Daisuke Okai

New measurement technique of the surface impedance of superconductors using the probe-coupling type microstripline resonator

We have developed a probe-coupling type microstripline resonator method for accurate measurement of the surface impedance of superconductors. By this improved microstripline resonator method, the surface impedance can be measured without attaching any contacts to the film. This paper reports the accurate and reproducible measurement process of surface impedance using the probe-coupling type microstripline resonator. The surface impedance of a YBCO thin film was measured using this technique. The measured results revealed that this technique may be used for the accurate measurement of surface impedance.

Microwave surface resistance of YBCO thin films on cerium oxide buffer

The effects of the crystallinity and surface roughness of CeO/sub 2/ buffer on R-plane Al/sub 2/O/sub 3/ substrate on the microwave surface resistance (R/sub s/) of YBa/sub 2/Cu/sub 3/O/sub y/(YBCO) thin films are discussed. We estimated R/sub s/ from the transmission characteristics of the microstrip line resonator at 25 K and 6.7 GHz. X-ray diffraction (XRD) of /spl theta/-2/spl theta/ and /spl phi/-scan showed that CeO/sub 2/ was completely [001]-oriented and in-plane aligned crystal. Four CeO/sub 2/ samples with different thicknesses were prepared using identical conditions except for the deposition time. The dependence of R/sub s/ on CeO/sub 2/ thickness was measured in the range from 10 nm to 200 nm. The value of R/sub s/ was minimum at CeO/sub 2/ thickness of 100 nm. The dependence of R/sub s/ vs CeO/sub 2/ thickness was similar to that of the amount of a-axis domains against the thickness. The crystallinity of thin CeO/sub 2/ was poor because the lattice was strongly strained by Al/sub 2/O/sub 3/. This affected the quality of the upper YBCO layer. In contrast, thick CeO/sub 2/ had excellent crystallinity. However, for the thickness of more than 100 nm a drastic change in surface morphology was observed by atomic force microscopy (AFM). A number of projections appeared on the CeO/sub 2/ surface. These projections act as nucleation centers for the a-axis domains.

Temperature Dependence of the Surface Resistance of a Bi?Sr?Ca?Cu?O Whisker Measured by the Probe-Coupled Microstrip Resonator Method

The temperature dependence of the surface resistance of Bi?Sr?Ca?Cu?O whiskers measured by the probe-coupled microstrip resonator method was examined. Two kinds of whiskers were measured: plate-like and wire-like. The surface resistances of the plate-like and wire-like whiskers were 0.65 m? and 1.6 m? at 53 K and 6.9 GHz, respectively. These values were approximately 4 ~10 times larger than that of a high-quality Bi2Sr2CaCu2Ox (Bi-2212) single crystal.

New surface resistance measurement technique of high-temperature superconductors using a probe coupling microstrip line resonator

We have developed a new surface resistance (R/sub s/) measurement technique of high-temperature superconductors using a probe coupling microstrip line resonator. In this technique, the probe coupling method is used to measure the R/sub s/ of superconductors without attaching any contacts to the superconductors. This paper reports the measurement process of the R/sub s/ of a superconducting fine-wire using this technique. The quality factors of the copper wires, gold fine-wire and the Bi-Sr-Ca-Cu-O whisker crystal were measured by the probe coupling resonator method. The measurement results revealed that this technique is feasible for the R/sub s/ measurement of the superconducting fine-wire.

Effect of Cavity’s Loss on the Measurement Accuracy of the Surface Resistance by Microstripline Resonator Method

We have examined the effect of the loss in the cavity on the measurement accuracy of surface resistance (Rs) of a superconducting thin film using a microstripline resonator. The Rs of a YBCO thin film was measured as a parameter of the height of the cavity’s ceiling. The investigation revealed that the loss in the ceiling affected the measurement accuracy of Rs for a comparatively lower ceiling height. However, when the ceiling’s height was sufficiently high, the effect was negligible.

New Measurement Technique of the Surface Resistance Rs Using the Microstripline Resonator

We have examined a new measurement technique of the surface resistance of a superconducting thin film using the microstripline resonator. In this technique, a probe coupling method is used to measure the surface resistance of the thin film without attaching any contacts to the film. It was found that the accuracy of measurement of the surface resistance by the probe coupling method is higher than that of the gap coupling method.

Examination of the Microstripline Resonator for Measurement of the Magnetic Penetration Depth, λ

We have examined a microstripline resonator for accurate measurement of the magnetic penetration depth, λ. We investigated the effect of the geometry of the microstripline resonator on the λ (T). It was found that the determination of the λ (T) is affected by the thickness of the microstripline resonator. The λ (0) of the YBa2Cu3O7-x thin film was measured using the microstripline resonator. The λ (0) was found out to be 0.37 μ m.

Study on Optimum Configuration of Microstrip Bandpass Filters

A hairpin type five-pole Chebyshev filter is designed using method of Wong et al. Frequency responses are simulated with an electromagnetic analysis simulator Sonnet EM. The center frequency, the fractional bandwidth and the ripple of high temperature superconducting (HTS) filter are 5.03GHz, 5% and 0.18dB, respectively. Characteristics of HTS filter with HTS ground plane (HTS/HTS- filter) are compared with that of HTS filter with Au ground plane (HTS/Au-filter) and Au filter with Au ground plane (Au/Au-filter) at 77K. The insertion loss of the HTS/HTS-filter is 0.073dB, while that of Au/Au-filter is 3.11dB. Although the fractional bandwidth of the HTS/Au-filter nearly same as HTS/HTS-filter, the insertion loss is 0.14dB larger than HTS/HTS-filter. The increase in insertion loss is due to the loss of the Au ground plane.