Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-11-06
2003-06-24
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S111000
Reexamination Certificate
active
06583830
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an active-matrix type electrooptical device, a projection-type display apparatus incorporating the electrooptical device, and a method for manufacturing the electrooptical device. Particularly, the present invention relates to an electrooptical device having a pixel switching thin-film transistor (TFT) in a laminate structure formed on a substrate thereof, a projection-type display apparatus incorporating the electrooptical device as a light valve, and a manufacturing method for manufacturing the electrooptical device.
2. Description of Related Art
Active-matrix type electrooptical devices suffer from a change in TFT characteristics as a result of photocurrent leakage that occurs when incident light enters a channel region of a pixel switching TFT in each pixel. Since an electrooptical device for use as a light valve in a projector uses a high-intensity light ray, blocking the admittance of light into the channel region of the TFT and the peripheral area of the channel region is important. A light shield layer, arranged on a counter substrate, that defines an aperture area of each pixel, or a data line, fabricated of a metal layer such as Al (aluminum) running over the TFT on a TFT array substrate blocks the admittance of light into the channel region or its peripheral area. A light shield layer, fabricated of a refractory metal, for example, is arranged on the TFT array substrate in a position facing the TFT from below. Such a light shield layer arranged beneath the TFT prevents light back-reflected from the TFT array substrate from entering the TFT in the electrooptical device. For example, in an optical system that is composed of a plurality of electrooptical devices combined with a prism, such a light shield layer prevents returning light such as a light ray passing through the prism from another electrooptical device from entering the TFT in one electrooptical device of interest.
For example, such an electrooptical device, having high light-shield performance, can be used as a light valve in a projection-type display apparatus which is subject to high-intensity light.
SUMMARY OF THE INVENTION
The above light shield techniques have the following disadvantages. For example, in the technique of using a light shield layer formed on a counter substrate or a TFT array substrate, the light shield layer and the channel region are substantially spaced apart from each other with a liquid-crystal layer, an electrode, and an interlayer insulator that are interposed therebetween. However, the light shield performance for blocking light that is obliquely incident on the area between the light shield layer and the channel region is not sufficient enough. In a compact electrooptical device to use as a light valve in a projector, the incident light is a light beam into which a lens converges light from a light source, and contains a significant component of obliquely incident light (for example, 10% of the incident light is oblique by 10 degrees to 15 degrees with respect to a direction normal to the substrate). Such insufficient light shield performance to the obliquely incident light creates a problem in operation.
Light entering the electrooptical device through an area having no light shield layer may be reflected off the top surface of the substrate, the top surface of the light shield layer formed on the substrate, or the underside of the data line, i.e., the inner surface of the data line facing the channel region. The light reflected in this way may be reflected again off the top surface of the substrate, or the inner surfaces of the light shield layer and the data line, thereby causing multiple reflections. The multiple reflections may reach the channel region of the TFT.
As a demand for display image with higher quality in the electrooptical device increases, the electrooptical device has a higher definition and a finer pixel pitch. Furthermore, as incident light rays intensifies in level to present a brighter image, a variety of conventional light shield techniques become unable to sufficiently block the admittance of light. Stray light causes a change in transistor characteristics of the TFT, resulting in flickering and leading to degradation of the display image quality.
Expanding the formation area of the light shield layer has been contemplated to increase light tightness. Expanding the formation area of the light shield layer makes it difficult to increase the aperture ratio of each pixel. It is noted that the aperture ratio needs to be increased for a brighter display image. The light shield layer beneath the TFT and the light shield layer (ex. a data line) over the TFT result in internal reflections and multiple reflections of obliquely incident light rays. The expanding of the formation area of the light shield layer increases internal reflections and multiple reflections of light and thus causes problems.
In view of at least the above problems, the present invention has been developed. It is an object of the present invention to provide an electrooptical device which features high light tightness, and presents a bright and high-quality image, a projection-type display apparatus incorporating the electrooptical device, and a method for manufacturing the electrooptical device.
To resolve the above problems, a first electrooptical device of the present invention includes a first substrate, a pixel electrode arranged above the first substrate, a thin-film transistor arranged above the first substrate and connected to the pixel electrode, and a first light shield layer arranged over the gate electrode of the thin-film transistor formed over and facing the channel region of the thin-film transistor with a gate insulator interposed therebetween, wherein the first light shield layer is formed, laterally surrounding the channel region as a light shield side wall.
In accordance with the first electrooptical device of the present invention, the first light shield layer deposited above the channel region of the TFT prevents light coming in from the top side of the first substrate from entering the channel region. The first light shield layer, laterally surrounding the channel region as the light shield side wall, prevents light from entering obliquely or laterally into the channel region. Since the present invention prevents light coming in from the top side of the first substrate from entering the channel region of the TFT, the electrooptical device is free from erratic operations of the TFT and a drop in reliability of the TFT.
In one embodiment, the first electrooptical device of the present invention can include a second substrate opposed to the first substrate, and an electrooptical material interposed between the first substrate and the second substrate. This embodiment presents a light-tight electrooptical device, such as a liquid crystal device, having the electrooptical material interposed between a pair of the substrates.
In another embodiment of the first electrooptical device of the present invention, a matrix of the pixel electrodes and the thin-film transistors can be arranged on the first substrate. In accordance with this embodiment, an active-matrix type electrooptical device such as a liquid crystal device having high light tightness can be achieved.
In another embodiment of the first electrooptical device of the present invention, the light shield side wall can be formed of the first light shield layer formed in a light shield side wall formation trench formed in an insulator below the first light shield layer.
The first electrooptical device having the above construction can be manufactured using the following method. Specifically, a method for manufacturing an electrooptical device including a first substrate, a pixel electrode arranged above the first substrate, and a TFT arranged above the first substrate and connected to the pixel electrode, includes forming, above the first substrate, the TFT including a channel region, a gate insulator formed on the channel region, and a g
Yamazaki Yasushi
Yasukawa Masahiro
Dudek James
Duong Tai
Oliff & Berridg,e PLC
Seiko Epson Corporation
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