Design and fabrication of an air-bridge microphone

Today\u27s hearing aids have many shortcomings: they are susceptible to environmental damage, cannot be worn while sleeping or in wet environments, are obtrusive and are expensive. New technologies are being developed which allow most all of these shortcomings to be addressed by placing a portion of the hearing aid within the middle ear. These new technologies require size reductions in several of the aid components, one of these being the microphone. Microelectromechanical Systems (MEMS) has already developed technologies that can be used to construct these microphones. Most microphones constructed using MEMS techniques employ a dual wafer design. the microphone membrane is constructed on one wafer and attached to a second wafer containing bonding pads and possibly additional sensing elements. The use of two wafers to manufacture one microphone reduces the yield of the process and requires an additional alignment and bonding step. Further, the methods used for fabrication are non-traditional and do not allow appropriate electronics to be easily fabricated with the microphone. An alternative approach is being investigated by this thesis. Here a single wafer and standard microelectronic processing techniques are used to fabricate the diaphragm, sensing elements and bonding pads. This approach will simplify construc tion and allow the possibility of including appropriate signal processing electronics on the microphone die. Equations are developed to predict the static and dynamic deflec tion and natural frequency of the microphone system. Optimal design strategies are used to minimize the microphone diaphragm area subject to electrical and mechanical constraints. A first generation microphone was fabricated. However, unanticipated processing constraints on the microphone design rendered the microphones inoperable. Several design modifications are noted to solve these problems and promote the successful fabrication of second generation microphones