Characteristics of TMR films with Oxidized Al-Hf Alloy barrier

Abstract

We investigated the tunnel magnetoresistance(TMR) and bias voltage dependence of the TMR with oxidized Al-Hf Alloy at the range of Hf content (CHf) from 0 at.% to 70 at.%. The TMR ratio was greatly increased from 9.6 % to 21.4 % when the CHf increased from 0 at.% to 17 at.% , and the critical AlHf thickness that appeared TMR raito was thinner with CHf increased. These results are explained by the consideration that a uniformity of the oxidation in the AlHf layer composed with an amorphous or a nano-crystallized state was better than that in the Al layer composed with the large grain-boundaries such as fcc-Al. The bias voltage dependence of the TMR with oxidized Al-Hf Alloy at CHf of 17 at.% also improved and the yield that tunnel junction had high breakdown voltage was better than that with Al-oxide barrier although barrier thickness became thin in order to decrease RA. These results indicate that the defects like pinholes in oxidized Al-Hf Alloy barrier decreased because the crystal structure of Al was changed into amorphous from fcc(111) by Hf.