A 10 GHz digital amplifier in an ultra-small-spread high-J/sub c/ Nb/Al-AlOx/Nb integrated circuit process
We describe a Josephson amplifier fabricated in a high-J/sub c/ process, which is operational to speeds of at least 10 GHz, the highest reported for a voltage-state amplifier. The amplifier converts /spl sim/200 /spl mu/V digital signals to /spl sim/5 mV at 10 GHz and could be used as an interface between two superconducting systems. The bit-error-rate of the circuit was /spl sim/5/spl times/10/sup -12/ at 5 GHz, the lowest reported; bit-error-rate measurements at 10 GHz were not possible. A high-J/sub c/ process which was used to fabricate the amplifier was developed at UC Berkeley with extremely low I/sub c/ spreads; at /spl sim/9.4 kA/cm/sup 2/ /spl sigma/ as low as 0.6% was observed. At /spl sim/10 kA/cm/sup 2/, the typical junction linear dimensions are 1.5 /spl sim/ 2 /spl 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.