Microstructure and electrical properties of magnetic tunneling junction: NiFe/Co/Ta/Al-oxide/Co

NiFe/Co/Ta/AlOx/Co tunnel junctions were synthesized and compared with the partially oxidized NiFe/Co/Ta-oxide/Co junction to study the effect of residual Ta metallic layer at the insulation layer. NiFe/Co/Ta/AlOx/Co junctions were created by inserting Ta films of different thickness between the bottom electrode and the Al-oxide. The highest magnetoresistance (MR) ratio of 15% was attained without the Ta film. As the Ta film thickness increased, the MR ratio markedly dropped. The existence of the Ta film led to the loss of spin polarization and subsequent lowering of the MR ratio. We have shown that 1–2 Å thick layer of Ta can be inserted and maintain the detectable level of MR ratio so that the AlOx/Ta layer could be used as the insulation layer with interdiffusion barrier in exchange-biased tunnel junctions. It was also suggested that the Ta-oxide/Ta could do better as the tunnel barrier if the oxidation of Ta could be precisely controlled.