Effect of piezoresistor configuration on output characteristics of piezoresistive pressure sensor: an experimental study

Piezoresistive sensing is one of the most frequently used transduction mechanism in pressure sensors. The piezoresistor placement on the diaphragm and the piezoresistor configuration play a pivotal role in determining the output characteristics of a pressure sensor. In this work, two different pressure sensors with different transverse piezoresistor configurations are studied to determine the effect of piezoresistor configuration on the sensitivity and non-linearity of the pressure sensors. A sensor structure with a square diaphragm size of 1,480 A mu m edge length and diaphragm thickness of 50 A mu m is chosen for the study. The design considerations for piezoresistor placement and the piezoresistor shapes are discussed in detail. The sensors are fabricated with bulk micromachined diaphragm and polysilicon piezoresistors. The sensor characteristics are determined for three temperatures, namely, -5, 25 and 55 A degrees C and for a pressure range of 0-30 Bar. The characterization results indicate that the design with two piezoresistor arms in transverse piezoresistor configuration (2 x 2 Design) has higher sensitivity than the single arm configuration (2 x 1 Design) by about 25 % at 25 A degrees C but it also has a higher non-linearity. The study shows the importance of selecting the proper piezoresistor configuration in the design of pressure sensors.