In-plane-aligned a-axis-oriented YBa2Cu3O7-δ (YBCO) thin films are attractive for the formation of planar intrinsic Josephson devices. In this study, these films were deposited by dc sputtering on LaSrGaO4 (LSGO) (100) substrates and the dependence of the characteristics on the deposition conditions was investigated. In-plane-aligned a-axis-oriented YBCO thin films were successfully grown in the substrate temperature range of 555-615. With the temperature gradient method, it was seen that the critical temperature of the film increased to 81 K. The current-voltage characteristic along the c-axis exhibited clear multibranch structures. These results indicate that ion-cleaning of the substrate surface broadens the growth temperature range of these films and planar intrinsic Josephson devices can be fabricated from these films.

In situ grown Y-Ba-Cu-O films were prepared on MgO substrate by rf magnetron sputtering with dc-biased substrate holder using a stoichiometric YBa2Cu3Oz target. The films were deposited at substrate temperature Ts about 660 and various substrate holder bias voltages VH. Influence of a dc bias voltage of substrate holder on the superconducting characteristics of Y-Ba-Cu-O thin films are investigated. Films with critical temperature higher than 80 K can be obtained at bias voltages from 20 V to 80 V for 500 mTorr. The optimum bias voltage to obtain the high Tc films depends on the sputtering gas pressure. The optimum bias voltages in 500 mTorr and 300 mTorr are 20 V and 150 V, respectively. The film morphology depends on the bias voltage rather than the sputtering gas pressure in this experiment and the smooth film surface is obtained at low voltages from 20 V to 40 V. For the films deposited at 80 V in 500 mTorr, the film of 200 nm thick is smoother than films of 400 nm and 700 nm thick. The deviation of the film composition is varied by the negative holder bias voltage. The critical temperature depends on the c-lattice parameter rather than the film composition. The films with short c-lattice parameter have the high Tc. The negative holder bias is effective for obtaining the high Tc films in the low pressure. However, in the high pressure, the films at the high bias voltages have slightly low Tc as compared with films at low bias voltage.

A sputtering system using dc hollow cathode discharge was developed for the propose of high Tc superconducting devices. Using this system, as-grown superconducting thin films of YBCO have been formed on MgO and SrTiO3 substrates. Influence of the sputtering conditions such as the substrate temperature and discharge gas pressure on the Tc and lattice parameter was investigated. It was found that superconducting films on MgO with Tczero higher than 87 K ere routinely obtained at the pressure of 820 mTorr (5%O2) and substrate temperature of 700 during deposition. The a/b-axis and c-axis oriented YBCO-PBCO hetero-structures were also successfully formed on MgO and SrTiO3 substrates.

Although larger scale integration enhances the practicability of superconducting Josephson circuits, several technical problems begin to emerge during its progress. One of the problems is the increase of current through a ground plane (ground current). Excess ground current produces additional magnetic field and reduces operation margins of the circuits, because superconducting Josephson devices are very sensitive to magnetic field. In this paper, we evaluate current distribution in a superconducting ground plane by means of both experiments and numerical calculation. We also verify two methods for suppressing the ground current. One is a slot structure in the ground plane, and the other is alignment of the current-extraction point. Suppression of the ground current is quantitatively evaluated.

B(P)SCCO films were prepared on MgO substrate by a double cathode dc sputtering with a mosaic BiχSrCaCuyOz and (Bi0.7Pb0.3)χ SrCaCuyOz target. The films were deposited at 200 and 550, and then annealed. We have obtained the B(P)SCCO films with Tc of 90-100 K under the condition of the deposition at 550 and the in-situ annealing in 200 Torr O2 and the post-deposition annealing at 860.

We present analytical expression for inductance of a superconducting stripline, a strip sandwiched by two superconducting ground planes. In our method, we utilize the analytical formula for a perfect-conducting stripline derived by Chang in 1976. To utilize Chang's formula, we first transform the structure of a superconducting stripline into that of a perfect-conducting stripline by reducing the thicknesses of the superconducting layers. The thickness reduction is "λ coth (t/λ)" for each (upper or lower) side, where λ and t are the field penetration depth and the layer thickness, respectively. Then, we apply Chang's formula to the transformed stripline model. The calculated results are in good agreement with the numerical and experimental results.