9 K operation of RSFQ logic cells fabricated by NbN integrated circuit technology

We report on the fabrication and the operation of all-NbN rapid single flux quantum (RSFQ) circuits. The NbN integrated circuit consists of NbN/AlN/Nb N tunnel junctions, Mo resistors, sputtered SiO2 insulating layers, and 400 -nm-thick NBN ground plane and wiring layer. The circuits were fabricated w ith the minimum junction size of 2 mum x 2 mum and the alignment margin of +/-0.5 mum. We designed RSFQ logic cells under critical current density of 2.5 kA/cm(2), sheet resistance of 2 Omega and sheet inductance of 1.4 pH. W e experimentally investigated de bias margin of the fabricated RSFQ cells a t 9 K. We observed relatively large de bias margin of more than +/-25% for a pulse splitter, a confluence buffer and an RS flip-flop, while the de bia s margin of a T dip-pop was less than +/-5%. We succeeded to demonstrate th e operation of 16-bit concurrent flow shift resister at 9 K.