Impact of external magnetic field on embedded perpendicular STT-MRAM technology qualified for solder reflow

External magnetic field resistance under write, read operations for perpendicular STT-MRAM qualified for 260°C solder reflow is comprehensively reported for the first time. We show that the most critical polarization direction is writing from parallel to anti-parallel state with external field opposed to both the final free layer direction and the bottom pinned layer direction. It is also found that free layer failure to switch is the major cause rather than unexpected pinned layer flipping. Furthermore, various key factors including temperature, write condition and MTJ film stack are also studied here. Finally, we demonstrate that a low chip failure rate of 0.001 ppm can be achieved with an ECC scheme for external magnetic fields up to 240 Oe at 85°C.