The base of the silicon substrate is constrained in all structural degrees of freedom. Also, a temperature of -200 °C is applied to the membrane to represent the manufacturing tension prestress.

Figure 53.5: Structural Boundary Conditions

A DC bias voltage of 1.5 V is applied to the membrane to illustrate the variation of capacitance with bias voltage. The backplate is grounded.

Figure 53.6: Electrical Boundary Conditions

The interaction between an acoustic pressure wave in a viscous fluid and a rigid wall is considered for specific structures according to the Low Reduced Frequency (LRF) approximation. The LRF Model object is specified as a Thin Layer of 2.2 μm.

Figure 53.7: Electrical Boundary Conditions

After a coupled field static analysis under structural and electrical loading (temperature and DC bias), a linear perturbation coupled field harmonic analysis is performed to analyze the response of the microphone to an incoming pressure wave. In that regard, a velocity of 0.01 m/s and an infinite radiation boundary are applied on the sound port inlet.

Figure 53.8: Acoustic Boundary Conditions in Pre-stress Coupled Field Harmonic Analysis