Dependency of Tunneling-Magnetoresistance Ratio on Nanoscale Spacer Thickness and Material for Double MgO Based Perpendicular-Magnetic-Tunneling-Junction.

Du-Yeong Lee,Jea-Gun Park,Song-Hwa Hong,Seung-Eun Lee

doi:10.1038/srep38125

Abstract

It was found that in double MgO based perpendicular magnetic tunneling junction spin-valves ex-situ annealed at 400 °C, the tunneling magnetoresistance ratio was extremely sensitive to the material and thickness of the nanoscale spacer: it peaked at a specific thickness (0.40~0.53 nm), and the TMR ratio for W spacers (~134%) was higher than that for Ta spacers (~98%). This dependency on the spacer material and thickness was associated with the (100) body-centered-cubic crystallinity of the MgO layers: the strain enhanced diffusion length in the MgO layers of W atoms (~1.40 nm) was much shorter than that of Ta atoms (~2.85 nm) and the shorter diffusion length led to the MgO layers having better (100) body-centered-cubic crystallinity.

Highlights

It was found that in double MgO based perpendicular magnetic tunneling junction spin-valves ex-situ annealed at 400 °C, the tunneling magnetoresistance ratio was extremely sensitive to the material and thickness of the nanoscale spacer: it peaked at a specific thickness (0.40~0.53 nm), and the TMR ratio for W spacers (~134%) was higher than that for Ta spacers (~98%)
The TMR ratio can be obtained by the current-in-plane tunneling (CIPT) technique without memory-cell patterning requiring a huge process integration; i.e., the four small probes are placed collinearly on a planar tri-layer, and a current is sent through the planar tri-layer through two probes (I+ and I− probes)
Comparing the TMR ratios in the cases of the Ta spacer and the W spacer obviously indicates that the use of 0.20 and 0.70 nm-thick W spacers resulted in least 35% higher TMR ratios in the comparison with the use of Ta spacers

Summary

Introduction

It was found that in double MgO based perpendicular magnetic tunneling junction spin-valves ex-situ annealed at 400 °C, the tunneling magnetoresistance ratio was extremely sensitive to the material and thickness of the nanoscale spacer: it peaked at a specific thickness (0.40~0.53 nm), and the TMR ratio for W spacers (~134%) was higher than that for Ta spacers (~98%). (i.e., the lower CoFeB layer and upper CoFeB layer) It has proven extremely difficult achieve a high TMR ratio in a double MgO based p-MTJ spin-valve using a nanoscale thickness Ta spacer at the BEOL temperature of 400 °C15,16. We investigated the dependency of the TMR ratio on the thickness and type of material (tantalum or tungsten) of spacers in double MgO-based p-MTJ spin-valves with a top free Co2Fe6B2 layer. The mechanism by which thickness and material of the spacer influence the TMR ratio was revealed by examining the static magnetization behavior, (100) bcc crystallinity, and depth profile of the atomic composition of the spin-valves

Methods

Results

Conclusion