Numerical and experimental study of the dynamic behavior of piezoelectric micromachined ultrasonic transducers (pMUTs)

In this study, a finite element code based on a combination of equivalent single-plate theory and classical laminated plate theory was used to study the dynamic behavior of the thin film membrane structures. The structure studied was piezoelectric micromachined ultrasonic transducer (pMUT) fabricated with MEMS technology. The membrane has two different shapes, square and rectangular. Two different types of boundary conditions were considered for modeling, namely, simply supported vs. clamped. It is demonstrated that the model generates correct qualitative trend for the mechanical responses of pMUT structure. Quantitatively, for relatively larger (greater than 1 mm) thin membrane structures, the measured fundamental frequencies fall between the predictions based on clamped and simply supported boundary conditions. However, for smaller structures, both predictions overestimate them. The possible reasons for this discrepancy include the interaction of membrane vibration with the supports of the structure, residual stress, DC bias voltage, parasitic capacitance, and uncertainty of the dimensions and material properties of the constituent thin films.