Experiments and simulations of picosecond pulse switching and turn-on delay time in Y–Ba–Cu–O Josephson junctions

We report our studies on single-picosecond electrical pulse switching of YBa2Cu3O7−x (YBCO) grain-boundary bicrystal Josephson junctions. The test structures consisted of coplanar strip (CPS) transmission lines that were patterned in 50 nm thick YBCO films prepared on (100) MgO bicrystal substrates. Each CPS contained a 5 μm wide, 10 μm long microbridge and a 5 μm wide grain-boundary Josephson junction. A train of 100 fs wide optical pulses from a Ti:sapphire laser was used to excite the microbridge and generate ∼2 ps wide electrical pulses, which were then applied to switch the junction. The junction response was studied at 20 K using a cryogenic electro-optic sampling system. We measured a 0.65 ps wide, single-flux-quantum pulse generated by the junction as well as a 0.7 ps junction turn-on delay time. Junction switching and turn-on delay time have been compared with numerical simulations.