Silicon carbide membranes for microelectromechanical systems based cmut with influence factors

Microelectromechanical Systems (MEMS) based capacitive micromachined ultrasonic transducer (CMUT) has many applications in medical imaging. Ultrasonic transducer technology has been long dominated by piezoelectric transducers, particularly in the medical ultrasound imaging. The best popular materials used for fabricating CMUT membranes are silicon nitride (Si 3 N 4 ), polysilicon, chromium and aluminum are characteristically used to shape electrodes on top of these membranes. But current technology of CMUT demands the silicon carbide (SiC) for membrane material where the electrode instead of being on top of the membrane is placed beneath the membrane. It offers greatest contiguity of the upper and subordinate electrodes. For this it decreases the transduction gap enlightening the electro-mechanical coupling and sensitivity of the device. Aside from this, it is reported that the CMUT has a resonance frequency of 1.7 MHz and a 3 dB-bandwidth of 0.15 MHz. Also, the higher Young’s modulus (260 GPa) of SiC with its little residual stress (± 30 MPa). Consequences in great strength and resilient CMUT membranes, which led to the studies presented in this paper. All the results are validated by FEM simulation

Squeeze Film Effect in Surface Micromachined Nano Ultrasonic Sensor for Different Diaphragm Displacement Profiles

In the present paper, we have analytically explored the small variations of the local pressure in the trapped air film of both sides of the clamped circular capacitive micromachined ultrasonic transducer (CMUT), which consists of a thin movable membrane of silicon nitride (Si3N4). This time-independent pressure profile has been investigated thoroughly by solving the associated linear Reynold's equation in the framework of three analytical models, viz. membrane model, plate model, and non-local plate model. The solution involves Bessel functions of the first kind. The Landau-Lifschitz fringing technique has been assimilated to engrave the edge effects in estimation of the capacitance of CMUT, which should be considered in the micrometer or lesser dimension. To divulge the dimension-based efficacy of the considered analytical models, various statistical methods have been employed. Our use of contour plots of absolute quadratic deviation revealed a very satisfactory solution in this direction. Though the analytical expression of the pressure profile is very cumbersome in various models, the analysis of these outputs exhibits that the pressure profile follows the displacement profile in all the cases indicating no viscous damping. A finite element model (FEM) has been used to validate the systematic analyses of displacement profiles for several radii and thicknesses of the CMUT's diaphragm. The FEM result is further corroborated by published experimental results bearing excellent outcome