Microstructure and electrical properties of annealed tunneling magnetoresistive junctions with plasma oxidized insulation layer

A low-resistance (1 KΩμm2) magnetic tunneling junction consisting of Ta (30 Å)/NiFe (30 Å)/Cu (200 Å)/NiFe (30 Å)/IrMn (100 Å)/CoFe (40 Å)/Al (8 Å)–oxide/CoFe (40 Å)/NiFe (200 Å)/Ta (50 Å) was fabricated with the plasma-oxidized insulation layer. When the junction was annealed at 200–300 °C, the junction showed continuous improvement of the magnetoresistance (MR) ratio measured at room temperature, reaching 48% at 275 °C. The resistance-area of the junctions also increased with the increasing temperature. Transmission electron microscopy revealed, prior to the heat treatment, rough interfaces at the insulation layer. After the annealing, the interfaces became much sharper and smoother. In addition, the grain size of the IrMn layer decreased considerably, which effectively increased the interfacial area. We believe that the observed microstructural changes led to the increased potential barrier and the subsequent enhancement of the MR.