Ultralow resistance-area product of 0.4Ω(μm)2 and high magnetoresistance above 50% in CoFeB∕MgO∕CoFeB magnetic tunnel junctions

An ultralow resistance-area $\left(\mathit{RA}\right)$ product of $0.4\Omega {\left(\mu \mathrm{m}\right)}^2$ was achieved in $\mathrm{Co}\mathrm{Fe}\mathrm{B}∕\mathrm{Mg}\mathrm{O}∕\mathrm{Co}\mathrm{Fe}\mathrm{B}$ magnetic tunnel junctions with a high magnetoresistance ratio of 57% at room temperature. Various growth conditions for polycrystalline MgO(001) tunneling barrier were optimized to improve the crystalline orientation of the MgO(001) layer, which resulted in a significant enhancement of magnetoresistance in an ultralow $\mathit{RA}$ region below $1\Omega {\left(\mu \mathrm{m}\right)}^2$ . Removal of residual ${\mathrm{H}}_2\mathrm{O}$ molecules from a growth chamber was especially effective in improving the crystalline orientation. The present achievements will enable the development of highly sensitive read heads for ultrahigh-density hard disk drives.