Magnetic-Field Orientation Dependence of Thermal Stability in Perpendicular STT-MRAM

Abstract

Under the influence of an external magnetic field, the macrospin model predicts that the free layer of a magnetic tunnel junction (MTJ) exhibits a minimum energy barrier when the applied field is oriented at 45°. However, recent chip-scale experiments have yielded inconsistent results, indicating the limitations of current models in accurately predicting MRAM’s magnetic immunity. In this work, we present a domain wall motion-based model that provides novel insights. By employing the small-angle approximation and linearizing the domain wall energy under the influence of a transverse magnetic field, we have derived an analytical formula that well fits the experimental data of the perpendicular STT-MRAM. Our findings indicate a minimum switching barrier occurring at a special field angle (~60°), which could be manipulated by the field strength and the magnetic properties of device. The proposed model enables a more precise quantitative assessment of magnetic immunity at the chip level and offers valuable guidance for device optimization and shielding method development.