Operation of HTS Toggle-Flip-Flop Circuit With Improved Layout Design

Toggle-flip-flop (T-FF) is one of the most important high-T
_c
superconducting single-flux quantum (HTS SFQ) circuit components and has been designed and fabricated by using YBa
₂
Cu
₃
O
_7-delta
ramp-edge junction technology. The circuit layout of the T-FF was improved to suppress the junction critical current (I
_c
) spread in the circuit. Test circuits, which include a T-FF with a single output for evaluating the logic operation and measuring the operating frequency, were fabricated and their operation characteristics were investigated. The T-FF circuit with a single output was successfully operated and finite direct current (dc) supply current margins were obtained at temperatures from 27 to 34 K. Moreover, the maximum operating frequency of the T-FF was estimated to be 360 GHz at 4.2 K and 114 GHz at 41 K. In addition, reduction of dc supply current margins due to thermal noise was also investigated. According to the numerical simulation in which parasitic inductances were taken into account, the narrowest margin in the T-FF circuit wider than plusmn10% was maintained with a bit-error rate (BER) of 10
^-6
up to 40 K