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Fabrication of high-temperature superconductor Josephson junctions by focused ion beam milling

We demonstrate the feasibility of white organic light-emitting diodes that exclude the transparent conductor indium-tinoxide. Instead, a highly conductive Orgacon™ PEDOT:PSS material in combination with a metal support structure is used as transparent anode and hole-injection layer. The PEDOT:PSS exhibits a conductivity of 460±20 S/cm and a work function of 5.35±0.05 eV. On ITO-free OLEDs on glass with an active area of ~6 cm ² the inclusion of 120 nm thick printed metal lines reduces the variation in brightness from 35% to 20%. The ITO-free concept based on PEDOT:PSS with printed metal structures is scaled up to large flexible OLEDs with a size of 150 cm 2 on a heat-stabilized Teonex® Polyethylene Naphtalate foil. The voltage distribution across the various electrodes was verified by a finite element model, allowing a prediction of the OLED brightness and homogeneity over large areas.

Using an optimized bridge geometry we have been able to make accurate measurements of the properties of YBa 2 Cu 3 O 7-d grain boundaries above T c .The results show a strong dependence of the change of resistance with temperature on grain boundary angle. Analysis of our results in the context of band-bending at the boundary allows us to estimate the height of the potential barrier present at the grain boundary interface.

Submicron YBa2Cu3O7−x bicrystal grain boundary junctions have been fabricated, for the first time, by a focused ion beam process. Although such a process has always been considered detrimental to the YBa2Cu3O7−x because of gallium contamination, high quality 24° [001] tilt junctions characterized by RSJ current–voltage characteristics, ICRN products of the order of 1–4 × 104 A cm−2 at 77 K and Fraunhofer-like modulation patterns have been obtained. No significant degradation has been observed over more than 3 months. The critical current density JC and the characteristic voltage ICRN show a clear maximum for widths of the order of the Josephson penetration depth. The asymptotic normal resistance shows a typical (width)−1 dependence, indicating that the FIB process does not increase the grain boundary resistivity of submicron junctions. Experimental results clearly show that FIB is a very powerful tool for the fabrication of high critical temperature superconducting circuits, requiring a small number of submicron Josephson junctions, and for fundamental physics analysis. It also allow the final tuning or repair of superconducting or more complex integrated superconducting–semiconducting devices.

The interface resistance of YBa 2 Cu 3 O 7 grain boundaries has been measured in the range 5-270 K by means of a Wheatstone bridge for 24 , 30 and 36 symmetric and 45 degree asymmetric, [001] tilt, thin film grain boundaries. A number of preliminary experiments have demonstrated the validity of the technique employed. Above, the grain boundary resistance decreases as the temperature is increased, and the temperature variation is more pronounced for higher angle boundaries. A number of possibilities for interpreting the data are considered.

Field angle dependent critical current, magneto-optical microscopy, and high resolution electron microscopy studies have been performed on

By lithographically fabricating an optimised Wheatstone bridge geometry, we have been able to make accurate measurements of the resistance of grain boundaries in Y 1-x Ca x Ba 2 Cu 3 O 7-δ between the superconducting transition temperature, T c , and room temperature. Below T c the normal state properties were assessed by applying sufficiently high currents. The behaviour of the grain boundary resistance versus temperature and of the conductance versus voltage are discussed in the framework charge transport through a tunnel barrier. The influence of misorientation angle, oxygen content, and calcium doping on the normal state properties is related to changes of the height and shape of the grain boundary potential barrier.