Principal Investigator Karl Berggren
The development of a practical supercomputer relies on having a scalable memory cell, energy efficient control circuitry, and the ability to read and write a state without sacrificing density. Typical superconducting memories relying on Josephson junctions (JJs) have demonstrated extremely low power dissipation (10-19 J) and rapid access times (< 10 ps), but suffer from large device dimensions and complex readout circuitry, mak- ing scalability a considerable challenge.
As an alternative to JJ-based superconducting memories, we have made a memory based solely on lithographic niobium nitride nanowires. The state of the memory is dictated by persistent current stored in a superconducting loop, while the write and read operations are facilitated by nanowire cryotron devices patterned alongside the memory loop in a single lithographic process. In addition to ease of fabrication, superconducting nanowires offer the advantage of relying on kinetic rather than geometric inductance, allowing the memory cell to be scaled down for high device density without sacrificing performance. Additionally, since persistent current is stored without Ohmic loss, the memory cell has minimal power dissipation in the static state.
We have demonstrated a 3 µm x 7 µm proof-of- concept device with an energy dissipation of ~ 10 fJ and a bit error rate < 10-7. Current work focuses on developing a multilayer fabrication process to expand the single memory element into an array and to reduce device dimensions for further density optimization.