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
1999-09-28
2001-05-15
Ngô, Ngân V. (Department: 2814)
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, C257S072000, C257S350000
Reexamination Certificate
active
06232622
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention is related to a semiconductor device and more specifically to a semiconductor device with heightened electric field effect mobility.
BACKGROUND OF THE INVENTION
A liquid crystal display (referred to as LCD, hereinafter) is composed of display picture elements disposed in a matrix arrangement and driving circuits which drives the display picture elements. In order to improve the displaying performance of the LCD, high electric field effect mobility is required for the transistors constituting the driving circuits, since a higher operation speed is demanded for such transistors compared with transistors constituting display picture elements.
Recently, fairly high electric field effect mobility has been achieved by using a polycrystalline silicon film as an active layer of a thin film transistor (referred to as TFT, hereinafter) constituting driving circuits.
Hence, TFTs (polycrystalline silicon TFTs) comprising polycrystalline silicon films as active layers have come to be used not only for transistors constituting display picture elements but also for transistors constituting driving circuits. Also an integrated type of LCD, where both of display picture elements and driving circuits are composed of polycrystalline silicon TFTs and formed on the same insulating substrate, has been developed.
For the LCD in which the display picture elements and the driving circuits are composed of polycrystalline silicon TFTs, higher mobility (higher speed) of the polycrystalline silicon TFT is required as the display picture element becomes finer.
A polycrystalline silicon film comprises multiple monocrystal grains and crystal grain boundaries are formed between these crystal grains. The polycrystalline silicon film also contains crystal defects. Therefore, when a polycrystalline silicon film is used as an active layer, electrons which pass through the polycrystalline silicon film are scattered by crystal grain boundaries and crystal defects, and cannot smoothly pass through a channel regions formed in the active layer. As a result, there is a problem that the electric field effect mobility of the polycrystalline silicon TFT cannot be so high as that of a TFT in which a monocrystalline silicon film is used as an active layer.
Therefore, there is a problem that the improvement of displaying performance of the LCD is limited when the display picture elements and the driving circuits of the LCD are composed of polycrystalline silicon TFTs.
SUMMARY OF THE INVENTION
The object of the invention is to present a semiconductor device provided with a semiconductor film which functions as an active layer of a transistor with high electric field effect mobility.
In order to attain this and other objects of the invention, there is proposed a semiconductor device comprising an insulating substrate, a non-monocrystalline semiconductor film which is formed on the insulating substrate and functions as a channel region of a transistor and as source-drain regions located across the channel region and a region which comprises a crystalline semiconductor formed in the non-monocrystalline semiconductor film of the channel region and whose properties are different from those of the non-monocrystalline semiconductor film.
Preferably, the non-monocrystalline semiconductor film is a polycrystalline semiconductor film and the crystalline semiconductor film is a monocrystalline semiconductor film. By providing the monocrystal region, electric field effect mobility can be heightened since electrons pass mainly through the monocrystal region, and cannot smoothly pass through a channel region of a polycrystal semiconductor film because of crystal grain boundaries and crystal defects therein.
In the invention, the non-monocrystalline semiconductor film may be an amorphous semiconductor and the crystalline semiconductor may be a monocrystalline semiconductor or a polycrystalline semiconductor. By providing the monocrystal or polycrystal region, electric field effect mobility can be heightened since electrons pass mainly through the monocrystal or polycrystal region, though electrons cannot smoothly pass through a channel region of an amorphous semiconductor film.
The invention further provides a liquid crystal display comprising a pair of insulating substrates disposed at a predetermined distance from each other, a display electrode defining a picture element disposed on one of the pair of insulating substrates, a liquid crystal filled between the pair of insulating substrates and a transistor for driving the picture element formed on one of the pair of the insulating substrates, wherein the transistor comprises a non-monocrystalline semiconductor film functioning as a channel region of the transistor, a region which comprises a crystalline semiconductor formed in a non-monocrystalline semiconductor film and whose properties are different from those of the non-monocrystalline semiconductor film, source-drain regions located across the channel region, and a gate electrode provided on the channel region via an insulating film.
Preferably, the non-monocrystalline semiconductor film is a polycrystalline semiconductor film and the crystalline semiconductor is a monocrystalline semiconductor.
The non-monocrystalline semiconductor film may be an amorphous semiconductor film and the crystalline semiconductor may be a monocrystalline semiconductor or a polycrystalline semiconductor.
Further, the transistor for such a liquid crystal display may either be of a top-gate type or a bottom-gate type.
REFERENCES:
patent: 5801400 (1998-09-01), Nishihata
patent: 5917225 (1999-06-01), Yamazaki et al.
patent: 5936292 (1999-08-01), Koide et al.
patent: 5939731 (1999-08-01), Yamazaki et al.
patent: 5959313 (1999-09-01), Yamazaki et al.
patent: 6049091 (2000-04-01), Yokoyama
Armstrong Westerman Hattori McLeland & Naughton LLP
Ngo Ngan V.
Sanyo Electric Co,. Ltd.
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