We proposed a two-terminal-electrode vertical thyristor and investigated its suitability as a cross-point memory cell without a selector from the viewpoints of p+- and n+-base region width and a vertically stacked doped-epitaxial-Si layer structure such as p++-emitter/n+-base/p+-base/n++-emitter or n++-emitter/p+-base/n+-base/p++-emitter. The proper p+- and n+-base-region width (i.e., 160 nm) and p++-emitter/n+-base/p+-base/n++-emitter layer structure could enable the development of a cross-point memory cell using the half bias concept by preventing misfit dislocations at the junctions between the n++-emitter and p+-base or n+-base and p++-emitter. It was also found that generation of the misfit dislocations originating from B or P atom segregation at junctions during doped-Si epitaxial-layer growth enhanced the strain at the junctions. The misfit dislocations at the junctions were produced when the strain at the junctions was greater than ∼4 × 10−4.

The current challenging issues for terra-bit-level perpendicular STT-MRAM cells have been reviewed in the view of four critical parameters such as TMR ratio, Δ, J ex , and α. The TMR ratio of p-MTJ spin-valves are reaching to < 150% at the BEOL of >350 o C. A single MgO based p-MTJ spin-valve could not satisfy Δ of > 74, proposing a double MgO based p-MTJ spin-valve. J ex in SyAF layer adequately met > 0.7erg/cm 2 at BEOL of > 350 o C. A Co 2 Fe 6 B 2 based p-MTJ spin-valve limits to α of 0.005, necessary to develop a low α material such as full Heusler half-metal. Thus, an essential challenge in the future is to satisfy four critical parameters simultaneously at > 350 o C and 300-mm TiN electrode wafers.19.2.2 IEDM14-483

The TMR ratio of Co2Fe6B2/MgO-based p-MTJ spin valves stacked with a [Co/Pd]n-SyAF layer decreased rapidly when the ex situ magnetic annealing temperature (Tex) was increased from 275 to 325 °C, and this decrease was associated with degradation of the Co2Fe6B2 pinned layer rather than the Co2Fe6B2 free layer. At a Tex above 325 °C the amorphous Co2Fe6B2 pinned layer was transformed into a face-centered-cubic (fcc) crystalline layer textured from [Co/Pd]n-SyAF, abruptly reducing the Δ1 coherence tunneling of perpendicular-spin-torque electrons between the (100) MgO tunneling barrier and the fcc Co2Fe6B2 pinned layer.

For the perpendicular-magnetic-tunneling-junction (p-MTJ) spin valve with a nanoscale-thick bottom Co2Fe6B2 free layer ex situ annealed at 400 °C, which has been used as a common p-MTJ structure, the Pt atoms of the Pt buffer layer diffused into the MgO tunneling barrier. This transformed the MgO tunneling barrier from a body-centered cubic (b.c.c) crystallized layer into a mixture of b.c.c, face-centered cubic, and amorphous layers and rapidly decreased the tunneling-magnetoresistance (TMR) ratio. The p-MTJ spin valve with a nanoscale-thick top Co2Fe6B2 free layer could prevent the Pt atoms diffusing into the MgO tunneling barrier during ex situ annealing at 400 °C because of non-necessity of a Pt buffer layer, demonstrating the TMR ratio of ~143 %.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1637-9) contains supplementary material, which is available to authorized users.

We investigated the effect of the presence of strained SiGe layer inserted between unstrained Si and buried oxide layer and the Ge concentration in strained SiGe layer on the memory margin of capacitor-less memory-cell. We observed that memory margin of unstrained Si on strained SiGe-on-insulator capacitor-less memory-cells increases with the Ge concentration of the strained SiGe layer and obtained memory margin at the Ge concentration of 19 at% that was 3.2 times larger than that at the silicon-on-insulator capacitor-less memory-cell. This enhancement was due to the potential-barrier lowering increasing exponentially with the Ge concentration resulting from higher hole confinement in spite of the reduction in the saturated drain current.