Abstract
Piezoelectric micromachined ultrasound transducers (PMUT) incorporating lead zirconate titanate PbZr0.52Ti0.48O3 (PZT) thin films were investigated for miniaturized high-frequency ultrasound systems. A recently developed process to remove a PMUT from an underlying silicon (Si) substrate has enabled curved arrays to be readily formed. This research aimed to improve the design of flexible PMUT arrays using PZFlex, a finite element method software package. A 10 MHz PMUT 2D array working in 3-1 mode was designed. A circular unit-cell was structured from the top, with concentric layers of platinum (Pt)/PZT/Pt/titanium (Ti) on a polyimide (PI) substrate. Pulse-echo and spectral response analyses predicted a center frequency of 10 MHz and bandwidth of 87% under water load and air backing. A 2D array, consisting of the 256 (16 × 16) unit-cells, was created and characterized in terms of pulse-echo and spectral responses, surface displacement profiles, crosstalk, and beam profiles. The 2D array showed: decreased bandwidth due to protracted oscillation decay and guided wave effects; mechanical focal length at 2.9 mm; 3.7 mm depth of field for -6 dB; and -55.6 dB crosstalk. Finite element-based virtual prototyping identified figures of merit—center frequency, bandwidth, depth of field, and crosstalk—that could be optimized to design robust, flexible PMUT arrays.
Highlights
The development of a miniature, ultrasound, finger vein imaging sensor for personal authentication in mobile phones, tablet and laptop computers, and personal electronic devices is of interest
Such devices would be enabled by thin-film, PbZr0.52 Ti0.48 O3 (PZT)-based piezoelectric micromachined ultrasound transducers (PMUTs)
The research described in this paper aims to improve the design of flexible PMUT arrays using an explicit, time-domain, finite element method software, PZFlex [24,25]
Summary
The development of a miniature, ultrasound, finger vein imaging sensor for personal authentication in mobile phones, tablet and laptop computers, and personal electronic devices is of interest. Fingerprint-based biometrics are used for this purpose, this method is fallible as fingerprints can be stolen or unclear, due to injury or chemical exposure. Finger vein structures are as unique to individuals, as fingerprint patterns are buried and protected under the skin. They can provide a more secure, but still accessible, means of personal authentication. Such devices would be enabled by thin-film, PbZr0.52 Ti0.48 O3 (PZT)-based piezoelectric micromachined ultrasound transducers (PMUTs). Mina et al [1] designed and fabricated 1D and 2D
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