Piezoresistive Low-Pressure Sensor for Harsh Environment Applications

摘要

This paper reports on a new piezoresistive pressure sensor designed for high temperatures and harsh environment applications. The fabricated sensor consists of a steel diaphragm that deflects in response to the applied pressure and transmits the resulting deflection directly (which means without any liquid) to the micromechanical sensor chip. The chip is made of Silicon-On-lnsulator (SOI) with dielectrically isolated piezoresistors. The electrical contact of the chip is realized using a new flip-Chip technology with gold bumps. This allows to increase the maximum operating temperature to approx. 300°C. In contrast to existing solutions, the pressure range can be easily adjusted within a wide range (0...2 bar up to 0...50 bar) by changing only the thickness of the steel diaphragm. For the 2 bar sensor, the static characterization at constant current supply (2mA) results in a sensitivity of about 100 mV/bar with a temperature coefficient of approx. +1·10~(-3) K~(-1). Further important characteristics are a natural frequency above 20 kHz and an acceleration error below 0.3 mbar/g. Main applications are the pressure measurement in the inlet and exhaust manifolds of combustion engines for mass airflow estimation and gas exchange analysis. Due to the flat and rugged front diaphragm, the sensor is also best suited for applications in plastics industry, i.e. in reactive injection molding (RIM).