Effect of deposition conditions and annealing temperature on tunnel magnetoresistance and structure of MgO-based double-barrier magnetic tunnel junctions

The performance of spintronics devices — such as magnetoresistive random access memories, non-volatile logics, and hard disk drives readers — has been improved over the past two decades due to the progress of tunnel magnetoresistance (TMR) ratios in MgO-based magnetic tunnel junctions (MTJs) [1]-[5]. To date the highest magnetoresistance ratio (604 %) was obtained using CoFeB electrodes and an insulating MgO tunnel barrier [6]. Although single-barrier MgO MTJs (SB-MT-Js) show excellent TMR values, driving voltages are limited due to the dielectric breakdown of the MgO barrier (approximately 1 V/nm). One possible way to increase the maximum voltage that can be applied to a device is to introduce a second tunnel barrier. As both barriers are in series, the voltage on each is halved with respect to the total applied voltage. An MTJ with two tunnel barriers is referred to as a double-barrier MTJ (DB-MTJ).