A feasibility study of AlN ultrasonic transducers fabrication using the multi-user PiezoMUMPs process for fingerprint scanning at GHz range

In this study, the feasibility of a piezoelectrical micromachined ultrasonic fingerprint sensor working at GHz range at CMOS-compatible voltage using the PiezoMUMPs process capabilities is explored analytically and through Finite Element Analysis. In addition to the advantages offered by ultrasonic fingerprint sensors based on MEMS technology, the all solid approach used here requires much lower driving voltage and provides higher operative frequency for improved axial resolution, overcoming some of the current limitations present in micromachined ultrasonic transducers. In this work we deal with the restrictions in the PiezoMUMPs process that arise due to the use of standard design rules that place constraints on the thicknesses, and materials that may be used, however, these inconveniences may be partially overcome by taking proper design considerations. Here we obtain output voltage in the mV range for an applied short pulse of 2 Vp at 1.6 GHz, showing the possibility to fabricate these piezoelectric micromachined ultrasonic transducers without requiring a customized process.