Enhanced analytical model for micromachined microphones

The advent of silicon micromachining has opened up numerous opportunities for the commercialization of many miniaturized sensors. Coupled with matured silicon technology, one of the beneficiaries is the capacitive micromachined microphone, a simple yet very elegant microsensor. For earlier MEMS microphones, because of the constraints of surface micromachining, a thin layer of air is enclosed within an etched cavity between a diaphragm and a backplate. Bulk micromachining, coupled with wafer bonding and DRIE (Deep Reactive Ion Etching), provides another attractive avenue of fabricating better performance and robust MEMS microphones. As a result, a more accurate and reliable modeling approach is required to reflect the shift in fabrication techniques. The theory of a condenser microphone is reviewed. With reference to a B & K MEMS microphone, the theoretical results are compared, which demonstrate good agreements with those reported experimental ones. In addition, the positive effect of an acoustic slot around the circumference of a backplate is also demonstrated.