GB1278210A - Improvements relating to semiconductir strain transducers - Google Patents

Abstract

1278210 Strain gauges FERRANTI Ltd 19 April 1971 [14 March 1970] 12409/70 Heading G1N [Also in Division H1] A strain transducer comprises a semi-conductor body with a thin portion containing strain sensitive resistors and a thicker support portion on or in which associated circuitry is formed. A typical pressure transducer is made by diffusing the resistors and circuit elements and an intermediate isolating ring in a P type epitaxial layer on a N type silicon substrate, and then removing the central part of the substrate by etching followed by spark erosion to provide a thick rimmed diaphragm. The resistors the limbs of which run in a 111 direction consist of four parallel strips at the centre and two diametrically opposed pairs of U-shaped elements so disposed outside the neutral circle that their response is equal and opposite to that of the central strips. Associated circuitry comprising a constant voltage source and line or amplifier 28 is disposed in four peripheral segments. The best matched pairs of resistors are connected into a bridge circuit and to the associated circuitry by aluminium tracks on an oxide passivating layer and/or by gold wires, utilizing bonding pads located on the neutral circle and rim. As seen in Fig. 5, the silicon body 11 is sealed by epoxy resin into a titanium housing with its rim resting on ceramic ring 43. The housing may be plugged into an associated socket containing further circuitry. Trimming and temperature compensating resistors may be located in the silicon body or mounted separately within the housing.