Abstract
The magnetotransport properties of tunnel junctions with the structure of Ta 5nm∕Cu20nm∕Ta 5nm∕Ni76Fe242nm∕Cu 5nm∕Mn75Ir2510nm∕Co71Fe29 4nm∕Al–N∕Co71Fe29 4nm∕Ni76Fe2420nm∕Ta5nm were investigated. When the Al thickness, nitridation time, and annealing temperature were 1nm(0.8nm), 50s(35s), and 280°C(300°C), tunnel magnetoresistance (TMR) ratio and resistance-area product were 49%(34%) and 3×104Ωμm2(1.5×104Ωμm2), respectively. In order to clarify the annealing temperature dependence of TMR ratio, the local transport properties were studied using conducting atomic force microscope for Ta5nm∕Cu20nm∕Ta5nm∕Ni76Fe242nm∕Cu5nm∕Mn75Ir25 10nm∕Co71Fe29 4nm∕Al(0.8nm)–N junction fabricated with the nitridation time of 35s and Ar+N2 plasma as a function of annealing temperature. The large TMR at 300°C, where the TMR ratio of the corresponding magnetic tunnel junction had the maximum value of 34%, could be well elucidated by the enhancement of the average barrier height ϕave, and the reduction of its fluctuation. After annealing at 340°C, the leakage current was observed and the TMR ratio decreased.
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