STRESS-SENSITIVE DIFFERENTIAL-AMPLIFIERS USING PIEZORESISTIVE EFFECTSOF MOSFET AND THEIR APPLICATION TO 3-AXIAL ACCELEROMETERS

A novel detection transducer, which can be applied to silicon integrat ed accelerometers and various mechanical sensors, is proposed. Mechani cal quantities such as acceleration and pressure, etc., are translated to voltage signals with a 'stress-sensitive differential amplifier' ( SSDA) using the piezoresistive effects of p-MOSFETs. Signal amplificat ion and adjustment of the sensitivity are realized with the SSDA, and removal of cross-axis errors is also performed for accelerometers. The operation of the SSDA is analysed theoretically, and its application to an integrated three axial accelerometer is presented as an effectiv e example. The characteristics of SSDAs have been evaluated with the f abricated three-axial accelerometers. A Z-axis sensitivity of 11 mV g( -1) is obtained even at a very small bias current (0.5 mu A). By chang ing the operating point of the SSDA, the sensitivity at a sufficient b ias current (above 10 mu A) is adjustable from 25 to 55 mV g(-1) in th e Z-axis, and from 3.0 to 6.5 mV g(-1) in the X- and Y-axes, respectiv ely. Observed temperature drift of the sensitivity at a rate of -2000 ppm degrees C-1 can be compensated by the adjustability of the sensiti vity. The SSDA is considered to be of possible use in an elemental det ection circuit for many types of integrated mechanical sensors due to its many advantages. (C) 1998 Elsevier Science S.A.