Giant tunnel magnetoresistance and high annealing stability in CoFeB/MgO/CoFeB magnetic tunnel junctions with synthetic pinned layer

TL;DR

This study demonstrates that incorporating Ru spacers in CoFeB/MgO/CoFeB magnetic tunnel junctions significantly enhances TMR ratios and annealing stability by promoting (001)-oriented crystalline growth in the pinned layer.

Contribution

It reveals the crucial role of Ru spacers in achieving high TMR ratios and thermal stability in magnetic tunnel junctions with synthetic pinned layers.

Findings

TMR ratio reaches 361% at 425°C with Ru spacers.

Ru spacers promote (001)-oriented bcc CoFeB growth.

MTJs with Ru spacers maintain high TMR at elevated annealing temperatures.

Abstract

We investigated the relationship between tunnel magnetoresistance (TMR) ratio and the crystallization of CoFeB layers through annealing in magnetic tunnel junctions (MTJs) with MgO barriers that had CoFe/Ru/CoFeB synthetic ferrimagnet pinned layers with varying Ru spacer thickness (tRu). The TMR ratio increased with increasing annealing temperature (Ta) and tRu, reaching 361% at Ta = 425C, whereas the TMR ratio of the MTJs with pinned layers without Ru spacers decreased at Ta over 325C. Ruthenium spacers play an important role in forming an (001)-oriented bcc CoFeB pinned layer, resulting in a high TMR ratio through annealing at high temperatures.