Smartphones today have attracted a continuous trend of pursuing narrow-bezel and full-screen displays. To allow for a more user-friendly front side fingerprint recognition in full-screen displays, it is crucial to develop an under-display type of fingerprint sensor. Among fingerprint sensing techniques, ultrasonic fingerprint sensing has been proved to be able to provide more distinctive features and give a high resistance to spoof attacks. However, until now no study about under-display ultrasonic fingerprint sensing has been reported. In this paper, for the first time, multilayer under-display ultrasonic fingerprint sensor structure using various active materials/structures were theoretically designed. Based on the theoretical analysis results, a PZT-5A based multilayer under-display ultrasonic fingerprint sensor with a resonant frequency of 20 MHz, and a -6-dB fractional bandwidth of more than 70% was fabricated. The prototyped sensor was characterized, and the fingerprint recognition capability was tested using a custom-made fingerprint-mimicking phantom. With the 1 μJ impulse driving signal, the sensor was manipulated to image a 2.0 mm × 1.0 mm section of fingerprint-mimicking phantom by mechanical scanning, obtaining an electronic image with 500 × 500 DPI. The fingerprint-mimicking phantom imaging results suggest that the 20 MHz broadband PZT based multilayer structure holds great potential for under-display ultrasonic fingerprint sensor applications.

中文翻译：

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用于显示屏下超声波指纹传感应用的宽带压电传感器

今天的智能手机已经吸引了追求窄边框和全屏显示的持续趋势。为了在全屏显示器中实现更加用户友好的正面指纹识别，开发一种屏下式指纹传感器至关重要。在指纹传感技术中，超声波指纹传感已被证明能够提供更显着的特征，并且对欺骗攻击具有很高的抵抗力。然而，到目前为止，还没有关于屏下超声波指纹传感的研究报道。本文首次从理论上设计了使用各种活性材料/结构的多层屏下超声波指纹传感器结构。根据理论分析结果，制造了基于 PZT-5A 的多层屏下超声波指纹传感器，其谐振频率为 20 MHz，-6-dB 分数带宽超过 70%。对原型传感器进行了表征，并使用定制的指纹模拟体模测试了指纹识别能力。在1 μJ脉冲驱动信号下，传感器通过机械扫描对2.0 mm × 1.0 mm的指纹模拟体模进行成像，获得500 × 500 DPI的电子图像。指纹模拟体模成像结果表明，基于 20 MHz 宽带 PZT 的多层结构在显示屏下超声波指纹传感器应用中具有巨大潜力。并使用定制的指纹模拟体模测试指纹识别能力。在1 μJ脉冲驱动信号下，传感器通过机械扫描对2.0 mm × 1.0 mm的指纹模拟体模进行成像，获得500 × 500 DPI的电子图像。指纹模拟体模成像结果表明，基于 20 MHz 宽带 PZT 的多层结构在显示屏下超声波指纹传感器应用中具有巨大潜力。并使用定制的指纹模拟体模测试指纹识别能力。在1 μJ脉冲驱动信号下，传感器通过机械扫描对2.0 mm × 1.0 mm的指纹模拟体模进行成像，获得500 × 500 DPI的电子图像。指纹模拟体模成像结果表明，基于 20 MHz 宽带 PZT 的多层结构在显示屏下超声波指纹传感器应用中具有巨大潜力。