Intrinsic Josephson Junctions on High-quality BSCCO-2212/2223 Superlattice Thin Films Grown by MOCVD
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Intrinsic Josephson Junctions on High-quality BSCCO-2212/2223 Superlattice Thin Films Grown by MOCVD K. Endo, H. Sato, T. Yoshizawa１, K. Abe, J. Itoh, K. Kajimura, H. Akoh Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Ibaraki, Japan １Tokyo Denki Univ., Kanda 101-8457, Tokyo, Japan
ABSTRACT We report on the successful preparation of intrinsic Josephson junctions on high-quality BSCCO-2212/2223 superlattice thin films grown by MOCVD. The surface of as-grown films was very smooth with the roughness of the order of a half unit cell. Mesas were effectively structured on the film by the liquid-nitrogen-cooled dry etching method. A typical I-V characteristic in the c-axis direction of a BSCCO film shows the hysteresis and multiple resistive branches. The number of branches is consistent with that of junctions calculated from the height of a mesa structure. This indicates that BSCCO-2212/2223 superlattice films consist of a series array of S(CuO2 bilayer) / I(SrO, BiO layers) / S(CuO2 trilayer) junction. The formation of stacked Josephson junctions was also confirmed by the temperature dependence and the magnetic field dependence of Ic.
INTRODUCTION Much attention has been focused on intrinsic Josephson junctions observed in Bi2Sr2CaCu2Ox (BSCCO-2212) single crystals from the viewpoint that Josephson characteristics control of artificial junctions and findings of new barrier materials as well as high frequency applications in the THz region [1, 2]. In order to improve integration possibilities for device applications, it is very important to fabricate Josephson junctions on high-quality thin films. We report on the successful preparation of intrinsic Josephson junctions on high-quality BSCCO-2212/2223 superstructure thin films grown by metalorganic chemical vapor deposition (MOCVD) for the first time.
FILM GROWTH We have prepared 50 nm thick BSCCO films on (100)SrTiO3 substrates by MOCVD. In this study, we used a cold-wall-type MOCVD apparatus with a horizontal reaction tube[3]. Figure 1 shows a schematic drawing of MOCVD apparatus. The source materials were triphenyl bismuth Bi(C6H5)3, bis(dipivaloylmethanato)-strontium Sr(DPM)2, -calcium Ca(DPM)2 and –copper Cu(DPM)2. The films were grown at 800℃ under the oxygen partial pressure of 3.6×103 Pa. As-grown BSCCO films were cooled down to 500℃ and annealed in-situ for 12 hr under 6.5×103 Pa argon atmosphere in order to decrease the hole carrier concentration. X-ray diffraction patterns of the film showed that the film consists of c-axis oriented BSCCO-2223/2212 superlattice, which has an apparent c-axis length
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