Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Amorphous semiconductor material
Patent
1994-11-22
1996-11-12
Mintel, William
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Amorphous semiconductor material
257 66, 257 72, 257291, 257292, 437 3, 437 4, 437 19, 437174, 437907, 437908, H01L 31062, H01L 31113
Patent
active
055742939
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a solid state imaging device and method for producing such a device, and in particular, relates to such a device and a method in which it has quick optical response time, a single common substrate may mount both an imaging device and transistors and/or switching elements for operating the imaging device, and plane operation is possible.
Recently, following the development of facsimile systems, an imaging device or an image sensor is required to be smaller in size, lighter in weight, and cheaper in cost. An image sensor used in facsimile systems is classified into three kinds: non-contact type, contact type, and complete contact type.
A non-contact type image sensor projects an image of a document on a CCD (charge coupled device) which has a single crystal PN junction, through a lens system. It is produced through a LSI process which has been established, and therefore, it has high productivity and has the advantage of low cost. However, it has the problems of volume and weight, as it must have a lens system.
A contact type and a complete contact type are superior to non-contact type in volume and weight. However, they have problems in producing process, and cost for assembling. Further, a contact type has the problem that it must use an expensive selfoc lens array. A complete contact type does not use a selfoc lens array. A contact type is superior in cost as it uses a thin glass as a substrate.
As for a contact type image sensor which is used in a facsimile system, a multi-chip type which mounts many MOS-LSI chips on a substrate, and a thin film type which uses a photo-diode made of amorphous silicon film as an optical sensor have been known. Those use a selfoc lens array.
A multi-chip type has the advantage that it has high producing yield rate and stable supply is possible, as it is produced through MOS-LSI process which is an established technique. However, it has the disadvantage that the characteristics are not uniform due to fabrication error.
On the other hand, as for a thin film type which is produced on an insulation substrate like glass or ceramics through thin film process, it is possible to obtain an image sensor with large area, and/or an image sensor having length equal to that of a manuscript. However, it has the disadvantage that the producing cost is high because it has many producing steps, and the producing yield rate is low.
As for an optical-electrical converter for an image sensor, a photo conductor type and a photo diode type have been known.
A photo conductor type measures resistance of an element made of for instance amorphous silicon which has the characteristics that resistance reduces upon illumination. A photo conductor type has the advantage that it less affected by noise since much current is flows through the element. However, it is not useful for high speed facsimile systems, as photo response is slow.
A photo diode type operates by taking carriers generated in depletion layer upon illumination in PIN junction by reversely biased potential. A photo diode type has the advantage that photo response is very quick. However, it has the disadvantage that it is much affected by noise as small current flows in a photo diode.
Further, a photo diode type has the disadvantage that the producing yield rate is low due to many complicated producing steps, since a photo diode is produced through steps different from those for reading circuits for the photo diode. Further, when a reading circuit is an external circuit, many chips must be used, and therefore, the total producing cost must be high.
Another prior art approach is shown in JP patent laid open publication 210877/1990 which uses a bipolar transistor. However, it has the disadvantage that it is difficult to produce a PN junction, and difficult for practical use.
In the above analysis, our conclusion is that a future solid state image sensor is an MOS thin film structure produced through LSI process.
However, a prior MOS silicon structure using amorphous silicon has the disa
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Arai Michio
Codama Mitsufumi
Inushima Takashi
Kobori Isamu
Sakamoto Naoya
Mintel William
Novack Martin M.
Semiconductor Energy Laboratory Co,. Ltd.
TDK Corp.
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