釔鋇銅氧 / 金 / 鉛的約瑟芬接面 製作與穿隧特性量測

Fabrication and Tunneling Characteristics of YBCO / Au / Pb Josephson Junction

吳欣怡(Shin-Yi Wu)

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/cycu200300487

摘要

本論文的主要研究工作包括：【一】利用射頻磁控濺鍍儀濺鍍高溫超導釔鋇銅氧(YBa2Cu3O7-δ ; YBCO)薄膜。【二】YBCO / Au / Pb約瑟芬接面的製作與特性量測，相對電極鉛( Pb )是以熱蒸鍍法製作。【三】不均勻的約瑟芬接面在磁場作用下的物理特性探討。
首先，我們利用氧化鎂 ( MgO ) 基板，改變鍍膜參數製作YBCO薄膜，比較其臨界溫度、薄膜表面粗糙度..等。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。
對於約瑟芬接面的物理特性探討，在實驗上，我們利用所製作出來的YBCO/Au/Pb約瑟芬接面，做電壓與電流（V-I）關係的量測、臨界電流與外加磁場（IC-B）關係的量測、臨界電流與溫度（IC-T）關係的量測和電導與電壓（G-V）關係的量測。經由這四項量測我們可以清楚看出下列幾個現象：
1. 經由V-I特性曲線，可以看出我們利用光學製版和濕式蝕刻技術所製作出之約瑟芬元件符合電阻分路模型（Resistively Shunted Junction，RSJ）的預測。
2. 藉由在不同磁場下所量測到的V-I曲線，可以清楚看出臨界電流(IC)與外加磁場(B)的關係，在B = 0時，具有最大IC值，呈現傳統Fraunhofer 繞射模型。
3. 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）隨著溫度（T）的增加而減少。
4. 經由G – V特性曲線，可以看出YBCO傾向s – wave 的超導配對對稱性，沒有d-wave的特性，由其他文獻得知，以此種製作方法所得的約瑟芬接面無法呈現出YBCO所有pairing symmetry的特性。

關鍵字

薄膜平面型穿隧接面 ； 超導配對狀態的對稱性 ； c-axis約瑟芬穿隧

並列摘要

The main work of this thesis consists of【1】epitaxial growth of YBCO superconducting thin films by RF sputtering .【2】 fabrication and characteristics of YBCO / Au / Pb Josephson junction with counter electrode Pb by evaporation .【3】physical properties of non-uniform Josephson junctions in applied magnetic field .
For the first part , we used MgO as our substrate . By the comparison of the critical temperature ( TC ) and surface roughness , we obtained the optimal parameters of our YBCO films . 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 .
Secondly , for the study of the characteristics of Josephson junction , we fabricated YBCO / Au / Pb sandwich - type Josephson junction and conducted the measurements of voltage - current ( V–I ) relation ; critical current–magnetic field ( IC - B ) relation ; the critical current - temperature ( IC -T ) relation and conductance–voltage ( G-V ) relation . Our observations showed that
(1) the V–I curves of our Josephson junctions fabricated by wet-etching photolithography agree well with the prediction of RSJ model .
(2) the magnetic field - varied V–I curves showed that the critical current - magnetic field relation exhibited a conventional Fraunhofer diffraction pattern with a global maximun of IC at B = 0 .
(3) the temperature - varied V–I curves show that the critical current decreases as the temperature increases .
(4) the G–V curve suggested that YBCO is superconductor with s–wave pairing symmetry , with no indication of d–wave pairing . Existing reports reveal that Josephson junctions fabricated with the method we used could not exhibit all the pairing symmetry of YBCO。

並列關鍵字

c-axis Josephson tunneling ； thin-film planar tunnel junctions. ； superconducting pairing state symmetry

參考文獻

[1] D. A. Wollman et al., Phys. Rev. Lett. 71, 2134 (1993).

[2] D. A. Brawner and H. R. Ott, Phys. Rev. B 50, 6530 (1994).

[3] C. C. Tsuei et al., Phys. Rev. Lett. 73, 593 (1994).

[4] D. A. Wollman et al., Phys. Rev. Lett. 74, 797 (1995).

[5] J. R. Kirtley et al., Nature（London）373, 225 (1995).