Study and characterization of plastic encapsulated package for a three-axis piezoresistive acceleromete with guard-ring structure

This study reports the performance of a three-axis piezoresisitvie accelerometer with a guard-ring structure after plastic packaging. The accelerometers, with and without guard-ring structure, are capped with glass substrate to form the glass/Si/glass sandwich and then encapsulated in plastic package. The testing results on these packaged accelerometers have shown that the guard-ring structure successfully suppresses the performance shift caused by plastic package for one order of magnitude. The glass/Si/glass sandwich structure adds air damping to the accelerometer, hence its resonant frequency is slightly reduced (less than 0.5%). Moreover, the guard-ring structure has relatively large stiffness and is considered as a rigid body, and its influence on the sensor dynamics can be ignored. In conclusion, the guard ring structure significantly reduces the performances variation of packaged sensor. Thus, the inexpensive plastic encapsulated package for accelerometers can be implemented on the real products.