Semiconductor pressure transducers

When silicon diffused transistors are stressed by applying localized pressure to the emitter surface, increases in base and collector current are observed. From the relationship between these currents and the emitter junction voltage, the changes are identified as increases in minority carrier currents. The results can be explained mainly by the decrease in energy gap in strained silicon. Detailed data on stressed diodes and transistors will be shown in support of this hypothesis. This phenomenon can be used to advantage in many kinds of pressure transducers. Microphones have been constructed in which acoustic power is transmitted to a transistor emitter region by means of a diaphragm and point assembly. Typical values obtained are: a sensitivity of 1 db above 1 volt for a pressure of 1 dyne/cm²(versus -34 db for a carbon microphone); a gain of 26 db (versus 14 db); a ratio of a.c. power out to d.c. bias power of 11% (versus .02%); signal to noise ratio of 55 db; the frequency response was limited by the diaphragm. Other devices such as hydrophones, phonograph pickups, and microminiature microphones also suggest themselves.