  Nanoscale magnetic tunnel junction (MTJ) devices can efficiently convert
thermal energy in the environment into random bitstreams for computational
modeling and cryptography. We recently showed that perpendicular MTJs activated
by nanosecond pulses can generate true random numbers at high data rates. Here,
we explore the dependence of probability bias-the deviations from equal
probability (50/50) 0/1 bit outcomes-of such devices on temperature, pulse
amplitude, and duration. Our experimental results and device model demonstrate
that operation with nanosecond pulses in the ballistic limit minimizes
variation of probability bias with temperature to be far lower than that of
devices operated with longer-duration pulses. Further, operation in the
short-pulse limit reduces the bias variation with pulse amplitude while
rendering the device more sensitive to pulse duration. These results are
significant for designing TRNG MTJ circuits and establishing operating
conditions.
