表面電漿現象應用於全彩式光偵測器及高靈敏度DNA生物感測器

Abstract

本論文主要分為兩個部分，第一部分探討表面電漿共振現象應用於全彩式光偵測器，第二部分探討表面電漿共振現象應用於高靈敏度DNA生物感測器。 現今全彩式光偵測器，每一個像素最上層為微透鏡，光線從微透鏡進入以染料製作的彩色濾波片進行分光，最後才進入元件底層光偵測器，其整體元件製程繁複。在此研究中，結合金屬材料和矽基材，作為蕭特基二極體光電元件，且在金屬層設計次波長之最密堆積的週期孔洞陣列，製作出能快速反應、零伏操作、且在有限元件面積可達到高像素的全彩式光偵測器。 當光進入偵測器後，因金屬之次波長週期性結構，引發表面電漿共振現象，致使在所設計之波段有異常穿透現象，且下方之蕭特基二極體，可直接將光能轉換成電訊號，以此單一元件即可取代既有的彩色濾波片和光偵測器，作為全彩式光偵測器。實際元件設計，利用三維有限時域差分法，找出最佳的參數，並製作元件並量測其外部量子效應，發現在可見光之不同波段，皆有良好分光效果，且以單一晶圓所製作出的紅藍綠三種光偵測器，可符合CIE 1931色彩空間所定義的RGB三原色，此為一製程簡易又有良好分光效果之全彩式光偵測器。 現今各類型DNA生物感測器中，受限於其理論機制和元件製作，在實際應用仍有許多問題，如：需長分析時間、易受環境干擾，元件製程複雜等，在本論文中，利用金屬孔洞週期陣列所產生的表面電漿共振現象於局部地區介電常數及電荷分佈極為敏感，而蕭特基二極體對接面處之環境亦特別敏感，製作出能快速感測、高靈敏度、低偏壓操作，可感測抗藥性金黃色葡萄球菌基因之片段DNA的DNA生物感測器。 實際元件設計，利用三維有限時域差分法，設計元件在太陽光頻譜照射下，即有良好的光電流產生，且此元件可在極低偏壓下操作。以此DNA生物感測器，量測單股和雙股抗藥性金黃色葡萄球菌基因片段之DNA分子，當 DNA分子靠近感測元件表面時，因表面電荷密度改變，在極短時間內，即會產生光電流增益，而由此增益值可作為DNA濃度之鑑別，此為靈敏且便利之DNA生物感測器。且實驗結果顯示，其最低量測值，可量測到10-16M之極低濃度DNA。另一方面，分別量測單股和雙股金黃色葡萄球菌抗藥性基因片段之DNA，對元件所產生之光電流增益，發現會所產生之光電流有所差異，因此元件可在極低濃度時，仍可對單股DNA和雙股DNA，有所鑑別。此DNA生物感測元件，在重複多次的實驗下，仍能維持其靈敏度，而不受干擾，其具有極佳的穩定度，可作靈敏、快速、而穩定的DNA生物感測器。 關鍵字：表面電漿共振現象、彩色濾波片、蕭特基二極體、全彩式光偵測器、DNA生物感測器、抗藥性金黃色葡萄球菌

In this thesis, surface plasmon resnonance (SPR) phenomenon was applied to develop color image sensors and highly sensitive DNA biosensors. In the commercial color image sensors, each pixel of the device usually consist three major parts：microlens, color filter and photodiode. The fabrication processes for the device are complicated. In this study, we combined the metal and silicon to form the Schottky diode and to develop color image sensors. We designed the sub-wavelength metallic hole arrays with different periods to filter the RGB colors in the visible regime. The color image sensors possessing metallic hole arrays and Schottky junction have many advantages of easy fabrication, rapid response, zero bias voltage requirement, and high pixels in a device area. When light incident into the devices, the SPR phenomenon will be induced by the structures of periodic metallic holes arrays. Due to the SPR phenomenon, there is extraordinary optical transmission in the spectral regimes of RGB colors. The Schottky junction (Metal/Si) of the devices can transform the energy of incident light into electrical signals. Therefore, we can replace the color filter and the photodiode by one device reported in this study. We used the three dimensional finite-difference time domain (3D-FDTD) method to find out the optimal parameters of the metallic hole array based color filters. After the simulation, we used the obtained parameters to fabricate the device and measure the external quantum efficiency of the devices. The results displayed the spectra of the RGB color image devices fabricated on the same wafer can fit to the color spectra defined by the CIE1931 color space. The second part of this thesis is DNA biosensors. Based on various detection principles of biosensors, there are many issues in determining the efficiency of sensors, such as long analysis time, environmental interactions, complicated device fabrication processes. In this study, we applied the SPR phenomenon which is sensitive to the local environment. The Schottky junction (metal/Si) are also sensitive to the area near junction to prepare SPR based biosensors with fast detection, highly sensitive, and low working voltage to detect the DNA sequence of Methicillin-resistant Staphylococcus aureus (MRSA). We also used 3D-FDTD methods to design the structure of the DNA sensors. The devices performed large photocurrent under low bias voltage and AM 1.5 light source. We used this biosensor to measure different DNA molecules. When the DNA molecules are closed to the surface of metallic hole arrays, DNA molecules can induce excess photo current in a short time, and the increased photo current can be used to detect ultralow concentration of DNA. The results in this study displayed that the limit of detection (LOD) of the DNA sensors can down to 10-16M. On the other hand, we used this device to measure single strand and double strands of DNA molecules, and found the DNA sensors possess the ability to distinct single strand and double strands DNA in very low concentrations.

Keywords : surface plasmon resonance , color filter, Schottky diode, color image sensor, DNA biosensor, Methicillin-resistant Staphylococcus aureus (MRSA)