JPH02230129A - Reflection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To eliminate the unevenness of luminance and the lowering of contrast on a display screen by forming a source electrode constituting a TFT on the outside of a reflection picture element electrode so that it is not superposed on the reflection picture element electrode. CONSTITUTION:In a reflection type liquid crystal display device, the source electrode 22 constituting a thin film transistor is positioned on the outside of the reflection picture element electrode 28 so that it is not superposed on the electrode 28. Thus, the capacity caused in the source electrode 22 and the reflection picture element electrode 28 in the case that the TFT is in an off-state is reduced. Even when the potential of the source electrode 22 is changed, the potential impressed on a picture element is changed little, that is, the potential impressed on liquid crystal 29 is held, so that the unevenness of luminance or the lowering of contrast on a display screen is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a reflective liquid crystal display device having an active element used in a projection display device.

2. Description of the Related Art In recent years, liquid crystal display devices using active elements have come to be used as pocket televisions or information terminals.

A conventional reflective liquid crystal display device will be explained below.

FIG. 3 is a sectional view of a conventional reflective liquid crystal display device, and FIG. 4 is a plan view of a substrate provided with a thin film transistor (hereinafter referred to as TPT). l is an insulating substrate, 2 is a source electrode, 3 is a gate electrode, 4 is a semiconductor section, 5 is a drain electrode, 6 is a gate insulating layer, 7 is an insulator layer, 8 is a reflective pixel electrode, 9 is a liquid crystal layer, 10 is The opposing common electrode, 1l, is an opposing transparent substrate.

The operation of the reflective liquid crystal display device configured as described above will be described below.

When a voltage is applied to the gate electrode 3 and the transistor is turned on, the signal current of the source electrode 2 flows to the drain electrode 5 and then to the reflective pixel electrode 9.

This drives the liquid crystal provided above the reflective pixel electrode 9 to switch light and obtain an image by taking contrast between pixels. Normally, the time for a signal to be written to one pixel is very short (current TV broadcasting (
For example, in the case of the NTSC system, this is about 1/60th of a second, whereas for the rest of the time, no voltage is applied to the gate electrode or a voltage of the opposite polarity to that in the on state is applied, and the transistor is in the off state. It is in. In this way, the voltage applied to the liquid crystal is held until the next gate electrode is selected and a new source signal is written.

Problems to be Solved by the Invention However, in the configuration in which the source electrode portion of the TPT overlaps the reflective pixel electrode as described above, when the TPT is in the off state, capacitance is generated between the source electrode and the reflective pixel electrode. When the potential applied to the source changes, the voltage applied to the liquid crystal changes. (FIG. 5) As a result, the voltage applied to the liquid crystal cannot be maintained. This has the disadvantage of causing uneven brightness and reduced contrast of the image.

The present invention solves the above-mentioned problems and aims to provide a reflective liquid crystal display device that can eliminate uneven brightness and decrease in contrast of a display screen.

Means for Solving the Problem In order to solve this object, the reflective liquid crystal display device of the present invention has a structure in which the source electrode constituting the TPT is formed outside the reflective pixel electrode so as not to overlap with the reflective pixel electrode. It has become.

Effect: With this configuration, it is possible to reduce the capacitance that occurs between the source electrode and the reflective pixel electrode when the TPT is in the off state, and even if the potential of the source electrode changes, there is little change in the potential applied to the pixel, which improves display performance. It is possible to suppress uneven brightness or decrease in contrast.

EXAMPLE Hereinafter, a reflective liquid crystal display device according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a reflective liquid crystal display device according to an embodiment of the present invention, and FIG. 2 shows a planar structure of a substrate provided with TPT of a reflective liquid crystal display device according to an embodiment of the present invention. It is something.

2I is a glass substrate as an insulating substrate, 22 is a source electrode,
23 is a gate electrode, 24 is non-quality silicon as a semiconductor part,
25 is a drain t pole, 26 is an amorphous silicon nitride layer as a gate insulating layer, 27 is a non-quality silicon nitride layer as an insulator layer, 2
8 is a reflective pixel electrode, 29 is a liquid crystal, 30 is indium tin oxide (ITO), and 31 is a glass substrate.

The operation of the reflective liquid crystal display device configured as described above is similar to that of the conventional example.

As described above, according to this embodiment, since the source electrode constituting the TPT does not overlap with the reflective pixel electrode 18, the capacitance generated between the source electrode and the reflective pixel electrode when the TPT is in the off state is reduced. Therefore, even if the potential of the source electrode changes, the potential applied to the pixel does not change much, and it is possible to suppress uneven brightness or decrease in contrast in display.

Effects of the Invention As described above, the present invention provides a reflective liquid crystal display device in which the source electrode constituting the thin film transistor is located outside between the reflective pixel electrodes so as not to overlap with the reflective pixel electrodes. This makes it possible to reduce the capacitance generated between the source electrode and the reflective pixel electrode when the TPT is off, and even if the potential of the source electrode changes, there is little change in the potential applied to the pixel. It is possible to realize a reflective liquid crystal display device in which the applied potential is maintained and uneven brightness or deterioration in contrast in display can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a reflective liquid crystal display device according to an embodiment of the present invention, FIG. 2 is a plan view of a substrate provided with a reflective liquid crystal display device TPT according to an embodiment, and FIG.
The figure is a cross-sectional view of a conventional reflective liquid crystal display device, FIG. 4 is a plan view of a substrate equipped with a TPT of a conventional reflective liquid crystal display device, and FIG. 5 is an equivalent circuit in a conventional reflective liquid crystal display device. It is a diagram. 21...Glass substrate, 22...Source electrode, 23...Gate electrode, 24...
Amorphous silicon, 25...Drain electrode, 26...
. . . Non-quality silicon nitride layer, 27 . . . Amorphous silicon nitride, 28 . . . Reflective pixel electrode. Name of agent Patent attorney Shigetaka Awano Haka 1 figure 1.3I Ichigarasu Motoki 30-ZTo /--Ittetsumasu 1L removal 1/-11 Hijima Tokan 1 clause Figure 1

Claims (3)

[Claims] (1) A substrate comprising a group of reflective pixel electrodes arranged in a matrix for displaying liquid crystal, a group of switching elements consisting of inverted staggered thin film transistors for supplying signals to the pixel electrodes, and and a substrate having a common electrode, which faces the substrate with a certain distance therebetween, and has a configuration in which the source electrode portion forming the thin film transistor does not overlap with the reflective pixel electrode. A reflective liquid crystal display device characterized by: (2) The reflective liquid crystal display device according to claim (1), wherein a plurality of switching elements are formed in each pixel. (3) The reflective liquid crystal display device according to claim (1), wherein an auxiliary capacitor is formed in each display pixel of the reflective pixel electrode group.