Design and fabrication of condenser microphone using wafer transfer and micro-electroplating technique

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 andstress, 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 mum, respectively, an air-gap thickness of 10 mum, 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 and12 V are -45.3 and -50.2 dB/Pa (at 1 kHz), respectively. The fabricated microphone shows aflat frequency response extending to 20 kHz.