Giga-hertz ultrasonic reflectometry for fingerprint imaging using epitaxial PbTiO3transducers

Kae Nakamura, Yuna Koike, Yusuke Sato, Takahiko Yanagitani*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

A fingerprint reader based on epitaxial PbTiO3 (PTO) transducer array operating thickness extensional mode in GHz range was fabricated. The device consisted of nine square transducers with 0.1 mm per side arranged 1.3 mm apart in a 3 × 3 array. Minimum conversion loss of the fabricated transducer was 2.5 dB at 0.8 GHz, and electromechanical coupling coefficient kt2 was estimated to be 28.9%. In contrast to MHz range ultrasonic fingerprint readers such as those based on piezoelectric micromachined ultrasonic transducers using a piezoelectric transducer and ScAlN, a GHz range transducer enables imaging in higher spatial resolution. Furthermore, PTO transducers have a high dielectric constant and electromechanical coupling coefficient kt2. A high dielectric constant realizes 50 ω impedance matching with small electrode area. The small acoustic source is expected to improve the spatial resolution of a fingerprint reader. We achieved the fingerprint imaging by evaluating the acoustic reflectance of the medium/transducer interface. Furthermore, piezostage that allows mechanical movement in the 100 nm order was introduced to image a 12 × 12 μm2 area with total of 3600 data points.

Original languageEnglish
Article number172903
JournalApplied Physics Letters
Volume121
Issue number17
DOIs
Publication statusPublished - 2022 Oct 24

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)

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