Influence of Intrinsic Thermal Stability on Switching Rate and Tunability of Dual-Biased Magnetic Tunnel Junctions for Probabilistic Bits

Abstract

Recently, magnetic tunnel junctions (MTJs) with superparamagnetic free layers (sMTJs) have been proposed as key components in probabilistic bits (p-bits). However, the average fluctuation rates of sMTJs are very sensitive to slight variations in the device dimensions, which creates a major obstacle to their realization in large-scale networks. One possible solution is to implement dual-biasing on p-bits to offset the effects of variations through onboard corrections. In our previous work, we demonstrated that dual-biasing has the unique capability of separate control over the high- and low-state dwell times, which adds an extra degree of tunability in the signals generated. However, these studies investigated dual-biasing on thermally stable MTJs; therefore, the maximum switching rates were lower than the gigahertz rates desired for sMTJ-based p-bit circuits. While dual-biasing on sMTJs rather than thermally stable MTJs would improve the switching rates, some of the flexibility and robustness of dual-biasing may be sacrificed due to the sensitivity of sMTJs. In this letter, we applied the dual-biasing method on 10 MTJs with varying thermal stability factors to test if sMTJs can achieve the same degree of separation between high- and low-state dwell-time tunability as thermally stable MTJs. Our results show that two degrees of tunability was achieved on all MTJs tested, thus demonstrating that dual-biased p-bits can achieve switching rates equal to or greater than single-biased sMTJs.