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Infrared Sensor with Fail Safe Switch Off Above 200 Degrees C

IP.com Disclosure Number: IPCOM000079863D
Original Publication Date: 1973-Sep-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Frank, WF: AUTHOR

Abstract

There is an extended field for the application of materials that show infrared photoconductivity below 200 degrees C, but lose this property irreversibly when they are heated to higher temperatures. For example, these materials can he used as sensors for an infrared alarm system. In such a system, both the interruption of the infrared beam as well as the excess of 200 degrees C is indicated, by a breakdown of the photovoltage measured across the sensor. Use of these materials can also be made whenever an electric current is to be switched on by infrared light, and a fail-safe switch-off at high temperatures is desired.

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Infrared Sensor with Fail Safe Switch Off Above 200 Degrees C

There is an extended field for the application of materials that show infrared photoconductivity below 200 degrees C, but lose this property irreversibly when they are heated to higher temperatures. For example, these materials can he used as sensors for an infrared alarm system. In such a system, both the interruption of the infrared beam as well as the excess of 200 degrees C is indicated, by a breakdown of the photovoltage measured across the sensor. Use of these materials can also be made whenever an electric current is to be switched on by infrared light, and a fail-safe switch-off at high temperatures is desired.

After a 1.5-MeV electron irradiation at room temperature, ordinary boron and aluminum doped silicon have the above-mentioned properties (i.e., photoconductivity during illumination with infrared light [wave-length < 4 mu] and irreversible disappearance of this photoconductivity after annealing above 200 degrees C). /1/ Therefore; electron irradiated B and Al doped Si are suitable materials for infrared sensors with fail-safe temperature switch-off.

They may particularly be used for a combined infrared alarm - fire alarm system.

The physical background of this behavior is that during a 1.5-MeV electron irradiation of silicon at room temperature, highly mobile vacancies and self- interstitials are produced. /2,3/ The self-interstitials disappear by annihilation at vacancies and by exchanges of their sites with substitutionally dissolved B - (Al-) atoms, thus generating B - (Al-...