Acoustic and magnetic MEMS components for a hearing aid instrument

Abstract

The design of two microelectromechanical (MEMS) devices that form pat of a micro acousto-magnetic transducer for use with a hearing-aid instrument is described in this paper. The transducer will convert acoustical energy into an electrical signal using a MEMS realization of a capacitive microphone. The output signal from the microphone undergoes signal conditioning and processing in order to drive a MEMS electromagnetic actuator. The resultant magnetic fid is used to exert a force on a high coercivity permanent micro magnet that has been implanted on the round window of the cochlea. The motion of the implanted magnet will develop traveling waves on the basilar membrane inside the cochlea to give a hearing capability. A high-sensitivity MEMS based capacitor microphone is designed using a polysilicon Germanium diaphragm. The microphone is constructed using a combination of surface and bulk micro machining techniques, in a single wafer process. The microphone diaphragm has a proposed thickness of 0.7 micrometers , an area of 2.6 mm2, an air gap of 3.0 micrometers and a 1 micrometers thick silicon nitride backplate with acoustical ports. An output voltage signal is obtained from the capacitor microphone using a capacitive voltage divider network and amplified by a simple source follower circuit. D