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Since the discovery of its superconductivity, magnesium diboride (MgB2) has been identified as a promising superconductor to be used in Josephson junction devices due to its high transition temperature, large energy gap, long coherence length, and expected easier fabrication of Josephson junctions as compared with high temperature superconductors. The high-quality MgB2 films and excellent tunnel barrier materials are the core elements for a Josephson junction. Here in this paper, all MgB2 thin film tunnel junctions with B tunnel barriers are fabricated in situ on sapphire substrates and their tunneling characteristics re investigated. The experimental results indicate that the MgB2/B/MgB2 junctions exhibit good tunneling characteristics. The deposition of the MgB2/B/MgB2 trilayer is carried out in a completely in situ process. The bottom and top MgB2 layers are grown to a thickness of 100 nm by hybrid physical-chemical vapor deposition (HPCVD) technique at about 973 K and in 102 Pa Ar atmosphere on a single crystal Al2O3 (0001) substrate. The 35-nm-thick amorphous B insulator layer is deposited using chemical vapor deposition method at 723 K and in 103 Pa pure Ar. In the process of the top MgB2 layer deposition, the amorphous B reacts with Mg in Mg vapor, leading to its thickness decreasing to 10 nm. Square-shaped junctions each with a size of 4 mm5 mm are determined by the metallic mask method. The resistivity temperature (R-T) curves and the DC current-voltage (I-V) curves of the MgB2/B/MgB2 junctions at different temperatures are measured by the four-point probe method in the physical property measurement system (PPMS). The experimental results show excellent superconducting properties of the top and bottom superconductor with high Tc (above 39.5 K), appreciable Jc values (107-108 A/cm2). In the I-V characteristics of junction at temperatures ranging from 4.2 K to 39.2 K, the junctions exhibit clear Josephson tunneling characteristics with jc～0.52 A/cm2 at 4.2 K, which remains nonzero up to 31.3 K. The hysteresis is pronounced at 4.2 K, becoming smaller as temperature increases, and eventually disappearing at around 19.2 K. By using the differential I-V curves, only gap is observed in differential conductance vs. voltage characteristics (dI/dV-V) curves, because MgB2 layer grown using HPCVD technique is always c-axis oriented and more than 99% contribution to the conduction is from band charge carriers.
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Keywords:
- MgB2/B/MgB2 Josephson junctions /
- metallic mask method /
- hybrid physics-chemistry vapor deposition
[1] Likharev K K, Semenov V K 1991 IEEE Trans. Appl. Supercond. 1 3
[2] Kameda Y, Yorozu S, Hashimoto Y, Terai H, Fujimaki A, Yoshikawa N 2005 IEEE Trans. Appl. Supercond. 15 423
[3] Mukanov O A, Gupta D, Kadin A M, Semenov V K 2004 Proc. IEEE 92 1564
[4] Mukhanov O A 2011 IEEE Trans. Appl. Supercond. 21 760
[5] Brake H J M T, Wiegerinck G F M 2002 Cryogenics 42 705
[6] Chen W, Rylyakov A V, Patel V, Lukens J E 1999 IEEE Trans. Appl. Supercond. 9 3212
[7] Choi H J, Roundy D, Sun H, Louie S G 2002 Nature 418 758
[8] Chen K, Zhuang C G, Li Q, Weng X, Redwing J M, Xi X X 2011 IEEE Trans. Appl. Supercond. 21 115
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[10] Singh R K, Gandikota R, Kim J, Newman N, Rowell J M 2006 Appl. Phys. Lett. 89 042512
[11] Kim T H, Moodera J S 2004 Appl. Phys. Lett. 85 434
[12] Cybart S A, Chen K, Cui Y, Li Q, Xi X X, Dynes R C 2006 Appl. Phys. Lett. 88 012509
[13] Ke Y Q, Zhou D F, Liu J, Zen M, Zhu H M, Zhang Y B 2009 Chin. J. Low Temp. Phys. 31 166 (in Chinese) [柯一青, 周迪帆, 刘珏, 曾敏, 朱红妹, 张义邴 2009 低温 31 166]
[14] Xu Z 2014 M. S. Thesis (Lanzhou: University of Lan Zhou) (in Chinese) [许壮 2014 硕士学位论文 (兰州: 兰州大学)]
[15] Zhou Z Y, Wang S, Yang F S, Yang J, Fu X H 2013 Chin. J. Low Temp. Phys. 35 425 (in Chinese) [周章渝, 王松, 杨发顺, 杨健, 傅兴华 2013 低温 35 425]
[16] Zhou Z Y, Wang S, Yang F S, Yang J, Fu X H 2013 J. Funct. Mater. 44 893 (in Chinese) [周章渝, 王松, 杨发顺, 杨健, 傅兴华 2013 功能材料 44 893]
[17] Bouquet F, Fisher R A, Phillips N E, Hinks D G, Jorgensen J D 2001 Phys. Rev. Lett. 87 180
[18] Kortus J, Mazin I I, Belashchenko K D, Antropov V P, Boyer L L 2001 Phys. Rev. Lett. 86 4656
[19] Zeng X H, Pogrebnyakov A V, Zhu M H, Jones J E, Xi X X 2003 Appl. Phys. Lett. 82 2097
[20] Rowell J M, Xu S Y, Zeng X H, Pogrebnyakov A V, Li Q 2003 Appl. Phys. Lett. 83 102
[21] Gross R, Chaudhari P, Dimos D, Gupta A, Koren G 1990 Phys. Rev. Lett. 64 228
[22] Brinkman A, Golubov A A, Rogalla H, Dolgov O V, Kortus J, Kong Y, Jepsen O, Andersen O K 2002 Phys. Rev. B 65 180517
[23] Kleinsasser A W, Miller R E, Mallison W H, Arnold G B 1994 Phys. Rev. Lett. 72 1738
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[1] Likharev K K, Semenov V K 1991 IEEE Trans. Appl. Supercond. 1 3
[2] Kameda Y, Yorozu S, Hashimoto Y, Terai H, Fujimaki A, Yoshikawa N 2005 IEEE Trans. Appl. Supercond. 15 423
[3] Mukanov O A, Gupta D, Kadin A M, Semenov V K 2004 Proc. IEEE 92 1564
[4] Mukhanov O A 2011 IEEE Trans. Appl. Supercond. 21 760
[5] Brake H J M T, Wiegerinck G F M 2002 Cryogenics 42 705
[6] Chen W, Rylyakov A V, Patel V, Lukens J E 1999 IEEE Trans. Appl. Supercond. 9 3212
[7] Choi H J, Roundy D, Sun H, Louie S G 2002 Nature 418 758
[8] Chen K, Zhuang C G, Li Q, Weng X, Redwing J M, Xi X X 2011 IEEE Trans. Appl. Supercond. 21 115
[9] Shim H J, Yoon K S, Moodera J S, Hong J P 2007 Appl. Phys. Lett. 90 212509
[10] Singh R K, Gandikota R, Kim J, Newman N, Rowell J M 2006 Appl. Phys. Lett. 89 042512
[11] Kim T H, Moodera J S 2004 Appl. Phys. Lett. 85 434
[12] Cybart S A, Chen K, Cui Y, Li Q, Xi X X, Dynes R C 2006 Appl. Phys. Lett. 88 012509
[13] Ke Y Q, Zhou D F, Liu J, Zen M, Zhu H M, Zhang Y B 2009 Chin. J. Low Temp. Phys. 31 166 (in Chinese) [柯一青, 周迪帆, 刘珏, 曾敏, 朱红妹, 张义邴 2009 低温 31 166]
[14] Xu Z 2014 M. S. Thesis (Lanzhou: University of Lan Zhou) (in Chinese) [许壮 2014 硕士学位论文 (兰州: 兰州大学)]
[15] Zhou Z Y, Wang S, Yang F S, Yang J, Fu X H 2013 Chin. J. Low Temp. Phys. 35 425 (in Chinese) [周章渝, 王松, 杨发顺, 杨健, 傅兴华 2013 低温 35 425]
[16] Zhou Z Y, Wang S, Yang F S, Yang J, Fu X H 2013 J. Funct. Mater. 44 893 (in Chinese) [周章渝, 王松, 杨发顺, 杨健, 傅兴华 2013 功能材料 44 893]
[17] Bouquet F, Fisher R A, Phillips N E, Hinks D G, Jorgensen J D 2001 Phys. Rev. Lett. 87 180
[18] Kortus J, Mazin I I, Belashchenko K D, Antropov V P, Boyer L L 2001 Phys. Rev. Lett. 86 4656
[19] Zeng X H, Pogrebnyakov A V, Zhu M H, Jones J E, Xi X X 2003 Appl. Phys. Lett. 82 2097
[20] Rowell J M, Xu S Y, Zeng X H, Pogrebnyakov A V, Li Q 2003 Appl. Phys. Lett. 83 102
[21] Gross R, Chaudhari P, Dimos D, Gupta A, Koren G 1990 Phys. Rev. Lett. 64 228
[22] Brinkman A, Golubov A A, Rogalla H, Dolgov O V, Kortus J, Kong Y, Jepsen O, Andersen O K 2002 Phys. Rev. B 65 180517
[23] Kleinsasser A W, Miller R E, Mallison W H, Arnold G B 1994 Phys. Rev. Lett. 72 1738
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