Different dielectric breakdown mechanisms for RF-MgO and naturally oxidized MgO

We investigate the voltage breakdown of the spin transfer torque magnetic random access memory (STT-MRAM) with perpendicular magnetic tunnel junctions (pMTJs). Different breakdown behaviors are observed for RF-MgO pMTJs and naturally oxidized MgO pMTJs. While the time-to-failure body distribution of the naturally oxidized MgO follows the Weibull distribution, that of RF-MgO follows the lognormal distribution. This result suggests distinctly different dielectric breakdown mechanisms for naturally oxidized MgO and RF-MgO. For low failure probability, the progressive voltage breakdown of RF-MgO (associated with the lognormal distribution) results in an order-of-magnitude reliability improvement over the abrupt breakdown of the naturally oxidized MgO. We show that RF-MgO is suitable for perpendicular STT-MRAM applications.