Analysis of fringing capacitance effect on the performance of micro‐electromechanical‐system‐based micromachined ultrasonic air transducer

Abstract

The work analyses the significance of fringing capacitance in modelling effectively the amplitude of the ultrasonic waves generated by silicon nitride membrane-based micromachined ultrasonic transducer (MUT). The amplitude of the ultrasonic waves is proportional to the displacement of the biased membrane under the influence of a sinusoidal signal. Fringing capacitance is significant as for operating the transducer in the medical imaging regime of frequency range 1–10 MHz, the dimension of the electrodes of the MUT capacitor becomes comparable with the separation between them. The device is modelled first without the fringing effect and then Palmer, Landau's and Younes Ataiiyan's approaches are considered for evaluating the fringing capacitance. The device is finite element method analysed by PZFLEX 3D simulator. The membrane displacement is evaluated with variation in device structural parameters of membrane radius and thickness, electrode separation and bias voltage for an extensive range of values. Fractional percentage error of the above analytical approaches is evaluated with respect to the PZFLEX which are regarded as closest to reality. Substantial decrease in the error is observed on modelling the device with the effect of the fringing capacitance.