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We have improved the properties of c-axis-oriented YBCO/PBCO/YBCO trilayer junctions using planarization of YBCO films. The root-mean-square value of the film roughness reduces to less than 60% of that of an as-grown film. The junctions made through the planarization exhibit RSJ-like current-voltage characteristics even for 20-nm-thick PBCO interlayers. The characteristic voltage is 0.16 mV at 50 K, which is remarkably improved compared to that of junctions without the planarization.