Rapid Single Flux Quantum T-flip flop operating up to 770 GHz

Rapid Single Flux Quantum (RSFQ) T-flip flops (TFFs) operating up to 770 GH z have been demonstrated at 4.2 K The devices, consisting of either resisti vely shunted or unshunted Josephson junctions, are fabricated using a plana rized Nb/AlOx/Nb trilayer process. Electron beam lithography is used to pat tern all levels with a minimum junction area less than 0.1 mu m(2). Critica l current densities of 0.5 mA/mu m(2) and 2.5 mA/mu m(2) are used for the s hunted (tested at 1.8 k) and unshunted devices (tested at 4.2 K) respective ly. The input and output frequencies of the TFFs are obtained from the inpu t and output voltages by the Josephson relation. The output voltage is exac tly half of the input voltage when the divide-by-two operation is correct.