Spin–orbit torque driven perpendicular magnetization switching in Re/CoFeB/MgO with high thermal stability

Abhijeet Ranjan,Chun-Liang Yang,Chia-Chang Lee,Chih-Huang Lai,Rudis Ismael Salinas Padilla

doi:10.1063/5.0073430

Abstract

Writing using spin–orbit torque (SOT) has been widely investigated in the field of magnetic random-access memory (MRAM). Heavy metal (HM)/CoFeB/MgO is the core of this SOT-MRAM structure. The heterostructure consisting of Ta as the spin current source and CoFeB/MgO as the perpendicular magnetic anisotropy (PMA) material is the most researched structure, owing to its high tunneling magnetoresistance ratio. However, Ta is difficult to integrate into the CMOS process due to its poor thermal stability against annealing at temperatures greater than 350 °C. Currently, β-tungsten (W) is the only HM with the CoFeB/MgO system, which can provide both thermal stability and SOT switching. Nevertheless, to achieve the high resistive β phase of W is a challenging task. Here, we report another material rhenium (Re) capable of providing thermally stable PMA up to temperature 425 °C with a perpendicular anisotropic field greater than 5000 Oe; Re possesses a spin hall angle (ϴSH) of 0.065 ± 0.003, and SOT switching can be achieved with a current density around 1.36 × 1011 A/m2. Our findings pave a new avenue for the material design of perpendicular SOT-based MRAM.

Highlights

Producing commercial magnetic random-access memory (MRAM) products with high density requires the free layer of the MTJ to keep perpendicular magnetic anisotropy (PMA) after annealing up to a temperature of at least 400 ○C, given that the back-end semiconductor processing is performed at a temperature of around 400 ○C.6,7
Other properties including the dead layer thickness, saturation magnetization (MS), and interfacial anisotropy (KS) of samples annealed at 400 ○C are shown in Figs. 2(a) and 2(b). tdead and MS were calculated from the plot MStCoFeB vs tCoFeB, as indicated in Fig. 2(a) for 400 ○C
We present a new heavy metal (HM) rhenium that could generate PMA in CoFeB/MgO systems after high temperature annealing up to 425 ○C

Summary

Introduction

Perpendicular magnetic tunnel junction (p-MTJ)-based magnetic random-access memory (MRAM) is the front-runner of the generation non-volatile memory due to its robust magnetization states, which are undisturbed by external perturbation except for a strong magnetic field.[1,2,3] Manipulation of magnetization in p-MTJ using electric current [either spin transfer torque (STT) or spin–orbit torque (SOT)] has already pushed the rise of p-MTJ MRAMs into commercial productions.[2,3,4,5] Producing commercial MRAM products with high density requires the free layer of the MTJ to keep perpendicular magnetic anisotropy (PMA) after annealing up to a temperature of at least 400 ○C, given that the back-end semiconductor processing is performed at a temperature of around 400 ○C.6,7 finding material systems with thermally stable PMA is of supreme importance. Heavy metal (HM)/CoFeB/MgObased p-MTJs have been commonly used due to their sufficiently high tunneling magnetoresistance (TMR) value.[8,9,10,11] a range of materials, including Ta, Mo, W, Hf, and Pd, have been shown to have PMA, only Mo and β-W can still reveal PMA after annealing at 400 ○C or higher temperature.[6,7] The origin of PMA in HM/CoFeB/MgO is believed to be mainly originating from the Fe–O orbital hybridization at the CoFeB/MgO interface and boron (B) out-diffusion.[6,7,12–15] the property of HM is another crucial factor affecting anisotropy and TMR, which needs to promote the CoFeB crystallization along MgO [002].16–19. Severe Ta diffusion destroys the PMA.[6,7]

Results

Discussion

Conclusion