Dong Ha Jung

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-tofailure 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.

3D Cross-Point Spin Transfer Torque Magnetic Random Access Memory

We explore a 3D cross-point spin transfer torque magnetic random access memory (STT-MRAM) array based on the integration of a perpendicular magnetic tunneling junction (pMTJ) with a matching two-terminal selector. The integrated two-terminal device provides a unique opportunity for a high density, low cost stackable storage class memory that can achieve a fast operation speed, long data retention, low bit error rate (BER) and high endurance. 55nm size pillar shaped pMTJ and selector devices have been fabricated and characterized. The selector is compatible with pMTJ whether it is in the high or low resistance state. The pMTJ can be RESET and SET after the selector turns on. We model the dynamic switching of the coupled pMTJ and selector devices. Our model shows the importance of the optimal matching of pMTJ magnetic properties with selector resistive properties to achieve high performance.