High-Temperature Pressure Sensor Package and Characterization of thermal stress in the assembly up to 500 °C

High temperature stable (500 degrees C) pressure sensors are required in arious fields like aerospace, automobile and manufacturing industries. However, reliable sensors working at such high temperatures are still not sufficiently developed [3]. Mainly, developing a high temperature stable package imposes new challenges due to thermal cross-sensitivity and temperature induced stresses [2]. Important challenges are to identify stable materials at high temperatures and stress-tolerant sensor mounting techniques. This current research work will mainly focus on the implementation of a high temperature (HT) concept for applications up to 500 degrees C as follows: 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 ceramic substrate has a membrane structure that was fabricated by ultrasonic machining. The deflection of the deforming membrane is transferred pointwise to the free end of the crystal inside the package using a quartz spacer. The strain produced 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 the sensing element. Despite the effort taken to minimize stresses in the assembly, the die attachment area will however experience thermal stress due to the mismatch of Thermal Coefficient of Expansion (TCE) of the different materials employed. Hence, it is necessary to evaluate the development of stress along the sensing element to prove the stress tolerant design of this sensor. Characterizing thermal stresses could be used to compensate for the offset signal and to optimize the sensor design. This research work will establish a method to develop a pressure sensor stable for operations up to 500 degrees C and also a final implementation of this concept is shown. This concept has potential for the generation of very compact wireless sensors working autonomously in high-temperature environments.