Dated back to 1980s, after the first demonstration of fabricating using silicon micromachining techniques, Micro-Electro-Mechanical-system (MEMS) microphones have been investigated for more than twenty years and recently, the industry has put more and more concentrations on this area. Compared with all other working principles, due to its simple fabrication process, measurement circuit, packaging issue and application requirements, piezoresistive type microphones are well suited for aero-acoustic measurements. The first generation single-crystalline silicon (sc-Si) based piezoresistive microphone bears the major problem of significant drift resulting from the leakage current of the piezoresistors isolating pn junctions. Its successor, poly-crystalline silicon (poly-Si) based piezoresist...[ Read more ]

Dated back to 1980s, after the first demonstration of fabricating using silicon micromachining techniques, Micro-Electro-Mechanical-system (MEMS) microphones have been investigated for more than twenty years and recently, the industry has put more and more concentrations on this area. Compared with all other working principles, due to its simple fabrication process, measurement circuit, packaging issue and application requirements, piezoresistive type microphones are well suited for aero-acoustic measurements. The first generation single-crystalline silicon (sc-Si) based piezoresistive microphone bears the major problem of significant drift resulting from the leakage current of the piezoresistors isolating pn junctions. Its successor, poly-crystalline silicon (poly-Si) based piezoresistive microphone, is invented to overcome this leakage problem by means of depositing poly-Si on dielectric insulating layer, such as silicon oxide or silicon nitride. However, this approach sacrifices the sensitivity due to the low piezoresistive gauge factor of poly-Si. New fabrication technique based on wafer bonding technologies has been demonstrated to realize sc-Si piezoresistors on amorphous dielectric insulating layer (silicon nitride), but the reported fabrication process is not cost-effective for real commercialization.

In this thesis, a sc-Si piezoresistive type aero-acoustic microphone based on silicon-to-nitride low temperature wafer bonding and Smart-Cut technologies has been designed, fabricated and tested. The measured resonant frequency of the microphone diaphragm is 520 kHz and the airborne sound sensitivity is 0.1μV / V / Pa .