Voltage-controlled magnetic anisotropy switching device using an external ferromagnetic biasing film

摘要

A voltage-controlled magnetic anisotropy (VCMA) switching device (and method of manufacture/use) comprising an external ferromagnetic biasing film, and embodiment in the form of a Magnetoresistive Random Access Memory MRAM in particular a magneto-electrical RAM MeRAM) memory device. The MRAM device includes a substrate, at least one magnetic tunnel junction (MTJ) stack 704 disposed thereon the substrate 702, wherein the MTJ stack 704 comprises a tunnel barrier layer 708 (e.g MgO) between a first ferromagnetic layer (e.g CoFeB) having a fixed magnetization (layer 706) and a second ferromagnetic layer (CoFeB) having unfixed magnetization (magnetic free layer 710), and a magnet 712 (which may be a permanent magnet) disposed adjacent to the second ferromagnetic layer. The magnet 712 may comprise a ferromagnetic biasing layer formed horizontally parallel to the substrate and aligned with the second ferromagnetic layer 710, and may comprise of a hard ferromagnetic layer (CoPt Cobalt Platinum ) or a soft ferromagnetic layer (NiFe Nickel Iron) pinned by an antiferromagnet. The first and second ferromagnetic layer may also comprise CoFeB layer. The magnetization of the second ferromagnetic layer precesses about a bias field from the magnet such that a magnetic polarity of the second ferromagnetic layer is reversed when an electrical bias field (voltage) is applied to the MTJ stack. The Magnetoresistive RAM (MeRAM) uses Tunneling Magnetoresistance (TMR) effect for readout, however the writing of information is performed by voltage controlled magnetic anisotropy VCMA of the tunnel barrier (e.g providing perpendicular anisotropy) as opposed to current controlled spin transfer torque STT or spin orbit torque SOT mechanisms. The emphasis is therefore on the application of a voltage via an electric field across the MTJ device, thus reducing the power requirements of memory devices.