrode for each of the picture elements. The additive capacity parts are transparent and, therefore, even if the additive capacities 23 are formed over the entire surfaces of the picture elements, the decrease in the opening rate of the picture elements and the deterioration in the display performance of the liquid crystal display device are obviated and since the additive capacities can be formed over the entire surface of the picture elements, the formation of the insulator layers 3 of the additive capacities to a larger film thickness is possible. Easy formation of the pinhole-free insulating films 6 is permitted as well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an active matrix liquid crystal display device using two-terminal elements.

[Conventional technology]

In recent years, as the capacity of liquid crystal display devices has increased, research and development of active matrix liquid crystal display devices has been progressing in order to improve display performance such as contrast.

Among these, liquid crystal display devices using two-terminal elements with simple manufacturing methods and structures are attracting attention.

However, two-terminal elements, especially metal-insulator-metal elements, have a large structural parasitic capacitance, so when pixel definition is increased, the capacitance ratio between the pixel and the two-terminal element cannot be maintained sufficiently, resulting in display characteristics leading to deterioration.

Therefore, for example, the following document describes that an additional capacitor is formed in each pixel to suppress the deterioration of display characteristics.

Nagone Hirai, Yuji Kato, Shohei Naemura, Chizoku Tani "Storage capacitor" High-definition MIM-LCD using IJ structure
J Television Society Technical Report Vol. 1.10. lI&L
47 pp, 1-6 Published February 1988 [Problems to be Solved by the Invention] However, in forming these additional capacitors, in the prior art, one of the upper and lower electrodes of the additional capacitors is made of K, for example, tantalum (Ta). ) An opaque metal that can form an oxide film through anodic oxidation is used as the conductive film.

Therefore, as the definition of pixels becomes higher, the ratio of the additional capacitance formation area to the pixel area increases, resulting in a significant decrease in the aperture ratio.

This results in a significant reduction in display performance in a transmissive liquid crystal display device.

An object of the present invention is to provide an additional capacitance structure that minimizes a decrease in the aperture ratio of pixels even when pixels have higher definition.

[Means for solving problems]

Therefore, the present invention is characterized in that a transparent conductive film is used for both the upper and lower electrodes of the additional capacitor in order to prevent the pixel aperture ratio from decreasing due to the formation of the additional capacitor.

〔Example〕

The present invention can be applied to two-terminal elements such as ring diodes and varistors, but here, the gold layer-insulator-metal (
Embodiments of the present invention will be described in detail with reference to the drawings, taking a device (hereinafter referred to as MIM) as an example.

FIG. 1 is a perspective view showing an MIM element, a pixel, and an additional capacitor according to an embodiment of the present invention.

In FIG. 1, first, a transparent conductive film such as ITO1SnO□ is formed on a lower glass substrate 1 by vapor deposition or sputtering, and this transparent conductive film is patterned by ordinary photolithography technology to form a lower electrode 2. Form. Next, tantalum pentoxide (Ta205) is formed on the lower electrode 2 as an insulating layer 3. This insulator layer 3
In this case, a Ta206 film was formed by sputtering, but if it is a transparent insulator, it can be made of Sin, SiN.
, polyimide resin, etc. may be used, and the forming method may be a CVD method, vapor deposition, spin coating method, or the like. Next, a film of Ta is deposited on the insulator layer 6 by sputtering, and patterned by photolithography as shown in FIG. 1 to form data lines 5.

By anodizing the Ta of the patterned data line 5, an insulating film 6 of the MIM element is formed. The anodic oxidation is performed in a 0.1 wt % citric acid aqueous solution by applying a voltage of 30 V to form an insulating film 6 with a thickness of about 50 nm.

Next, a transparent conductive film such as ITO, SnO, etc. is deposited by sputtering, and the upper electrode 4, which is the pixel electrode (including the counter electrode of the MIM element), is formed by ordinary photolithography. The material and formation method of the upper electrode 4 are the same as those of the lower electrode 2. The lower electrode 2, the insulator layer 3, and the upper electrode 4 constitute an additional capacitor 23.

A liquid crystal 10 is formed between the lower substrate 21 formed by the above steps and the upper substrate 22 constituted by the upper glass substrate 7 and the transparent electrode 8, and as shown in the cross-sectional view in FIG. 2, an alignment film 9 is formed. A liquid crystal cell is formed according to the usual liquid crystal cell manufacturing process of performing an alignment treatment by using a sealing material 11 and sealing with a sealing material 11.

FIG. 3 shows an equivalent circuit diagram of the matrix formed in the liquid crystal cell.

The two-terminal element 25 and the additional capacitor 26 are connected in series between the data line 26 and the timing line 27.
A voltage determined from K is applied to the liquid crystal 24. The counter electrode of the liquid crystal 240 is the upper glass substrate 7
It is connected to the transparent electrode 8 of. Therefore, the additional capacitance 23 needs to be sufficiently larger than the capacitance of the liquid crystal 24.

In the above example, the pixel dimensions are 230 μm x 135
The dimensions of the μm additional capacitance are 150 μm x 120 μm, the thickness of the insulating layer 3 is 1 μm, and the MIM element size is 88 μm.
The thickness of the insulating film 6 made of Ta205 is approximately 50 nm.
And so. As a result, each capacitance is pixel capacitance: approximately 0.3
pF, additional capacitance:, 3.4pF, element capacitance: 0.24p
It becomes F.

〔Effect of the invention〕

According to the present invention, even if the additional capacitance is formed over the entire surface of the pixel, since the additional capacitance portion is transparent, the pixel aperture ratio is reduced.
The display performance of the liquid crystal display device is not deteriorated. In addition, since the additional capacitor can be formed over the entire surface of the pixel, it is possible to increase the thickness of the insulating layer of the additional capacitor, and it is possible to easily form a pinhole-free insulating film ('I'a2 o
When using s, the thickness may be 1 to 2 μm).

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an embodiment of a two-terminal element, pixel electrode, and additional capacitance according to the present invention, Fig. 2 is a sectional view showing a liquid crystal cell according to an embodiment of the present invention, and Fig. 3 is a perspective view showing an embodiment of a liquid crystal cell according to the present invention. It is a modeled circuit diagram. 2...Lower electrode, 3...Insulator layer, 4...Upper electrode, 23...Additional capacitance. Fig. 1 Mu bow 6

Claims (1)

[Claims] A two-terminal active matrix liquid crystal display device in which each pixel has an additional capacitance formed by a lower electrode, an insulator layer, and an upper electrode, characterized in that the upper electrode and the lower electrode are both made of a transparent conductive film. A two-terminal active matrix liquid crystal display device.