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Investigation of Unwanted Conductive Paths in a Transistor

IP.com Disclosure Number: IPCOM000096503D
Original Publication Date: 1963-Jun-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Steiner, SA: AUTHOR [+2]

Abstract

Unwanted conductive paths which produce leakage currents can occur between the emitter and collector of a transistor. It is important to know of the existence of such paths in order to eliminate them. Pipes are local conductive paths of such small cross-section that staining procedures do not indicate their presence. Channels are surface-state conductions which produce unwanted conductive paths and also are difficult to investigate. This apparatus facilitates the determination of the existence of and the study of these unwanted paths.

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Investigation of Unwanted Conductive Paths in a Transistor

Unwanted conductive paths which produce leakage currents can occur between the emitter and collector of a transistor. It is important to know of the existence of such paths in order to eliminate them. Pipes are local conductive paths of such small cross-section that staining procedures do not indicate their presence. Channels are surface-state conductions which produce unwanted conductive paths and also are difficult to investigate. This apparatus facilitates the determination of the existence of and the study of these unwanted paths.

Conductive connections are made to the emitter, base and collector regions 10, 11 and 12 of a transistor 13 (A) by means of conductive probes 14, 15 and 16, respectively. Adjustable source 17 reversely biases the collector region with reference to the base region. One end of field-inducing 6 mil diameter probe 18 having a 1 micron dielectric tip 19 of silicon monoxide rests on the surface of base region 11 or on a protective insulating film over it. The other end of probe 18 is connected to the positive terminal of adjustable bias source 20. Its negative terminal is connected to probe 16. Voltmeter 21 is connected in parallel with resistor 22 between the emitter and base probes 14 and 15 to measure the voltage developed between them. The magnitude of this voltage is representative of leakage current which flows between the emitter and collector regions of the transistor and is caused by unwanted surface states. Processing steps employed in the fabrication of a transistor such as etching, washing and glass coating can produce unwanted residual surface impurities or states.

The relation of probe 18 to base region 11 of planar transistor 13 is in B. Assuming that substantially ideal surface conditions are encountered on the transistor, the changes observed in the voltage applied to meter 21, for various c...