Microstrip Resonator Technique Research Articles

Design of highly sensitive temperature sensor based on photonic band gap structure

In this paper, a novel microstrip resonator technique for temperature sensing is proposed, designed, and implemented using a hybrid planar microstrip line and photonic band gap (PBG) structure. To implement the PBG structure of the microstrip line, a microfluidic channel with periodic form is introduced into the substrate and filled with water. The operation principle of the sensor is based on a frequency shift due to the variation in the center of the band gap, which in turn changes with the variation of the permittivity of water, which relates to the temperature. The different empirical expressions describing the complex permittivity with the resonant frequency were carried out. The proposed sensor is simple in design and low cost, which may be applied in different applications at the industrial.

Improvement of microwave characteristics for high-T c superconductor (YBCO) films by ion irradiation treatment

Measurements of the microwave surface impedance for high-temperature superconductor YBa2Cu3O7−x (YBCO) films irradiated by 3 MeV Au2+ ions at three irradiation doses (1010 cm−2, 1011 cm−2, and 1012 cm−2) were carried out at different temperatures (below the critical temperature of T с ≈ 90 К) and various rf current amplitudes by the use of the microstrip resonator technique. A noticeable decrease in the surface resistance and an enhancement of the linear response range at low temperatures were observed for moderately irradiated film exposed to an irradiation dose of 1011 cm−2, while at higher irradiation doses (1012 cm−2) an increase in the surface resistance and a decrease in the linear response range were observed for all temperatures below T c. These results are discussed in the framework of phenomenological theory for the microwave response of superconductors with nano-sized structural defects.

A study on stress affecting the microwave surface resistance of YBCO high temperature superconducting thin films

We calculate stress in YBa 2Cu 3O 7− x /MgO (YBCO/MgO) and YBa 2Cu 3O 7− x /LaAlO 3 (YBCO/LAO) by XRD of the sample, σ 1 = −1.2 GPa and σ 2 = −1.4 GPa, respectively, which shows that the stress in YBCO/LAO is stronger than that in YBCO/MgO. In addition, microwave response of the two pieces of thin films is also investigated by microstrip resonator technique. Surface resistance and penetration depth of the films are obtained by analyzing S 21 resonant curves of the microstrip resonator, the penetration depth λ 0 = 280 nm for YBCO/MgO and λ 0 = 265 nm for YBCO/LAO, and surface resistance R s = 0.376 mΩ for YBCO/MgO and R s = 2.660 mΩ for YBCO/LAO at 78 K, 10 GHz. The results show stronger stress in YBCO/LAO which lead to a larger microwave surface resistance than YBCO/MgO's. Some rational explanations are also analyzed and discussed in the paper.

THE EFFECT OF THE INTERACTION BETWEEN THE FILMS AND THE SUBSTRATES ON THE MICROWAVE PROPERTIES Of YBCO THIN FILMS

The microwave properties of YBa 2 Cu 3 O 7- x / LaAlO 3 (YBCO/LAO) and YBa 2 Cu 3 O 7- x / MgO (YBCO/MgO) thin films have been investigated by microstrip resonator technique. The penetration depth λ0(0 K ) and the microwave surface resistance Rs can be obtained by analyzing the experimental data of the temperature dependence of resonant frequency, unload quality factor of the microstrip resonator. The stress in the two thin films can be obtained from their XRD patterns. The result shows that the stronger stress in YBCO/LAO thing film makes it have larger microwave surface resistance at lower temperature.

THE MICROWAVE PROPERTIES OF THE DOUBLE-SIDED THIN FILM MgB2 RESONATOR

Double-sided magnesium diboride ( MgB 2) thin films have been grown on double-sided polished sapphire substrates by the technique of hybrid physical chemical vapor deposition (HPCVD). The zero resistance temperature ( Tc ) of the films is higher than 37 K. The microwave characteristic of the double-sided MgB 2 thin films at 8.7GHz is studied systematically by the microstrip resonator technique. Surface resistance of the thin films is extracted by analyzing the resonance curves at different temperatures, and it is 1.2 mΩ at 11K.

Microwave Response of MgB2/Al2O3 Superconducting ThinFilms by Microstrip Resonator Technique

Double-sided superconducting MgB2 thin films are deposited ontoc-Al2O3 substrates by the hybrid physical chemicalvapour deposition method. The microwave response ofMgB2/Al2O3 is investigated by microstrip resonatortechnique. A grain-size model is introduced to the theory of microstripresonators to analyse microwave properties of the films. We obtaineffective penetration depth of the films at 0 K (λe0 = 463 nm)and surface resistance (Rs = 1.52 mΩ at 11 K and8.73 GHz) by analysing the resonant frequency and unload qualityfactor of the microstrip resonator, which suggests that the impuritiesand disorders of grain boundaries of MgB2/Al2O3 result inincreasing penetration depth and surface resistance of the films.

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.

Microstructure and temperature dependence of microwave penetration depth of Ag doped Y 1Ba 2Cu 3O 7− x thin films

We report the measurements of magnetic penetration depth λ( T) of Ag-doped YBa 2Cu 3O 7− δ (YBCO) thin films in the thickness range 1500–4000 A and temperature range 18–88 K. The films are in situ grown by laser ablation on 〈1 0 0〉 LaAlO 3 substrates. The penetration depth measurements are performed by microstrip resonator technique. A correlation of λ( T) with the film microstructure observed with atomic force microscopy has shown that λ( T) depends critically on the film microstructure. Temperature dependence of magnetic penetration depth has also been studied for best quality films. The experimental results are discussed in terms of BCS theory (s-wave pairing) and d-wave Pairing with and without unitary scattering. The results are found to be best fitted to the d-wave model with unitary scattering limit. Near T c, we have also compare the (3D) XY critical regime and the Ginzburg–Landau (GL) behaviour.

A systematic study of the role of Nd/Ba disorder on the superconducting properties of Nd 1 + x Ba 2 - x Cu 3 O 7 - δ thin films

The role of Nd/Ba disorder on the superconducting properties of Nd1+xBa2-xCu3O 7 - δ epitaxial thin films has been systematically studied. The temperature dependence of the ab-plane penetration depth of highly c-axis epitaxial samples having different Nd/Ba composition has been measured by an inverted microstrip resonator technique. Stoichiometric films (x = 0) exhibit a linear penetration depth at low temperature, while Nd-rich films (0 < x < 0.3) show a T2 law. We find that for low Nd excess it is possible to obtain a reasonable fit of the data in the full temperature range using the d-wave picture, with the assumption that Nd at Ba site plays the role of unitary scattering center. At high concentration, the low temperature data can be instead explained supposing that excess Nd acts as impurity with intermediate strength. The dependence of the critical temperature and of the zero temperature superfluid density on disorder have been also studied. It is found that these two quantities are correlated in a way analogous to what reported for YBCO films and single crystals having Zn, Ni impurities at Cu site. An attempt to explain the results using a s-wave approach, as in the two-gap model, is able to reproduce the data but gives results quantitatively conflicting. On the contrary a self-consistent picture within a d-wave framework can be obtained taking into account the effect of localization and suppression of the order parameter at impurity sites in the case of both low and high impurity content.

DC magnetic field induced anomalous microwave response in YBCO thin films: temperature dependence

Using a microstrip resonator technique, the magnetic field dependence of the surface impedance Z s= R s+ jX s, where R s is the surface resistance and X s the surface reactance, of superconducting YBa 2Cu 3O 7− d thin films has been measured at a frequency of 1.1 GHz and at different temperatures. The anomalous microwave response, where R s decreases in the presence of low dc magnetic fields, has been observed for all the samples under test at different temperatures. The anomalous microwave effect is found to be stronger at higher temperatures. The threshold field H *, at which the surface resistance show a minimum, decreases with temperature and it is governed by the competition between the anomalous effect at low fields and the vortex mechanism at high fields.

Sensitivity of R/sub s/-measurement of HTS thin films by three prime resonant techniques: cavity resonator, dielectric resonator, and microstrip resonator

The microwave surface resistance, R/sub s/ measurement of YBa/sub 2/Cu/sub 3/0/sub 7/ /sub -/spl delta// (YBCO) thin film deposited on 10 mm /spl times/ 10 mm LaAlO/sub 3/ substrate using three prime resonating techniques, namely, cavity end plate substitution technique (20 GHz), dielectric resonator technique (18 GHz), and microstrip resonator technique (5 GHz), is reported. In addition, theoretical analysis for each technique has been performed to calculate the relative percentage error in the measured R/sub s/ -value of the YBCO thin film as a function of temperature. It has been found that the shielded dielectric resonator provides far better sensitivity for R.-measurement of the YBCO thin film with minimum relative percentage error (<4%) in the temperature range from 20 K to transition temperature of YBCO thin film compared to the other two techniques.

Synthesis and microwave properties of TI2Ba2CaCu2O8 superconducting films grown by MOCVD

We report on the synthesis, structural and electrical characterization of high quality Tl2Ba2Ca1Cu2O8 (Tl-2212) superconducting films. The samples have been grown ex-situ on mm2 LaAlO3 (100) substrates by a combined approach of metal-organic chemical vapor deposition (MOCVD) and thallium vapor diffusion. The morphological and compositional nature of the c-axis oriented films has been investigated by SEM and X-ray analyses. Typical values of K and MA/cm2 at 77 K have been measured. Microwave measurements have been performed at f = 87 GHz inserting the film in a copper cavity and at f =1.5 GHz on patterned samples using a microstrip resonator technique. A penetration depth nm is evaluated by fitting the microwave data with phenomenological equations. The minimum value of the surface resistance measured at 4.2 K is 60 and 6 m at 1.5 GHz and 87 GHz respectively. The microwave data are described in the context of a modified two fluid model. An evaluation of the temperature dependence of the scattering rate has been performed through the simultaneous measurement of the surface resistance and the penetration depth.

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.

Magnetic-field-induced anomalous microwave response in superconducting YBa2Cu3O7−δ thin films

The magnetic-field-induced decrease of microwave surface impedance, Zs=Rs+jXs, of superconducting YBa2Cu3O7−δ thin films is investigated using a microstrip resonator technique. Through measuring Zs as the direct current (dc) magnetic field is increased from zero to a certain value Hmax and subsequently decreased back to zero, it is found that Zs(Hdc) is totally reversible if Hmax does not exceed the threshold field H*, at which Rs shows a minimum, while it is irreversible if Hmax is larger than H*. It is confirmed that the anomalous effect happens in a vortex-free state. The threshold field H* is identified with the lower critical field for the vortices penetrating into the superconducting thin films. The anomalous effect is believed to be mainly contributed by the imperfect microstructure of the superconducting thin films.

ON THE ROLE OF Nd/Ba DISORDER ON THE SUPERCONDUCTING PROPERTIES OF Re1(NdxBa2-x)Cu3O7-δ (Re=Nd, Y) THIN FILMS

The role of disorder on the superconducting properties of Re 1( Nd x Ba 2-x ) Cu 3 O 7-δ (Re=Nd, Y) epitaxial thin films has been studied. The films are deposited by Ar+O 2 magnetron and diode dc sputtering from targets characterised by different x (0, 0.08 and 0.12). In situ X-ray Photoemission Spectroscopy (XPS), Scanning Tunneling Microscopy (STM), and non-conventinal X-ray diffraction measurements have been used to determine the exact composition and the structural properties of each sample. The temperature dependence of the ab-plane penetratin depth of highly c-axis epitaxial samples, characterised by different Nd/Ba ratios, has been determined by an inverted microstrip resonator technique. Results on the Nd 1+x Ba 2-x Cu 3 O 7-δ system show that only stoichiometric films exhibit a linear penetration depth at low temperature while Nd-rich films show a T 2 law. Preliminary measurements on the Y 1( Nd x Ba 2-x ) Cu 3 O 7-δ system confirm these results. The data are analysed in the framework of the d-wave model taking into account the effect of impurities on the superconducting properties.

Experimental observation and simulation of unusual microwave response for the superconducting microstrip resonator at small dc magnetic field

An unusual microwave response of the surface impedance Zs of high-Tc thin films at an applied small dc magnetic field (Bdc) at 77 K, namely a decrease of Zs, is observed with the microstrip resonator technique. The resonant frequency is 1.107 GHz. The direction of Bdc is parallel or perpendicular to the a-b plane. Bdc ranges from 0 to 200 G. It is found that the surface resistance (Rs) at Bdc parallel to the a-b plane first decreases with Bdc and then increases above a crossover field. The Rs behaviour for Bdc perpendicular to the a-b plane is the same but with a different crossover field. The two behaviours can be collapsed to one curve by scaling the crossover fields. The changes of surface reactance Xs correlated linearly with the changes of Rs in the ranges of Bdc. The ratios rH of changes of Rs and Xs (rH = Rs/ Xs) are 0.5 at Bdc less than the crossover field and 0.1 at Bdc greater than the crossover field. The measurements also show that the crossover field is independent of rf input power. A phenomenological model is also proposed to explain this unusual behaviour. By adjusting fitting parameters the computed results agree with the experimental results qualitatively.

Properties of TBCCO 2212 Thin Films for Electronic Applications

We report on the synthesis and structural and electrical characterization of high quality Tl 2 Ba 2 Ca 1 Cu 2 O x superconducting thin films. The samples have been prepared ex-situ by a combined approach of Metal-Organic Chemical Vapor Deposition (MOCVD) and thallium vapor diffusion. The films have been grown on 10×10 mm 2 (100) LaAlO 3 substrates. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analyses (EDX) have investigated the morphological and compositional nature of the films. The transport properties have been measured using both a four-probes and an inductive method. The highest critical temperature and critical current density are 104 K and 1 × 106A/cm2 respectively. The microwave response of two samples has been studied using a microstrip resonator technique. The best surface resistance values are below 200 μΩ at 1.2 GHz and 4.2 K. Measurements of the field dependence of the surface resistance have been performed.

Single and Double Side YBCO Thin Films for X-Band Microwave Filters and Devices

The properties of high quality single side and double side YBa 2 Cu 2 O 7-δ (YBCO) thin films deposited on LaA1O 3 substrates by pure oxygen d.c. sputtering are reported. The single side films are highly c -axis oriented with their a (or b) axis parallel to that of the substrate. The critical temperature is higher than 91 K with transition width less than 0.5 K, while the critical current density Jc is higher than 3 MA/cm2 at 77 K. The best double side samples exhibit no appreciable differences in the superconducting properties of the films deposited on the two different sides. X-ray analyses show in both cases highly c-axis oriented thin films with comparable values of the c -axis length (1.169 nm). The microwave properties are tested by a microstrip resonator technique. The surface resistance is lower than 80 μΩ at 77 K and f=5.4 GHz while the penetration depth at low temperature is in the range 150-200 nm.

Investigation of microwave current effect on parameters of YBCO thin films in microstrip resonator structure

The effect of microwave (MW) current on the parameters of YBCO thin films deposited on LaAlO 3 substrates was investigated at 77 K and 4.23 GHz using the microstrip resonator technique. Approximate expressions for the hysteretic loss contribution to the HTS film surface resistance were drawn and used to interpret the MW current dependence of the surface resistance. Information about the critical current density, the current dependent part of the surface resistance and the penetration depth of the vortex lines were obtained by this approach for YBCO films of different quality.

Microwave penetration depth measurements of AgYBa 2Cu 3O 7−δ thin films

The penetration depth λ of 5 wt.% Ag-doped YBa 2Cu 3O 7−δ (YBCO) thin films has been measured using microstrip resonator technique. The films are grown in situ by laser ablation on 〈1 0 0〉 LaAlO 3 substrates. We found a minimum value of surface resistance, R s of 215 μΩ at 77 K and 10 GHz for a film thickness of about 3000 Å. Temperature dependence of magnetic penetration depth has also been studied for best quality films in the temperature range of 18–88 K. The experimental results are discussed in terms of BCS theory ( s-wave pairing) and d-wave pairing with and without impurity scattering. The corresponding value of λ (0) has been found to be 1400 Å for Ag doped YBCO film.