Calibration technique for MEMS membrane type strain sensors

A MEMS based piezoresistive strain sensor was designed, fabricated and calibrated. A single strip of doped n-polysilicon sensing material was patterned over a thin Si/sub 3/N/sub 4//SiO/sub 2/ membrane. The silicon wafer was etched beneath this thin membrane. The intent of this design was to fabricate a flexible MEMS strain sensor. A calibration technique for measuring the strain sensor performance is described. The sensor calibration technique (to find the relationship between change in resistance and strain) entails developing a repeatable relationship between the change in sensor resistance and the strain measured at the sensor. The sensor sensitivity is evaluated by embedding the sensor in a vinyl ester epoxy plate and loading the plate. This calibration technique captures the effects of strain transfer to the stiff silicon wafer.