Demonstration of Single-Flux-Quantum 64-B Lookup Table With Cryo-CMOS Decoders for Reconfiguration

We propose a compact single-flux-quantum (SFQ) lookup table (LUT) that uses CMOS decoder circuits for reconfiguration to improve scalability. Reconfiguration by external control currents. An
n×n
-bit LUT is composed of a two-dimensional array of memory cells and cryo-CMOS decoders. The memory cell at the target address is set to a logic “1” state when the corresponding
x
- and
y
-directional control currents are both applied from the CMOS decoders and is reset to logic “0” when a reset current is applied. Cryo-CMOS decoders are integrated with the SFQ LUT to reduce the number of control current lines (from 2
n
+1 to 2log
₂
n
+2) from the room-temperature electronics for LUT reconfiguration. For demonstration, we designed and fabricated a 64-b SFQ LUT integrated with CMOS decoders using the AIST 2.5-kA/cm
²
Nb standard process and the Rohm 180-nm CMOS process. Experimental results confirm the correct functionality of the SFQ LUT reconfigured by the CMOS decoders. All operating SFQ memory cells in the experiment showed almost the same control current margins. The proposed reconfiguration method is scalable in terms of the number of interconnections and control current margins for SFQ memory cells.