Piezoresistive Pressure Sensors for Applications in Harsh Environments—A Roadmap

Abstract

Piezoresistive mechanical sensors play a very important role in modern industries. MEMS pressure sensor market is one of the biggest markets among all MEMS components [1]. Global pressure sensor market is growing from $6.4 billion in 2012 to $8.8 billion in 2018. The main applications are automotive, medical, consumer electronics, industry and aerospace/defense. Today, there is a growing demand for cost effective high-temperature and harsh- environment semiconductor devices, capable of operating at temperatures in the 500 °C range. Developments in energy, aircraft and space applications, automotive electronics, the oil and gas industry, the plastic and chemical industry, and the military sector are among the main drivers for research on high-temperature sensors and electronics. Existing semiconductor devices based on silicon are limited to operating temperatures below 150 °C, as thermal generation of charge carriers severely degrades device operation at higher temperatures. The development of SOI (silicon on insulator) technology helped to extend device’s operating temperatures to approximately 400 °C. However, at temperatures over 400 °C, the material silicon reaches its physical limits as plastic deformation starts to occur when mechanical stress is applied. Silicon carbide is considered to be the most promising semiconductor for future high-temperature and harsh-environment applications as it features a unique combination of favorable physical, electrical, mechanical, and chemical properties. It is an extremely hard and robust material with a high thermal stability, and is chemically inert up to temperatures of several hundred degrees. Moreover, it has a higher thermal conductivity than copper, and its wide energy bandgap allows operation at high temperatures and in high radiation environments without suffering from intrinsic conduction effects. Performance and reliability of metal-semiconductor contacts, conducting paths and the capability of etching 3D mechanical structures in SiC (such membrane or bridge) remain limiting factors for high-temperature operation of SiC electronic mechanical sensors today. In this chapter we discuss and review materials (Silicon, pSOI, SOI, 3C-SiC and 4H/6H-SiC) and technologies, which are applicable to realize MEMS piezoresistive mechanical sensor elements for applications at elevated temperatures.