  Stochastic p-Bit devices play a pivotal role in solving NP-hard problems,
neural network computing, and hardware accelerators for algorithms such as the
simulated annealing. In this work, we focus on Stochastic p-Bits based on
high-barrier magnetic tunnel junctions (HB-MTJs) with identical stack structure
and cell geometry, but employing different spin-orbit torque (SOT) switching
schemes. We conducted a comparative study of their switching probability as a
function of pulse amplitude and width of the applied voltage. Through
experimental and theoretical investigations, we have observed that the Y-type
SOT-MTJs exhibit the gentlest dependence of the switching probability on the
external voltage. This characteristic indicates superior tunability in
randomness and enhanced robustness against external disturbances when Y-type
SOT-MTJs are employed as stochastic p-Bits. Furthermore, the random numbers
generated by these Y-type SOT-MTJs, following XOR pretreatment, have
successfully passed the National Institute of Standards and Technology (NIST)
SP800-22 test. This comprehensive study demonstrates the high performance and
immense potential of Y-type SOT-MTJs for the implementation of stochastic
p-Bits.
