We study the effect of the oxide layer on current-induced perpendicular magnetization switching properties in Hf vertical bar CoFeB vertical bar MgO and Hf vertical bar CoFeB vertical bar TaOx tri-layers. The studied structures exhibit broken in-plane inversion symmetry due to a wedged CoFeB layer, resulting in a field-like spin-orbit torque (SOT), which can be quantified by a perpendicular (out-of-plane) effective magnetic field. A clear difference in the magnitude of this effective magnetic field (H-z(FL)) was observed between these two structures. In particular, while the current-driven deterministic perpendicular magnetic switching was observed at zero magnetic bias field in Hf vertical bar CoFeB vertical bar MgO, an external magnetic field is necessary to switch the CoFeB layer deterministically in Hf vertical bar CoFeB vertical bar TaOx. Based on the experimental results, the SOT magnitude (H-z(FL) per current density) in Hf vertical bar CoFeB vertical bar MgO (-14.12 Oe/10(7) A cm(-2)) was found to be almost 13x larger than that in Hf vertical bar CoFeB vertical bar TaOx (-1.05 Oe/10(7) A cm(-2)). The CoFeB thickness dependence of the magnetic switching behavior, and the resulting H-z(FL) generated by in-plane currents are also investigated in this work. (C) 2015 AIP Publishing LLC.