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Analysis by I-V Curves for Intrinsic Josephson Junctions of Tl2Ba2CaCu2Ox Thin Films on MgO Substrates
Shuichi YOSHIKAWA Masaaki NEMOTO Kazuhiro SHIMAOKA Isao YOSHIDA Yorinobu YOSHISATO
IEICE TRANSACTIONS on Electronics
Publication Date: 1997/10/25
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Issue on Basic Properties and Applications of Superconductive Electron Devices)
Tl2Ba2CaCu2Ox thin film, intrinsic Josephson junction, millimeter wave,
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We successfully observed curent-voltage (I-V) curves which showed the behavior of intrinsic Josephson junctions using Tl2Ba2CaCu2Ox (Tl-2212) thin films on MgO substrates by structuring mesas and measuring the electrical transport properties along the c-axis. For a 55 µm2 mesa, a hysteretic I-V curve was observed up to 80 K, which showed that series-connected SIS-type junctions are formed. Compared with the critical current density (Jc) of more than 106 A/cm2 parallel to the ab-plane, an anisotropic Jc of 1.4102 A/cm2 along the c-axis was observed at 4.9 K. By focusing on the I-V curve at lower bias current, the constant voltage jumps measured at the first seven branches were estimated to be 26 mV. The normal resistance (Rnk) of a unit SIS junction was estimated to be 580 Ω by substituting the measured voltage jump in the Ambegaokar and Baratoff relation. Using the calculation for McCumber parameter (βc), the capacitance (Ck) of the unit SIS junction was estimated to be 3.610-10 F/cm2 at 77 K. The IckRnk product was estimated to be 6.4 mV and the cut-off frequency (fc1/2πRnkCk) was calculated to be 3.1 THz at 77 K. The Jc and the hysteresis decreased with an increase in the mesa area, and finally, for a 300300µm2 mesa, a resistively shunted junction (RSI) like curve without hysteresis was observed up to 98 K. A Jc of 5.6101 A/cm2 along the c-axis was observed at 6.4 K. This may be explained by the higher content of conductive grain boundaries for a larger mesa area.