高溫超導約瑟芬元件的製作與特性量測

Fabrication and Characteristics of YBCO Josephson Devices

張砥中(Ti-Chung Chang)

指導教授 ： 賴再興

中原大學/理學院/應用物理研究所/碩士(2003年)

https://doi.org/10.6840/cycu200300441

摘要

中文摘要
本論文的主要研究工作包括：（一）高溫超導約瑟芬接面及其元件的製作、（二）直流式超導量子干涉元件與陣列式超導量子干涉元件的製作以及特性量測之研究、以及（三）不均勻的約瑟芬接面在磁場作用下的物理特性探討。
我們利用階梯式的鈦酸鍶基板，成功的製作出約瑟芬接面元件；經由實驗結果得知：基板的蝕刻技術、高溫超導薄膜的品質，皆對於所製作出約瑟芬接面元件的品質有很大的影響。
對於約瑟芬接面的物理特性探討，在實驗上我們利用所製作出狹橋寬4μm的直流式超導量子干涉元件與陣列式超導量子干涉元件，做電流與電壓（V-I）關係的量測，以及電壓與外加磁場（V-Φ）關係的量測。經由這兩項量測我們可以清楚看出下列幾個現象：
（1） 經由所量測出之V-I曲線，可以看出我們利用光學製版乾式蝕刻技術所製作出之約瑟芬元件能符合電阻分路模型（Resistively Shunted Junction，RSJ）的結果。
（2） 藉由在不同溫度下所量測到的V-I曲線，可以清楚看出臨界電流（Ic）會隨著溫度（T）的增加而減少。
（3） 經由所量測出之V-Φ曲線，可以看出我們所通的偏壓電流越大，其電壓調制幅度越大，當電壓調制幅度達到極大值之後，電壓調制幅度就會隨著所通的偏壓電流增加而減少與理論相符。
（4） 理論上陣列式超導量子干涉元件的最大電壓調制幅度會隨著所串聯之超導量子干涉元件的個數成疊加的關係，但我們所製作出的陣列式超導量子干涉元件，並沒有明顯的疊加關係，且隨著個數的增加其週期性趨於雜亂，其原因為其中的約瑟芬接面不均勻性所造成的結果。
在理論部分我們模擬了各種不均勻約瑟芬接面在外加磁場作用下的臨界電流（Ic）對外加磁場（B）的關係圖並且加以比較。

關鍵字

超導 ； 約瑟芬元件

並列摘要

Abstract
The main work of this thesis consists of (1) the fabrication of high-Tc-superconducting Josephson junctions ; (2) the fabrication and characteristics of dc SQUID and SQUID array ; (3) physical properties of non-uniform Josephson junctions in applied magnetic field .
Using step substrates of STO , we have successfully fabricated Josephson junctions and devices . Our experimental results show that , the etching process of the substrate and the quality of the YBCO superconducting films are factors that strongly affect the quality of the Josephson devices .
For the studies of the characteristics of Josephson junctions , we have fabricated dc SQUIDs and SQUID array with line width of 4μm . From the measurements of voltage-current (V-I) relation and voltage-magneticc (V-Φ) relation of the devies , we found
(1) the V-I curves of our Josephson junctions fabricated by dry-etching photolithography agree well with the RSJ model .
(2) the temperature-varied V-I curves show that the critical current (Ic) decreases as the temperature increases .
(3) the measured V-Φ curves show that , the larger the applied bias , the larger the amplitude of the voltage medulation , which agrees with the theoretical prediction .
(4) for the SQUID array , in the theory , the amplitude of the voltage modulation is proportional to the number of SQUID in series , but we did not observe this kind of proportionality in our samples , and the periodicity is kind of mixed up as the number of SQUID increased . our Josephson junctions .

Finally , we simulated the relation between the critical current (Ic) and applied magnetic field (B) for a non-uniform Josephson junction and made comparison with our experimental results .

並列關鍵字

Josephson ； superconductor

參考文獻

[1] B. D. Josephson, “Possible New Effects in Superconductive Tunnelling”, Phys. Lett., 1, 251（1962）.

[2] B. D. Josephson,“Coupled Superconductors”, Rev. Mod. Phys. 36, 216（1964）.

[3] B. D. Josephson, “Supercurrents Through Barriers”, Adv. Phys. 14, 419（1965）.

[4] J. G. Bednorz, and K. A. Müller, “Possible High Tc Superconductivity in the Ba-La-Cu-O System”, Z. Phys. B64, 189（1986）.

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