Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-09-27
2003-12-23
Loke, Steven (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S345000, C257S349000, C438S149000, C438S479000
Reexamination Certificate
active
06667517
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an electrooptical device and an electronic device in which a MIS transistor is formed in a semiconductor layer on an insulating layer in such a manner as to avoid floating substrate effects.
2. Description of Related Art
The SOI (silicon on insulator) technology is used to form a semiconductor device such as a transistor using a semiconductor layer such as a single-crystal silicon layer formed on an insulating material. The semiconductor devices according to the SOI technology are advantageous in that they can operate at a high speed with low power consumption and in that a high integration density can be achieved. Thus, the semiconductor devices according to the SOI technology may be advantageously applied to electrooptical devices such as a liquid crystal device.
In the case of a MIS transistor in the form of a bulk semiconductor device, the channel region of the MIS transistor is generally fixed at a particular potential via a substrate on which the MIS transistor is formed. Therefore, no degradation occurs in electrical characteristics such as a reduction in the breakdown voltage due to extrinsic bipolar transistor effects caused by a change in the potential of the channel region.
However, in SOI-type MIS transistors, because the bottom of the channel is completely isolated by the underlying insulating film, the channel region is not fixed at a particular potential and is held in an electrically floating state. If excess carriers are generated by impact ionization which occurs when carriers accelerated by the electric field near the drain region collide with the crystal lattice, the excess carriers accumulate in the bottom part of the channel. The excess carriers accumulated in the bottom part of the channel result in an increase in the potential of the channel. As a result, the NPN structure (in the case of the n-channel transistor) including the source, the channel, and the drain acts as an extrinsic bipolar device, which causes an abnormal current to flow. Thus, degradation in the electrical characteristics such as a reduction in the breakdown voltage occurs. These phenomena caused by the electrically floating channel are called floating substrate effects.
One known technique to avoid the above problems due to the floating substrate effects is to form a body contact region electrically connected to the channel region via a particular path, thereby removing the excess carriers from the channel region, so as to suppress the floating substrate effect.
However, if a body contact region is formed in a MIS transistor used in a pixel area of an electrooptical device such as a liquid crystal device, the body contact region makes it difficult to produce pixels with a high density. In particular, in the case of a transmissive electrooptical device, the body contact region results in a reduction in the aperture ratio. Also, in the case where a body contact region is formed in a peripheral driving circuit in an area other than the pixel region, the body contact region results in a reduction in the integration density. In electrooptical devices used in electronic devices such as a projection-type display device, when high-intensity light is incident on pixels, carriers are generated by optical excitation. This causes a loss in the charge stored in pixel storage capacitors. As a result, non-uniformity such as flicker occurs in a displayed image.
In view of the above, it is an object of the present invention to provide an electrooptical device having a transistor in which floating substrate effects peculiar to SOI are suppressed, particularly for use in an electronic device in which the problem of leak current induced by optical excitation is notable, e.g., a projection-type display device, as well as an electronic device incorporating such an electrooptical device.
SUMMARY OF THE INVENTION
In order to achieve the above objects, the present invention provides a semiconductor device formed in a semiconductor layer on an insulating layer according to various aspects as described below.
According to a first aspect of the present invention, there is provided an electrooptical device comprising a substrate including a base substrate, a first insulating layer formed on the base substrate, and a semiconductor layer formed on the first insulating layer, the electrooptical device further comprising the following elements formed on the substrate: a plurality of scanning lines, a plurality of data lines extending so as to cross the plurality of scanning lines; pixel transistors each connected to one of the plurality of scanning lines and also to one of the plurality of data lines; pixel electrodes connected to the respective pixel transistors; and a peripheral circuit including a driving transistor for driving the pixel transistors, the electrooptical device including a pixel transistor or a driving transistor in which at least either a region including the boundary between a channel region and a source region or a region including the boundary between the channel region and a drain region has a defect density higher than that of the channel region.
In the pixel transistors or the driving transistor according to the first aspect of the present invention, the defects in the region with the higher defect density than the channel region acts as a carrier recombination center. As a result, accumulation of excess carriers is prevented and the floating substrate effects are suppressed.
According to a second aspect of the present invention, there is provided an electrooptical device comprising a substrate including a base substrate, a first insulating layer formed on the base substrate, and a semiconductor layer formed on the first insulating layer, the electrooptical device further comprising the following elements formed on the substrate: a plurality of scanning lines, a plurality of data lines extending so as to cross the plurality of scanning lines; pixel transistors each connected to one of the plurality of scanning lines and also to one of the plurality of data lines; and pixel electrodes connected to the respective pixel transistors, the pixel transistors being formed such that at least either a region including the boundary between a channel region and a source region or a region including the boundary between the channel region and a drain region has a defect density higher than that of the channel region.
In the pixel transistors according to the second aspect of the present invention, the defects in the region with the higher defect density than the channel region acts as a carrier recombination center, which prevent accumulation of excess carriers, thereby allowing the floating substrate effects to be suppressed without forming a body contact. Thus, it is possible to achieve an electrooptical device with a high aperture ratio.
According to a third aspect of the present invention, there is provided an electrooptical device comprising a substrate including a base substrate, a first insulating layer formed on the base substrate, and a semiconductor layer formed on the first insulating layer, the electrooptical device further comprising the following elements formed on the substrate: a plurality of scanning lines, a plurality of data lines extending so as to cross the plurality of scanning lines; pixel transistors each connected to one of the plurality of scanning lines and also to one of the plurality of data lines; pixel electrodes connected to the respective pixel transistors; and a peripheral circuit including a driving transistor for driving the pixel transistors, the pixel transistors or the driving transistor being formed such that at least either a region including the boundary between a channel region and a source region or a region including the boundary between the channel region and a drain region has a defect density higher than that of the channel region.
In the pixel transistors or the driving transistors according to the third aspect of the present invention, the defects in the region with the hi
Kang Donghee
Loke Steven
Seiko Epson Corporation
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