Modeling and process design optimization of a piezoelectric micromachined ultrasonic transducers (PMUT) using lumped elements parameters

This paper proposes a novel design process of a piezoelectric micromachined ultrasonic transducer (PMUT) for achieving the best operating performance. The electromechanical coupling coefficient (EMCC) k2 for thin-film piezoelectric devices defining PMUT performance was investigated analytically for design optimization. A unimorph PMUT disk formed by a piezoelectric lead zirconate titanate (PZT) active layer on silicon (Si) substrate was chosen for this study. In the first part, the lumped element parameter was used to develop the EMCC model as a function of PMUT geometrical and physical parameters. The EMCC model was used to study the effects of electrode coverage and substrate thickness on PMUT performance. In the second part, we used the electrical equivalent circuit to calculate the input impedance Zin and consequently the EMCC (k2). The k2 extracted from Zin showed a consistent agreement with that determined by the theoretical model developed in the first part. Thus, this modeling approach plays an essential role for the design process of PMUT.