Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2000-07-21
2003-12-02
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S059000, C257S291000, C257S435000, C257S443000, C257S448000, C257S457000, C257S459000
Reexamination Certificate
active
06657230
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electro-optical device of the type driven by an active matrix, as well as to the method of producing such an electro-optical device. More particularly, the present invention pertains to a technical field of an electro-optical device having a conductive layer which serves to provide excellent electrical connection between pixel electrodes and pixel-switching thin film transistors (referred to as “TFT”, hereinafter), and also to a method of producing the electro-optical device.
2. Description of Related Art
Hitherto, an electro-optical device of the type driven by a TFT active matrix has a TFT array substrate on which numeral scanning lines and data lines which run in orthogonal directions in a crossing manner are arranged. Numerous TFTs disposed at the points where the scanning lines and data lines cross each other are also arranged. Each TFT has a gate electrode connected to one of the scanning lines and has a semiconductor layer, the source region of which is connected to a data line, while the drain region of the semiconductor layer is connected to the pixel electrode.
The source region, the drain region, and an intervening channel region therebetween are constituted by a semiconductor layer formed on a TFT array substrate. The pixel electrode has to be connected to the drain region of the semiconductor layer, across the laminate structure including the scanning line, capacitance line, data line and a plurality of inter-layer insulation films which serve to electrically isolate these lines from one another. The interlayer distance between the semiconductor layer of the laminate structure and the pixel electrode is as long as 1000 nm or greater, particularly in the case of a positive stagger-type having a top-gate structure, in which a gate is provided on the semiconductor layer formed on a TFT array substrate, or in case of a coplanar-type polysilicon TFT. This makes it difficult to form a contact hole through which the semiconductor layer and the pixel electrode are to be electrically connected to each other. More specifically, a greater depth of etching correspondingly impairs the etching precision, posing a risk of the semiconductor layer being undesirably penetrated and perforated, although the etching has to be stopped upon reaching the semiconductor layer. It is therefore extremely difficult to form such a deep contact hole by a dry etching process alone. One solution is to use both dry etching and wet etching in combination, but such a solution inevitably enlarges the diameter of the contact hole due to the use of the wet etching process, making it difficult to lay out necessary wiring and electrodes in restricted areas available on the substrate.
Under this circumstance, a currently developed technique employs, when achieving electrical connection between a data line and a source region via a contact hole formed in an interlayer insulating film formed on the scanning lines and leading to the source region, a contact hole formed in this inter-layer insulating film and reaching a drain region, a relaying conductive layer generally referred to as a barrier layer and formed on the interlayer insulating film and constituting the same layer as the data line, an additional interlayer insulating film formed on the data line and the barrier layer, and a contact hole formed in the additional inter-layer insulating film and extending from a pixel electrode to the barrier layer, whereby the pixel electrode is connected to the drain region.
In the meantime, a multi-plate-type color projector has been developed which incorporates three units of electro-optical devices such as a liquid crystal display device of the type described above, the three units respectively serving as a red (R) light valve, a green (G) light valve and a blue (B) light valve. For instance, as shown in
FIG. 20
, the three units of electro-optical devices
500
R,
500
G and
500
B individually perform optical modulation so as to produce light rays of three colors which are then synthesized by a prism
502
to form composite light rays which are then projected on a screen. The synthesis of light rays by the prism
502
involves a problem in that the green light G is not reflected by the prism
502
while the red R and blue B light rays are by the prism
502
. Consequently, the green light G undergoes turns of a number which is smaller by one than the number of turns sustained by the red and blue light rays R and B. Obviously, this problem occurs when the optical system is arranged such that the R light or the B light, rather than the G light, pass through the prism without being reflected. The same problem is encountered also when the light rays of the three colors are synthesized into the projected light by means of an optical element used as a substituent for the prism
502
, e.g., a dichroic mirror. In this occasion, the electro-optical device
500
G for the green color light rays is arranged to cause inversion of image signals from left to right and vice versa by a suitable means, and is driven in such a manner that the scanning direction is reversed to that employed in the electro-optical devices
500
R and
500
B, thus displaying an inverted image.
The electro-optical devices of the kind described is now facing an increasing demand for higher quality of the displayed images. To meet such a demand, critical factors are higher degree of definition or resolution of the image display area or implementation of micro-fine pixel pitch, as well as a high pixel aperture ratio, i.e., to increase in each pixel the ratio of the light-transmitting aperture area to the non-aperture area which blocks light rays. Implementation of micro-fine pixel pitch, however, poses another problem: namely, since the production technique limits refining of geometric factors such as electrode size, line width and contact-hole diameter, the pixel aperture ratio is undesirably reduced when the pixel pitch is made smaller, as a result of increase of the ratio of the area occupied by the lines, electrodes and so on.
Another problem accompanying the micro-finer pixel pitch is as follows. From the view point of production technique, there also is a limit in the reduction of thicknesses of the TFTs and conductive layers such as those serving as data lines, scanning lines and capacitance lines, as well as thicknesses of intervening inter-layer insulation films. Consequently, the size of a step or height difference appearing on the surface of each pixel electrode, between an area where a line or an element is formed and an area devoid of such line and element, is increased as a matter of comparison with other dimensions. Rubbing of an oriented film having a step generates a liquid crystal disclination region. The above-mentioned relative increase of the step height correspondingly increases the area of such disclination region. Consequently, the disclination region protrudes out of the non-aperture region which surrounds the aperture region of each pixel in a manner like a grating. A solution to this problem might be to cover and conceal the entire disclination region by a light-shield film formed on a counter substrate. Such a solution, however, excessively reduce the area of the aperture region in each pixel, thus posing another problem.
Experiments and studies made by the present inventor proves that the location and extent of disclination caused by the presence of a step on the pixel electrode surface largely depend on the direction of rubbing. It is assumed here that a TN (Twisted Nematic) liquid crystal is used. In such a case, when the TN liquid crystal has clockwise twisting direction as viewed from the counter substrate, rubbing performed in the directions of scanning lines and data lines causes a greater disclination region to appear at the right end portion of the aperture region of each pixel, as a result of the presence of a step on the pixel electrode surface. Conversely, when the TN liquid crystal has counterclockwise twisting direction as
Lee Eddie
Seiko Epson Corporation
Warren Matthew E.
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