Development of miniature wide-angle lens for in-display fingerprint recognition

Since the beginning of this year, the full screen mobile phone has been more and more popular. Because the traditional capacitive fingerprint sensor cannot work under the display, it should be placed on the side or back of the phone. However, it is unfavorable to the consumer experience. Therefore, the demand for in-display fingerprint recognition technology has arisen. The in-display fingerprint identification technology can be divided into optical and ultrasonic fingerprint identification. Because the ultrasonic fingerprint identification is limited by low yield rate and high cost at present, the optical fingerprint identification is more popular in market. The optical fingerprint identification is advantageous for the identification not affected by dry or greasy fingers, higher yield and lower cost. In this study, the miniature wide angle lens under the display is developed for the OLED panel. For optical fingerprint identification, the illumination is inevitable. In comparison with the LCD panel, the OLED panel needs not the backlighting because each pixel has its own light. The optical sensor is based on the principle of the frustrated total internal reflection (FTIR). The ridge of the finger destroys the total internal reflection (TIR), and then the dark pattern appears. On the contrary, the valley of the finger satisfies the TIR condition, and then the bright pattern generates. Because the camera is implemented in the narrow space of the mobile phone, the ultra-wide field of view and extremely short total track length are neceßary. In this study, the optical design can succeßfully meet the requirement for fingerprint recognition.