Single element 3-terminal pressure sensors: A new approach to pressure sensing and its comparison to the half bridge sensors

Abstract

We report the development of a novel 3-terminal single element piezoresistor for ultra-miniature pressure sensor applications and compare its performance to that of a traditional half Wheatstone bridge design. The pressure sensors reported here are 0.69-French in size (1F= 333µm) and are designed and batch-fabricated using SOI (silicon on insulator) and DRIE (deep reactive ion etching) technologies. One of the major applications of this device is for blood pressure monitoring using ultra-miniature 1F catheters. The combination of SOI and DRIE technologies results in uniform diaphragm thickness and complete elimination of the post-processing dicing step by micromachining “die separation streets” during the DRIE process. The novel 3-terminal single element design and half Wheatstone bridge sensors were optimized using finite element analysis (FEA). Performance characteristics of the half bridge and 3-terminal sensors, i.e. sensitivity, nonlinearity (NL%), temperature coefficient offset (TCO) and drift were measured and compared. It was determined that the 3-terminal pressure sensors (3-TPS) had greater sensitivity, better non-linearity and lower drift compared to half bridge design sensors. The 3-TPS devices were also less sensitive to alignment errors.