指紋辨識光路設計─孔洞遮罩及微透鏡之分析探討

Abstract

近年來，由於觸控裝置的發展日漸成熟。為了迎合市場的需求，科技發展的方向也逐漸轉往不同的便利性功能，例如本論文所探討之與生物辨識相關的技術概念「屏下指紋辨識器FoD(Frigenprint on Display)」。此技術將手機裝置與一濾訊裝置做結合，其中濾訊裝置包含了微透鏡陣列(Micro-lens array)、黑色矩陣(Black Matrix)以及最下方之光感測器(Photo Detector)來達到屏幕上之按壓指紋的影像辨識。而本論文主要探討在此裝置的設計下，其光路之濾訊設計的遮擋層及微透鏡設計對指紋辨識的影響程度為何。 本論文使用Zemax光學追跡軟體模擬結合了指紋辨識光路之手機以及手指指紋按壓在屏幕上之接觸情形。軟體以光學上較著名的菲涅耳方程式(Fresnel equation)及吸收穿透率；各層介面之間的介面反射、透射作為最基本的運算方式，並且提供材料自定義之設計方式，供使用者模擬各種實際存在的材料。並透過軟體內Ray trace功能模擬指紋訊號到達感測器的情形作為最後的成效數據。 除了以指紋辨識裝置原型作為參考外，本論文也嘗試在黑色矩陣上使用例如摻黑的光阻材料SU-8及金屬鉻(Cr)等不同材料作為孔徑設計，經由分析後了解指紋辨識需要遮罩提昇MTF以及微透鏡提升RV。孔洞遮擋層的厚度越薄；並且其穿透率越低越好，最後在實驗中推測鉻金屬(Cr)是相當符合以上條件的材料。

In recent years, touch device has developed to a mature stage. Cater to the market’s needs; people turned the developing direction of technology to convenience functions. Like the Biometric technology discussed in this thesis and called “FoD(Fingerprint on display)”. This technology combines the smartphone and an optical filter design, which contain the micro-lens array, black matrix, and photodetector to recognize the fingerprint on the touchscreen. This thesis mainly discusses how the aperture and microlens influent the fingerprint image in this design. This thesis used the optical ray tracing software “ZEMAX” to simulate a smartphone with FoD and a touching finger. The software uses the calculation methods, such as Fresnel’s equation, optical absorbance, transmittance, and reflectance properties, to compute all surfaces’ transmitting situation. Also, some functions allow users to define their material to simulate any material that precisely exists in nature. And in the final, we use the “ray tracing” in the Zemax to simulate the last fingerprint image data in the sensor. Besides, we use the smartphone prototype with FoD and attempt to replace the black matrix with different material as black-doping photoresist “SU-8” or metal “Cr”. After we analyzed, we concluded that the fingerprint recognition aperture improves MTF value, and microlens improves RV value. The thickness of the apertures is as thin as better, and its transmittance is most important. And Cr is a better material choice that fits the conditions for aperture in this paper.