Study on the packaging technology for a high-G MEMS accelerometer

High-G accelerometers have a variety of applications with severe shock loadings especially in crash and impact environments. The package for a high-G accelerometer should provide both protection against such harsh environments and necessary communications with outside the package. The residual stress caused by packaging process which degrades the sensor performance should be considered at the beginning of packaging design. The accelerometer in this study is based on a piezoresistive structure fabricated by a standard MEMS fabrication process A glass cap was anodically bonded to the structure to protect the movable parts. Then a packaging substrate was fixed to above structures with an adhesive material. FEM simulation based on a simplified structure of the accelerometer has been applied in static analyses in order to find out the potential stress brought by the package. The affection of different adhesive and packaging materials on the acceletometer performance was simulated. The results of simulations show that both the Young's modulus of the adhesive and the coefficient of thermal expansion (CTE) of packaging substrate could have a significant impact on the initial output of the accelerometer. An experiment study on the affection was also conducted, and the results were similar to the results of FEM(finite element method) simulations for the simplified structure. Thus the FEM simulation of such simplified structure could serve as the basic of accelerometer packaging design. Based on former results, optimized process was suggested in the package of the accelerometer and the packaged accelerometer was tested with satisfactory results.