Transient Behaviors of A High Temperature SOI Based Pressure Sensor

Silicon on insulator (SOI) is becoming a more favorable technology to make membrane in MEMS as compared to traditional poly-silicon due to its high temperature capability and more uniformity in controlling its geometry. In our study, a high temperature pressure sensor is designed based on a SOI based MEMS chip bonded on the cantilever beam. A unique structure is designed to shelter the thermal shock which could occur in testing and operation. In our modeling, transient thermo-mechanical modeling is conducted. A thermal shock with the maximum temperature of 2000degC is applied to exposed areas of the packaging structure, and the maximum temperature could keep steady for 1500ms during the thermal shock. Detailed temperature field as a function of time is provided on the chip, which shows that the chip temperature is well below the required specification which is on the level of within 500ms. In addition, the deformation and stress of the packaging structure with various packaging bonding materials are also provided by our models. For this packaging structure, the selection of the bonding materials is an important factor during the packaging design process. The performance, such as the linearity, range and life-time, for the packaging structure of the pressure sensor is also limited by the CTE (coefficient of temperature expansion), Young´s modulus, and thermal conductivity of bonding materials which all are considered in the selection of bonding materials. The packaging structure with relatively soft bonding materials shows uniform deformation among the piezo-resistive areas, while the strain and stress distribution of the packaging structure also could obtain the optimization in operation