高溫超導雙磊晶穿隧元件之製作與特性研究

Abstract

本研究深入的探討了一種雙磊晶結構，利用釔鋇銅氧(YBCO)/二氧化鈰(CeO2)/氧化鎂(MgO)與釔鋇銅氧/氧化鎂之間的雙磊晶邊界，在高溫超導體釔鋇銅氧薄膜上製作人工晶界。實驗中使用離軸式射頻磁控濺鍍系統，以氧化鎂做為成長基板，成長二氧化鈰薄膜，經過光學微影與離子蝕刻的製程產生晶界後，再以脈衝雷射蒸鍍系統沉積釔鋇銅氧高溫超導薄膜，並嘗試利用鈦酸鍶(SrTiO3)做為緩衝層，藉此降低釔鋇銅氧薄膜與氧化鎂基板間的晶格不匹配。利用X-ray晶格繞射儀與原子力顯微鏡做薄膜的特性量測，並利用低溫電性量測系統與超導量子穿隧儀來進行其電性與磁性的探討。 我們測量了製作出來的釔鋇銅氧薄膜的臨界溫度與臨界電流密度。並量測了其元件特性且深入的研究此具有晶界之超導薄膜的性質，結果都顯示此種新型結構可能可以改進人造晶界，使元件具有很好的特性與IcRn值，也展現出此技術對於改進約瑟芬接面之製程的具有很大的可能性。

An bi-epitaxial technique for the fabrication of high temperature superconducting YBa2Cu3O7-δ (YBCO) artificial grain-boundary is researched. We have studied a bi-epitaxial structure, YBCO/CeO2/MgO and YBCO/MgO boundary. The CeO2 layers are grown on MgO substrates by using RF magnetron sputtering. Then, we define the grain boundary by optic lithography and ion-milling. YBCO films are grown by pulsed laser deposition (PLD). And try to add a SrTiO3 (STO) buffer layer to avoid the lattice mismatch between the pure YBCO film and the MgO substrate. The crystalline orientation and the surface morphology are characterized by X-ray diffraction and atomic force microscope (AFM). The electric and magnetic properties are also well studied by using low temperature measurement and superconducting quantum interference device (SQUID). The superconducting YBCO films reveal a high transition temperature Tc (R=0), and a critical current density in a zero magnetic field Jc which is large at 77 K. By measuring the characteristics of this device, and studying the properties of this superconducting thin film with grain-boundary, we find that this new structure can improve the artificial grain-boundary, and make device reveal very good properties with a high IcRn product, showing that this technique creates an opportunity to improve the fabrication of Josephson junction applications.