臺灣博碩士論文加值系統

指紋辨識技術是一種生物辨識技術，常用於需要人員身份確認的使用情境。近年來行動裝置已大量地使用指紋辨識技術來加密上鎖，讓使用者可以確保個人隱私，並且快速地存取與控管個人資料。相較於光學式與電容式指紋辨識感測器，超聲波式指紋辨識感測器具有較高解析度與耐髒污的特性，因此本文旨在利用有限元素分析研究超聲波指紋辨識感測器之特性，藉由模擬取代實驗以減少開發時間與降低開發成本。首先利用有限元素分析軟體COMSOL Multiphysics計算手指按壓下辨識感測器之電壓變化，藉由週期性結構的設定分析最佳操作頻率，並與實驗結果比較，用以驗證模擬的可行性與正確性。再分析指紋辨識感測器之黏著層厚度，模擬當厚度變化時對辨識能力之影響。接著模擬全尺寸疊構探討指紋中心位置與寬度的辨識度，結果顯示感測器之可辨識範圍為中間處5 mm，指紋中心位置與寬度誤差低於50 µm。最後，探討聲阻抗匹配層對反射率之影響，推導匹配層之最佳聲阻抗值，並藉由簡化模擬分析確認模擬與公式推導有一致的結果。另外，也模擬具有聲阻抗匹配層之超聲波式指紋辨識感測器，結果顯示聲阻抗匹配層確實能提升超聲波指紋辨識感測器之辨識能力。

Fingerprint identification technology is one kind of biometric identification technology and has been widely used for personal identification in mobile devices to ensure personal privacy and quickly access personal data. Compared to optical and capacitive fingerprint sensors, ultrasonic fingerprint sensor has higher resolution and less sensitive to stain. Therefore, this thesis aims to study the characteristics of ultrasonic fingerprint sensors using finite element analysis (FEA) for reducing experimental time and development cost.Firstly, the FEA software, COMSOL Multiphysics, is used to calculate the voltage difference of the sensor between finger valley and ridge. The optimal operating frequency is analyzed by the periodic structure setting, and the feasibility and correctness of the simulation tool is verified by comparing with the experimental results. The influence of the adhesive film thickness on the recognition performance is also studied. Then, the full-scale sensor is simulated for exploring the identification correctness on the center position and width of fingerprints. The results show that the identifiable range of the sensor is 5 mm in the middle region, and the error of the fingerprint center position and width is less than 50 µm. Finally, the acoustic impedance matching layer is conducted to improve the recognition performance of an ultrasonic fingerprint sensor. The optimal acoustic impedance of the matching layer is calculated based on the one dimension wave propagation theory and simplified FEA model. In addition, ultrasonic fingerprint sensors with several kinds of acoustic impedance matching layers are also analyzed. The results show that the acoustic impedance matching layer can indeed improve the recognition performance of an ultrasonic fingerprint sensor.

誌謝 I
摘要 II
ABSTRACT III
目錄 V
圖目錄 VII
表目錄 X
符號表 XI
第一章 前言 1
1.1研究動機 1
1.2文獻回顧 4
1.3本文架構 10
第二章 超聲波式指紋辨識感測器之介紹 11
2.1壓電效應 11
2.2聚偏二氟乙烯-三氟乙烯材料之介紹 12
2.3一維波傳理論之反射與穿射 14
2.4超聲波式指紋辨識器之感測機制 15
第三章 超聲波式指紋辨識感測器之模擬 19
3.1有限元素分析之模擬設定 19
3.2數據運算方式 27
3.3週期性疊構之模擬結果 30
3.3.1最佳操作頻率之分析 30
3.3.2黏著層厚度之影響 34
3.4全尺寸疊構之模擬結果 37
3.4.1指紋寬度250 µm 37
3.4.2指紋寬度355 µm 44
第四章 聲阻抗匹配層之模擬 47
4.1聲阻抗匹配層對反射率之影響 47
4.2具有聲阻抗匹配層指紋辨識感測器之週期性疊構模擬結果 50
4.3具有聲阻抗匹配層指紋辨識感測器之全尺寸疊構模擬結果 54
第五章 結論與未來展望 58
5.1結論 58
5.2未來展望 59
參考文獻 60

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