The microwave properties of single crystalline TiO2 (rutile) were investigated. At a frequency of 7.5 GHz the loss tangent tan δ was found to increase from 1.4×10−7 at 4 K to 4×10−6 at 70 K for electric fields parallel to the crystallographic a,b plane. The high permittivity of 105 and the small tanδ in combination with the low microwave losses of high temperature superconductors (HTS) were utilized to construct a miniaturized X-band resonator with a high quality factor Q. An assembly of two YBa2Cu3O7 films of 8 mm in diameter separated by a rutile cylinder of 2 mm height provides a TE011 resonance at 9.7 GHz with Qs ranging from 6×105 at 10 K to 105 at 70 K. Frequency scaling of the losses in rutile and in the HTS films indicates Qs in excess of 106 at 1.8 GHz using YBa2Cu3O7 films of two inches in diameter. Such resonators are considered to be key elements for high-power filters in mobile communications.

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High quality YBa2Cu3O7−x films on silicon-on-sapphire were grown using a multiple buffer layer, consisting of YSZ and CeO2. Ion channeling reveals the high crystalline perfection of the YBa2Cu3O7−x films. A channeling minimum yield for the Ba signal as low as 3% was measured. The normal state resistivity of 200 μΩ cm at 300 K, critical temperatures above 90 K, with transition widths down to 0.5 K, critical current densities above 2×106 A/cm2 at 77 K and surface resistance values of 1.4 mΩ at 18.9 GHz and 77 K confirm the high quality of the YBa2Cu3O7−x films. These results are very promising for integrated superconductor and semiconductor applications.

We have investigated dielectric resonators (SDROs) fabricated from single crystalline LaA103 shielded by two epitaxial films of Y Ba2Cu307 (YBCO).At the resonant frequency of the TEoll-mode of 5.6GHz unloaded quality factors QO of 8 x lo5 at 20K and 4 x lo5 at 60K were obtained. These values were limited by dielectric losses in LaA103. At 50K we obtained a QO of 2 x lo5 at a level of dissipated rf power of 2 W corresponding to an average rf magnetic surface field of 1500e. Moreover, we used one SDRO as a feedback for a HP8349 amplifier to measure oscillator phase noise. At BOK and helium gas cooling the phase noise was beyond the sensitivity limit of our HP8565 spectrum analyzer of about -9OdBc/Hz at an offset frequency of 1kHz. For operation with Stirling cooler microphonics dominates the noise properties.