  Perpendicular magnetic tunnel junctions (p-MTJs) switched utilizing bipolar
electric fields have extensive applications in energy-efficient memory and
logic devices. Voltage-controlled magnetic anisotropy linearly lowers the
energy barrier of ferromagnetic layer via electric field effect and efficiently
switches p-MTJs only with a unipolar behavior. Here we demonstrate a bipolar
electric field effect switching of 100-nm p-MTJs with a synthetic
antiferromagnetic free layer through voltage-controlled exchange coupling
(VCEC). The switching current density, ~1.1x10^5 A/cm^2, is one order of
magnitude lower than that of the best-reported spin-transfer torque devices.
Theoretical results suggest that electric field induces a
ferromagnetic-antiferromagnetic exchange coupling transition of the synthetic
antiferromagnetic free layer and generates a field-like interlayer exchange
coupling torque, which cause the bidirectional magnetization switching of
p-MTJs. A preliminary benchmarking simulation estimates that VCEC dissipates an
order of magnitude lower writing energy compared to spin-transfer torque at the
15-nm technology node. These results could eliminate the major obstacle in the
development of spin memory devices beyond their embedded applications.
