Fabrication, Packaging and Characterization of Platinum based Pressure Sensors for Operation at 500 °C

Inhalt:
The application of micromechanical sensors in extreme harsh environments like combustion engines, turbines or chemical reactors can improve the controlling-efficiency and reduce pollutant emissions. This work presents the design concept of high temperature pressure sensors, capable to operate up to 500 °C, the fabrication with micro-technologies and the assembly processes. A resistive Wheatstone bridge, based on platinum resistors was designed. The sensor function was modelled using FEM simulations and optimized for a maximum operation pressure of 20 bars. Furthermore the influence of geometric and material dependent parameters on the pressure signal was investigated. With microtechnologies like bulk-micromachining of silicon, reactive ion etching (RIE), lithography and thin film sputtering the transducers were fabricated. Subsequently, the sensors were assembled with a glass soldering process on AlN and Si3N4, low coefficient of thermal expansion (CTE) ceramic substrates. For the high-temperature stable interconnection, platinum thin wire-bonds and a flip-chip-process with gold stud-bumps were realized. The fabricated sensor-assemblies were characterized with respect to their pressure sensitivity at 20 °C and their cross sensitivity on temperature with a heat-chamber set-up until 500 °C. A pressure sensitivity of 75 muV/V·bar and a temperature dependency of 2.1 muV/V·K were observed for a flip-chip assembled sensor with Si3N4-substrate.