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

Pressure sensors working at high temperatures of 500 deg 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 deg 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 deg C) has been implemented using polymers and a Si-based strain gauge. For operating temperatures up to 500 deg 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.