Comparison between Capacitive Micromachined Ultrasonic Transducers with Circular and Square Microplates

The Capacitive Micromachined Ultrasonic Transducers (CMUTs) are constructed on silicon substrate in which one electrode is highly doped at top and other is metal layer on suspended silicon membrane resting on silicon dioxide walls. The moving part of CMUT wall is made from silicon nitride membrane. They are efficient transmitters and receivers for air coupled non-destructive evaluation applications, generating or detecting ultrasonic waves by vibrating membrane featuring fixed circumference. Despite the advantages and their broad bandwidth, studies indicates that the overall sensitivity of CMUT's need to be improved to match piezoelectric transducers. This paper presents an approximate analytical solutions and comparison between circular and square plates for the static deflection caused by electrostatic forces and pull-in voltage by using MATLAB. The evaluation of the electrostatic force between the two plates is simplified due to the fact that the electrostatic gap is much smaller than lateral dimensions of the device. This has been seen that the deflection of circular is better than the square microplates. These theoretical analyses are helpful for design and optimization of such devices.