  Voltage-gate assisted spin-orbit torque (VGSOT) writing scheme combines the
advantages from voltage control of magnetic anisotropy (VCMA) and spin-orbit
torque (SOT) effects, enabling multiple benefits for magnetic random access
memory (MRAM) applications. In this work, we give a complete description of
VGSOT writing properties on perpendicular magnetic tunnel junction (pMTJ)
devices, and we propose a detailed methodology for its electrical
characterization. The impact of gate assistance on the SOT switching
characteristics are investigated using electrical pulses down to 400ps. The
VCMA coefficient ({\xi}) extracted from current switching scheme is found to be
the same as that from the magnetic field switch method, which is in the order
of 15fJ/Vm for the 80nm to 150nm devices. Moreover, as expected from the pure
electronic VCMA effect, {\xi} is revealed to be independent of the writing
speed and gate length. We observe that SOT switching current characteristics
are modified linearly with gate voltage (V_g), similar as for the magnetic
properties. We interpret this linear behavior as the direct modification of
perpendicular magnetic anisotropy (PMA) and nucleation energy induced by VCMA.
At V_g = 1V, the SOT write current is decreased by 25%, corresponding to a 45%
reduction in total energy down to 30fJ/bit at 400ps speed for the 80nm devices
used in this study. Further, the device-scaling criteria are proposed, and we
reveal that VGSOT scheme is of great interest as it can mitigate the complex
material requirements of achieving high SOT and VCMA parameters for scaled
MTJs. Finally, how that VGSOT-MRAM can enable high-density arrays close to two
terminal geometries, with high-speed performance and low-power operation,
showing great potential for embedded memories as well as in-memory computing
applications at advanced technology nodes.
