Development of Novel Prototype Scalable Magnetoresistive Random Access Memory
نویسنده
چکیده
MRAM has received a great deal of attention in recent years for its potential to become a universal memory capable of nonvolatility, infinite cycleability, fast switching speeds, high density, and low cost. However, the limitations of conventional design architectures have made MRAM difficult to realize. In this work, a new annular currentperpendicular-to-plane (CPP) giant magnetoresistive (GMR) design architecture is presented to achieve robust single-step switching, reasonably low switching currents, and good thermal stability. Four scalable pseudo spin valve annular designs are examined, including three repeats of a CoFe/Cu/NiFe tri-layer stack, single-repeat CoFe/Cu/CoFe top and bottom spin valves with Cu laminations in both the reference and storage layer for enhanced GMR, and a single-repeat NiFe/CoFe/Cu/CoFe bottom spin valve tri-layer stack with Cu laminations in the reference layer only. Each sputter deposited film stack is fabricated into a 600 nm outer diameter, 200 nm inner diameter ring and test structure using a combination of electron beam lithography, optical lithography, ion milling, reactive ion etching, and chemical mechanical planarization. The ensuing current induced magnetic switching properties are obtained from the major and minor hysteresis loops measured for each design. The results demonstrate multiple-step switching in the CoFe/Cu/NiFe three-repeat tri-layer and CoFe/Cu/CoFe top spin valve rings. Conversely, the CoFe/Cu/CoFe bottom spin valve and NiFe/CoFe/Cu/CoFe rings demonstrate clean, robust, single-step magnetic switching, with significant spin transfer torque observed in the NiFe/CoFe storage layer of the latter design. Following a field induced initialization process, a robust trapped domain wall pair switching mode is observed in the NiFe/CoFe/Cu/CoFe rings, demonstrating that low power is attainable.
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