Influence of parasitic capacitance on the oxide SFQ circuit operation

Characteristics of SFQ (single flux quantum) circuits have been found to much change when parasitic capacitances are increased beyond a critical value. The characteristic change of the SFQ operation is especially enhanced when junction the IcRn (I-c being the critical current and R-n being the normal resistance) value is much more than 1 mV. Details of this characteristic change were studied by using a ring oscillator. In the normal operation mode, an oscillation frequency gradually increased with a supply current. On the other hand, the oscillation frequency is almost independent of the supply current and jumps at a certain supply current in the anomalous operation mode. The ring oscillator circuit was fabricated by using YBa2Cu3O7-x ramp edge junctions. Such a ring oscillator behavior was experimentally shown by measuring the supply current dependence of the oscillation frequency. (C) 2007 Elsevier B.V. All rights reserved.