Power Reduction of Josephson Random Access Memory Using Stochastic Resonance

A superconducting quantum interference device (SQUID) is used as a memory cell in a superconducting Josephson random access memory (RAM) system. In the Josephson RAM, power is mainly consumed by driver circuits, which drive word and bit lines to select the target memory cell. We investigated the power reduction of READ/WRITE operation of the SQUID memory cell by using a stochastic resonance phenomenon. By using a noise-assisted state transition of the SQUID, the driving current required for the READ/WRITE operation of the memory cell can be reduced. We investigated optimum bias and noise conditions where stochastic resonance efficiently occurs on the basis of analog circuit simulation that takes influences of thermal noises into account. According to the simulation results, the power dissipation required for READ/WRITE operation can be reduced by approximately 20% under the optimum bias and noise conditions when the error rate of READ/WRITE operation is 10
^-10
. We designed a 1-bit rf-SQUID memory cell using the AIST 2.5 kA/cm
²
Nb standard process 2, and tested the cell by applying a white noise from the room-temperature instrument. The probability that a datum is written to the memory cell and read out correctly was measured under various bias and noise conditions. We have experimentally observed stochastic resonance and obtained the error rate of 10-5 when the power dissipation of READ/WRITE operation is reduced to 80% compared to the conventional Josephson RAM.