Na 0.5 K 0.5 NbO 3 thin films have been grown on LaAlO3(001) substrates using rf magnetron sputtering from a Na and K enriched target. X-ray diffraction showed that the films are epitaxial with mosaic broadening as narrow as 0.044°. Interdigital Au finger electrodes were photolithographically defined on the film surfaces. The dielectric properties of these interdigital capacitors were measured at 1 MHz from room temperature down to 50 K. The capacitor showed 35% tunability at room temperature and a loss tangent of 0.007 without dc bias applied. The loss decreased further with increasing dc bias. For lower temperatures, the capacitance exhibited a broad maximum at ∼200 K, which is possibly linked to a phase transformation of the Na0.5K0.5NbO3 film.
Epitaxial (001) oriented SrTiO3 films have been deposited on LaAlO3(001) substrates by off-axis radio frequency magnetron sputtering in Ar:O2 gas mixtures at substrate temperatures ranging from 650 to 850 °C. For the deposition conditions used, stoichiometric targets yielded 20% Sr-deficient films, whereas Sr-enriched targets (Sr1.1Ti0.9O3.0) resulted in stoichiometric films. The Sr-deficient films had a mosaic structure and a larger lattice parameter in comparison to bulk SrTiO3. The stoichiometric films on the other hand had a much higher crystalline quality in the as-deposited condition. The mosaicity of the latter films was primarily limited by the crystalline quality of the LaAlO3 substrates. The lattice parameters of the stoichiometric films were also smaller than the Sr-deficient ones and closer to the bulk value. The dielectric properties of the stoichiometric films were superior to the Sr-deficient films. For films with a thickness of ∼300 nm, the typical dielectric constants as measured at ∼77 K and 1 MHz were determined to be 820 and 500, for the stoichiometric and Sr-deficient films, respectively. Also the capacitance change, as a direct current bias voltage was applied to an interdigital capacitor, was higher for the stoichiometric film, 27.3% as compared to 8.6% when applying a bias of 300 V at 77 K. We also demonstrate the effectiveness of thermal annealing in improving both crystalline quality and dielectric properties, especially for the Sr-deficient films.
Articles you may be interested inOptimization of a Josephson voltage array based on frequency dependently damped superconductor-insulator-superconductor junctions Rev. Sci. Instrum. 74, 3510 (2003);We report h!gh-f~equency mixing at 75 GHz using superconductor-insulator-superconductor (SIS) tunnel JunctIOn arrays of various length and composition. Short (6-junction) arrays, both of Pb (I~) and ofPb, and long (36-junction) arrays ofPb are used. The array geometry and antenna couphng can be scaled to 300 GHz with existing technology. Comparing the experiments to each other a~d to th~ory provides criteria for SIS mixer design. The measured single side band (SSB) conversIOn loss IS as good as 2.0 ± 0.9 dB. This is marginally the best published conversion result for any resi~ti:ve mixer with~ut image rejection, and quantitatively agrees with the quantum theory of ~lxI.ng. W ~ exa~me ~osephson effect noise in this device and give a rough upper frequency hmlt for smgle-JunctIon SIS mixers. Conversion maxima are also noted close to the half-gap singularity present in Pb (In) junctions.PACS numbers: 85.25. + k 6366
Arrays of 10 or 40 series-connected small densely packed Josephson tunnel junctions were successfully operated as parametric amplifiers at 10 GHz. Between 50 and 90% of the junctions in an array were observed to work coherently in the amplification process. Signal gain exceeding 24 dB was achieved with a pump power as low as -50 to -70 dBm. A power width (i.e., the range of the pump power for a gain within 3 dB of the peak gain) of 0.25 dB and a bandwidth of IS MHz were measured for 20-dB gain. The power width was in accordance with theory but the bandwidth was reduced, probably due to noise saturation effects. The latter effects can be reduced by lowering the input noise temperature or by including an external band limitation. The noise temperature was also increased by saturation; however, with an external bandwidth of 60 MHz, a noise temperature of 30 ± 20 K was measured. The application of a magnetic field has proved extremely useful as a means of tuning the amplifiers to stable high-gain operating points. This tuning was also utilized in evaluating the amplifier parameters, and the theory by Feldman, Parrish, and Chiao has been verified. The upper frequency limit for a lead tunnel junction amplifier ought to be well above 300 GHz.
Evidence for the superconducting proximity effect in junctions between the surfaces of YBa2Cu3O x thin films Appl.
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