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In this paper we will describe the main results of the activity aimed to develop a prototype of superconducting receiver front-end (HTS RFE) for specific application in UMTS network. The system has been specifically designed to reach very low noise figure on the receiving channel to exploit the best performance in terms of sensitivity of the up-link channel.

In this paper the performances of superconducting devices based on fractal layout are discussed. Depending on their shape, fractals are characterized by self-similarity and/or space-filling properties. The former allows the design of superconducting filters with highly reduced dimensions and no appreciable loss of performance, whereas the latter is the basis for the fabrication of multi-band antennas which hold promise for very interesting applications. Our attention was focused on the square Koch loop and the Sierpinski gasket geometries. In particular, prototype four pole filters for UMTS (Universal Mobile Telecommunications Systems) applications based on Koch resonators have been designed. Measurements performed on prototype devices fabricated by using double-sided superconducting thin films are reported and compared with simulations.

In this paper, the design principles of a new miniaturized superconducting planar filter configuration is presented. The configuration is based on the combined use of dual-mode cross-slotted patch resonators and stepped resonators. Four-pole filters exhibiting a quasi-elliptical response and with operating frequencies in K-, L-, and C-bands have been designed as a test vehicle of the new configuration. The analyzed topology exhibits a high degree of miniaturization, requiring less than 50% of the area occupied by filters based on dual-mode or hairpin resonators. The physical origin of the transmission zeros is discussed, deriving equivalent-circuit descriptions that are capable of reproducing the measured frequency response. In order to confirm the validity of the introduced design principles, experimental performances on an exemplary L-band filter, realized using a YBCO film deposited on an MgO substrate and exhibiting a 3% fractional bandwidth, are presented. The measured frequency response obtained at T = 77 K agrees well with the simulations, presenting an insertion loss of 0.1 dB and a power handling of 34 dBm.

This Letter reports on the design and realization of HTS dual-mode cross-slotted filters presenting a more compact size if compared with the traditional dual-mode patch filters. Dual-stage filters operating in C band and presenting Chebyshev or quasi-elliptical responses have been realized and tested by using YBa2Cu3O7-x (YBCO) films. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 389–392, 2002>; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10331

Passive microwave filters based on HTS films are very promising for telecommunication applications. We report on the design, obtained using a commercial 2.5D software, and the realization of filters, fabricated with double sided YBCO films grown on LaAlO 3 substrates, for both receiving and transmission systems. For the receiving side, planar multi-pole interdigital L-band filters with 75 MHz transmission bandwidths have been fabricated on 2" substrates. Up to 80 K this kind of filter, based on a Tchebischev response, shows an insertion loss lower than 0.5 dB with a ripple of 0.3 dB for a maximum input power of 2 Watts. For the transmitting side, dual-mode filters represent one of the main interesting configuration to exploit since they can combine a high power handling capability with miniaturization requirements. A novel kind of dual-mode C-band filter based on cross slotted square resonators is presented. The novelty of the proposed structure is to use a pair of unequal crossed slots that are formed on a square patch resonator such that its structure size can be significantly reduced. A prototypal device operating at 3.7 GHz is fabricated with different type of couplings on 10 × 10 mm 2 LaAlO 3 substrate to showcase our proposal. The behavior of the filter as a function of the input power has been tested up to 2 Watts limited by the amplified power supply.

The design and realization of a simple and reliable convertible diode/magnetron deposition system allowing the in situ production of both high-T-c superconducting oxide films and low-T-c superconducting metallic films is presented. The ability to produce high-quality double-sided in situ films with uniform characteristics over 2 " diameter targets is demonstrated. This apparatus can represent a valid alternative to more sophisticated, less flexible deposition systems and is well suited for application in the large-scale production of superconducting filters for wireless communications.

We report on superconducting magnesium diboride MgB(2) thin films grown on both YSZ and MgO substrates, with two different orientations, namely [110] and [211]. MgB(2) off-axis growth mode (namely, with the c-axis tilted with respect to the film surface's normal) is achievable on these substrates. Depending on the type and orientation of the substrate, tilting angle can be varied. As a consequence of tilted growth, anisotropic transport properties are observed. In very thin films, resistance measurements provide an estimate of the resistivity anisotropic ratio rho(c)/rho(ab), where rho(c) is the resistivity along the c axis and rho(ab) is the in-plane resistivity. All these findings clearly demonstrate that tilted MgB(2) films offer new exciting possibilities to both investigate intrinsic fundamental properties of MgB(2) and to explore possible applications in planar superconducting devices

Bi 2 Sr 2 CaCu 2 O x thin films have been obtained on MgO and sapphire substrates by complete electron-beam evaporation of a bulk pellet and subsequent ex-situ oxigen annealing. Careful control of the initial stoichiometry and of the annealing procedure allowed to obtain high quality films with T cO =85 K. The films were polycrystalline but highly textured with the c-axis perpendicular to the substrate plane and critical current density of 5·10 4 A/cm 2 . In order to test the microwave properties of the films an innovative method, based on the measure of the quality factor of a ring microstrip resonator, has been set up. Preliminary measurements of the surface impedance versus rf power of BSCCO films on MgO substrate are presented.

We describe the preparation, structural and transport properties of CH3NH3SnBr3 organic-inorganic hybrid films (500 nm thick), which crystallize as cubic perovskites. They were deposited by single source thermal ablation technique, in a 10(-6) mbar vacuum chamber on glass, polymeric and crystalline substrates. X-ray diffraction proved that they were well crystallized and c-axis oriented. Resistivity measurements as a function of temperature showed a semiconductor behaviour. The activation energy, Delta E, was estimated by fitting the linear portions of the resistivity vs. temperature plots and was found to be (0.30 +/- 0.01) eV in the 260-230 K temperature interval. A significant change in resistivity was observed at a low temperature T=225 K in coincidence with the structural distortion in the Sn-Br-Sn chains. A field effect device was used to determine the charge carrier type and mobility as a function of temperature and field. The charge carriers were hole type. Their mobility at room temperature was about 10(-5) cm(2)V(-) s(-1). It increased by two orders of magnitude at 320 K and exhibited an almost exponential dependence on the applied gate voltage.

We present a study on the power dependence of the microwave surface impedance in thin films of the novel superconductor MgB2. 500 nm thick samples exhibiting critical temperatures ranging between 26 and 38 K are synthesized by an ex-situ post-anneal of e-beam evaporated boron in the presence of an Mg vapor at 900 C. Preliminary results on films grown in situ by a high rate magnetron sputtering technique from stoichiometric MgB2 and Mg targets are also reported. Microwave measurements have been carried out employing a dielectrically loaded niobium superconducting cavity operating at 19.8 GHz and 4 K. The study shows that the electrodynamic response of MgB2 films is presently dominated by extrinsic sources of dissipation, appearing already at low microwave power, likely to be ascribed to the presence of grain boundaries and normal inclusions in the samples., 10 pages, 3 figures, proceedings of the conference EUCAS 2001, submitted to Physica C

Using miniaturized hairpin resonators and following the Chebychev model, we have designed and fabricated superconducting filters with a centre frequency of 2.2 GHz and a bandwidth of 5 MHz. The measured unloaded Q-factor of the resonator fabricated on LaAlO3 using YBCO thin film is 47,000 at 60 K. Prototype filters with three and four poles have been realized by using Nb thin films. The measured performances do not show appreciable degradations up to 10 dBm.

LuNi 2 B 2 C films have been prepared by a Pulsed Laser Deposition technique. The deposition parameters have been optimized to reach good superconducting, structural and morphological properties with high reliability. In order to deposit different patterned layers for in-situ junctions production, a special set-up for the in situ interchanging of shadow masks has been developed. We studied the growth of different materials to be used as barrier layers. New results on the temperature dependence of the LuNi 2 B 2 C gap using S/N contact junctions are presented and discussed.

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.

We have studied the effect of thickness on the structure and superconductivity of Nd1.2Ba1.8Cu3O7+x (NdBCO) epitaxial films deposited on SrTiO3 (100) substrates. High quality NdBCO films were deposited by high oxygen pressure sputtering. The samples have been carefully characterized by transport measurements and X-ray diffraction using conventional and synchrotron radiation sources. Two structural transformations are observed. The first one is a crossover from the orthorhombic and twinned structure, typical of thick samples, to a pseudotetragonal phase at thickness lower than 60 unit cells. The pseudotetragonal phase exhibits peculiar X-ray diffuse scattering around the Bragg reflections, associated to nanostructured twinned domains. The second one appears at thickness lower than 20 unit cells and is assigned to a pseudotetragonal-tetragonal transition. The transport properties are not modified at the first crossover, while a substantial decrease of T-c and of the number of holes is observed at the pseudotetragonal-tetragonal transformation. Our results suggest that the structural rearrangement and the transport properties are explained by the ordering of Cu(I)O chains. (c) 2007 Elsevier B.V. All rights reserved.

We discuss the feasibility of a new type of high temperature superconducting bolometer operating in the sub-millimeter region (λ>300μm) of the spectrum in the temperature range 80K:100K. We use the sharp resistive transition of Bi 2 Sr 2 CaCu 2 O 8+x superconducting single crystals as sensitive thermometer. The sensor is thermally coupled to a thin diamond substrate covered on the back side with a bismuth film that performs the absorbtion of the radiation. Such a detector should have large sensitive area and short time response due to the low heat capacity of both crystal and substrate. We describe the results of the electrical bolometric characterization, noise measurements and optical calibration carried out on the first prototype and use them to predict the Noise Equivalent Power (NEP) of a well designed detector

Cryogenic detectors based on superconducting-normal phase transition of a thinfilms are particularly interesting for their potential application in high energy physics experiments. In this paper we discuss results concerning the response of a narrow strip of NbVN irradiated by low energy X-rays. We observed voltage pulses induced by a 55 Fe 6 Kev X-ray source in a current biased 2 gm wide detector operating at 1.4 K. An efficiency of almost 60% was estimated at bias current higher than 0.7 Ic.

We describe the properties of a prototype bolometer operating at liquid nitrogen temperature based on a Bi 2 Sr 2 CaCu 2 O 8+x single crystal 15 μm thick grown by the flux method. The use of thin single crystals having low thermal capacities was suggested by the request of decreasing the response time τ of the device. Preliminary results indicate that single-crystal-based far infrared bolometers can be competitive with the commercial detectors operating at room temperature.

Superconducting thin film particle detectors can be specially attractive for minimum ionizing particle detection due to the high efficiency and low sensitivity to radiation damage. In this paper we describe the fabrication procedure and the characterization of (NbV)N films and the set-up of photolithography processes to realize well defined submicron lines on these films in order to produce and test, in the near future, full operating detectors based on such material.

Niobium nitride (NbN) is one of the leading materials for superconducting thin film applications such as electronic devices and coated r.f. cavities for high energy physics. In the following the fabrication technique of superconducting magnetron-sputtered NbN films is described and the experimental results are discussed.

High quality NbN-NbO X -Pb Josephson devices have been fabricated by r.f. diode sputtering. The critical temperatures of the NbN films were as high as 16.8 K. The junction geometry was defined by photolithography and the oxide barrier was obtained by thermal oxidation or by a plasma oxidation technique. Very low leakage currents have been obtained, corresponding to values of the parameter Vm = 80 mV (Vm = I O × 2 mV/I (2mV)). The junction microwave quality factor Q and other a.c. properties have been measured in the frequency range 20 - 300 GHz by looking at the devices self-resonant modes. Q values up to 120 at 4.2 K have been found in the low frequency range, indicating potential performances of these devices for microwave applications such as Josephson voltage standards. Theoretical analysis of the results shows that the main contribution to the losses is related to the NbN films surface impedance.

Dual mode high temperature superconducting (HTS) filters represent an interesting device class for telecommunication application since they combine a high power handling capability with a miniaturized size. Here we report on the design and realization of dual mode cross slotted filters presenting a more compact size if compared with the traditional dual mode patch filters. Single stage filters operating in C-band with 1% fractional bandwidth have been designed and tested at prototype level by using double sided YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) and Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ (Tl-2212) superconducting films grown on LaAlO/sub 3/ substrates. The YBCO filter presents insertion losses IL=1 dB and a power handling higher than 10 dBm at T=77 K while the Tl-2212 allows operation at higher temperatures with comparable performances. Dual stage (four poles) and four stage (eight poles) filters with 1% fractional bandwidth operating in C-band and presenting a Chebyshev or a quasi elliptical response have been analyzed. Finally, a four stage filter fitting well on a 1"/spl times/1" substrate was designed.