Si-based Spin Metal-Oxide-Semiconductor Field-Effect Transistors with an Inversion Channel

We demonstrated Si-based bottom-gate-type spin metal-oxide-semiconductor field-effect transistors (spin MOSFETs) with an electron inversion channel at room temperature. Our spin MOSFETs were fabricated on a (001)-oriented silicon-on-insulator (SOI) substrate with a p-type ultrathin (8 nm) Si layer, in which the channel length was 0.4, 0.7, and 1.5 μm, the spin injector/detector were ferromagnetic multilayer (from top to bottom) Fe(4nm)/Mg(1nm)/MgO(1nm) tunnel junctions, and a 200-nm-thick buried oxide layer was used for the gate dielectric. In magnetoresistance measurements with various gate electric fields and source-drain electron currents, clear spin-valve signals were obtained for all the bias conditions. The change of all the spin-valve signals were analyzed to reveal "spin drift" that can enhance the effective spin diffusion length by the lateral electric field parallel to the electron transport in the inversion channel, based on our original formula that takes into account the distribution of the lateral electric field. The effective spin diffusion length becomes larger by 3 - 4 times than the intrinsic spin diffusion length λS = 0.41 μm owing to the increase in the lateral electric field. It was confirmed that the spin drift is very useful to achieve larger spin-valve signals in spin MOSFETs with an electron inversion channel.