Interfacial Engineering Strategies for Efficient Spin–Orbit Torque Devices with Pt Alloys

Abstract

To make spin−orbit torque magnetic randomaccess memories (SOT-MRAMs) become competitive enough to replace the contemporary memory architecture, it is of great importance to utilize conductive SOT materials that possess large damping-like spin−orbit torque (DL-SOT) efficiencies and backend-of-line (BEOL) compatibility. In this work, we report a BEOLcompatible CoFeB/MgO-based heterostructure with the Pt−Cr alloy as the spin current source (SCS) and inserted a Pt/Co/Pt composite layer to achieve texture decoupling and ferromagnetic coupling. A thermally robust perpendicular magnetic anisotropy (PMA) of the hybrid heterostructure can be retained after annealing at 400 °C for 1 h, while maintaining large DL-SOT efficiencies of the annealed Pt−Cr alloys (ξ DL ∼ 0.34 for Pt 0.70 Cr 0.30 ). Additionally, by optimizing the current distribution with a resistive Pt spacer layer, it is possible to simultaneously enhance the current-to-effective field conversion ratio (H z eff /I) and retain the apparent ξ DL (ξ DL ∼ 0.37 for Pt 0.79 Cr 0.21 ). Moreover, the critical switching current density can be reduced from J c Pt ∼ 2.0 × 10 7 A•cm −2 for Pt to J c Pt 0.70 Cr 0.30 ∼ 4.9 × 10 6 A•cm −2 for Pt 0.70 Cr 0.30 without tampering the thermal stability of the annealed heterostructure. These interfacial engineering strategies provide directions to integrate Pt-based SCSs with large ξ DL into a BEOL-compatible platform for future SOT-MRAM devices with PMA.

Field-Free Spin–Orbit Torque Switching via Oscillatory Interlayer Dzyaloshinskii–Moriya Interaction for Advanced Memory Applications

“…By reduction of t , the i-DMI strength is maximized at 275.2 Oe when t = 0.6 nm. Furthermore, reducing the capping Pt thickness provides the potential to integrate such a heterostructure with modern CoFeB/MgO/CoFeB-based magnetic tunnel junctions (MTJs) via FM coupling. − Hence, the tuning of capping Pt layer thickness is as essential as the optimization of other layers to achieve optimal i-DMI (the influences from the IMA CoFeB layer and the Pt spacer are detailed in Sections S5 and S6, Supporting Information). The optimized layer structure is identified as Ta(0.5)/CoFeB(1.4)/Pt(3.3)/Co(0.7)/Pt(0.6), which we refer to as the “asymmetric Pt design”; it underwent subsequent measurements to evaluate its performance in field-free, current-induced magnetization switching.…”