Optimizing free layer of Magnetic Tunnel Junction for true random number generator

Abstract

True random number generators (TRNGs) should ideally generate lengthy chains of non-repeating, uncorrelated bit-streams that are efficient in terms of both energy and area. Current TRNG designs include source of randomness such as CMOS or non-volatile memory based devices with additional circuitry to improve the quality of randomness leading to power and area overhead. This paper addresses these issues by improving the randomness of the Spin-Orbit Torque (SOT)-Magnetic Tunnel Junction cell. Motivated by the observation that free layer thickness of Magnetic Tunnel Junction (MTJ) can be scaled to design a low-barrier device, the paper proposes a novel source of randomness called $\Delta$SOT. This device is then used to design TRNG circuits that achieves high quality random telegraphic switching behavior without any additional circuitry making it suitable for ultra-low power applications. Evaluations show that $\Delta$SOT-TRNG has significant reduction in energy (51%) and area (66%) compared to state-of-the-art MTJ based TRNG design. Furthermore, the work shows that the improved switching speed of the reduced barrier junction can results in 65% increase in throughput compared to MTJ based TRNG design.