This thesis develops the design methodology and fabrication procedures for a MEMS-based square planar acoustical sensor microarray for use in a hearing instrument to improve speech intelligibility in noisy and reverberant environments. The proposed microarray offers the potential of controlled directional sensitivity with a reasonably constant beamwidth over the audio frequency range when used in conjunction with an appropriate digital signal processor. The microarray consists of nine identical square-shaped capacitive-type acoustical sensors in a 3 x 3 planar layout and has a footprint area of 4.6 x 4.6 mm². Each sensor has a sensitivity of 10.3 mV/Pa when biased at 12 volts. A beamforming algorithm pertaining to MEMS realization of a square planar array of uniformly spaced identical acoustical sensors has been developed. A new analytical model has been developed that provides a better approximation to the pull-in voltage of capacitive type square diaphragm acoustical sensors as compared to existing models.

A MEMS-based three-dimensional modular package has been developed for the microarray where silicon has been used as the package material. The package realizes a complete microsystem by holding the microarray, necessary microelectronics dies and a power source in stacked submodules. Two different schemes have been developed to establish intermodular electrical connectivity. The first scheme uses pressure-dependent cantilevered bridge-type microspring contacts that are fabricated as an integral part of a package submodule. The second scheme uses a MEMS-based microbus card to establish intermodular connectivity by using interconnection channels that are present in each package submodule.

The design methodology and fabrication process was developed through the extensive use of simulation tools. The actual fabrication processes have been simulated and the resulting microstructures have been analyzed using three-dimensional electromechanical finite element techniques (FEA). The FEA results closely match theoretical values predicted by the design methodology.

The design has been sent for analysis and prototype fabrication costing to the Corning-IntelliSense Corporation. The design was found to be robust and a price quotation for the microarray fabrication has been received. The physical implementation will take place when the collaborating private sector firm and a MEMS foundary have reached a confidentiality agreement.