Since the discovery of the large spin Hall effect in certain heavy metals, there has been continuous interest in utilizing this spin-orbit torque (SOT) effect in constructing a non-volatile memory that can be switched by an electric current. The key to future application of this type of memory is achieving both a short write time and a low write current, which will lower the energy cost compared to existing and other emerging memory technologies. We demonstrate an efficient way of reducing the switching current in tungsten-based three terminal magnetic tunnel junctions (MTJs) with in-plane magnetization (IPM) using a sub-atomic layer of Hf dusting inserted between the free FeCoB layer and the MgO tunnel barrier. We show with a simple FeCoB-MgO-FeCoB MTJ structure that in addition to low write current, fast pulse switching can be achieved with pulses ≤ 1 ns. We also confirm that in an SAF balanced MTJ structure with a PtHf spin Hall channel that the nanosecond switching behavior is typical of the switching of IPM three terminal spin-orbit-torque devices. We report write error rate of these structures down to ∼10-6at for 1 ns pulses, demonstrating feasibility for high performance cache memory. © 2018 SPIE.