Packaging Effects on MEMS Pressure Sensor Hysteresis

Abstract

Micro-electro-mechanical systems (MEMS) have allowed high precision pressure sensors to be manufactured at low cost, but they typically exhibit some level of hysteresis behaviour, which is believed to be primarily due to the materials used to package them. In order to evaluate the effects of the different packaging materials and processes, in this study, the performance of piezoresistive absolute pressure MEMS was measured for each of the first two packaging stages of the product assembly process. Sensing elements first packaged in a "floating exposed" configuration and then in an "attached exposed" configuration were compared. These two different packaging configurations exhibited distinct hysteresis behaviour when thermally cycled. After applying a third order polynomial fit to the raw data, stabilized and moving hysteresis loops were observed for the floating exposed and attached exposed configurations respectively. The stabilized hysteresis is believed to originate from the inelastic behaviour of the die metallisation, whereas the nonstabilized behaviour stems from the adhesive used to attach the die to the housing.

Relative Contributions of Packaging Elements to the Thermal Hysteresis of a MEMS Pressure Sensor

“…In addition to the L1 and L2 packaging configurations, as described in Table 1, a floating L1 configuration (L1-F) was also achieved as an intermediate packaging step between the standard L0 and L1 configurations. Without being subjected to any prior thermal preconditioning, ten units were initially packaged in this L1-F configuration, following the method described by Hamid et al [39]. The sensing elements in this configuration were supported by only the wire bonds and were therefore considered to be "floating".…”

“…The system used to temperature and pressure cycle test the different packages was identical to the one previously described by the authors [39]. The sensors were mounted to a metal manifold, as shown in Figure 3, and a Druck "PACE6000" was used to control the air pressure.…”

“…The manifold and SEs were placed in a TAS environmental chamber with electrical connectors and cables to convey the voltages to be measured using a Keysight 6.5 digit resolution digital voltmeter and an external datalogger. As discussed in [39], the electrical instrumentation and pressure controller were not inside the environmental chamber and were therefore not subjected to any significant thermal cycling, but only to small fluctuations of the test laboratory ambient (25 • C ± 2 • C). It was therefore assumed that the thermal variation of the measurement system did not affect the accuracy of the measurements of the sensors under testi.…”