A 10 GHz digital amplifier in an ultra-small-spread high-Jc Nb/Al-AlOx/Nb integrated circuit process

We describe a Josephson amplifier fabricated in a high-J(c) process, which is operational to speeds of at least 10 GHz, the highest reported for a voltage-state amplifier. The amplifier converts similar to 200 mu V digital signals to similar to 5 mV at 10 GHz and could be used as an interface between two superconducting systems. The bit-error-rate of the circuit was similar to 5 x 10(-12) at 5 GHz, the lowest reported; bit-error-rate measurements at 10 GHz were not possible. A high-J(c), process which was used to fabricate the amplifier was developed at UC Berkeley with extremely low I-c spreads; at similar to 9.4 kA/cm(2) sigma as low as 0.6% was observed. At similar to 10 kA/cm(2), the typical junction linear dimensions are 1.5 - 2 mu m, sizes for which it is not possible - with available tools - to make reliable vias that are smaller than the junction, We use a nonplanarized junction process, where the via for contact of a wiring layer to a junction can be larger than the junction.