Determination of the thickness of Al oxide films used as barriers in magnetic tunneling junctions

Abstract

Aluminum films oxidized in oxygen atmosphere are widely used in magnetic tunneling junctions (MTJs). We have determined the oxidation depth of these films by Fourier transform infrared (FTIR) spectroscopy in reflection-absorption mode. The oxide/Al interfaces are found to be abrupt and the thickness of the oxide layer increases slowly with exposure to oxygen, after a rapid onset. These results provide a physical picture of observed changes in the magnetotransport of MTJs as a function of Al thickness and oxidation time. The results also agree well with the empirically found optimum oxide growth condition which yields a maximum magnetoresistance.