Three-Terminal Superconducting Digital Transistor

Discrete array of small Josephson junctions can exhibit flux-flow behavior, which is drastically different from that of long Josephson junctions. In particular, the flux-flow voltage does not monotonically increase with magnetic field; rather, it decreases after a threshold until it reaches zero. Here, using simulation and experimental results, we show that the flux-flow voltage switches abruptly to zero if a magnetic field larger than the threshold is applied to a part of the array. This provides for a digital NOT gate in which the flux-flow voltage corresponds to digital state 1 and zero voltage denotes digital state 0. For a device size of 230 μm, a switching frequency of 15 GHz is evaluated, which can be improved by downsizing the device. Since this device provides gain, its input and output are isolated and has unlimited fan-out, designing and implementing various digital systems is easily accomplished.