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PHOTOSITE FOR MONOLITHIC THIN-FILM SILICON, FULL-WIDTH LINEAR RASTOR INOUT SCANNER

IP.com Disclosure Number: IPCOM000025433D
Original Publication Date: 1985-Jun-30
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 128K

Publishing Venue

Xerox Disclosure Journal

Abstract

In electronic copiers, a Raster Input Scanner (RIS) converts optical information ,generated from a document into an electrical signal. Conventional practice is to use a small (about 1 inch) RIS consisting of a photodiode array coupled with a CCD scanning array to convert the optical information into a serial charge-bit stream. An improvement over conventional practice is to use a full-width "linear".array to accomplish the same task. One approach investigated by some in research is to use a full-width, thin-film hydrogenated-amorphous Si array of photodiodes accessed by scanning and logic circuits fabricated in single-crystal Si, the thin-film amorphous photodiode array and the Si chips being mounted on the same circuit board. Such an assembly illustrates a hybrid approach to a thin-film, full-width array.

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PHOTOSITE FOR MONOLITHIC Proposed Classification THIN-FILM SILICON, FULL-WIDTH
LINEAR RASTOR INPUT SCANNER Int. CI. G02b 5/18 Joseph J. Wysocki

U.S. CI. 350/161

In electronic copiers, a Raster Input Scanner (RIS) converts optical information ,generated from a document into an electrical signal. Conventional practice is to use a small (about 1 inch) RIS consisting of a photodiode array coupled with a CCD scanning array to convert the optical information into a serial charge-bit stream. An improvement over conventional practice is to use a full-width "linear".array to accomplish the same task. One approach investigated by some in research is to use a full-width, thin-film hydrogenated-amorphous Si array of photodiodes accessed by scanning and logic circuits fabricated in single-crystal Si, the thin-film amorphous photodiode array and the Si chips being mounted on the same circuit board. Such an assembly illustrates a hybrid approach to a thin- film, full-width array.

An improvement is to use a full-width, thin-film crystalline Si array to replace the single-crystal-Si chips used in the hybrid approach, retaining at the same time the amorphous Si photodiode array. One difficulty with this approach is the technological difference in fabrication of amorphous and crystalline arrays. Hydrogenated amorphous devices require low temperature ( 5350° C) deposition processes in general, while crystalline devices require higher ones (> 600° C). Thus, there is a restriction on how the monolithic array can be constructed.

This restriction would be lessened if the Si material in the RIS were of the same nature, either all amorphous, or all crystalline. Because of carrier mobility limitations, amorphous material cannot be used in all functions required. Use of crystalline Si in all functions, on the other hand, faces the difficulty of poorer photogeneration efficiency in the photosites because of the lower absorption of visible light in crystalline as opposed to amorphous Si. Roughly speaking, this absorption is ten times greater in amorphous than in crystalline Si.

A hydrogenated-amorphous-Si layer of thickness lpm can effectively absorb all of the incident visible light whereas a crystalline Si layer ten times thicker would be required. A layer thickness of 10 Am no longer is suited to thin-film technology; so such a thickness would impose fabricational difficulties of its own in this context.

However, thin-film crystalline Si for the photosite material may be used if its light absorption is effectively improved. Absorption depends not only upon the nature of the absorption process, but also upon the thickness of material exposed to light. In general, then any "light-trapping cavity" which leads to multiple traversals of the abso...