基於金屬-介電質-金屬架構之蕭特基勢壘表面電漿共振生物感測器：設計、製程與驗證

Abstract

表面電漿子共振是一種發生在金屬-介電質介面的物理現象，在滿足激發條件時，可見光至紅外波段的入射光與金屬內部電子耦合，改沿著金屬-介電質介面傳播，推動電子集體振盪，形成沿介面傳播的電荷密度波，並且此效應對於介面及附近幾百奈米空間內的微小物理參數變化極為敏感，基於這種特性，表面電漿子共振現象成為近年來感測器研究的熱門領域。傳統表面電漿子共振感測器受限於光學激發架構，在維持感測器性能的前提下，其微小化面臨技術瓶頸，而龐大的體積也大大限制了表面電漿子共振生物感測器在室內和室外臨場檢測、田野檢測、床邊檢測和居家照護方面的應用。 本研究創新性地提出在金屬-介電質表面電漿子共振激發架構上形成新的金屬-介電質-金屬蕭特基接觸，利用表面電漿子共振激發熱載流子生成和蕭特基勢壘光電流篩選機制，從理論上解釋表面電漿子共振致光電流生成的原理，以及討論以光電流量測取代傳統光學量測的可行性。基於理論研究的結論，本研究設計了一款金屬-介電質-金屬架構表面電漿子共振生物感測器。在材料選擇上，本研究使用電洞運輸材料氧化銦錫提升光電流生成效率，討論多種氧化物型半導體材料的特性，並藉以確定由Au-TiO2形成蕭特基接觸、TiO2-Ti形成歐姆接觸。在圖形設計上，本研究先後介紹了元件圖形設計及薄膜厚度設計的原因，借助FDTD模擬對設定的感測器架構進行表面電漿激發模擬，從而驗證參數。本研究利用微影製程和薄膜製程完成感測器製造，並設計了一系列實驗，電壓-電流特性量測實驗、表面電漿激發量測實驗，以及物質辨別實驗等，對感測器的功能進行驗證。依據目前的實驗結果，感測器晶片在物質辨別與濃度辨別方面的表現沒有達到理論預期，針對此實驗結果，本論文也從原理、設計、製程及實驗角度檢討了可能存在的問題，並提出未來改善的方向。

We proposed a Metal-Dielectric-Metal structure based Surface Plasmon Resonance Biosensor in this thesis. Surface Plasmon Resonance (SPR) is a physical phenomenon which can be described as a result of interactions occurring at metal-dielectric interface between infrared or visible frequency electromagnetic waves and surface charges in the metal. The most useful merit of SPR, being extremely sensitive to the complex refractive index changing near the interface within a distance range from ~10nm to ~100nm, make SPR become an intensively studied and developed biomedical and biochemical technology in recent decades. Conventional SPR sensors or commercialized instruments are based on detection of reflected light with a relatively complicated optical and mechanical system, which makes those machine very large and rigorously restricted to operate inside laboratory. Facing the growing needs of field test, bedside test or other spot test outside the laboratory, a miniaturized SPR sensor based on electro-optical conversion theory are designed, fabricated, and tested in this article. The mentioned energy conversion process and collection is realized by adding another metal layer to the original Metal-Dielectric SPR bilayer excitation structure, which is called the Metal-Dielectric-Metal structure. Theoretical basis including plasmonic hot carriers generation, current flow through a Schottky barrier under a local bias caused by SPR, is explained and discussed. On the basis of theoretical discussion, a device which contains five layers with different patterns is designed. Specifically, a Schottky barrier is formed at Au-TiO2 boundary, while an Ohmic contact is formed at TiO2-Ti boundary, and ITO are used as HTM to assist the carrier pairs separation. Simulation tools, such as Lumerical FDTD and MATLAB, are used in this research to calculate the optimized thickness. The proposed sensor is fabricated via microlithography and thin-film processing technologies, and tested through a series of experiments. Results of series of experiments indicate that the fabricated sensor does not function as expected. Likely reasons are discussed and summarized in the conclusion, and so are the solutions.