Impact of encapsulation materials on the performance of silicon-based solid state high pressure sensors with surface trenches

This paper reports on the impact of encapsulation materials on the performance of solid state high pressure sensors based on a Si-glass stack with surface trenches etched into the Si chip comprising piezoresistive stress sensing elements. The sensor chips are assembled in TO39 pressure housings and encapsulated using materials including two silicone gels, two silicone rubbers, an epoxy resin and Parylene C. The pressure related sensor output up to 60 MPa is extracted over the temperature range from -40 to 125°C using custom made pressure setups. Further, the offset and sensitivity drift of the sensors are investigated under cyclic loading up to 0.6 MPa. In comparison to sensors encapsulated using the softer materials, i.e., the silicone gels and rubbers, a significant increase in pressure sensitivity at room temperature is observed for devices packaged in epoxy resin. However, the corresponding output signals of these systems underlie a large drift ultimately leading to the failure of the devices.