Concept and Implementation of High-Temperature Pressure Sensor Package up to 500 °C

Inhalt:
Pressure sensors working at high temperatures of 500 °C impose new challenges in packaging due to thermal cross-sensitivity and temperature induced stresses on the package. Other major issues are to identify stable materials at high temperature and stress-tolerant sensor mounting techniques. This research work will mainly focus on developing a pressure sensor assembly for applications up to 500 °C. A micro strain gauge is patterned onto a Langasite (LGS) or Si that is attached to a ceramic substrate (Al2O3) like a cantilever. This is accomplished by a flip-chip interconnection using gold stud bumps and glass under-filler. The ceramic substrate has a membrane structure fabricated by ultrasonic machining. The membrane transfers the pressure to the cantilever-shaped transducer inside the package. The strain produced in the cantilever is measured by the change of resistance of the strain-gauge. For wireless sensing, the strain gauge will be replaced by a SAW delay line in future versions. As proof of the design concept for the elimination of thermal stresses between membrane and sensing device, a low-temperature model (up to 200 °C) has been implemented using polymers and a Si-based strain gauge. For operating temperatures up to 500 °C, the polymers are replaced by glass solders. In this paper, processes to generate different parts of the assembly such as the sensing element, ceramic housing with membrane, electrode interconnection, flip-chips and the final assembly of the package will be discussed. The first proto-type of this assembly is tested for its functionality, and corresponding results are presented.