Microwave Surface Resistance Measurements Research Articles

High-Temperature Measurement Technology for Microwave Surface Resistance of Metal Materials

The resonant cavity method is a commonly used method for high-temperature testing of the complex permittivity of dielectric materials. When a resonant cavity is used for high-temperature testing, the microwave surface resistance of the cavity metal material will deteriorate due to factors such as oxidation reaction and thermal fatigue, resulting in a decrease in testing accuracy and repeatability. Therefore, when designing a high-temperature resonant cavity, the temperature response characteristics of the microwave surface resistance of the cavity metal material should be obtained in advance. In this paper, a high-temperature measurement method of microwave surface resistance of metal materials based on a separate cylindrical resonator is proposed, a mathematical model of microwave surface resistance inversion based on the resonator quality factor is established, and a high-temperature measurement system of microwave surface resistance is integrated. The reliability of the proposed method and system is verified through simulation and experiment. The measurement frequency covers 7-18 GHz, and the maximum test temperature reaches 500°C. Systematic error of microwave surface resistance measurement at room temperature is less than 3%.

Lift-Off and Tilt Effect in Microwave Surface Resistance Measurement Using TE011 Mode Cylindrical Cavity

Measurement of surface resistance at microwave or higher frequency bands is needed for applications, such as accelerators, microwave systems, and integrated circuits. Cylindrical cavity resonators operating at TE₀₁₁ mode have been applied in surface resistance measurement for decades. It is common that samples under test are usually used as one of the cavity&#x2019;s endplates and contact the cylinder side wall directly, which cannot be regarded as noncontact measurement. In this article, through quantitative research on lift-off effect of samples under test, we explore the possibility of realizing noncontact surface resistance measurement by intentionally introducing an air gap (ranging from &#x007E;0 to 10 mm) between the samples and the cavity side wall. From the results of both electromagnetic simulations and experiments, it can be concluded that by taking care of the sample&#x2019;s tilt effect, surface resistance can be measured in a noncontact manner. Measurement results of polished metal plates with electrical conductivity ranging from &#x007E;2 to 58 MS/m (measured with standard eddy current method) show that the relative measurement error is expected to be less than 10&#x0025;. Compared with related publications, the focus of this work is put on the lift-off effect and a larger range of air gap is introduced. The obtained results indicate that the air-gap size may be an additional consideration in the design of surface resistance measurement system for special applications, such as temperature-dependent measurements in vacuum chamber, <i>in situ</i> diagnosis tools.

Characterizing the Distribution of Microwave Surface Resistance of HTS Film Based on Metal Ring

This paper presents a novel method for measuring the microwave surface resistance distribution of high-temperature superconducting thin films by a dielectric resonator with a metal ring. After calibration, the effect of metal ring loss on measurement accuracy is negligible. The measurement resolution is determined by the internal diameter of the metal ring, which makes the design of the device more flexible. Therefore, measurement with high resolution and convenience can be achieved simultaneously by using a metal ring with proper size and operating at a relatively low frequency. A test device working at 32 GHz with TE01(1 + δ) mode was developed. Its resolution is a circular area with a diameter of 5 mm and an area of 19.6 mm2. The unloaded quality factor of the test device is more than 140,000, when it is loaded by the calibration cavity. The test device has a relative uncertainty of less than 6%, which complies with the uncertainty (20%) specified by the international standard for the microwave surface resistance measurement of high-temperature superconducting (HTS) thin film. The surface resistance distribution of a 2-in. YBCO/LAO/YBCO superconducting film sample was measured by this test device.

A novel method for the measurement of frequency-character of surface resistance of HTS thin film

A novel method for microwave surface resistance measurement of high temperature superconductor thin film at multi-frequency by multimode of sapphire rod is introduced. This method has the advantages of high sensitivity and large dynamic range of the measurement. By using this method, the frequency dependent microwave surface resistance of a single piece of high temperature superconductor thin film can be characterized within one temperature cycle. This method is capable of reducing the amount of work in surface resistance measurement and providing supports to the research and the industrialization of high temperature superconductor thin film.

Fluxon dynamics in Li–Al codoped [formula omitted] by microwave surface resistance measurements

The magnetic-field-induced variations of the microwave surface resistance, R s , have been investigated in ceramic Mg 1− x (LiAl) x B 2, with x in the range 0.1 – 0.4 . The measurements have been performed on increasing and decreasing the DC magnetic field, H 0 , at fixed temperatures. At low temperatures, we have observed a magnetic hysteresis in the R s ( H 0 ) curves in all the investigated samples. On increasing the temperature, the range of H 0 in which the hysteretic behavior is visible shrinks; however, in the sample with x = 0.1 it is present up to temperatures close to T c . We show that the field dependence of R s can be quantitatively justified taking into account the critical-state effects on the fluxon lattice only in the sample with x = 0.4 . On the contrary, in the samples with x < 0.4 the hysteresis exhibits an unusual shape, similar to that observed in others two-gap MgB 2 samples, which cannot be justified in the framework of the critical-state models.

Strong reduction of the field-dependent microwave surface resistance in YBCO with BaZrO3 inclusions

We present measurements of the magnetic field dependent microwave surface resistance in laser-ablated YBa2Cu3O7-δ films on SrTiO3 substrates. BaZrO3 crystallites were included in the films using composite targets containing BaZrO3 inclusions with mean grain size smaller than 1 μm. X-ray diffraction showed single epitaxial relationship between BaZrO3 and YBa2Cu3O7-δ. The effective surface resistance was measured at 47.7 GHz for 60<T<90 K and 0<μ0H<0.8 T. The magnetic field had a very different effect on pristine YBa2Cu3O7-δ and YBa2Cu3O7-δ/BaZrO3, while for μ0H=0 only a reduction of Tc in the YBa2Cu3O7-δ/BaZrO3 film was observed, consistent with dc measurements. At low enough T, in moderate fields YBa2Cu3O7-δ/BaZrO3 exhibited an intrinsic thin film resistance lower than the pure film. The results clearly indicate that BaZrO3 inclusions determine a strong reduction of the field-dependent surface resistance. From the analysis of the data in the framework of simple models for the microwave surface impedance in the mixed state we argue that BaZrO3 inclusions determine very steep pinning potentials.

Microwave surface resistance measurement of hts films using dielectric resonators

An open-ended dielectric resonator method and experimental apparatus for measuring microwave surface resistance of the high Tc superconducting thin films are reported. Making use of two sapphire rods the quality factor related to the losses of the resonator except its superconducting part can be evaluated. The Rs value of an individual superconducting thin film can be determined without any assistance of other superconducting films or calibrators. This measurement provides a convenient and absolute approach for Rs-measurement of high Tc superconducting thin films. Also the error in the Rs-measurement with the method was discussed.

Microwave characterization of laser ablated Y 1Ba 2Cu 3O 7− x thin films

In the present study we report the measurements of microwave surface resistance ( R s) of YBCO thin films on LaAlO 3 substrate as a function of temperature, thickness and magnetic field by microstrip resonator technique. The T c( R = 0) of the films is 90 K and J c > 10 6 A/cm 2 at 77 K. The microwave surface resistance has been measured for films of various thicknesses. The value of R s has been found to be initially decreased with increasing film thickness due to increase in number of defects. A minimum microwave surface resistance has been obtained for film thickness of about 300 nm. The increase of R s with film thickness above 300 nm is possibly due to degradation of the film microstructure as observed with Atomic Force Microscopy. Temperature dependence of surface resistance has been studied for best quality films. The field induced variations of surface resistance are also investigated by applying dc magnetic field perpendicular to stripline structure and surface of the film. A general linear and square field dependence of R s at low and high value of fields has been observed with critical field value of 0.4 T which confirms the microwave dissipation induced by flux flow in these resonators at 10 GHz frequency. The hysteresis of R s in dc field observed for field value above critical field shows the higher value of surface resistance in decreasing field than in increasing field which is in agreement with one state critical model and is a characteristic of homogeneous superconductors.

Fluxon dynamics by microwave surface resistance measurements in MgB 2

Field-induced variations of the microwave surface resistance, R s( H), have been investigated in high-density ceramic MgB 2. At low temperatures, several peculiarities of the R s( H) curves cannot be justified in the framework of models reported in the literature. We suggest that they are ascribable to the unconventional vortex structure in MgB 2, related to the presence of two gaps. On the contrary, the results near T c can be accounted for by the Coffey and Clem model, with fluxons moving in the flux-flow regime, provided that the anisotropy of the upper critical field is taken into due account.

Role of twins in peak effect phenomenon observed at microwave frequencies in high Tc superconductor thin films

Measurements of microwave surface resistance, R s, at subcritical currents as a function of temperature with varying dc magnetic field upto 0.8 T have shown peak effect (PE) in epitaxial DyBa 2Cu 3O 7− δ (DBCO) and YBa 2Cu 3O 7− δ (YBCO) thin films grown by pulsed laser deposition on 〈1 0 0〉 LaAlO 3 substrates. Microwave measurements were performed on microstrip resonators as test vehicles. Occurrence of a peak in R s in dc magnetic field is governed by the nature and concentration of defects. Evidence shows that thinner films with a higher ratio of areal density of extended defects, n e (such as twin boundaries), to the areal density of point defects, n p, show PE at the measurement frequencies 4.88 and 9.55 GHz; whereas, thicker films (⩾3000 Å) with a smaller n e/ n p ratio do not show PE. 2500 Å thick YBCO film shows a double peak structure at 9.55 GHz, thereby suggesting two sets of twin boundaries in this film having different κ p values. Measurements carried out on low-twinned LaAlO 3 substrates show that 2400 Å thick DBCO film does not exhibit the PE phenomenon at 4.88 GHz upto to an applied field of 0.8 T; this indicates that twins propagated from the LaAlO 3 substrates are responsible for the occurrence of PE at microwave frequencies. Oxygen ion irradiation (90 MeV, 3 × 10 13 ions/cm 2) of 2500 Å DBCO film has been found to shift the peak to lower temperature at 4.88 GHz, but significantly suppress the peak at 9.55 GHz. Depinning frequency, ω p vs. T plot obtained for the 2400 Å DBCO film shows a peak due to the peak in its R s vs. T plots.

Factors affecting the microwave surface resistance of crack-free thick YBCO films on sapphire substrates

We investigated the influence of the composition of YBCO film, deposited on sapphire 〈 R〉 substrates with CeO 2 buffer layers, on their microwave surface resistance. Y-rich YBCO films, 0.5-μm thick, deposited onto a 250-Å thick CeO 2 film showed good crystallinity, a smooth surface and low R s value. Results of the Hall constant measurement and the chemical state analysis infer that the composition deviation of the film from 1-2-3 stoichiometry to Y-rich does not produce defects, such as a second phase, and resulted in a small residual resistance which manifests itself in the microwave surface resistance measurement.

Observation of weak-limit quasiparticle scattering via broadband microwave spectroscopy of a d-wave superconductor.

There has long been a discrepancy between microwave conductivity measurements in high temperature superconductors and the conductivity spectrum expected in the simplest models for impurity scattering in a d-wave superconductor. Here we present a new type of broadband measurement of microwave surface resistance that finally shows some of the spectral features expected for a d(x2-y2) pairing state. Cusp-shaped conductivity spectra, consistent with weak impurity scattering of nodal quasiparticles, were obtained in the 0.6-21 GHz frequency range in highly ordered crystals of YBa2Cu3O6.50 and YBa2Cu3O6.99.

Optical emission spectroscopy of the plasma during sputter deposition of YBCO films for microwave applications

YBCO thin films are currently used in several HTS-based electronics applications. The performance of devices, which may include microwave passive components (filters, resonators), grain boundary junctions or spintronic multilayer structures, is determined by film quality, which in turn depends on the deposition technology used and growth parameters. We report on results from nonintrusive Optical Emission Spectroscopy of the plasma during YBCO thin film deposition in a high-pressure on-axis sputtering system under different conditions, including small trace gas additions to the sputtering gas. We correlate these results with the compositional and structural changes which affect the DC and microwave properties of YBCO films. Film morphology, composition, structure and in- and out-of-plane orientation were assessed; T/sub c/ and microwave surface resistance measurements were made using inductive and resonator techniques. Comparison was made with films sputtered in an off-axis 2-opposing magnetron system.

Peak-effect, a new phenomenon observed at microwave frequencies in high Tc superconductor thin films

Measurements of microwave surface resistance in magnetic fields (parallel to c-axis), ranging between 0.2 and 0.9 T, of high quality epitaxial DyBa 2Cu 3O 7− y and YBa 2Cu 3O 7− y superconducting thin films show a pronounced peak near the superconducting transition temperature. It is more pronounced at a frequency of 9.55 GHz as compared to 4.88 GHz. The exact nature of the peak is somewhat sample-dependent thereby indicating that the nature and distribution of defects in the films or the pinning sites determine the nature of the peaks; however, it follows the general trend that as the magnetic field is increased the peak shifts towards the lower temperature and is absent when the field is zero. The temperature and field dependence of the peak suggests that this peak could be associated with the order–disorder transition of the flux-line lattice. The peak-effect shows strong frequency dependence close to the depinning frequency of the flux line lattice. We explain our data in terms of the temperature dependence of the Labusch parameter within the collective pinning scenario in type II superconductors.

Surface impedance of R 1(Nd xBa 2− x)Cu 3O 7− δ (R=Nd, Y) thin films

We have studied the effect of Nd/Ba substitution on the superconducting properties of R 1(Nd x Ba 2− x )Cu 3O 7 (R=Nd, Y) thin films by using microwave penetration depth and surface resistance measurements. Data on samples characterised by a Nd-excess of 4–5% have been collected by using a microstrip resonator at frequencies of 1.44 and 9.7 GHz and a symmetric dielectric resonator technique in TE 0 1 1 mode at 19.8 GHz. A quadratic bT 2 low temperature dependence of the penetration depth is observed for the Nd-rich samples, with the coefficient b decreasing with the frequency. The data can be reasonably explained in a d-wave framework supposing that Nd at Ba site behaves, both in Nd 1+ x Ba 2− x Cu 3O 7 and Y 1(Nd x Ba 2− x )Cu 3O 7, as a resonant impurity, as confirmed by scanning tunnelling spectroscopy. The changes of the temperature dependence of the penetration depth with the frequency can be explained with a two fluid approach taking into account the frequency dependence of the complex conductivity.

Hysteresis measurement of anomalous microwave surface resistance in superconducting thin films

The anomalous decrease in microwave surface resistance, R s, of superconducting YBa 2Cu 3O 7−d (YBCO) thin films in the presence of a low dc magnetic field is studied using a microstrip resonator technique. We have done a dc field hysteresis measurement of R s to study the effects of vortex penetration on the anomalous effect. It is shown that the anomaly happens at a field level far below the low critical field, H c1, strip of the superconducting microstrip and that the vortex (Abrikosov) penetration would eliminate the anomalous effect observed at low field. This implies that the anomalous effect does not originate from vortices.

Observation of proximity effect in YBCO/Au bilayer films by microwave surface resistance measurements

Measurements of surface resistance R s for YBCO films covered with thin Au layer of thickness d are carried out at 67 GHz in the temperature range 100–60 K. Measured R s( d) dependence exhibits a large maximum at small d≈20 nm which cannot be explained by the simple model of normal metal–HTSC bilayer surface resistance. The difference is attributed to the proximity effects at the YBCO/Au interface.

Laterally resolved microwave surface-resistance measurement of high-T/sub c/ superconductor samples by cavity substitution technique

Microwave surface impedance measurement of a high-temperature superconductor (HTS) is a sensitive probe to test its quality, particularly if a microwave device is to be fabricated. Most microwave characterization employs resonance techniques in which the components of the surface impedance are extracted from the measured Q value and the shift in the resonance frequency. In this paper, we present a modification of the widely used complete end-plate substitution technique to measure the surface resistance of samples having dimensions smaller than the dimension of the end plate at 20 GHz, as well as to facilitate the laterally resolved surface resistance measurement of large-area HTS samples. From the knowledge of the electromagnetic-field configuration in a TE/sub 011/-mode cylindrical cavity, the loss contribution from the HTS sample is analyzed theoretically and measured experimentally in the temperature range of 20-100 K. The design of the cavity is discussed to optimize the sensitivity of the measurement by the placement of the sample and to maximize the difference in the measured Q value.

Microwave surface resistance measurements on the heavy fermion superconductor UPt 3

The relative change of the microwave surface resistance has been measured as a function of temperature in the superconducting and normal states of UPt 3 using a cavity perturbation technique. With our frequency range of ∼9–38 GHz, the microwave photon energy (ℏ ω) is ∼20–95% of the estimated zero-temperature (BCS) energy gap (2 Δ 0) of UPt 3. The surface resistance shows a change in slope as the signature of T c and has a significantly weaker temperature dependence in the superconducting state than would be predicted by the Mattis–Bardeen theory. At higher frequencies, the slope tends to change by a smaller amount. No indication of collective modes at any of the frequencies was observed down to the lowest temperatures measured (∼0.1 K).

Microwave surface resistance of YBCO bulk samples prepared by addition of HgO to YBCO system

The paper reports microwave surface resistance (R/sub s/) measurement on yttrium barium copper oxide (YBCO) bulk samples, prepared by an alternate route, namely by addition of mercury oxide (HgO) to YBCO system. R/sub s/ is measured using a TE/sub 011/ mode cylindrical cavity, at 20 GHz, by the end plate substitution technique. HgO added to the YBCO system has the advantage that oxygen in HgO acts as a copious source of oxygen and therefore does not require sintering in oxygen flow. Powder X-ray diffraction studies confirm the formation of pure orthorhombic 123 phase without any indication of Hg or known Hg compounds. The specimen with 0.5 wt.% of HgO added to the YBCO system showed superior superconducting properties including microwave surface resistance (22.5 m/spl Omega/ at 77 K and 20.0014 GHz). The R/sub s/ has also been measured as a function of the area of the sample that yields consistent value confirming surface homogeneity. This is believed due to stoichiometric oxygenation and large number of well connected grains.