Abstract
We have designed and fabricated various diaphragm-based piezoelectric microphones with film-layer structure SiN1/poly-Si/SiN2/ZnO/parylene/Al/parylene (from bottom to top) that contain various square “holes” uniformly distributed over the whole diaphragm with various hole ratios (defined to be the ratio between the total area of the holes and the whole diaphragm area). The holes (which are formed by etching out all the layers except SiN2 and top parylene in the diaphragm) are to release the residual stress in the diaphragm. We have fabricated and analyzed various microphones with and without the holes, and have observed that the microphones with the holes have significantly larger acoustic sensitivities and diaphragm displacements than those without any hole. The best microphone sensitivity of the hole-array microphones has been over 12 times greater than that of the no-hole microphones. Also, we have observed that the center displacement of the diaphragm is dependent on the hole ratio but not on the hole size. We have corroborated the experimental results with FEM analysis.