JPH032839A - Reflective liquid crystal light valve element - Google Patents

Abstract

PURPOSE:To decrease the influence of scanning line and signal line potentials on picture element electrode parts and to allow high-quality display by forming reflecting picture element electrodes to the thickness of >=1/5 the thickness of a liquid crystal layer. CONSTITUTION:The picture element electrodes 105 on a substrate 101 is formed to the film thickness of >=1/5 the thickness of the liquid crystal layer 106. Namely, the liquid crystal light valve element of a reflection type is constituted by utilizing the parts exclusive of the spacings for electrically separating the adjacent picture element electrodes from each other as picture element parts and forming the scanning lines 102 and the signal lines 103 present via insulating layers 110 between the adjacent picture element electrodes. The liquid crystal electric field distribution of the picture element parts is, therefore, liable to be changed by the influence of the scanning line and signal line potentials but the influence on the liquid crystal electric field distribution of the picture element parts is sufficiently decreased by adopting the above-mentioned structure. The high-grade display is thus executed without lowering the contrast ratio as a light valve.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a reflective liquid crystal light valve element useful for use in a video projector for displaying high-definition television images and the like.

2. Description of the Related Art Conventional video projectors for consumer use are of the type using a CRT.

However, since it is difficult to simultaneously increase the brightness and resolution of CRT tubes, video projectors using CRTs have dark screens (and require expensive optical systems such as large-diameter projection lenses). , it has problems such as increased size and weight.
Although this is considered to be acceptable to some extent in the case of TSC televisions, it will be a serious obstacle for future high-definition television displays.

As an alternative to the CRT method, there are already light valve type projectors (some proposals have been made, but none of them have been put into practical use at the consumer level in terms of performance or price; in recent years, light valves using liquid crystals have been proposed). In particular, active matrix drive liquid crystal light valves are attracting attention.Active matrix drive is a drive method that is said to be contrasted with conventional simple matrix drive, in which pixel electrodes arranged on a matrix This is a method in which switch elements are provided for each, and electrical signals that control the optical characteristics of the liquid crystal are independently supplied to each picture element electrode through these switch elements.Therefore, there is no loss talk unlike in the conventional simple matrix method. It has the characteristic of maintaining high contrast even when displaying a large capacity.However, most of the liquid crystal light valve type video projectors that have been proposed so far are
As shown in Japanese Patent No. 0383, a transmissive liquid crystal light valve is used. In the case of a projector using such a transmission type liquid crystal light valve, there is a limit to the pixel density due to the aperture ratio of each pixel. This is because the region of the switch element formed for each picture element limits the picture element area. Furthermore, in the case of a transmission type projector, there is a possibility that the strong light transmitted through the light valve induces light conduction in the pixel switch elements, deteriorating the image quality.

Therefore, as shown in Japanese Patent Application Laid-Open No. 62-62922, a liquid crystal light valve with a reflective structure in which a picture element electrode is formed on the picture element switch element via an insulating layer so as to cover the picture element switch element. A video projector using In the case of such a structure, it is possible to improve the pixel aperture ratio and light conduction, which were problems in the transmission type structure, and it is suitable for high density.

Problems to be Solved by the Invention However, in the above configuration, the pixel electrodes are formed near the scanning lines and signal lines, so the voltage from these lines affects the electric field distribution in the pixel area. This has led to the problem that display quality has deteriorated as a result.

In view of the above-mentioned problems, the present invention reduces the influence of the scanning line and signal line potentials on the pixel electrodes in an active matrix type liquid crystal light valve with a reflective structure, thereby enabling high-quality display. A reflective liquid crystal light valve element is provided.

Means for Solving the Problems In order to solve the above problems, the reflective liquid crystal light valve element of the present invention has a plurality of scanning lines (gate lines), signal lines (source lines), and a matrix pattern corresponding to each intersection. An insulating layer is formed on a thin film transistor array having an inverted staggered structure arranged in the insulating layer, and a drain electrode of the thin film transistor and a pixel electrode formed on the insulating layer are connected through a contact hole formed in the insulating layer. A liquid crystal light valve element having a reflective structure, comprising: a first substrate including a connected thin film transistor array having a reflective structure; a second substrate having an electrode that transmits visible light; and a liquid crystal layer between the substrates.
The film thickness of the picture elements and electrodes on the first substrate is set to be 115 or more with respect to the thickness of the liquid crystal layer.

The action-reflection type liquid crystal light valve element uses a space other than the gap for electrically separating adjacent picture element electrodes as a picture element part, and a scanning line is connected between the adjacent picture element electrodes via an insulating layer. , a configuration in which signal lines exist. Therefore, the liquid crystal electric field distribution in the picture element section is likely to change due to the influence of the scanning line and signal line potentials, but the structure of the present invention makes it possible to sufficiently reduce the influence on the liquid crystal electric field distribution in the picture element section. This enables high-quality display without reducing the contrast ratio of the light valve.

Embodiment FIG. 1 shows the structure of a reflective liquid crystal light valve element according to an embodiment of the present invention. Figure 2 (A) is a cross-sectional structural diagram thereof, and Figure 2 (B) is a plan view of the reflective thin film transistor array section. In FIG. 1, 101 is a glass substrate, and 102 and 103 are scanning lines and signal lines, respectively. 104 is a transistor section. 105
106 indicates a picture element electrode, 106 indicates a liquid crystal layer, and scanning line 10
By operating the transistor selected in step 2, the voltage of the signal line 103 is applied to the liquid crystal layer 106 through the picture element electrode 105. 107 indicates the opposite glass substrate, and 10th indicates a transparent layer formed thereon. Further, 109 indicates a counter substrate 107 corresponding to the scanning lines and signal lines 102 and 103 formed on the glass substrate 101.
It is a light shielding layer formed on top.

As shown in Figure 1, picture elements? The HF 1105 is formed on the transistor section 104 via an insulating layer 110 and is connected to the transistor section through a contact hole 111. This allows the area other than the gap for electrically separating adjacent picture element electrodes to be used as a picture element portion.

In this way, when the thin film transistor array has a reflective type structure, unlike a transmissive type, there is a great advantage that the aperture ratio does not decrease even when the density is high. Therefore, it can be said that the reflective structure is a structure that is extremely suitable for increasing density.

However, even in the reflective structure of the present invention shown in FIG. 1, as the density is increased, the liquid crystal layer in the picture element electrode is affected by the voltage from the signal line and the scanning line, and the liquid crystal layer in the picture element electrode is affected by the electric field. Uniformity will occur. In particular, when driving a liquid crystal, as shown in Figure 2, the signal line is driven by reversing the polarity of the voltage every frame, so the upper part of the display screen (relatively quickly after the voltage of the signal line is reversed) is driven. (pixel that is selected) and the bottom of the display screen (pixel that is selected late after the polarity of the signal line voltage is reversed)
In this case, the polarity relationship between the pixel voltage held and the signal line voltage is different. That is, at the top of the screen, the polarities of the pixel voltage and the signal line voltage held are the same most of the time, while at the bottom of the screen, they are of opposite polarity most of the time. As a result, the electric field distribution in the liquid crystal layer differs between the upper and lower parts of the screen, resulting in a difference in display characteristics, particularly contrast between the upper and lower parts of the screen. FIG. 3 shows twisted nematic ink (TN) with a thickness of 5 (μm) as a liquid crystal layer in the configuration of the reflective liquid crystal light valve element of the present invention shown in FIG.
) A-3 with a film thickness of 1 (μm) as the liquid crystal and insulating layer 110
Using iNx, picture elements? The difference in contrast ratio between the top and bottom of the screen is plotted when the film thickness of the ilt pole is changed. The horizontal axis shows the film thickness of the picture element electrode, and the vertical axis shows the contrast ratio at the bottom of the screen when the contrast ratio at the top of the screen is 1. Further, the size of the picture elements used in this experiment was 30 (μm) pitch. As can be seen from FIG. 3, when the thickness of the picture element electrode is less than 1 (μm), the contrast at the bottom becomes worse than the contrast at the top of the screen. In Figure 4, the film thickness of the picture element electrode is 1.2
(μm) and plots the contrast difference between the top and bottom of the screen when the thickness of the insulating layer 110 is changed. This result shows that the influence of the contrast difference on the thickness of the insulating layer is small. It has also been found that the influence of the contrast difference between the top and bottom of the screen can be almost ignored if the thickness of the picture element electrode is approximately 0.2 or more relative to the thickness of the liquid crystal layer.

Effects of the Invention As described above, in the configuration of the reflective liquid crystal light valve element according to the present invention, by making the film thickness of the reflective picture element electrode 115 times larger than the thickness of the liquid crystal layer, the display picture element can be made very thin. It is possible to provide a liquid crystal light valve that does not reduce contrast even when the density is high. In addition, this can be achieved simply by controlling the film thickness, and has great practical value.

[Brief explanation of drawings]

FIG. 1 is a structural explanatory diagram of a reflective liquid crystal light valve element according to the present invention, and FIG. 1(A) is a cross-sectional view thereof;
Figure (B) is a plan view of the reflective thin film transistor array. FIG. 2 is an explanatory diagram of a typical driving method for a single-film transistor, and FIGS. 3 and 4 are graphs showing display characteristics when the picture element electrode film thickness and insulating stone film thickness of the thin film transistor are varied. 101...Glass substrate, 102...Scanning line, 103...Signal line, 104...
Transistor section, 105... Picture element electrode, 106
...Liquid crystal layer, 107...Counter glass substrate, lO8...Transparent electrode, 109...
Light shielding layer, 110... Insulating layer, 111...
...Contact hole. Name of agent: Patent attorney Shigetaka Awano Ror--
-Glass Fuji 102-11-poor i 14 JO3...-layer g 迨106...-Qing crystal 1

Claims (1)

[Claims] Multiple scanning lines (gate lines) and signal lines (source lines) and
An insulating layer is formed on a thin film transistor array with an inverted staggered structure arranged in a matrix corresponding to each intersection point, and a drain electrode of the thin film transistor is connected to the insulating layer through a contact hole formed in the insulating layer. a first substrate including a thin film transistor array with a reflective structure connected to the formed picture element electrode; a second substrate having an electrode that transmits visible light; and a liquid crystal with a reflective structure having a liquid crystal layer between the substrates. In the light valve element, the film thickness of the picture element electrode on the first substrate is relative to the thickness of the liquid crystal layer.
1. A reflective liquid crystal light valve element characterized in that it is 1/5 or more.