GB1067467A - Improvements in or relating to electromechanical transducers - Google Patents

Abstract

1,067,467. Semi-conductor transducers. SIEMENS A.G. Aug. 4, 1964 [July 23, 1963], No. 30699/64. Heading H1K. [Also in Divisions G1 and H4] A semi-conductor electromechanical transducer consists of a junction transistor having a pressure-transmitting needle bearing on its base electrode or base zone. The collector current of the transistor decreases as the pressure applied to the needle increases. (The Specification refers to a known transducer in which pressure applied to the emitter of a junction transistor causes an increase of the collector current). Silicon and germanium are suitable semi-conductors. In the embodiment of Fig. 1 (not shown) an oxide-protected planar NPN silicon transistor has a U-shaped aluminium base electrode 5 surrounding the strip-shaped aluminium emitter electrode 4. The pressure-transmitting needle bears on the base zone 2 through a hole in one side limb of the base electrode. To obtain maximum sensitivity the thickness of the base zone in the vicinity of the needle is decreased by local etching. The needle (consisting of ruby, boron carbide, or molybdenum) may be subjected to a mechanical bias so that the transistor is operated in a region of high pressuresensitivity. In operation, the standing collector current is set as low as possible consistent with reasonable current gain. The transducer just described may be used alone, or may be incorporated in a circuit with the known transducer mentioned above when the needles of the two transistors are arranged to move together and the circuitry is so chosen that the changes in collector currents are added in the output circuit. The same effect may be achieved in the transducer described with reference to Fig. 4 (not shown), in which a single planar transistor has pressure-transmitting needles bearing on both its base and emitter electrodes. The mechanical arrangements are such that the two needles move in opposite directions so that their effects on the collector current are additive. In all the pressure sensitive transistors mentioned above, it is not only the collector current which is varied by the applied pressure; the current gain is also affected and one may therefore take from the collector of such a transistor a modulated form of an alternating carrier fed to the emitter. The transducers may be used in microphones, vibrometers, accelerometers, listening apparatus, barometers and other pressure-measuring devices.