Bottom-inlet-type micro-electro-mechanical system acoustic sensors based on two polyimide/amorphous-Si sacrificial layers
A bottom-inlet-type micro-electro-mechanical system acoustic sensor based on two polyimide/a-Si sacrificial layers is presented. A diaphragm was adapted to be on the top side of the sacrificial layers, showing the bottom-inlet structure for the package, which has the sensitivity of more than 3 dB compared with that of the top-inlet type. Also, the fundamental CMOS process implemented with Al electrodes was applied to have simple releasing steps by O2 ashing and XeF2 isotropic etching because of their material etching selectivity. The sensor module had a sensitivity of −38.9 dBV/Pa at 1 kHz with a bias of 9.2 V in the sweep range from 100 Hz to 16 kHz. In addition, to evaluate the open-circuit sensitivity, structure-based equivalent circuit modelling was performed with lumped parameters. The modelled sensitivity was in good agreement with the measured sensitivity in the error rate of 4.3% under 8 kHz, demonstrating the validity of the modelling. The modelled open-circuit sensitivity was determined to be −37.2 dBV/Pa at 1 kHz using the proposed lumped model.
