Browse Prior Art Database

Shadow Free Phototransistor

IP.com Disclosure Number: IPCOM000096426D
Original Publication Date: 1963-May-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Thomas, JE: AUTHOR

Abstract

This back-illuminated phototransistor has emitter and base regions 10 and 11, respectively, created by diffusing conductivity-directing impurities into a high resistivity epitaxial layer 12 on a low resistivity supporting starting wafer 13. Layer 12 can have a thickness of about one mil. A protective insulating coating 14 covers the two junctions which come to the upper surface of the device. Solder-ball terminals 15 and 16 form ohmic connections to the emitter and collector regions.

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Shadow Free Phototransistor

This back-illuminated phototransistor has emitter and base regions 10 and 11, respectively, created by diffusing conductivity-directing impurities into a high resistivity epitaxial layer 12 on a low resistivity supporting starting wafer 13. Layer 12 can have a thickness of about one mil. A protective insulating coating 14 covers the two junctions which come to the upper surface of the device. Solder-ball terminals 15 and 16 form ohmic connections to the emitter and collector regions.

A centrally disposed cavity 17 is etched in the low-resistivity starting wafer 13 by jet-etching techniques to make the transistor highly sensitive to incident light which is represented diagrammatically by the arrow. The rate of etching of wafer 13 is considerably faster than that of its higher-resistivity epitaxial layer 12. This factor can be employed to terminate the etching near the interface 18. A layer 19 of glass or other transparent material can be used to protect the lower surface of the device. The disposition of terminals 15 and 16 and the mode of illumination are such that, from the operational point of view, the transistor is shadow-free.

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