Spin-transfer, switching current distribution and reduction in magnetic tunneling junction-based structures

Spin transfer switching current distribution within a cell and switching current reduction were studied at room temperature for magnetic tunnel junction-based structures with resistance area product (RA) ranged from 10 to 30 Omega-mu m(2) and TMR of 15%-30%. These were patterned into current perpendicular to plane configured nanopillars having elliptical cross sections of area similar to 0.02 mu m(2). The width of the critical current distribution (sigma/average of distribution), measured using 30 ms current pulse, was found to be 3% for cells with thermal factor (KuV/k(B)T) of 65. An analytical expression for probability density function p(I/I-c0) was derived considering a thermally activated spin transfer model, which supports the experimental observation that the thermal factor is the most significant parameter in determining the within-cell critical current distribution. Spin-transfer switching current reduction was investigated through enhancing effective spin polarization factor eta(eff) in magnetic tunnel junction-based dual spin filter (DSF) structures. The intrinsic switching current density (J(c0)) was estimated by extrapolating experimental data of critical current density (J(c)) versus pulse width (tau), to a pulse width of 1 ns. A reduction in intrinsic switchin. 9 current density for a dual spin filter (DSF:Ta/PtMn/CoFe/Ru/CoFeB/Al2O3/CoFeB/spacer/CoFe/PtMn/Ta) was observed compared to single magnetic tunnel junctions (MTJ:Ta/PtMn/CoFe/Ru/CoFeB/Al2O3/CoFeB/Ta). J(c) at tau of 1 ns (similar to J(c0)) for the MTJ and DSF samples were 7 x 10(6) and 2.2 x 10(6) A/cm(2), respectively, for identical free layers. Thus, a significant enhancement of the spin transfer switching efficiency is seen for DSF structure compared to the single MTJ case.