High Performance Piezoresistive Micro Strain Sensors

This paper presents results of studies on the high performance silicon piezoresistive bridge strain sensors. The microfabricated, boron diffused, piezoresistive strain sensors constructed in Wheatstone bridge structure were used in this work. The temperature stability and time drift problems were studied and improvements were made. Experimental results showed heavily doped sensors are less sensitive to temperature variation but with lower gauge factor as compared with lower doped sensors. In order to solve time drift problem in packaged sensor modules, the stiffness of sensors has to be reduced. The thickness of sensors was reduced from 500 mum to 30 mum by using MEMS structure with novel processes. The drift problem was improved from 7.6% for 500 mum-thick devices to 0.2 % for 30 mum-thick devices.