Tunneling cryotron flip-flop

Abstract

We have constructed tunneling cryotron flip-flops, have observed current transfer from one leg to the other, and have measured the time required for current transfer to be 2 nsec. The results are in agreement with the model previously proposed.1 The tunneling cryotron flip-flop consists of two devices in parallel, linked by a wholly superconducting path. A current is fed to the parallel devices; the current is steered from one device to the other by application of a control pulse. The measurements have been made on a loop of 1.16 in. in length (L=1.08×10-10H), containing two 10 mil diam junctions, having zero-field critical currents of 21 mA and 29 mA, respectively (in operation these are biased to near maxima on the gain curves, at 33 mA and 42 mA). The measuring apparatus is similar to that previously described. 1 In operation, a current of 20 mA is transferred from one device to the other by the application of a 2 mA control pulse, a gain of 10. The time required for this current to transfer, Δttransfer, is 1.4 nesc≤Δttransfer≤2.0 nsec, with an uncertainty of at most 0.4 nsec. According to the previously proposed model of a constant gap voltage driving the loop inductance and which does not include the junction transition times (Ref. 1), the transfer time for 20 mA of current should be 2 nsec. One implication of this excellent agreement is that the junction transition time is appreciably smaller than the previously measured upper bound of 800 psec. 2 Additional operating details will be discussed. © 1968 The American Institute of Physics.