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 article, for the first time, multilayer under-display ultrasonic fingerprint sensor structure using various active materials/structures were theoretically designed and compared. Based on the theoretical analysis results, a lead zirconate titanate (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 to meet the requirements of resolution and sensitivity for the under-display ultrasonic fingerprint imaging applications. The prototyped sensor was characterized, and the fingerprint recognition capability was tested using a custom-made fingerprint-mimicking phantom. The phantom images were acquired based on the pulse-echo imaging method. 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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用于屏下超声波指纹传感应用的宽带压电传感器


如今的智能手机不断追求窄边框和全屏显示。为了在全屏显示下实现更人性化的正面指纹识别，开发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独特的特征，并且对欺骗攻击具有较高的抵抗力。但迄今为止，尚未见有关于屏下超声波指纹传感的研究报道。本文首次对采用各种活性材料/结构的多层屏下超声波指纹传感器结构进行了理论设计和比较。基于理论分析结果，制作了一种基于锆钛酸铅（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%，满足屏下超声波指纹成像应用对分辨率和灵敏度的要求。对原型传感器进行了表征，并使用定制的模拟指纹模型测试了指纹识别能力。基于脉冲回波成像方法获取幻影图像。在1μJ的脉冲驱动信号下，操纵传感器通过机械扫描对2.0mm×1.0mm的仿指纹体模进行成像，获得500×500DPI的电子图像。模拟指纹幻像成像结果表明，基于 20 MHz 宽带 PZT 的多层结构在屏下超声波指纹传感器应用中具有巨大潜力。