UBC Theses and Dissertations
A PolyMUMPs Capacitive Micromachined Ultrasonic Transducer Cai, Ming
This work presents the design of Capacitive Micromachined Ultrasonic Transducers (CMUTs) with one and multiple bottom electrodes and their fabrication using the PolyMUMPs technique provided by MEMSCAP Inc. It also reports a new behavioral model of the CMUTs written in VHDL-AMS, complemented by a comparison between finite element analysis, behavioral simulations and experimental measurements on the newly fabricated CMUT arrays. As an improvement on a previously developed VHDL-AMS CMUT behavioral model , where the CMUT was treated as a movable rigid plate capacitor, a mode decomposition approach was used in the present work to better approximate the dynamics of the CMUT membrane. Besides the frequency responses, time responses and electro-mechanical conversion efficiency, the simulation results also showed the electrostatic spring softening effect, and the optimization of the DC/AC voltage ratio that leads to a maximum transmitted acoustic power. The CMUT membrane capacitance variation predicted by the model compares favorably with results from the finite element analysis, with better matching than the previously developed models. Polytec Micro System Analyzer (Polytec MSA-500) using Laser Doppler Vibrometry was used for the experimental characterization, in which the pull-in voltage, vibration modes and their respective resonant frequencies were determined. Characterization results were compared with the ones from the finite element analysis and the behavioral model simulations, and excellent agreement was shown.
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