  A novel fabrication process, which uses wafer transfer and
micro-electroplating technique, has been proposed and tested. In this paper,
the effects of the diaphragm thickness and stress, the air-gap thickness, and
the area ratio of acoustic holes to backplate on the sensitivity of the
condenser microphone have been demonstrated since the performance of the
microphone depends on these parameters. The microphone diaphragm has been
designed with a diameter and thickness of 1.9 mm and 0.6 $\mu$m, respectively,
an air-gap thickness of 10 $\mu$m, and a 24% area ratio of acoustic holes to
backplate. To obtain a lower initial stress, the material used for the
diaphragm is polyimide. The measured sensitivities of the microphone at the
bias voltages of 24 V and 12 V are -45.3 and -50.2 dB/Pa (at 1 kHz),
respectively. The fabricated microphone shows a flat frequency response
extending to 20 kHz.
