Ultrathin Multilayer P(VDF-TrFE) Film-Based Piezoelectric Resonator for High-Quality Under-Display Fingerprint Recognition

Ultrasonic fingerprint recognition has been proved an effective biometric authentication technology adopted commonly in mobile devices nowadays. A 12 MHz P(VDF-TrFE) film-based piezoelectric ultrasonic transducer with four-layers resonant structure is presented for high-quality under-display ultrasonic fingerprint imaging. The thickness of the transducer stack is no more than 120 μm, which facilitates the installation of under-display applications. The transmitting sound pressure at the distance of 6mm is measured to be ~ 6000 Pa/V at 12 MHz by a hydrophone system, which is consistent with the analytical calculation result. Pulse-echo response for the ultrasonic transducers sticking on a phone display is demonstrated, and the 100 mV maximum received amplitude and 20.5 mV/V receiving sensitivity are achieved. The fingerprint imaging capability of the presented transducer is validated by scanning a fabricated fingerprint-mimicking phantom, achieving a lateral resolution of 100 μm. Electronic images of the fingerprint with a SNR of 15.6 and normalized voltage difference between finger ridges and valleys about 2.1 mV/V are demonstrated, indicating promising qualities in under-display fingerprint recognition.