Spin-Based MOSFETs for Logic and Memory Applications and Spin Accumulation Signals in CoFe/Tunnel Barrier/SOI Devices

New innovative ferromagnetic source/drain technologies on Si for next-generation-transistor applications are researched and developed using CoFe/AlO_xn⁺-Si and CoFe/MgO n⁺-Si junctions. As evidence of the spin accumulation in the n⁺-Si conduction channels, nonlocal spin signals and four-terminal nonlocal-Hanle signals are presented for CoFe/MgO/SOI devices. The spin diffusion times determined by four-terminal nonlocal-Hanle signals are consistent with those observed in three-terminal Hanle signals. The relatively long spin diffusion time of τs=1.4 nsec and relatively large spin polarization P=0.43 at room temperature for CoFe/MgO/SOI devices were observed, when fitting to the existing diffusion model for spin injection and accumulation. We have observed the marked enhancement of the absolute value of three-terminal voltage changes via Hanle-type spin precessions (|ΔV|) as a function of interface resistance in the temperature range between 20 K and 300 K. We also have observed the asymmetric bias voltage dependence on ΔV. In terms of the reason of marked enhancement of |ΔV| as a function of interface resistance, the spin absorption into ferromagnet would be most effective. For the explanation of the asymmetric bias voltage dependence, we should take into account two additional possible origins. Moreover, we succeed in decreasing the interface resistance for CoFe/MgO/ n⁺-Si junctions down to 36 Ωμm² by using evaporation method for MgO deposition.