JPS6097385A - Thin film transistor substrate for liquid crystal display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film transistor substrate used as one substrate of an image display device holding a liquid crystal therebetween.

Thin film transistors (TPTs) using amorphous silicon (Fl-81) or the like have a large area and can be manufactured at low temperatures, making them ideal for inexpensive liquid crystal display devices using glass substrates. As an example of a display device in which TPTs are arranged in a matrix, a unit pixel portion thereof is shown in FIG. 1(b). Figure 1 (a
) shows its equivalent circuit. The unit pixel is T
In addition to the PT 5, the liquid crystal 3, and the counter electrode 4, a charge holding capacitor 6 is incorporated between the drain 62 of the TPT and the common electrode 61.

This capacitor 6 is important for maintaining the signal voltage with respect to TPT leakage current and voltage level shift (voltage level shift) due to the presence of gate-drain capacitance, and usually has a value of several prO. The counter electrode 4 is made of a bright conductive film such as indium tin oxide (ITO) and is formed on the glass plate 2-A, and the TPT 5 and the capacitor 6 are formed on the other glass substrate 1. The latter will be referred to as a thin film transistor substrate (TPT substrate). As shown in FIG. 1(b), this TPT substrate consists of a glass substrate 1. - TFT5 and capacitance 6 are configured υ, Tll'T6
are gate electrode 52 (X line), source electrode 51 (X line), 8-81 film 53, drain electrode 54, gate insulating film 55 to g#), capacitor 6 is common electrode 61, insulating film 63, display electrode It consists of 62.

In the case of a transmission type liquid crystal display, the display electrode 62 is made of a transparent conductive film such as ITO, and is connected to the drain electrode 54 . In the case of a transmission type liquid crystal display, a transparent conductive film is also used for the common electrode 61. In the case of a reflective type, both electrodes do not need to be transparent. Normally, a 5102 film formed by plasma 0VD or the like is used for the gate insulating film 55 and the insulating film 63. However, if a glass containing an alkali metal, such as an inexpensive soda glass, is used as the substrate 1, 810? It enters into the film or the A-81 film and affects the characteristics of TPT, causing problems in initial characteristics and reliability.

The present invention was made to solve the problem of Shino, and utilizes a silicon nitride film that prevents the diffusion of alkali metal from the glass substrate. In particular, the present invention uses this 7-licon nitride film to form a capacitance within a pixel, and has the advantage of not requiring any additional special steps.

The present invention will be explained in detail below using the drawings. FIG. 2 shows a cross-sectional view of a unit pixel based on one embodiment of the present invention. A common electrode 61 is directly formed on the glass substrate 1 containing alkali metal, and a nitride film 56 covers the surfaces thereof. The display electrode 62 is disposed on the common electrode 62 via the nitride film 56° and the gate insulating film 55, forming the entire capacitor 6. TFT5
On the nitride film 62, a gate electrode 52, a gate insulating film 55,
It is formed by the a-81 film 55, the source electrode 51, and the drain/electrode 54. According to this structure, the TFT 5 is separated from the substrate 1 by the nitride film 56, so that it is less susceptible to the effects of substances contained in the substrate 1. The thickness of this nitride film 56 is
It is determined by the value of capacitance 6, but typically cL1 ~
05 μm and P +! Deposited by VD or optical OVD.

FIG. 5 is a cross-sectional view of a unit pixel according to another embodiment of the present invention. In this example, the nitride film 56 coating the glass substrate 1 functions as part of the gate insulating film of the TFT 5 and also plays a role as an insulating film for the capacitor 6.

Gate electrode 52 and common electrode 6 formed directly on substrate 1
No. 1 has no problem even if it is contaminated with alkali metal, and the oxide film 55 and the a-Bi film 53 on the nitride film 56 are less affected by this.

Although the a-8i TFT has been explained above as an example, the p-8i TFT can also be used in TPTs made of other structural materials.

TP using a semiconductor thin film crystallized by beam annealing etc.
The present invention is also applicable to T. The common electrode 61 and the display electrode 62 are covered with a transparent conductive film (for example, TO or SNO).
t), the present substrate can be used as a transmissive liquid crystal display device, and if at least one of both electrodes is made opaque with metal or the like, the present substrate can be used as a reflective type liquid crystal display device.

[Brief explanation of drawings]

Figures 1(a) and 1(b) are diagrams showing an equivalent circuit diagram and an example of the cross-sectional structure of a unit pixel of a conventional TPT matrix array for a liquid crystal display device. 1 shows an example of the cross-sectional structure of a unit pixel according to the present invention. 1...Substrate, 2...Counter substrate, 3...Liquid crystal, 4...
...Counter electrode, 5...TFT, 6...Capacitance, 61.
...Common electrode, 62...Display electrode, 56 River nitride film, 5
5...Gate insulating film. Applicant Seiko Ichiko Kogyo Co., Ltd. Agent Patent Attorney Mogami Xun Figure 1 co) Figure 1 (I) ~, 25 b Figure 2 6 to Figure 3

Claims (1)

[Claims] (1) In a thin film transistor substrate for a liquid crystal display, in which pixels are arranged in a matrix, each consisting of a thin film transistor, a display electrode connected to the drain of the transistor, and a common electrode forming a capacitance with the display electrode, the common electrode is made of an alkali metal. an insulating film partially containing at least a silicon nitride film is provided on the common electrode, and the display electrode and at least the semiconductor thin film region of the transistor are formed on the insulating film. A thin film transistor substrate for liquid crystal display, characterized by: