Performance of YBCO Step Edge Josephson Junctions for Different Film Thickness to Step Height Ratio

Step edge Josephson junction devices of YBa 2 Cu 3 O 7‐ x films on SrTiO 3 substrates are fabricated, and the device performance is studied for different t / h ( t : the thickness of the film, h : step height) ratios. After depositing YBCO films on the step etched substrates, photolithography, and ion beam etching techniques are used to fabricate three devices with t / h ratios of ≈0.4, 0.7, and 1.2. The critical temperatures ( T c ) of the devices are ≈82, 85, and 88 K, respectively. The critical current ( I c ) and normal state resistance ( R n ) are observed to be t / h ratio dependent. The critical current values at 70 K for the devices with t / h ratios of 0.4, 0.7, and 1.2 are ≈425, 550, and 820 μA, respectively. The I c R n product at 70 K is ≈2.06, 2.76, and 0.43 mV for t / h ratios 0.4, 0.7, and 1.2, respectively, which indicates that the t / h ratio of 0.7 is optimum for the device performance. The current versus voltage curves at 68 K are fitted using the resistively shunted junction model using the Portable Superconducting Circuit Analyzer (PSCAN2) simulator, which suggests that there can be normal conducting links present across the microbridge, and it becomes effective for I > I c , contributing to excess current.