Fabrication of a dual-planar-coil dynamic microphone by MEMS techniques

A dual-planar-coil miniature dynamic microphone, one of the electro-acoustic transducers working with the principle of the electromagnetic induction, has been realized by semiconductor micro-processing and micro-electro-mechanical system (MEMS) techniques. This MEMS microphone mainly consists of a 1 mu m thick diaphragm sandwiched by two spiral coils and vibrating in the region with the highest magnetic flux density generated by a double magnetic system. In comparison with the traditional dynamic microphone, besides the miniaturized dimension, the MEMS microphone also provides 325 times the vibration velocity of the diaphragm faster than the traditional microphone. Measured by an audio analyzer, the frequency response of the MEMS microphone is only 4.5 dBV Pa(-1) lower than that of the traditional microphone in the range between 50 Hz and 20 kHz. The responsivity of -54.8 dB Pa(-1) (at 1 kHz) of the MEMS device is competitive to that of a traditional commercial dynamic microphone which typically ranges from -50 to -60 dBV Pa(-1) (at 1 kHz).