Perpendicular magnetic tunnel junction (p-MTJ) spin-valves designed with a top Co2Fe6B2 free layer and a nanoscale-thick tungsten bridging and capping layer
Source abstract
Abstract
Recently, p-MTJ spin-valves with top Co2Fe6B2 free layers have been widely studied. They potentially experience crystallinity degradation in the face-centered-cubic (fcc) structure of the MgO tunneling barrier as a result of the diffusion of Ta atoms and a significant amount of Fe atoms from the Co2Fe6B2 free and pinned layers. A new design of the p-MTJ spin-valve using a nanoscale-thick W bridging and capping layer demonstrated the absence of significant crystallinity degradation in the fcc structure and showed a limited diffusion of Fe atoms, thus achieving a TMR ratio of ~143% at an ex-situ annealing temperature of 400 °C. Coating quantum tunneling devices with thin metallic bridges may lead to magnetic memory cells smaller than 20 nanometres. Dynamic-random-access memory (DRAM) devices are popular because of their simple one-transistor, one-capacitor construction, but they are tricky to produce at nanoscale dimensions. A promising way to construct alternative DRAM devices based on perpendicular magnetic tunnel junctions (p-MTJ) has now been outlined by Jea-Gun Park and colleagues from Hanyang University in South Korea. Their device, which sandwiches a magnesium oxide tunnel barrier between layers of magnetic cobalt—iron—boron films, uses external magnetic fields to switch between on and off memory states. Normally, such p-MTJ devices suffer from degraded magnesium oxide crystallinity and deleterious diffusion of iron atoms. However, the team found that nanoscale-thin layers of tungsten placed under and above the magnetic films prevented premature device breakdown. New design of the p-MTJ spin-valve using W bridging and capping layer demonstrated no significant crystallinity degradation and no considerable Fe atoms diffusion, thus achieving the TMR ratio of ~143% at an ex-situ annealing temperature of 400 oC. A better crystallinity of the MgO layer for W case than Ta case would be related to less diffusion amount of metal atoms and lattice strain in MgO layer. In addition, higher Fe and Co atom concentrations of Co2Fe6B2 free and pinned layers for W case than Ta case would be associated with less solubilities in W layers than Ta layers.
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Research context
OpenAlex topics: Magnetic properties of thin films · ZnO doping and properties · Semiconductor materials and devices
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References (37)
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