Quantifying modal shapes in smart piezoelectric ultrasonic transducer array: Modeling and experiment

In this paper, a novel technique has been developed to quantify modal shapes in piezoelecric functional thin films-based micromachined ultrasonic transducers (pMUTs) for ultrasonic diagnostics. To obtain high sensitivity, an array of smart pMUTs is designed and successfully fabricated with epitaxially grown functional eutectic Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin film on Si(111)/γ - Al₂O₃(111)/SrRuO₃(111) substrates. Incorporating crystalline γ- Al₂O₃ insulator on Si substrates permitted to control smartly the orientation of piezoelectric film. The characterization is performed employing advanced 3D finite element modeling taking crystallographic anisotropy into account. Modal shapes were captured experimentally using Laser Doppler Vibratometry (LDV). In this pioneering work, an excellent correlation is realized between different resonance frequencies and mode shapes corresponding to different energy states obtained in computations and experiments. Quantification of eigenfrequencies with mode shapes has shown significant influence on transmit-receive characteristics of pMUTs. Utilizing the correlation results, ultrasonic wave transmitting experiment was successfully carried out using fabricated pMUTs as a transmitter and a commercial PZT hydrophone as a receiver.