In-Display Proximity and Gesture Sensor with Piezoelectric Polymer Technology

The present work explores the feasibility of utilizing Qualcomm Technologies' existing in-display piezoelectric polymer technology for implementing proximity and gesture sensing applications in smartphones. A finite element analysis (FEA) model was developed, including a full transducer with thin film transistor (TFT), organic light-emitting diode (OLED) and cover glass (CG) stack with optional spacer and backerlayers. The model was validated by comparing the simulated and measured sound pressure level (SPL), in an air medium. Full optimization of the transducer stack was performed, identifying the coverage of the transducer relative to the CG width as the main parameter defining the output SPL performance. A novel segmented transducer approach was proposed, in which the location of transducer segments is designed based on the expected mode-shape of operation and allows for electrical reconfigurability for optimal performance at different frequencies. Increases in the output SPL of up to 17 dB at frequencies of operation close to 40 kHz were achieved as compared to the baseline transducer case. The Tx and Rx performance were also compared to industry standards, revealing comparable performance levels. An experimental demonstration, of an actual piezoelectric transducer adhered to a commercial CG, proved the approach feasible for pulse-echo detection and distance measurement when using a human hand as the reflector.