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

Pressure sensors working at high temperatures of 500 degrees C are required in various fields like aerospace, automobile and many industries. However, reliable sensors working at such high temperature are still not sufficiently developed. Mainly, developing a high temperature stable package imposes new challenges due to thermal cross-sensitivity and temperature induced stresses. Other major issues are to identify stable materials for high temperatures and stress-tolerant sensor mounting techniques. This research work focuses on the implementation of a stress-tolerant pressure sensor design for applications up to 500 degrees C: A micro strain gauge is deposited and patterned on a Langasite (LGS) crystal. It is attached to a ceramic substrate (Al2O3) like a cantilever by flip-chip interconnection and glass solder underfill. The flip-chip bonding is done using gold stud bumps. The ceramic substrate has a membrane structure which is fabricated by ultrasonic machining. The deflection of the deforming membrane will be transferred pointwise to the free end of the crystal inside the package. The strain induced on the cantilever is measured by the change of resistance of a microstrain gauge. This special design concept aims at the elimination of thermal stresses between membrane and sensing device, which could induce cross-sensitivity. In this paper, processes to develop the complete assembly are presented including the choice of materials and fabrication methodology for individual parts. The resulting sensor package is stable for operations up to 500 degrees C.