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

摘要

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