A high sensitivity semiconductor strain sensitive circuit

The application of the piezoresistive strain sensitivity of MOS transistors to a high sensitivity strain sensor is described. The basic physical mechanism involved is thought to be the variation of mobility of the charge carriers, which gives rise to a change in the gain factor, β, of the device. The non linear nature of the MOST is exploited in a 4 transistor bridge circuit configuration and a circuit using 2 transistors biassed with external constant current sources. Sensitivities up to 20 V/millistrain may be obtained with the supply voltage setting a limit to the dynamic range. The transducer circuit is limited by its drift performance and is better suited to sensing vibrations rather than steady strains.