Qualcomm's new in-display ultrasonic fingerprint reader can read two fingers at once - The Verge
In-display Fingerprint Sensors: Types and Working
Qualcomm's second-gen ultrasonic fingerprint reader is bigger and faster than the original - The Verge
Ultrasonic fingerprint sensor using a piezoelectric micromachined ultrasonic transducer array integrated with complementary metal oxide semiconductor electronics: Applied Physics Letters: Vol 106, No 26