Study towards nanoelectronics of small-sized Josephson superlattice using high T_c superconductors

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The inherent characteristic of small-sized intrinsic Josephson junctions in Bi_2Sr_2CaCu_2O_y single crystals and their nanoelectronics applications have been investigated. In this study, we obtained the following results.(1)Submicron device fabrication process using electron beam lithography and Ar ion milling was established. Such technology realizes the controllable and reproducible device fabrication. (2)We fabricated mesa structure with different sizes involving intrinsic Josephson junctions and studied the size dependence of their characteristics. As a result, it was found that the gap voltage of about 60mV is independent of junction area. In addition, we found that the critical current density rapidly decreases as the junction area becomes the submicron region because of the contribution of the Coulomb blockade effect. (3)The distribution of switching current into normal state in stacked intrinsic Josephson junctions increases with increasing the junction area. The obtained results were analyzed by using the thermal activated model and we found that the increase in the distribution of the switching current is due to flux fluctuation rather than thermal noise. Additionally, we found that the temperature dependence of critical current is systematically changed as the junction area reduces and it is consistent with the RSJ model including thermal noise. (4)For example of nanoelectronics application of intrinsic Josephson junction, we fabricated the single Cooper pair tunneling device, the voltage standard device and dc SQUID using them.