A study on the viscous damping effect for diaphragm-based acoustic MEMS applications

With miniaturization, better performance and inexpensive devices can be realized with coveted features such as improved reliability, faster response time, cost effectiveness and mass production capability. For miniaturized mechanical structures, viscous damping dominates the dissipation mechanism, which can have an adverse effect on both the frequency response characteristics and the mechanical–thermal noise. For silicon condenser microphones, an optimized viscous damping value has its origin in a well-designed backplate structure. There is an optimum acoustic hole location in the backplate and it is concluded that the location of acoustic holes has more influence on the microphone performance than the number of holes in the backplate. It is also demonstrated experimentally, via a PZT/Si diaphragm-based acoustic device, that its frequency response characteristics can be optimized by attaching a silicon backplate with optimized slots and holes. The bandwidth of the acoustic device is approximately 16 kHz with an estimated A -weighted mechanical–thermal noise of 28.6 dB(A).