The Microstructure and Electrical Properties of YBCO Microbridge with Variable Thickness Fabricated by Focused Ion Beam

本論文中，我們將討論不同連結區域(link region)厚度所製作出高溫超導釔鋇銅氧( YB2C3O7-δ-YBCO)微橋其微結構與電性分析。利用聚焦離子束(Focus Ion Beam，FIB)，製作奈米尺度下不同厚度的YBCO微橋，當微橋接面厚度控制在奈米尺度下，將呈現弱連結效應。 利用聚焦離子束在厚度約150 nm、寬度5~8μm的微橋上進行局部性的離子蝕刻，將微橋接面寬度控制在1μm、厚度介於40-90 nm間，並利用場發射穿透式電子顯微鏡(FE-TEM)檢驗不同厚度弱連結處的微結構。發現Ga+離子束會佈植破壞成非晶態結構(amorphous structure) 橫向、縱向約20-30 nm，當厚度低於40 nm時底部幾乎沒有完整的YBCO晶格結構；隨著微橋厚度變少，超導特性會隨著厚度變淺而變差，臨界溫度(Tc)與臨界電流(Ic)會跟著變小。在退火過程中氧含量成功的恢復，微橋的超導特性會變好。In this paper, we controlled the thickness about the link region produced by the microbridges of high-temperature superconducting YBCO (YB2C3O7-δ). In this thesis, Focus Ion Beam (FIB) was used to control different thickness of YBCO microbridges. And when the thickness of the microbridge was controlled under the nanometer scale, it showed weak link behavior. YBCO microbridges were fabricated with widths of 5-8 μm and thickness 150 nm using standard techniques of photolithography and Ar+ ion milling. To control the thickness of the micro-bridge was maintained between 40 and 90 nm. Using field-emission transmission electron microscope (FE-TEM) to observe the structure of the Variable Thickness Bridge (VTB), Ga+ damages horizontally and vertically into the amorphous structure about 20-30 nm. When the thickness was below 40 nm, there was little complete part of YBCO structure in the bottom. As the thickness of the micro-bridge decreased, critical temperature (Tc) and critical current (Ic) became smaller. The successful recovery of oxygen content during the annealing process, the superconductivity of the microbridge became better.致謝.........................................i 摘要.......................................ii Abstract........................................iii 目錄.............................................iv 表目錄.......................................... vi 圖目錄........................................ vii 第一章 導論...................................1 1-1引言..........................................1 1-2 約瑟芬接面與超導量子干涉元件之應用..................3 1-3 文獻..................................................4 第二章 基本理論說明................................7 2-1 約瑟芬效應................................7 2-2 電流-電壓特徵曲線..............................12 第三章 樣品製作..........................15 3-1 濺鍍高溫超導體YB2C3O7-δ薄膜........................15 3-2 鍍金.............................................20 3-3 微影製程的介紹..........................................22 3-4 製作微米尺度下的超導微橋................................23 3-5 製作奈米尺度下的弱聯結(Weak Link)： 聚焦離子束系統-局部性蝕刻.............................28 第四章 實驗結果與分析.............................33 4-1 SRIM模擬...............................33 4-2 探討奈米尺度下YBCO的VTB結構..................38 4-3 改變微橋的厚度：電阻與溫度分析........................51 4-4 改變微橋的厚度：電壓與電流特徵曲線..................53 4-5 串聯70-80 nm厚微橋的特性分析.............................56 4-6 聚焦蝕刻50-60 nm厚微橋與經退火程序的特性分析.......62 第五章 結論..............................................67 參考文獻.......................................6