Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
1997-10-31
2001-10-23
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C438S152000, C438S154000, C438S219000, C117S935000
Reexamination Certificate
active
06306213
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electro-optical device which comprises thin film transistors (referred to hereinafter as TFTs) and to a method for manufacturing such a device.
2. Description of the Prior Art
More attention is now paid to flat displays than to CRTs (cathode ray tubes) for use in office automation (OA) machines and the like, and particularly, there is an increasing demand for large-area display devices. There is also an active and rapid development in the application field of flat displays such as wall television (TV) sets. Furthermore, there are demands for color flat displays and finer display images.
A liquid crystal display device is known as a representative example of a flat display. A liquid crystal display device comprises a pair of glass substrates having incorporated therebetween a liquid crystal composition together with electrodes, and the images are displayed by the change of state of the liquid crystal composition upon application of an electric field thereto. The liquid crystal cells may be driven by the use of a TFT or other switching devices, or by making it into a simple matrix structure. In any case, a driver circuit is established at the periphery of a display to supply signals for driving liquid crystals to column lines (extending in Y direction) and row lines (extending in X direction).
The driver circuit is generally composed of a single crystal silicon MOS integrated circuit (IC). The IC is provided with pad electrodes, each corresponding to each of the display electrodes, and a printed circuit board is incorporated between the pad and the display electrodes to connect first the pad electrode of the IC with the printed circuit board and then the printed circuit board with the display. The printed circuit board, which in general is made of an insulator board made from materials such as a glass fiber-reinforced epoxy resin or a paper filled epoxy resin, or of a flexible plastic board, requires an area equivalent to or even larger than the display area. Similarly, the volume thereof should have to be made considerably large.
Thus, because of the construction as described hereinabove, a conventional display suffers problems as follows:
(1) A superfine display cannot be realized. Since each of the wirings of the display electrodes for the X direction and the Y direction of the matrix, or the source (drain) wirings or the gate wirings should be connected individually to each of the contacts on the printed board, the minimum distance between the connecting portions technologically achievable by the up-to-date surface mounting technology is limited to a certain length;
(2) A display device as a whole occupies a large area and volume. A display device comprises indispensable parts in addition to the display itself, inclusive of the printed circuit board, the ICs, and the connecting wirings, which require an area and volume about several times as large as those of the display alone; and
(3) The connections are of low reliability. Quite a large number of connections should be established between the main display and the printed circuit board, as well as between the printed circuit board and the ICs; moreover, not a small weight is casted on the connecting portions.
As a means to overcome the foregoing problems, there is proposed, particularly in a display device comprising an active matrix as the switching device, to construct a display device comprising the active device and the peripheral circuits on a same substrate using TFTs rather than semiconductor chips. Such a construction indeed solves the three problems mentioned hereinabove, however, it newly develops problems as follows:
(4) The production yield of the display is low. Since the peripheral circuits also are made from TFTs, the number of the devices to be fabricated on the same s ubstrate is increased and hence the production yield of the TFT is lowered;
(5) The production cost is increased. Since the peripheral circuit portion comprises a very complicated device structure, the circuit pattern accordingly becomes complicated and hence the cost increases. Furthermore, with the increase in the multilayered wiring portion, an increase in process steps as well as a decrease in the production yield of the TFTs occur; and
(6) It requires a treatment at a high temperature and hence the use of an expensive quartz substrate becomes requisite. Since a quick response is required to the transistors which constitute the peripheral circuit, the semiconductor layer should be treated at a high temperature to obtain a polycrystalline layer to be used a s the transistors.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the six problems mentioned above by taking balance among them and to provide a more economical electro-optical device at a high yield.
This and other objects of the present invention have been attained by an electro-optical device comprising a pair of substrates and an electro-optical modulating layer having sandwiched therebetween, said pair of substrates consisting of a first substrate having provided thereon thin film transistors and matrix lines comprising a plurality of gate wires (extending e.g. in Y direction) and a plurality of source (drain) wires (extending e.g. in X direction), and a second substrate facing the first substrate, wherein, among the peripheral circuits being connected to the matrix lines, only one direction side of said peripheral circuits is constructed from thin film semiconductor devices fabricated by the same process utilized for the thin film transistors, and the rest of the peripheral circuits is constructed from semiconductor chips. The electro-optical modulating layer may comprise a liquid crystal.
In the electro-optical device according to the present invention, the peripheral circuit only on one side is fabricated as TFTs. In such a manner, a general use economical ICs can be utilized on one side, while fabricating the side comprising peripheral circuits which are not commercially available or which are costly, as TFTs.
Furthermore, by making only one side into TFTs, the number of the TFTs in the peripheral circuit portion can be considerably reduced. For example, the number of the TFTs can be halved in case the peripheral circuits for the X and the Y directions have the same function. Thus, the production yield of a TFT on the same substrate is increased by two times in a simple calculation.
According to another embodiment of the present invention, there is provided an electro-optical device comprising a first substrate having provided thereon a pixel matrix furnished with complementary TFTs and matrix lines comprising a plurality of gate wires (extending e.g. in Y direction) and a plurality of source (drain) wires (extending e.g. in X direction), said first substrate making a pair with a second substrate faced thereto and an electro-optical modulating layer having supported between the pair of substrates, characterized by that at least a part of the peripheral circuits being connected to the matrix lines is fabricated into complementary TFTs similar in structure of the active matrix (e.g. the complementary TFTs of the pixel matrix) and being fabricated also in a same process as that of the active matrix, and that the rest of the peripheral circuits are constructed by semiconductor chips, said peripheral circuits being connected to the X or Y direction matrix wires having established on the first substrate. The electro-optical modulating layer may comprise a liquid crystal.
More precisely, the electro-optical device according to the present invention is characterized by that the peripheral circuit is not wholly fabricated into TFTs, but only those portions having a simple device structure, or those composed of a small number of devices, or those comprising an IC not easily available commercially, or those comprising an expensive IC, are fabricated as TFTs. It is therefore an object of the present invention to increase the production yield and to reduce the production cost
Kunemund Robert
Nixon & Peabody LLP
Robinson Eric J.
Semiconductor Energy Laboratory Co,. Ltd.
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