An analytical and FEM simulation-based study of the dependence of capacitance profile on structural parameters of CMUT with and without vent.

This paper presents the capacitive behaviour of a Capacitive Micromachined Ultrasound Transducer (CMUT). A Finite Element Method (FEM)-based simulation is proposed to characterize the capacitance of CMUT with different geometrical parameters. The structure of the CMUT under scrutiny consists of an aluminum top electrode on a thin movable membrane of silicon nitride (Si₃N₄) separated by an air gap from the bottom electrode. The capacitance of the CMUT plays an important role in its proper functionality. The current study attempts to explore the calculation and variation of capacitance with different geometrical parameters. Because of the smaller dimension of the device, the effect of fringing is also taken into account. A new empirical formulation has been developed to study the capacitance of the CMUT with vented cavities, and the accuracy of the theory is justified with FEM simulation for single-vented CMUT. The analytical results are validated with simulation and published experimental results. Keeping the similar geometrical shape of the fabricated structure, this model predicts 94.28 kHz resonant frequency which is very close to the experimental result (106 kHz). [ABSTRACT FROM AUTHOR]