Ultrasonic fingerprint sensor using a piezoelectric micromachined ultrasonic transducer array integrated with complementary metal oxide semiconductor electronics

• Published in: Applied physics letters Vol. 106; no. 26
• Main Authors: Lu, Y., Tang, H., Fung, S., Wang, Q., Tsai, J. M., Daneman, M., Boser, B. E., Horsley, D. A.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 29-06-2015
• Subjects: AMPLIFIERS; AMPLITUDES; Applied physics; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CMOS; Computer simulation; EUTECTICS; Fingerprinting; Fingerprints; FINITE ELEMENT METHOD; Frequency response; GRATINGS; Integrated circuits; Interconnections; LASERS; Metal oxide semiconductors; Metal oxides; MHZ RANGE 01-100; Micromachining; OSCILLATION MODES; OXIDES; Parasitics (electronics); PHANTOMS; PIEZOELECTRICITY; Polydimethylsiloxane; Scanning; SEMICONDUCTOR MATERIALS; Sensor arrays; SENSORS; SILICON; STEELS; Transducers; Ultrasonic transducers; Vibration mode
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4922915

This paper presents an ultrasonic fingerprint sensor based on a 24 × 8 array of 22 MHz piezoelectric micromachined ultrasonic transducers (PMUTs) with 100 μm pitch, fully integrated with 180 nm complementary metal oxide semiconductor (CMOS) circuitry through eutectic wafer bonding. Each PMUT is directly bonded to a dedicated CMOS receive amplifier, minimizing electrical parasitics and eliminating the need for through-silicon vias. The array frequency response and vibration mode-shape were characterized using laser Doppler vibrometry and verified via finite element method simulation. The array's acoustic output was measured using a hydrophone to be ∼14 kPa with a 28 V input, in reasonable agreement with predication from analytical calculation. Pulse-echo imaging of a 1D steel grating is demonstrated using electronic scanning of a 20 × 8 sub-array, resulting in 300 mV maximum received amplitude and 5:1 contrast ratio. Because the small size of this array limits the maximum image size, mechanical scanning was used to image a 2D polydimethylsiloxane fingerprint phantom (10 mm × 8 mm) at a 1.2 mm distance from the array.