A YBaCuO-Nonsuperconductive YBaCuO-YBaCuO coplanar Josephson junction has been fabricated, using Nonsuperconductive YBaCuO thin film deposited on an MgO(100) substrate with intentional and very local damage which was created by Focused Ion Beam. The YBaCuO grown on the damaged section of the substrate turned out to be non-superconductor, due to implanted Ga ions and the change in the crystal quality, facilitating formation of an S-N-S junction. We found the important fact that the critical current density decreased exponentially with inverse of the junction length which was changed from 0.2 to 1 µm, and that Ga ion was detected in the thin films of the junctions, and that the thin films of the junctions were formed by a mixture of an amorphous, a polycrystal and a crystal, which is confirmed by Transmission Electron Diffraction. And the damaged substrate gave rise to Ga segregation and the mixed crystal, which played an very important role to form the normal metallic YBCO thin film of the Josephson junction. All these facts are related with the S-N-S junctions.

YBa2Cu3O7-δ co-planar Josephson junctions by Focused Ion Beam were characterized by changing the thickness of YBa2Cu3O7-δ films. The junctions had the thickness dependence of the characteristics. The characteristics were dominantly divided into two types. One had the I-V curve of a flux-flow junction and a weak magnetic response. The other had the I-V curve of RSJ, the IcRn product from 0. 1 mV to 0. 5 mV at 4. 2 K, and a good magnetic response. The critical current density of the junctions increased exponentially with increasing film thickness. From the observation of the junction surface, the junction length was decreased with increasing film thickness by the horizontal growth of the normally grown YBaCuO. In the thicker film (above 240 nm), the microshorts of the normally grown YBaCuO on the abnormally grown YBaCuO area were observed. It is considered that the main part of Josephson current for the junctions changes from the abnormally grown YBaCuO to microshorts when increased with the film thickness.

The capability of a high-temperature superconducting sigma-delta modulator was studied by means of circuit simulation and FFT analysis. Parameters for the circuit simulation were extracted from experimental measurements. The present circuit simulation includes thermal-noise effect. Successive FFT analyses were made to evaluate the dynamic range of the sigma-delta modulator. As a result, the dynamic range was evaluated as 60.1 dB at temperature of 20 K and 56.9 dB at temperature of 77 K.

We fabricated ramp-edge junctions with barriers by modifying surface and integrating ground-planes. The fabricated junctions had current-voltage characteristics consistent with the resistive shunted-junction model. We also obtained a 1-sigma spread in the critical current of 7.9% for 100 junctions at 4.2 K. The ground-plane reduced the sheet inductance of a stripline by a factor of 3. The quality of the ground-plane was improved by using an anneal in oxygen atmosphere after fabrication. The sheet inductance of a counter-electrode with a ground-plane was 1.0 pH per square at 4.2 K.