Yoshiaki Terashima

2 GHz tunable superconducting band-pass filter using a piezoelectric bender

Abstract We have developed a 2 GHz tunable superconducting band-pass filter using a piezoelectric bending actuator. The filter is a 12-pole microstrip line structure on 50 mm diameter LaAlO 3 substrate and has low loss and sharp skirt characteristics. The center frequency was 1.94 GHz and the attenuation characteristics were 30 dB at 1 and 3 MHz apart from the lower and higher band-edge, respectively. A sapphire (Al 2 O 3 ) plate was stacked on the filter with an air gap and the gap thickness was controlled electrically from the outside of a refrigerator using a piezoelectric bending actuator. The center frequency of the filter could be adjusted within 11 MHz in such a manner that the low loss and sharp skirt characteristics were not degraded.

A high-resolution electron microscopy study on epitaxial infinite- layer SrCuO2 thin films grown on a SrTiO3 (100) substrate

Abstract The authors investigated defect structures introduced into so-called infinite-layer SrCuO 2 thin films sputtered on a SrTiO 3 (100) substrate. By means of both cross-sectional and plan-view high-resolution electron microscopy (HREM), it has been revealed that the films were epitaxially grown with their c -axis normal to the substrate surface, and several types of defect structures have been estimated. They were essentially composed of double Sr-O planes that make {100} atomic walls. It is remarkable that such walls tended to arrange as loop-like configurations, and also could produce a different ordered structure, i.e., a Sr 2 CuO 3 -like structure in local regions. The authors propose defect structural models in the epitaxial infinite-layer SrCuO 2 thin films in detail.

Tuning properties of 2 GHz superconducting microstrip-line filters

We have fabricated a 2 GHz 12-pole superconducting microstrip line filter and a 2-pole electrically tunable filter using interdigital electrodes and dielectric film. The change of the dielectric constant of a SrTiO/sub 3/ film, stacked on the filter, by applying a bias voltage between the electrodes leads to the tunability. The range of the center frequency modulation was 13 MHz (0.7%) at 60 K, 75 kV/cm. The microwave frequency response was improved by modification of the electrode structure. This tuning method is considered to be promising in that individual resonance elements in multi-pole filters can be tuned independently.

HTS hairpin microstrip filter on r-cut sapphire substrate

We have developed a 17-pole high-temperature superconductor thin-film hairpin microstrip filter on r-cut sapphire substrate. We determined the optimum orientation of hairpin resonators on r-cut sapphire substrates, considering the anisotropy of dielectric permittivity. With optimum orientation, the desired frequency response was realized. On the other hand, when the orientation was not the optimum, the frequency response was violently disturbed. The cause of the disturbance of the frequency response was investigated.

Bandwidth tunable high-Tc superconducting filter

Abstract We have developed a high- T c superconducting band-pass filter, whose center frequency and bandwidth can be tuned independently, with steep attenuation at both lower and higher band edges. This tunable filter is composed of two different types of band-pass filters, one with steep attenuation at the lower band edge and the other with steep attenuation at the higher band edge. Two filters are connected in series and each filter is covered with additional dielectric plates, respectively. The tuning characteristics of the entire filter can be controlled by adjusting the distances between the dielectric plates and the substrate. The entire filter was fabricated monolithically on a 30-mm-wide and 60-mm-long LaAlO 3 substrate. A center frequency of 1.93 GHz, a 3 dB bandwidth of 20 MHz, and an attenuation of 30 dB, 1.0 MHz apart from both band edges, were obtained for the entire filter. Then, a sapphire plate was set above each of two filters, and a center frequency tuning of 10 MHz and a bandwidth tuning of 5 MHz were obtained by adjusting the distances between the substrate and the sapphire plates.

High-Tc superconducting tunable filter with steep attenuation

Abstract We developed a compact RF receiver front-end subsystem using a high- T c superconducting sharp-skirt band-pass filter with a center frequency tuning function. The subsystem had two pairs of the tunable filter and an LNA on board. A 23-pole hairpin-type 2-GHz microstrip-line filter was fabricated with YBa 2 Cu 3 O y thin films deposited on a 35-mm-wide and 70-mm-long sapphire substrate. Attenuation characteristics were more than 40 dB at 1 MHz, apart from both the lower and the higher pass-band edges. For center frequency tuning, a 1-mm-thick dielectric sapphire plate was stacked on the filter, and the filtering characteristics were tuned by moving the plate using a piezoelectric bending actuator. The range of the center frequency modulation was more than 10 MHz with no significant degradation of the low-loss and sharp-skirt characteristics.

Electrically tunable YBa2Cu3Oy resonators using interdigital electrodes and dielectric film

Abstract We have fabricated electrically tunable YBa2Cu3Oy (YBCO) resonators using interdigital electrodes and a dielectric film, and have investigated their tuning capabilities. The tuning section, which consists of an SrTiO3 (STO) dielectric film and SrRuO3 (SRO) interdigital electrodes, was stacked on a half-wavelength microstrip line resonator. The change of the dielectric constant of the STO film by applying a bias voltage between the electrodes leads to the tunability. The range of frequency modulation and the quality factor were 10 MHz (0.21%) and 2100 at 40 K, 75 kV/cm, respectively. This tuning method has an advantage over conventional methods in that individual filter elements can be tuned independently and a high quality factor is expected.

Fault Current Limiter Using YBa 2 Cu 3 O 7−x Superconductive Film

The aim of this study is to investigate the applicability of high-Tc-superconducting films in a fault current limiter (FCL) without liquid nitrogen (L-N2). The FCL element consists of a 200 nm-thick YBCO film having a current limiting area 4 mm wide and 90 mm long. A half-cycle-alternating voltage (50 Hz) was applied to the above element which had been cooled by a refrigerator. When a voltage of 100 Vrms (150A) was applied at 77K, the YBCO film became resistive at 13 A and the fault current rapidly decreased to 7 A in less than 0.5 ms. At lower temperature, 74K, the transition current increased to more than 30 A, while the limited current remained less than 9 A. These results suggest that a superior FCL system without L-N2 will be obtained.

2 GHz band superconducting band-pass filter with parallel resonators structure

A 2 GHz band 2-pole narrow bandwidth superconducting band-pass filter with the parallel structure of the half-wavelength microstrip line resonator was developed. The novel filter was realized by planar structure for the first time. The novel parallel filter operating at 60 K had center frequency of 1.909 GHz, insertion loss of 0.77 dB, 3 dB bandwidth of 0.49%, and maximally flat type characteristic. Moreover, the allowable maximum power of the novel parallel filter was 1.14 dB higher than that of the conventional filter. Given these features, a superconducting narrow-band filter for transmitters for next-generation mobile RF applications is expected to be realized by applying these filters.

Microwave surface resistance of epitaxial YBa2Cu3O7−x films

Abstract The microwave surface resistance R s at 10 GHz was measured for the epitaxial YBa 2 Cu 3 O 7− x films deposited on a MgO (001) substrate by the sputtering method. These films were completely oriented with the c -axis normal to the surface and the in-plane alignments were YBa 2 Cu 3 O 7− x [100]|MgO[100] and YBa 2 Cu 3 O 7− x [010]|MgO[100], having a little or no fraction of misaligned grains or domains with large-angle boundaries. The R s values of the films correlated with the domain size more strongly than with the fraction of misorientation, implying that the domain boundaries themselves, even if they were not large-angle domain boundaries, lead to the increase of the surface resistance. The weak couplings between the domains are considered to be the main cause of the increase in the microwave surface resistance.