Abstract
This paper gives a detailed electroacoustic study of a new generation of
monolithic CMOS micromachined electrodynamic microphone, made with
standard CMOS technology. The monolithic integration of the mechanical
sensor with the electronics using a standard CMOS process is respected in
the design, which presents the advantage of being inexpensive while having
satisfactory performance. The MEMS microphone structure consists mainly of
two planar inductors which occupy separate regions on substrate. One
inductor is fixed; the other can exercise out-off plane movement. Firstly,
we detail the process flow, which is used to fabricate our monolithic
microphone. Subsequently, using the analogy between the three different
physical domains, a detailed electro-mechanical-acoustic analogical
analysis has been performed in order to model both frequency response and
sensitivity of the microphone. Finally, we show that the theoretical
microphone sensitivity is maximal for a constant vertical position of the
diaphragm relative to the substrate, which means the distance between the
outer and the inner inductor. The pressure sensitivity, which is found to
be of the order of a few tens of μV/Pa, is flat within a bandwidth from 50
Hz to 5 kHz.
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