Bing K. Yen

Perpendicular magnetic tunnel junction with thin CoFeB/Ta/Co/Pd/Co reference layer

Integration of high density spin transfer torque magnetoresistance random access memory requires a thin stack (less than 15 nm) of perpendicular magnetic tunnel junction (p-MTJ). We propose an innovative approach to solve this challenging problem by reducing the thickness and/or moment of the reference layer. A thin reference layer structure of CoFeB/Ta/Co/Pd/Co has 60% magnetic moment of the conventional thick structure including [Co/Pd] multilayers. We demonstrate that the perpendicular magnetization of the CoFeB/Ta/Co/Pd/Co structure can be realized by anti-ferromagnetically coupling to a pinned layer with strong perpendicular anisotropy via Ruderman-Kittel-Kasuya-Yosida exchange interaction. The pMTJ with thin CoFeB/Ta/Co/Pd/Co reference layer has a comparable TMR ratio (near 80%) as that with thick reference layer after annealing at 280 °C. The pMTJ with thin reference layer has a total thickness less than 15 nm, thereby significantly increasing the etching margin required for integration of high density pMTJ array on wafers with form factor of 300 mm and beyond.

High performance perpendicular magnetic tunnel junction with Co/Ir interfacial anisotropy for embedded and standalone STT-MRAM applications

High volume spin transfer torque magnetoresistance random access memory (STT-MRAM) for standalone and embedded applications requires a thin perpendicular magnetic tunnel junction (pMTJ) stack (∼10 nm) with a tunnel magnetoresistance (TMR) ratio over 200% after high temperature back-end-of-line (BEOL) processing up to 400 °C. A thin reference layer with low magnetic moment and strong perpendicular magnetic anisotropy (PMA) is key to reduce the total thickness of the full pMTJ stack. We demonstrated strong interfacial PMA and a perpendicular Ruderman-Kittel-Kasuya-Yosida exchange interaction in the Co/Ir system. Owing to the additional high PMA at the Ir/Co interface in combination with a conventional CoFeB/MgO interface in the Ir/Co/Mo/CoFeB/MgO reference layer, the full film pMTJ showed a TMR ratio over 210% after annealing at 400 °C for 150 min. The high TMR ratio can be attributed to the thin stack design by combining a thin reference layer with the efficient compensation by a thin pinned layer. The ann...

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.

Perpendicular magnetic tunneling junction switching dynamic modes, extreme events, and performance scaling

The performance of the state-of-the-art perpendicular magnetic tunneling junction (pMTJ) device is fundamentally determined by the physics of material “extreme events.” A dynamic mode approach is used to study “extreme events” of stochastic nonlinear magnetization switching, including magnetic interactions and non-uniform magnetization dynamics. Our theory and experiment show that the magnetization switching “extreme events” are well characterized by the dynamic modes of interacting magnetic systems. The dynamic modes provide a clear understanding of the physical processes of the magnetization switching “extreme events.” We predict markedly different pMTJ scaling behaviors for spin transfer torque, spin-orbit-interaction torque, and thermal fluctuations at different operation speeds and bit error rate conditions. Understanding these scaling behaviors is critical for existing and emerging pMTJ device applications.