Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-06-08
2003-09-30
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S059000, C257S350000, C257S364000, C257S365000, C257S377000, C257S401000
Reexamination Certificate
active
06627957
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention disclosed in the specification relates to a semiconductor device constituted by using a thin film transistor having a plurality of gate electrodes. Further, the present invention relates to a method of fabricating the semiconductor device.
2. Description of Related Art
In recent years, there has been increased thin film transistors using polycrystal silicon films in semiconductor layers. According to a thin film transistor using a polycrystal silicon film, high speed operation that is faster than operation of a thin film transistor using an amorphous silicon film by two digits or more can be performed since a mobility thereof is large.
Therefore, there poses a problem of hot carrier effect in which hot carriers generated in a channel jump into a gate insulating film and deteriorate a threshold voltage or a mutual conductance.
Conventionally, in respect of the above-described problem, there has been known a thin film transistor of a multi gate type alleviating the hot carrier effect by providing a plurality of gate electrodes and weakening an electric field applied on a single gate.
FIG. 5
shows an example where a thin film transistor of a conventional double gate type is used as a switching element of a pixel matrix portion of a liquid crystal display device.
As shown by
FIG. 5
, a semiconductor layer
02
and a source wiring
25
form a contact at a source electrode
22
. Further, the semiconductor layer
02
is extended while meandering and intersects with a gate wiring
26
at regions
21
and
21
′. Further, the semiconductor layer
02
and a pixel electrode
24
form a contact at a drain electrode
23
. Portions of the gate wiring at the intersected regions
21
and
21
′ function as gate electrodes.
As is an apparent from
FIG. 5
, the conventional multi gate type thin film transistor is constituted by the gate wiring
26
in a substantially straight line shape and the meandering semiconductor layer
02
.
By adopting such a constitution, a distance between the source and the drain is prolonged and therefore, the ON resistance is increased. Further, the resistance of a semiconductor layer is generally larger than that of a metal conductor and therefore, in respect of the semiconductor layer
02
meandering as shown by
FIG. 5
, the high frequency impedance of the meandering portion is increased which gives rise to deterioration of the element.
It is the object of the present invention disclosed in the specification to resolve the above-described problem.
SUMMARY OF THE INVENTION
According to an aspect of the present invention disclosed in the specification, there is provided a semiconductor device, wherein a meandering gate wiring traverses a substantially straight line portion of a semiconductor layer of a thin film transistor by a plurality of times thereby providing a plurality of gates.
According to other aspect of the present invention, there is provided a semiconductor device, wherein a switching element of a pixel matrix portion of a liquid crystal display device is a multi gate type thin film transistor in which a meandering gate wiring traverses a substantially straight line portion of a semiconductor layer by a plurality of times thereby providing a plurality of gates.
Further, the above-described gate wiring is featured in comprising a metal having the resistance smaller than the resistance of the semiconductor layer.
According to other aspect of the present invention, there is provided a method of fabricating a semiconductor device including a step of forming a semiconductor layer having a substantially straight line portion on a substrate, a step of forming a gate insulating film and a metal conductive film above the semiconductor layer, a step of pattering the metal conductive film into a gate wiring, a step of doping impurities to the semiconductor layer with the gate wiring as a mask and a step of irradiating a laser beam wherein the gate wiring meanders and intersects the substantially straight line portion of the semiconductor layer by a plurality of times.
According to the present invention, the gate comprising a metal having small resistance is meandered and therefore, an increase in impedance in the resistance imposed on the meandering portion is small. Further, there is no meandering portion in the semiconductor layer and therefore, deterioration by heat generation or the like can be restrained.
Further, the distance between the source and the drain is shortened compared with that in the conventional example and therefore, the ON resistance can be reduced and the thin film transistor having high mobility can be fabricated.
REFERENCES:
patent: 4917467 (1990-04-01), Chen et al.
patent: 5338959 (1994-08-01), Kim et al.
patent: 5378913 (1995-01-01), Hoeltge
patent: 5589702 (1996-12-01), Alter
patent: 5616935 (1997-04-01), Koyama et al.
patent: 5644147 (1997-07-01), Yamazaki et al.
patent: 5789781 (1998-08-01), McKitterick
patent: 5789791 (1998-08-01), Bergemont
patent: 5808595 (1998-09-01), Kubota et al.
patent: 5811846 (1998-09-01), Miura et al.
patent: 5821560 (1998-10-01), Arai et al.
patent: 5949111 (1999-09-01), Morikawa et al.
patent: 6020598 (2000-02-01), Yamazaki
Clark Sheila V.
Fish & Richardson P.C.
Ortiz Edgardo
Semiconductor Energy Laboratory Co,. Ltd.
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