Effects of Annealing Temperature on the Local Current Conduction of Ferromagnetic Tunnel Junction

Abstract

Ferromagnetic tunnel junctions, Ta/Cu/Ta/NiFe/Cu/<TEX>$Mn_{75}$</TEX> <TEX>$Ir_{25}$</TEX> <TEX>$Co_{70}$</TEX> <TEX>$Fe_{30}$</TEX>/Al-oxide, were fabricated by do magnetron sputtering and plasma oxidation process. The effect of annealing temperature on the local transport properties of the ferromagnetic tunnel junctions was studied using contact-mode Atomic Force Microscopy (AFM). The current images reflected the distribution of the barrier height determined by local I-V analysis. The contrast of the current image became more homogeneous and smooth after annealing at <TEX>$280^{\circ}C$</TEX>. And the average barrier height <TEX>$\phi_{ave}$</TEX> increased and its standard deviation <TEX>$\sigma_{\phi}$</TEX> X decreased. For the cases of the annealing temperature more than <TEX>$300^{\circ}C$</TEX>, the contrast of the current image became large again. And the average barrier height <TEX>$\phi_{ave}$</TEX> decreased and its standard deviation <TEX>$\sigma_{\phi}$</TEX> increased. Also, the current histogram had a long tail in the high current region and became asymmetric. This result means the generation of the leakage current that is resulted from the local generation of a low barrier height region. In order to obtain the high tunnel magnetoresistance(TMR) ratio, the increase of the average barrier height and the decrease of the barrier height fluctuation must be strictly controlled.led.