CMUT – Capacitive Micromachined Ultrasound Transducers

Members: Michael Leung and Matthew Haines

Background: Capacitive Micromachined Ultrasound Transducers (CMUT) is a MEMS based ultrasound transducer. Traditionally, CMUTs are made from piezoelectric materials, however recent developments have enabled CMUTs to gain popularity as they offer many advantages over their counterpart. By being created in silicon, CMUTs offer the advantage to be batch produced with tight parameters using micro-machining processes, similarly to accelerators, pressure sensors, and other common MEMS devices. This also enables for embedding of the electronics on the same wafer, greatly reducing the size and cost of such devices. The functionality is simple; a thin silicon membrane is suspended over a gap, covered with an electrode. At the bottom of the gap is another electrode, forming a capacitor. By applying a voltage bias across the electrodes, an attractive force pulls the thin membrane, and deflects the membrane. By applying DC and AC voltage signals, the membrane’s position can be dynamically controlled to create an ultrasound pulse.

Abstract: In the report, I discus about the various membrane deflection estimates that are known, and compare them to FEM models obtained with COMSOL for both circular and square membranes. First the circular model is examined, for which membrane deflection is known and well understood. Next, the square is examined, using deflection profiles given by thin and thick membranes, and finally by the Galerkin method. After validating the Galerkin method, anisotropic silicon is used, and the model is used to validate the Galerkin method, the only method able to account for the anisotropic behavior of silicon.

 

More information: You can read a copy of the final report here. You can also find more information about CMUT on Kuri-Yakub’s webpage, one of the original inventors of the CMUT.

 

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