Tsuyoshi Takenaka

X-Band Mixing Performance of Y1Ba2Cu3O7-x Step-Edge Junction

The X-band mixing performance of some step-edge junctions using Y1Ba2Cu3O7-x films has been evaluated. The mixing conversion efficiency (η) depends predominantly on normal resistance (R n) of a junction, which determines impedance matching for the microstrip signal line. Under constant impedance conditions obtained from temperature dependence of R n, conversion efficiency (η) increases with increase of the I cR n product. In the range of 12 GHz, however, the efficiency is saturated above the I cR n product of 1 mV. This tendency agrees with our simulation based on the resistively shunted junction (RSJ) model.

Effect of Ar+O2 Plasma Etching on Microwave Characteristics of YBa2Cu3O7-x Based Resonators

We present an improvement in the patterning process of microwave devices by suppressing the oxygen effusion from the patterning edge of YBa2Cu3O7-x (YBCO) thin film. The damage in the edge is estimated from unloaded Q factors of YBCO-based micro-stripline resonators, because the high frequency current is limited along the edge. The unloaded Q factors increase with the oxygen content during the plasma etching. This result suggests that oxygen radicals in the Ar+O2 plasma restore the oxygen in the edge and reduce the loss of microwave devices.

Preparation and Transport Properties of TI-Ba-Ca-Cu-O Superconducting Films by Metalorganic Deposition

Thin films of the T1Ba2Ca2Cu3Oy (Tl-(1223)) system are prepared on SrTiO3(100), LaAlO3(100) and MgO(100) substrates by means of the deposition of a Ba-Ca-Cu-O precursor by the metalorganic deposition (MOD) method with the reaction of T12O3 vapor. The Tl-(1223) films (1 μm thickness) are composed entirely of the (1223) phase and have a highly c-axis-oriented structure. The films on SrTiO3 have Tc zero = 106 K and show a high transport critical current density (Jc) of 6.3 X 105 A/cm2 at 77 K in a zero magnetic field. When the magnetic field is applied perpendicular to the a-b plane, the Jc values are 2.0 X 104 and 6.0 X 105 A/cm2 at 77 and 40 K in a 1 T field, respectively. Moreover, the history effect of Jc in the magnetic field is not observed at 77 K below 0.1 T. These results indicate that the Tl-(1223) film, formed by the MOD method, has strong magnetic flux pinning characteristics and good intergranular connectivity. The surface resistance of the films on SrTiO3 and LaAlO3 are lower than that of the film on MgO substrate at 77K using a cavity at 24 GHz. This is because the films on SrTiO3 and LaAlO3 are highly c-axis oriented with good in-plane epitaxy with respect to the substrate.

Correlation between structural and superconducting properties in Tl-Ba-Ca-Cu-O thin films

We have investigated a correlation between structural and superconducting properties by means of transport and microwave techniques in Тl1Ва2Са2Сu3Ох (Tl-(1223)) thin films on SrTiO3, LaAlO3 and MgO(lOO) substrates. Our Tl-(1223) thin films on SrTiO3 prepared by MOD method have a high Jc of 6.3X105A/cm2 at 77K in a zero magnetic field. When the magnetic field was applied perpendicular to the a-b plane, we have found that the field transport properties of the Tl-(1223) thin films were superior to those of the Tl-(2223) and Bi-(2223) thin films. Then the hysteretic effect of Jc in the magnetic field was not observed at 77K below 0.1T. Moreover, The surface resistance of the films on SrTiO3 and LaAlO3 substrates were lower than that of the film on MgO substrate at 78K using cavity perturbation technique. Because the films on SrTiO3 and LaAlO3 are highly c-axis oriented with good in-plane epitaxy with respect to the substrate.

Microwave Properties of TI-Ba-Ca-Cu-O Thin Films by Metalorganic Deposition

TIBa2Ca2Cu3Oy superconducting films have been deposited by metalorganic deposition method on SrTi03(100),LaAI03(100), and MgO(IOO) substrates. Surface resistances,Rs, of the films were measured by a microwave cavity resonator at 24GHz. In the cases on SrTiO3(100) and LaAlO3(100) substrates, Rs of Tl-(1223) were lower than that of the gold below about 11 OK. The 15GHz micro-stripline resonator of the film was made on LaAlO3(100) substrate by the wet etching method. The unloaded Q of this resonator was 4.5 times higher than that of Au at 77K.

Characteristics of Thin Film YBCO Micro-Stripline Resonator by Laser Etching

The micro-stripline type resonators have been fabricated by YBCO films using maskless laser etching methods. YBCO thin films on MgO(100) substrates are deposited by pulsed excimer laser. In addition, standard photolithography and Ar ion milling process is used for comparison. Unloaded Q factors of 3000 at 77K are obtained for both fabrication methods. This value is higher than that of about 800 of Au resonator.

Superconducting Properties of YBCO Thin Films Deposited on Grainboundary Free Y2O3 Substrates

Y2O3 single-crystal was grown by Verneuil method. The crystallinity (FWHM004 = 61”) is comparable or superior to the other commercial substrates for superconducting films. The crystalline structure is cubic, and there is no phase transition in the range of 77 – 2,570K. The dielectric constant of Y2O3 substrate is smaller than 9, which is comparable to MgO. Not only c- axis, but also a-axis oriented YBCO film have been grown on Y2O3 (001) substrates by control of substrate-temperature like MgO, and SrTiO3. The width of the interface between YBCO and Y2O3 is less than 100A, which indicates the interface is very sharp and stable.