Dependence of tunnel magnetoresistance in MgO based magnetic tunnel junctions on Ar pressure during MgO sputtering

TL;DR

This study demonstrates that Ar pressure during MgO sputtering significantly influences the surface quality, orientation, and resulting tunnel magnetoresistance ratios in MgO-based magnetic tunnel junctions, achieving high TMR at room temperature.

Contribution

It reveals how high Ar pressure during MgO sputtering enhances surface smoothness and orientation, leading to improved TMR ratios in magnetic tunnel junctions.

Findings

High Ar pressure (10 mTorr) yields smooth, highly (001) oriented MgO.

TMR ratio reaches 355% at room temperature after annealing.

Deep-submicron MTJs show high TMR at low resistance-area products.

Abstract

We investigated dependence of tunnel magnetoresistance effect in CoFeB/MgO/CoFeB magnetic tunnel junctions on Ar pressure during MgO-barrier sputtering. Sputter deposition of MgO-barrier at high Ar pressure of 10 mTorr resulted in smooth surface and highly (001) oriented MgO. Using this MgO as a tunnel barrier, tunnel magnetoresistance (TMR) ratio as high as 355% at room temperature (578% at 5K) was realized after annealing at 325 C or higher, which appears to be related to a highly (001) oriented CoFeB texture promoted by the smooth and highly oriented MgO. Electron-beam lithography defined deep-submicron MTJs having a low-resistivity Au underlayer with the high-pressure deposited MgO showed high TMR ratio at low resistance-area product (RA) below 10 ohm-um^2 as 27% at RA = 0.8 ohm-um^2, 77% at RA = 1.1 ohm-um^2, 130% at RA = 1.7 ohm-um^2, and 165% at RA = 2.9 ohm-um^2.