Ultrasonic Fingerprint Sensor Using a Piezoelectronic Micromachined Ultrasonic Transducer Array Integrated with CMOS Electronics. Applied Physics Letters, 2015 DOI: 10.1063/1.4922915 ...

Capacitive sensors, on the other hand, are small and compact, and less prone to spoofing. Capacitive sensors also, however, are susceptible to poor readings depending on your fingers' condition.