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Design and characterization of a MEMS membrane for a fiber optic microphone

Özmen, Göktuğ Cihan
The most critical part of a fiber optic MEMS microphone is the sensing element. The sensing element, membrane, is designed such that the microphone operates in the desired range with desired sensitivity. In this thesis, a MEMS membrane is designed and characterized which is aimed to be used in a fiber optic microphone with responsivity to the audible frequency range. This membrane is electrically deflectable and it has symmetrically located air holes. The design is microfabricated through the commercially available multi-user multi-project service (POLYMUMPS, MEMSCAP Inc., France). The optical and electrical characterizations of the membrane are performed by impedance analyzer and laser vibrometer, respectively. Since the design is to be used in an optical interferometry based microphones, the surface of the membrane is coated by gold. The transient and steady state analysis of the membrane is utilized and both the overall and the spatial response of the membrane is obtained. The fundamental resonance of the membrane is 28 kHz. From laser vibrometer measurements under 100 mV peak-to-peak voltage and 1V DC bias conditions, the peak displacement is found to be 10 nm. The applied voltage is converted to the pressure and the sensitivity of the membrane is calculated to be 40 nm/Pa at 28 kHz. By spatial analysis of the design, symmetry is also verified. This thesis offers a new approach to the design of MEMS membrane for optical microphones.