4PO9-10 Nondestructive Imaging of the Microwave Properties of Superconducting Thin Film Devices with a Scanning Microwave Near-field Microscope

Y.J. Feng, L. Liu, Q.G. Liu, L.X. You, L. Kang, S.Z. Yang, and P.H. Wu, Department of Electronic Science and Engineering, University of Nanjing, Nanjing, 210093, P.R. China

Presenting Author: Y.J. Feng

Recently, the superconducting microwave devices have found significant applications in high-performance wireless communication system due to their very low losses and high quality factor. For commercializing these microwave devices, one of the major obstacles is the inhomogeneous microwave properties over large-area superconducting thin films. It is quite important to study the local microwave properties, such as the surface resistance of the thin film or the dielectric constant of the substrate over the whole wafer. In this paper, nondestructive microwave scanning techniques have been used to image the local microwave properties of the planar microwave devices. A coaxial cavity together with a niobium tip has been used as a probe in the scanning microwave near-field microscope. Spatial resolution has been demonstrated by mapping both the lines with different widths and separations in metal films and the line patterns in metal multilayers. Quantitative images of the surface resistance of metal film samples as well as the dielectric constant of the substrates have been obtained. Local surface resistances at 3 GHz have been imaged on microwave devices prepared by laser ablated YBaCuO thin films. The influence of the patterning process on the spatial variation of the surface resistance in the YBaCuO thin film devices has been studied systematically, which would be helpful in evaluating the performance of the devices.

4PO9-11 YBCO Hot-Electron Bolometer Mixer

S. Cherednichenko 1, D. Meledin 1, G. Gol'tsman 1, E. Gershenzon 1, F. Ronnung 2, and D. Winkler 2. 1 Department of Physics, Moscow State Pedagogical University, Moscow 119435, Russia. 2 Department of Physics, Chalmers University of Technology and Goteborg University, Goteborg S-412 96, Sweden.

Presenting Author: S.I. Cherednichenko

We present superconducting mixer based on the hot- electron phenomenon in YBa₂Cu₃O_7-d superconducting thin film driven into resistive state. The frequency down-conversion is obtained due to inertial nonlinearity of hot- electron bolometer (HEB). The time constant of the HEB is defined by the electron temperature relaxation time, which relates to the electron- phonon interaction time in the film. The strong electron-phonon interaction in YBa₂Cu₃O_7-d film theoretically provides the intermediate frequency bandwidth as wide as 140 GHz. The phonons of the film serve as a heat sink and the poor heat link of phonons to the substrate leads to the low mixing efficiency. Here we present an investigation of the YBa₂Cu₃O_7-d HEB mixers which were performed with modulation and mixing techniques in IR and submillimeter wave ranges. We found out that the phonon cooling rate becomes more efficient as the mixer size scales down to 0.2 m. We show that at such scale there is no back flow of hot phonons from the substrate into the film and the experimental data agrees with the acoustic mismatch theory. We also performed a comparative study of the YBa₂Cu₃O_7-d HEB mixers at IR and submm ranges. Different ways of the mixer behavior was observed. A model for an explanation of the experimental results is proposed in the report.

4PO9-12 The Effect Of A "Microwave Window" On The Performance Of An HTS Antenna

Zhu Meihong 1, Cao Bisong 1, Huang Hesheng 1, Zhang Xuexia 2, Liu Tao 1, Liu Tiejun 3, Tu Guibing 4, Jin Shulin 4, Zhou Yueliang 5, He Meng 5, and Cui Dafu 5. 1 Department of Physics, Tsinghua University, Beijing 100084, P.R. China. 2 Department of Electrical Engineering, Tsinghua University, Beijing 100084, P.R. China. 3 Beijing Institute Environment Feature, Beijing, 100854, P.R. China. 4 Cryogenic Laboratory, Academia Sinica, Beijing, 100080, P.R. China. 5 Institute of Physics, Academia Sinica, Beijing, 100080, P.R. China.

Presenting Author: Z. Meihong

When an aircraft reenters the atmosphere, a plasma layer is formed on the surface of the aircraft because of the friction between the aircraft and the atmosphere. As a result, the transmission of the electromagnetic waves from the aircraft is blocked. Theoretical calculation showed that a right-hand circularly polarized electromagnetic wave has much less loss through the plasma if a strong magnetic field is applied along the transmission direction of the electromagnetic wave. Based on this space application, a circularly polarized High Temperature Superconducting (HTS) antenna with excellent performance was prepared and installed in metal dewar equipped with a low temperature superconducting magnet. In order to let the microwave signals from the antenna pass through the metal dewar a "microwave window" must be made. The effect of the"microwave window" on the HTS antenna's performance was investgated in this paper. Although the window was in the antenna's near and Fresnel zones, the signal attenuation in the far field resulting from the "microwave window" can be reduced to less than 1dB. The configuration of the "microwave window" was also given.

4PO9-13 Development of a Novel Substrateless RF Resonator Using Single Domain YBa₂Cu₃O_x

Donglu Shi 1, D. Qu 1, Altan Ferendeci 2, and David Mast 3. 1 Department of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH 45221. 2 Department of Electrical and Computer Engineering, University of Cincinnati, Cincinnati, OH 45221. 3 Department of Physics, University of Cincinnati, Cincinnati, OH 45221.

Presenting Author: D. Shi

Large single domain YBa₂Cu₃O_x materials have been successfully fabricated with superb rf properties by employing a seeded-melt growth (SMG) method. Based on these high-quality single domain YBCO, several novel rf resonators and filters have been designed and develolped. The cavity consists of a hollow cylindrical cup covered by a polished plate, which operaties in the TM₀₁₀ mode. All cavity parts are made of single-domain YBa₂Cu₃O_x without any dielectric materials. The measured Q has reached a high value of 10 200 at 18.4 GHz. Our experimental data show great promise in the development of rf components using single domain high temperature superconductors. To investigate the effects of structural ordering on the surface resistance, the smaill cubic single domain YBCO samples have been treated with flowing oxygen in a wide range of temperatures of up to 700° C. After oxygenation, the surface resistance has been measured at 12.95 GHz in a magnetic field up to 1.9 T. The results of these surface measurements data have been compared with bulk properties measured by the ac susceptibilty measurements. The results have shown consistent behaviors from both measurements. The broadening of the transitions correspond well between the two methods indicating a similar underlying mechanism that dominates the fundamental superconducting parameters of the single domain materials.

4PO9-14 Enhancement of R_s-Measurement Sensitivity of HTS Thin Films by Microstrip Resonator Technique

N.D. Kataria 1, M. Misra 1, and R. Pinto 2. 1 JVS & SQUID Group, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi-110 012. 2 Solid State Physics Group, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400005, India.

Presenting Author: N.D. Kataria

Microstripline resonators are routinely used to characterize the surface resistance (R_s) of HTS thin films. In half-wavelength microstrip resonator fundamental resonant mode is accompanied by harmonic modes at frequencies approximately integral multiple of the fundamental resonant frequency. The measurement sensitivity of the resonator is primarily determined by the Q-value of the resonant structure and is directly related to the dynamic range of the Q-value for the change in the Rs-value of the of the HTS strip and the ground plane. The characteristic parameters of the resonator shows higher measurement sensitivity at higher harmonic modes compared to the fundamental mode.

Half-wavelength microstrip resonator was designed and fabricated on a Ag-doped YBCO thin film deposited on lanthanum aluminate substrate by PLD technique. The ground plane of the resonator was made by depositing copper by e-beam evaporation. Microwave was coupled to the resonator through capacitive gap. The length (=7.8mm) of the resonator provided the fundamental frequency at ~5 GHz. The resonators charcteristics, such as, the resonant frequency, 3-dB bandwidth and insertion loss were measured as a function of temperature at fundamental as well as at first harmonic (9.84 GHz) and second harmonic (14.42 GHz). The measured Rs data of the film using these three harmonic modes show frequency dependance as Rs~1.6. Theoretical analysis was carried out to estimate the measurement sensitivity associated with the harmonics as well as its dependence on the R_s-value of the ground plane. The geometrical factors of the strip and the ground plane were evaluated using Wheeler's incremental inductance rule. The results showed that the R_s-measuement at higher order mode to be more sensitive than at fundamental frequency. Also, measurement sensitivity depended strongly on the Rs-value of the ground plane and could be improved by minimizing its value.

4PO9-15 HTS Bandpass Filters Using Parallel Coupled Microstrip-Stepped Impedance Resonator

Dong-Chul Chung and Young Hee Lee, Dept. of Physics and Semiconductor Physics Research Center, Chonbuk National University, Chonju, Chonbuk 561-756, Korea

Presenting Author: D.-C. Chung

We report the characteristics of high-T_c superconducting (HTS) bandpass filter with the center frequency of 17h.25 GHz. YBa₂Cu₃O_7-x thin film was prepared using the Pulse-Laser Deposition technique. The filters were composed of non-uniform microstrip lines, which wwere the stepped impedance resonators (SIR). This approach has an advantage for the compact filter structure. The impedance ratio of the SIR was 0.5 in this work. In the measured responses, this HTS filter showed the insertion loss of -0.5 dB at maximum and other results of our filters were in a good agreements with the simulation results.

4PO9-16 A Practical Microwave Subsystem of HTS Filter Integrated with Coaxial Pulse Tube Refrigerator

Hong Li 1, Tiefeng Shi 1, Luwei Yang 1, Yuan Zhou 1, Jingtao Liang 1, Yusheng He 1, and Aisheng He 2. 1 Cryogenic Laboratory, Chinese Academy of Sciences, P.O. Box 2711, Beijing 100080, China. 2 Northern University of Technology, Beijing 100041, China.

Presenting Author: H. Li

Pulse tube refrigeration is a promising and competitive new technology involving no moving parts at low temperature. It has been proven that pulse tube refrigerator is one of the best candidates for cryogen-free cooling HTS devices and forming practical HTS microwave subsystem. Aiming to the practical use as a front-end receiver, a wide-band filter with central frequency of 5.6 GHz has been designed. This new type 8-pole Chebyshev filter has a special echelon configuration and was fabricated on a YBCO thin film. A new type coaxial pulse tube refrigerator has also been developed. In this configuration, the pulse tube is sheathed by the regenerator and such a compact design provides better accommodation for the high T_c superconducting devices and the necessary electronic circuits. To ensure its long lifetime reliability, a modified commercial air conditioning compressor and a rotary distributive valve are used in this system. 3 watts of cooling power at 50 K has been achieved with about 480 watts input power. Integrated with the refrigerator, the filter shows satisfactory performance with low insertion loss ((less than 0.6 dB)) and high out band rejection (better than 60 dB). A low noise amplifier is also under development and gains in sensitivity and selectivity are achieved due to the steeper filter skirts, lower filter insertion loss and the reduced noise figure in the cooled LNA.

4PO9-17 Design and Performance of Miniaturized HTS Coplanar Waveguide Meanderline Bandpass Filters

Haruichi Kanaya 1, Takuhiro Nakamura 1, Tatsunori Sintou 1, Keiji Yoshida 1, Tetsuji Uchiyama 2, Hisashi Shimakage 2, and Zhen Wang 2. 1 Department of Electronics, Graduate School of Information Science and Electrical Engineering, Kyushu University, Fukuoka 812-8581, Japan. 2 Kansai Advanced Research Center Communications Research Laboratory, Hyogo 651-2401, Japan.

Presenting Author: T. Nakamura

Design and performance of coplanar waveguide (CPW) microwave bandpass filters (BPFs) using high T_c superconducting (HTS) films have been studied. We designed BPFs for mobile at f₀=2GHz and satellite at f0=10GHz telecommunications, respectively (f₀:central frequency). The BPFs made of CPW requires the coating of only one side of the substrate with a superconductor. The size of the CPW BPFs can be uniformly reduced in scale without changing its characteristic impedance. Moreover, It is possible to make a miniaturized filter by adopting the meanderline geometry.

In order to realize the J inverter, we employed the interdigital capacitance. BPFs were designed by the transmission-line model (equivalent circuit model). We obtained the same microwave properties of both straight and meanderline BPF at 10GHz. But, at 2GHz, we obtained the different properties of both BPF. So, we re-designed by considering transmission meanderline model. It is shown that the size of the filters can be greatly reduced by introducing CPW with a meanderline geometry. Experiment of a prototype miniaturized CPW filter with its computer-simulated performance will be presented.

4PO9-18 Microwave Surface Resistance Measurement of High-T_c Superconducting Ag-doped YBCO Thin Films by Three Different Resonant Techniques

Mukul Misra 1, N.D. Kataria 1, R. Pinto 2, J. John 2, G.P. Srivastava 3. 1 JVS & SQUIDs Group, National Physical Laboratory, New Delhi-110 012, India. 2 Solid State Physics Group, Tata Institute of Fundamental Research, Mumbai-400 005, India. 3 Dept. of Electronic Science, University of Delhi, South Campus,Benito Juarez Road, New Delhi-110 021, India.

Presenting Author: M. Misra

In this paper, we report the surface resistance, R_S, measurement of the Ag-doped YBCO thin films as a function of frequency, temperature and power by employing three different resonating techniques, namely: cavity endplate substitution (20 GHz), dielectric resonator (18 GHz) and microstrip resonator (5 GHz, 9.8 GHz and 14.5 GHz). Theoretical analysis has been made for each technique to extract the R_S-value of the sample from the measured Q-value of the resonating structure. The analysis is used to estimate the measurement sensitity of the techniques and for optimum designing of the resonating structures to achieve the maximum sensitivity within the given constraints.

The R_S of laser ablated Ag-doped YBCO thin films deposited on 10mm x 10mm LaAlO₃ substrates showed conventional behavior with temperature by all the three techniques. The value of frequency exponent a , (R_S µ w a ) is found to be approximately 1.6 which is, within the range 1.4 ³ a ³ 2.0, reported by many workers. Experimental results show that the dynamic range of the measured Q-value for the change in the R_S-value of the sample is minimum for the cavity resonator technique and maximum for the dielectric resonator technique indicating that later technique provides more sensitive R_S measurement than the other two techniques. In a cavity resonator the magnitude of the maximum rf magnetic field H_rf^max is small and insufficient to study the rf power dependence of the HTS thin films. In dielectric resonator, R_S increases linearly with input rf power upto the available maximum power (20dBm). However, the patterned thin film microstrip resonator showed onset of non-linear effects at around 15dBm input power. The crossover maximum current density J_r^fc measured at the onset for the fundamental (4.9 GHz), first (9.8 GHz) and second (14.5 GHz) harmonic modes at temperatures 77K (40K) are respectively 4.2 x 10⁵ (6.6 x 10⁶), 2.4 x 10⁵ (3.5 x 10⁶) and 1.6 x 10⁵ (2.2 x 10⁶) A/cm.

4PO9-19 Effects of Split Gap on the Microwave Properties of YBCO Ring Resonators

H.K. Zeng, J.Y. Juang, K.H. Wu, T.M. Uen, and Y.S. Gou, Department of Electrophysics, National Chiao-Tung University, Hsinchu, Taiwan, R.O.C.

Presenting Author: Y.S. Gou

Microwave ring resonators made of high-T_c superconducting (HTS) thin films are of considerable interest owing to their geometry advantages in possibly resolving the extremely non-uniform current distribution commonly encountered by the stripline resonators. Recently, we have succeeded in fabricating HTS ring resonators by using the double-side deposited YBCO films on LaAlO₃ (LAO) substrates. With the use of YBCO ground plane quality factor (Q) over 10⁴ at resonating frequency of 3.6 GHz has been demonstrated. By measuring the temperature dependence of frequency shift (D f) and Q, the physical parameters such as surface resistance, surface reactance, and penetration depth of the HTS materials were studied. Furthermore, by creating a narrow gap in the same ring structure, we found that not only the resonating frequency occurred at the half of the original one (i.e. at 1.8 GHz) but also the temperature dependence of the various parameters changed drastically. Detailed results and model analyses base on capacitance-coupled (induced by the gap) effects will be discussed.