We report the fabrication and characterization of thin-film grain boundary junctions in Tl-based superconductors on bicrystal substrates. Post-deposition processed Tl2Ba2CaCu2O8 films were grown on bicrystal SrTiO3 substrates, with varying degrees of misorientation angle θ. Critical current densities and current-voltage curves had a strong dependence on θ. For θ≥10°, there was a two-to-three order of magnitude reduction in critical current density, and for θ≥20°, the current-voltage curves displayed resistively shunted junction behavior. These high angle grain boundary junctions have features at 77 K that are attractive for device applications, including sharp voltage onsets, well-behaved dc magnetic and rf field dependence, IcRn products as large as 300 μV, and low 1/f noise. Simple dc superconducting quantum interference devices fabricated with these junctions exhibited transfer functions of up to 30 μV/Φ0 at 77 K.

-This paper describes the realization of compact 360 degree phase-shifter MMICs using thin-film BST varactors in a series cascade of all-pass networks. Unlike conventional delayline structures, all-pass networks provide constant phase shift with small variation of insertion loss. In similar fashion, very broadband phase-shifters can be implemented by cascading allpass networks with staggered center-frequencies. Using a thinfilm BST technology for the varactors, extremely compact and low-cost phase-shifter structures have been developed. Selected results are shown in the 1-30GHz range.

1/f noise measurements performed on Tl2Ba2Ca1Cu2O8 thin films show that the amplitude of the noise spectral density (Sv/V2) in the normal state may be comparable with that in conventional metals, in contrast with the much larger Sv/V2 observed in other copper oxide materials. In the superconducting transition region the 1/f noise is greatly reduced in some films that are highly aligned along the c axis.

We have observed an unusual hysteresis loop in rf power dependence of high-temperature superconductor (HTS) coplanar transmission lines. At 77 K and 1 GHz, the signal transmission was linear (insertion loss <0.1 dB) until the input power (Pin) reached a critical value of Pc=0.4 W. An abrupt drop by ∼37 dB in the transmitted power (Pout) was observed at Pin=Pc followed by a slow increase (Pout∝Pin0.62) for Pin≳ Pc. As Pm was then decreased, it retraced the previous curve only until Pin=Pc. However, as Pin was reduced further Pout did not rise until Pin=158 mW, at which Pout started to increase rapidly and returned to the linear regime for Pin<71 mW. Such a sharp transition and a strong hysteresis effect were unique to the HTS line whereas a gold line with an identical structure did not exhibit these characteristics. This behavior may be utilized for potential applications of new HTS microwave power (current) limiters and switches. Several possible origins for the hysteresis effect are proposed and discussed.

This paper describes the design and characterization of a lumped-element tunable IF filter using thinfilm barium strontium titanate (BST) varactors. The filter was designed to operate from 30-88MHz in three separate switchselectable bands with a 0-12V DC control voltage. A relatively constant insertion loss of <5dB was obtained over the desired tuning range.The circuit was also characterized over temperature from -40°C to +80°C, showing relatively little change in insertion loss over temperature, but a slight reduction in tuning range at elevated temperatures.