Flexible CoFeB/MgO-based magnetic tunnel junctions annealed at high temperature (≥350 °C)

This study investigates the effect of high-temperature (350-500 degrees C) annealing on CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) directly formed on a flexible polyimide substrate, which has superior thermal tolerance. As the annealing temperature increases, the tunnel magnetoresistance (TMR) ratio enhances and reaches up to similar to 200% at an annealing temperature of 450 degrees C. The annealing temperature dependence is similar to that of MTJs fabricated in the same way on a thermally oxidized silicon substrate. Images taken by a scanning transmission electron microscope confirm the improvement of the crystallization of the CoFeB and MgO layers, which can be an important factor in enhancing the TMR ratio. Furthermore, the endurance of the flexible MTJ against repeated stretching of its substrate is investigated. The TMR ratio shows no change during and after a 1000-cycle application of a tensile strain larger than 1%. The high TMR ratio and strain endurance demonstrated in this study suggest that the flexible MTJ structure is a promising candidate for a future strain-sensing device. Published under license by AIP Publishing.