Abstract

Microphones are ordinary pressure sensors with an optimum behavior in a certain pressure and frequency range. The fundamental elements of a condenser microphone comprises of a diaphragm, backplate, airgap, and rear volume cavity. In order to analyze any system for its response behavior due to a particular loading, it is essential to obtain the characteristic properties of the system in terms of the natural frequencies, mode shapes and damping. This is done by solving a free vibration problem. The natural frequencies and mode shapes of the diaphragm of square and circular shapes including those with cutouts (openings) and abrupt changes in thickness are obtained. The results show that the natural frequencies increase as the size of cutout increases, and also when the abrupt change in thickness increases. But, the increase due to abrupt change in thickness is very small when compared that of the plate with cutout. In the present investigation, silicon micromachining technology is used to fabricate the condenser microphone. The condenser microphone is fabricated from two wafer chips, one containing the silicon membrane and the other the Pyrex glass (#7740) which forms the backplate. Between the capacitance circuit. Lithographic techniques are used to manufacture the condenser microphone with specially shaped backplates which contain the airgap and side volume cavity. An Anodic bonding technique is used to bond the silicon membrane with the backplate. The silicon diaphragm is used as the moving electrode and the Pyrex glass backplate is made into a back electrode by a thin deposition of metal on it