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 YB a2Cu3O7-x, (YBCO) grain-boundary bicrystal Josephson junctions. The test st ructures consisted of coplanar strip (CPS) transmission lines that were pat terned in 50 nm thick YBCO films prepared on (100) MgO bicrystal substrates . Each CPS contained a 5 mu m wide, 10 mu m long microbridge and a 5 mu m w ide grain-boundary Josephson junction. A train of 100 fs wide optical pulse s from a Ti:sapphire laser was used to excite the microbridge and generate similar to 2 ps wide electrical pulses, which were then applied to switch t he junction. The junction response was studied at 20 K using a cryogenic el ectro-optic sampling system. We measured a 0.65 ps wide, single-flux-quantu m pulse generated by the junction as well as a 0.7 ps junction turn-on dela y time. Junction switching and turn-on delay time have been compared with n umerical simulations.