不同厚度釔鋇銅氧高溫超導薄膜的微波表面損耗

Abstract

本文主要探討如何利用微波量測釔鋇銅氧高溫超導微波微帶線之品質 因數，而瞭解其表面電阻損耗隨溫度變化的情形。實驗方面，包括雷射蒸 鍍薄膜的技術、製作微帶線元件的技術、元件的補氧技術和微波量測等。 理論方面，以二流體理論說明微波損耗隨溫度變化的關係。最重要的，由 實驗分析，吾人得知在不同膜厚溫度高於0.85Tc時，膜厚愈薄膜薄元件的 表面電阻為較大，換言之，其有效穿透深度λeff值隨薄膜愈小而愈大， 這個推論與我們計算之λeff(0)的趨勢是一致的。這對將來分析超導體的 穿透深度之研究提供一個重要的有效參數。在溫度小於0.85Tc時，表面電 阻趨近常數，與膜厚無關。除此之外，我們也利用此量測技術得知製作最 佳品質薄膜的雷射蒸鍍條件。 The YBCO high-T superconducting microstrip lines have beenfabricated and its quality factor (Q) is measured by Microwave Network Analyzer. It allows us to find out how their surface resistance changes with temperatures. There are two aspects in our work. On the one hand, detailed descriptions of the pulse laser deposition (PLD) technology, fabrication of microstrip lines, oxygen supplement system, microwave measurements… etc have been presented, respectively. On the other hand, the mechanism of microwave surface losses change with temperatures in accord with the assumption of two-fluid model has been demonstrated theoretically. In particular, according to our data, we conclude that the thinner the films, the larger the surface resistance when the temperature is higher than 0.85Tc. It also gives a justification of the thickness dependence of the effective penetration depth λeff, which increaseswith decreasing thickness of thin films. The result is consistent with the other's calculation and prediction of λ eff(0). When the temperature is lower than 0.85T , the surface resistance will approach to a constant and is independent of the thickness of thin films. As a result, it provides animportant clue to uncover the nature of the penetration depth in high Tc superconductors directly.