4PO9-20 Temperature Dependence of Penetration Depth in YBa₂Cu₃O_7-d Measured by Microwave 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: H.K. Zeng

YBa₂Cu₃O_7-d (YBCO) superconducting ring resonators with YBCO ground plane were fabricated using double-sided deposited YBCO films on LaAlO₃ (LAO) substrates. We systematically varied the oxygen content of YBa₂Cu₃O_7-d in both of the ring resonator and the ground plane. At fully oxygenated condition (d =005), the resonator exhibits a quality factor Q>10⁴ at 16K, The London penetration depth D l = l (T)-l (5K) obtained from the analyses of frequency shift D f and f displays a linear behaviour over a wide range of temperatures. By reducing the oxygen stoichiometry, although the transition temperature T_c, frequency shift D f is still linear in temperature, except that the slope changes with increasing oxygen deficiency. Since the strong linear dependence of D l at low temperature has been considered to be a characteristic of d-wave pairing symmetry, the current result showed imposed some further insight within this scenario in underdoped regime.

4PO9-21 Comparison between the Quality Factors of Microstrip Resonators Using Films Made by Deeping Pyrolisis and Laser Ablation Processes

M.T. de Melo 1, M.J. Lancaste 2, J.M. Ferreira 3, and J. Albino Aguiar 3. 1 Centro de Educação/CAP, Universidade Federal de Pernambuco, 50740-530, Recife, PE, Brazil. 2 Superconducting Research Group, The University of Birmingham, B15, 2TT, United Kingdom. 3 Departamento de Física, Universidade Federal de Pernambuco 50670-901, Recife, PE, Brazil.

Presenting Author: M.T. de Melo

Devices were fabricated by both processes laser ablation of YBa₂Cu₃O₇ thin film on MgO substrate and dipping pyrolysis of YBa₂Cu₃O_7-d on yttria-stabilized-zirconia (YSZ). In order to find the quality factors of the resonators and the surface resistances of the superconducting films, two Hybrids YBCO / Substrate/ Copper Microstrip resonators were set up. Both the MgO and the YSZ substrate strip dimensions were 2.4mm x 9.4mm x 0.5mm. The device was mounted in a brass housing which was built and sealed by soldering the two halves together in order to make it impervious to liquid nitrogen. The microwave power was capacitively coupled into the ends of the resonators using k-connector pins. The resonator responses were measured in transmission mode using a HP8720A network analyser. The best laser ablated film response at the fundamental frequency f₀ @ 7.2GHz had an unloaded quality factor of Q_o @ 1158 and the best dipping pyrolysis thin film at the fundamental frequency f₀ @ 6.3GHz had an unloaded quality factor of Q_o @ 507. However dipping pyrolysis thin films presented a better homogeneity over the YSZ substrate which is more suitable for resonator with wider substrate strip.

4PO9-22 Effective Propagation Parameters of Superconducting Wide Microstrips

M.T. de Melo 1, M.J. Lancaste 2, A. Belfort 3, J.M. Ferreira 4, and J. Albino Aguiar 4. 1 Centro de Educação/CAP, Universidade Federal de Pernambuco, 50740-530, Recife, PE, Brazil. 2 Superconducting Research Group, The University of Birmingham, B15, 2TT, United Kingdom. 3 Departamento de Eletrônica e Sistemas, Universidade Federal de Pernambuco, 50740-530, Recife, PE, Brazil. 4 Departamento de Física, Universidade Federal de Pernambuco, 50670-901, Recife, PE, Brazil.

Presenting Author: M.T. de Melo

Using the two fluid model theory and the basic equations for a short length of a transmission line the effective surface resistance (R_eff) and effective inductance concepts were used to investigate the influence of the film thickness on the wave propagation in a wide superconducting microstrip resonator. Phase velocity, attenuation coefficient and quality factor were theoretically related and described as a function of both the film and the dielectric thicknesses. Analyses were carried out assuming the film thickness (t) and the substrate thickness (h) in the ranges of 5-200nm and 0.01- 100m m, respectively. For a London penetration depth like l _L(0)=200nm and t = 100nm, R_eff becomes approximately five times bigger than the intrinsic surface resistance R_ss. In microwave frequencies, considering l _L smaller than the film thickness like l _L 296nm (at 7GHz and 77.3K) a travelling wave slows down more and more as t and h is made smaller and smaller. Moreover, the attenuation of the transmission line increases leading the unload Q to be decreased. For l _L > t the current density equation in the two fluid model has been modified and some preliminary results are shown as we take the non-local electrodynamics into account.

4PO9-23 Measurements of the effective electrodynamical parameters of Nb microstrip resonator

V.A. Dravin, A.L. Karuzskii, A.E. Krapivka, and A.V. Perestoronin, P.N.Lebedev Physical Institute of RAS, Leninsky pr. 53, 117924 Moscow, Russia

Presenting Author: A.L. Karuzskii

We have developed an experimental method for simultaneous determination of the most important electrodynamical parameters of a resonator: the effective dielectric permittivity and the effective length (the effective magnetic permeabilty). A method is based on the partial filling of a resonator cavity by the dielectric medium with low, controllably variable permittivity. For microstrip resonators partially filled with helium, the linear dependence of squared frequency on helium permittivity has been found experimentally.

Coefficients of this linear dependence have been related to the effective permittivity and the effective length of microstrip resonator. As a result, the simple technique for a fast and precise determination of the effective parameters of a microwave unit has been proposed. This method needs neither special test fixtures and circuit standardization nor additional model assumptions. Effective permittivities and effective lengths have been measured for Nb superconducting halfwave microstrip resonators in microwaves. Possibilities of the evaluation of superconducting material characteristics by the proposed technique are discussed.

4PO9-24 Analysis of a Trilayer Microstrip Line with Superconducting Strips

Vincent Mathew 1, A.G. Vedeshwar 2, and G.P. Srivastava 1. 1 Department of Electronic Science, University of Delhi South Campus, New Delhi 110021, India. 2 Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India.

Presenting Author: V. Mathew

This paper presents an analysis of a multilayered microstrip line comprising of three dielectric layers and two superconducting strips interspersing between them at the two interfaces. The analysis is carried out using the spectral domain approach. Accordingly, Maxwell’s equations are solved for the structure in Fourier transform domain and then a set of Green’s functions of impedance type is derived which connects the strip current and the transverse electric field at the two interfaces, by imposing the boundary conditions at the interfaces. The superconducting strips are modeled as thin sheets of complex impedance. The dispersion relation is derived in a Galerkin’s procedure by using a set of basis functions for the surface current on the strips.

The propagation parameters, corresponding to the uncoupled mode are evaluated as functions of frequency, operating temperature and film thickness. The attenuation and dispersion exhibit interesting features.

4PO9-25 Fabrication of microstrip bandpass filters using YBCO thin films and the package for the filters

Tao Liu 1, Hesheng Huang 1, Meihong Zhu 1, Yonggang Zhao 1, Bisong Cao 1, Xuexia Zhang 2, Yueliang Zhou 3, Meng He 3, and Dafu Cui 3. 1 Department of Physics, Tsinghua University, Beijing 100084, P.R. China. 2 Department of Electrical Engineering, Tsinghua University, Beijing 100084, P.R. China. 3 Institute of Physics, Academia Sinica, Beijing, 100080, P.R. China.

Presenting Author: H. Huang

A 5-pole forward-coupled microstrip bandpass filter is presented. The center frequency and the fractional bandwidth are 3 GHz and 5%, respectively. The filter was fabricated using 10mm-15mm high temperature superconducting (HTS) YBCO film on a 0.5-mm thick LaAlO₃ substrate. Characteristics of HTS filter with Ag ground plane (HTS/Ag-filter) are compared with that of Ag filter with Ag ground plane (Ag/Ag-filter). In addition, a microstrip 3-pole parallel-coupled bandpass filter with 5% fractional bandwidth at a center frequency of 6 GHz was designed and fabricated using 10mm-15mm HTS film on a 0.5-mm thick LaAlO₃ substrate. We also studied the issues related to HTS filter microwave packaging, including the interconnections from the HTS filter inside the package to the outside circuit and the structure of the package. The HTS filters showed good performance with less than 0.3dB insertion loss and sharp skirt.

4PO9-26 Properties of Single and Double Sided Tl₂Ba₂CaCu₂O₈ Films and Applications for Devices in the Microwave Region

Graziella Malandrino 1, Anna M. Borzi 1, Laura Perdicaro 1, Ignazio L. Fragala 1, Antonello Andreone 2, Antonio Cassinese 2, Francesco Palomba 2, and Giulia Pica 2. 1 Dipartimento di Scienze Chimiche, Università di Catania, I-95125 Catania, Italy. 2 I.N.F.M. and Dipartimento di Scienze Fisiche, Universita' di Napoli Federico II, Piazzale Tecchio 80, I-80125, Naples, Italy.

Presenting Author: I.L. Fragala

We report on the synthesis of high quality single and double-sided Tl₂Ba₂CaCu₂O₈ (2212) films for passive filter applications. A combined metal-organic chemical vapor deposition (MOCVD) and a thallium vapor diffusion approach has been used to grow ex -situ superconducting films on LaAlO₃ (100) 10x10 mm² substrates. In particular, a novel MOCVD methodology has been applied to the fabrication of double-sided BaCaCuOF matrices, while different conditions have been tested for the thallium vapor diffusion step. The geometries adopted in the reactors used for the double-sided films proved crucial both to control the Tl₂O partial pressure over the sample and to achieve reproducibility phase control and homogeneity on both sides.

The morphological and compositional nature of the films has been investigated by SEM and XRD. There is evidence of highly oriented c-axis grains and well-interconnected grain boundaries. Inductively measured transport properties showed typical values of T_c =104 K and J_c = 0.5 MA/cm² at 77 K. Microwave measurements have been performed at f=1.3 GHz with a microstrip resonator technique. X-band passive filters have been realized and tested. In particular, an analysis of the non-linear properties of films has been carried out through intermodulation measurements in the microwave region and compared with similar YBa₂Cu₃O₇ devices.

4PO9-27 Microwave Complex Resistivity in YBCO Films Above T_c: Effects of Fluctuations

D. Neri 1, R. Marcon 1, R. Rogai 1, E. Silva 1, R. Fastampa 2, M. Giura 2, S. Sarti 2, A.M. Cucolo 3, C. Beneduce 3, M. Boffa 3, and M.C. Cucolo 3. 1 Dipartimento di Fisica E.Amaldi and Unità INFM, Università degli Studi Roma Tre, Via della Vasca Navale 84, 00146 Roma, Italy. 2 Dip. di Fisica and Unità INFM, Università La Sapienza, 00185 Roma, Italy. 3 Dip. di Fisica and Unità INFM, Università di Salerno, 84081 Baronissi, Italy.

Presenting Author: R. Fastampa

We present measurements of the (a,b) plane complex resistivity at 24 GHz in nearly-optimally doped YBCO films with T_c = 90.3 K. Measurements are taken with a resonant cavity, in the end-wall configuration. The attention is focused on the behavior above T_c, where we discuss the data in terms of 2D and 3D fluctuations. An anisotropic 3D model better adapts to our results. However, we find that gaussian fluctuations are unable to describe our data both well above and in the vicinity of the critical temperature. The discrepancy well above T_c is recovered by including a short-wavelength cutoff in the calculation of the frequency-dependent fluctuational conductivity. In order to follow the slowing down of the fluctuations at T_c, we treat the region close to T_c including the quartic term of the order parameter in the Ginzburg-Landau functional within the Hartree approximation. We then find excellent agreement with our data from high temperature (T = 1.3 T_c) down to T_c. The imaginary part of the resistivity is sensitive to the choice of the quasiparticle scattering time, which results to be of order 1ps in all the samples measured.

4PO9-28 Film-thickness dependence of the microwave properties of YBCO films

Akihiko Akasegawa, Kazunori Yamanaka, and Teru Nakanishi, Inorganic Material & Polymers Laboratory, Fujitsu Laboratories Ltd., Atsugi 243-0197, Japan

Presenting Author: A. Akasegawa

A thick superconducting film for microwave devices such as resonators and filters must exhibit higher Q-values and also operate at higher temperatures. Previously, it has been observed that as the physical vapor deposited YBCO film thickness increases the crystalline quality deteriorates. It appears that there is a direct relationship between the grain orientation and Q- values. As a result, we examined the film-thickness dependence on the microwave properties and the microstructure of c-axis oriented YBCO films with thickness up to 1ƒÊm grown on MgO(100) substrates by pulsed laser deposition. It was found that the thicker films which contained misoriented grains showed an increase in R_s. The number of misoriented grains in the film appeared to be related to the density of CuO crystalline outgrowths. Film roughness appeared to be caused by CuO outgrowths which allowed misoriented grains to grow preferentially in thicker films resulting in higher R_s. By lowering the film growth rate, the number of CuO outgrowths in the film was greatly reduced. This allowed us to prepare a film with c-axis oriented grains which showed a low surface resistance, R_s, and unloaded Q in excess of 100,000 in a 2 GHz microstrip line resonator.

4PO9-29 On the components of microwave losses in Nd_0.67Sr_0.33MnO_3-x films

Mikhail Strikovski 1, Lei-Ming Xie 1, John Miller, Jr. 1, V.V. Srinivasu, and Jaroslaw Wosik 1,2. 1 Texas Center for Superconductivity, Houston, TX. 2 Department of Electrical Engineering, University of Houston, 4800 Calhoun Rd. Houston, TX 77204-5932, USA.

Presenting Author: M. Strikovski

For monolithic tunable microwave HTS devices, ferromagnetic perovskite oxides are attractive candidates to be used instead of ferrite materials crystallographically incompatible with HTS. However, better understanding of mechanism and components of the additional losses of microwave radiation caused by the magnetic perovskite film is needed to optimize device processing. In this study, relations between the losses of 13 GHz radiation in epitaxial Nd_0.67Sr_0.33MnO_3-x films and their dc transport and magnetic characteristics are studied in the 20– 300 K temperature range as function of the film oxygen content (process- dependent) and stress (film thickness– dependent).

Both, the reduced oxygen content in the as– deposited films and the substrate mismatch induced stress in the thinner films result in less loss. Relations observed suggest the microwave losses in the films are rather due to inhomogeneity in their magnetic microstructure than due to the degree of magnetization. Direct relation between the linewidth of the FMR resonance and the normalized film losses is observed, that suggests the magnetic inhomogeneity control of the losses. The results show that the losses in NSMO films with essential magnetization can be lowered via optimizing the film thickness and processing. The films optimized to have largest CMR effect are not necessarily optimal for application in microwave devises.