MgB2超導薄膜研製與微橋製作

Abstract

摘要 為了研製MgB2的微橋，利用磁控濺鍍及在自行設計的不銹鋼盒內作高溫退火，在Al2O3的基座上生成MgB2薄膜。目前所製得的最佳MgB2薄膜其超導臨界溫度（Tc）約為24 K，ΔT約為2 K，表面平坦度為8 nm。該等薄膜看起來有約500 nm結晶顆粒，但不具六角形晶粒。從X光繞射分析譜與硼的K-edge近緣X光吸收光譜確認目前的樣品為MgB2薄膜。 利用紫外光微影蝕刻（UV-light lithography）製程製作線寬為3 μm與4 μm的MgB2微橋，由測量電阻率隨溫度變化曲線可見臨界溫度下降約3 K及ΔT變大至約5 K。 使用電子束微影蝕刻（E-Beam lithography）製程製作出線寬為0.5 μm、10 μm與20 μm的MgB2微橋，同樣的也使用賓州大學製作的MgB2薄膜（Tc為41 K，ΔT～ 0.2 K），作出10 μm與20 μm的MgB2微橋。兩相比較，發現我們製作的薄膜，其Tc的下降及ΔT的變大均比賓州大學製作的來的差，可見得結晶顆粒的大小及樣品內雜質的多寡對蝕刻後的樣品品質有影響。就10 μm微橋的臨界電流密度（Jc）來作比較，發現我們樣品的Jc比賓州大學樣品的Jc來的差。ABSTRACT In order to fabricate a nano-bridge from MgB2 film, a MgB2 film was produced through RF sputtering and ex-situ annealing process, the film of MgB2 was grown on the Al2O3（1 02） substrate. The best film we obtained had superconducting transition temperature of 24 K with transition width ΔT ≒ 2 K. The root mean square roughness of the surface was found to be 8 nm. The average size of the crystalline grain was about 500 nm, yet no hexagonal shape could be observed. The identification of MgB2 phase in the film was confirmed by XRD measurement and boron K-edge X-ray absorption near-edge spectrum. Comparison of our film with the one that fabricated by using hybrid physical-chemical vapor deposition (HPCVD) method (Tc = 41 K and ΔT ≒ 0.2 K) was made for the change of Tc , ΔT and Jc after e-beam lithography. All of these quantities were observed to be worse for our film than the HPCVD film, possibly due to the impurity and less homogeneity of the film we produced.