P(VDF-TrFE) Thin-Film-Based Transducer for Under-Display Ultrasonic Fingerprint Sensing Applications

The use of fingerprint for biometric identification is one of the most prevalent authentication methods applied today in smartphones. In the course of pursuing narrow-bezel and full-screen display, the under-display fingerprint sensor is considered to be a user-friendly and practical solution for newer models of smartphone. While under-display optical fingerprint sensor has been commercially available in various smartphones, it demonstrates limitations such as sensitivity to humidity and contaminations including oil and water as well as easy to spoof. Ultrasonic fingerprint sensing has been proved to be able to overcome these limitations. In this study, P(VDF-TrFE) piezoelectric polymer-based transducer was reported, for the first time, for under-display ultrasonic fingerprint sensing applications. In specific, a 40 MHz ultrasonic transducer using a layer of 10~μm thick P(VDF-TrFE) thin-film was designed, fabricated, and characterized. The under-display ultrasonic fingerprint sensing capability of the prototyped transducer was experimentally validated using phantoms of real fingerprint. Electronic images of fingerprint with resolution of 500 ×DPI were obtained through under-display ultrasonic fingerprint sensing tests. The lateral resolution of the transducer was calculated to be ~70μm . The results of this study illustrate promising advances in under-display ultrasonic fingerprint sensing applications.