The role of Mg interface layer in MgO magnetic tunnel junctions with CoFe and CoFeB electrodes

Hyunsoo Yang,Stuart Parkin,See-Hun Yang

doi:10.1063/1.3690139

Hyunsoo Yang, Stuart Parkin + Show 1 more

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https://doi.org/10.1063/1.3690139

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Abstract

The tunneling spin polarization (TSP) is directly measured from reactively sputter deposited crystalline MgO tunnel barriers with various CoFe(B) compositions using superconducting tunneling spectroscopy. We find that the Mg interface layer thickness dependence of TSP values for CoFeB/Mg/MgO junctions is substantially different from those for CoFe/Mg/MgO especially in the pre-annealed samples due to the formation of boron oxide at the CoFeB/MgO interface. Annealing depletes boron at the interface thus requiring a finite Mg interface layer to prevent CoFeOx formation at the CoFeB/MgO interface so that the TSP values can be optimized by controlling Mg thickness.

Highlights

A large tunneling magnetoresistance (TMR) is one of the most important attributes of magnetic tunnel junctions (MTJs)
It was predicted that crystalline tunnel barriers can produce extremely high tunneling spin polarization (TSP) and TMR values
TMR ratios as high as thousands of percent were predicted from MgO based MTJs1,2 and a giant TMR ratio up to 604% at room temperature has been observed recently with MgO(100) tunnel barriers after intense research activities.[3,4,5,6,7]

Summary

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Tunnel magnetoresistance of 604% at by suppression of Ta diffusion in pseudo-spin-valves annealed at high temperature. It was predicted that crystalline tunnel barriers can produce extremely high tunneling spin polarization (TSP) and TMR values. TMR ratios as high as thousands of percent were predicted from MgO based MTJs1,2 and a giant TMR ratio up to 604% at room temperature has been observed recently with MgO(100) tunnel barriers after intense research activities.[3,4,5,6,7] The origin of this giant TMR effect is the active spin filtering of crystalline MgO barrier in addition to ferromagnetic electrodes’ spin polarization, and the measurement of TSP value and sign in electrode/barrier is critical to understand TMR in MTJs. In this work, the TSP values of reactively sputtered MgO based MTJs using various CoFe(B) compositions are compared to that of CoFe/MgO as a function of Mg interface layer thickness. It is found that the tunnel barrier height increases with thermal annealing in both CoFe and CoFeB cases exhibiting the improved barrier condition

Data Fit

Findings

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