Barrier thickness dependence of the magnetoresistance in Ta O x magnetic tunnel junctions

A systematic study has been conducted on the dependence of the magnetoresistance (MR) ratio on the barrier thickness in Ta O x -based magnetic tunnel junctions. The relatively low MR ratio ( < 10 % ) for the thinnest barriers studied decreases rapidly with increasing thickness. From Rutherford backscattering analysis and current-voltage measurements evidence for a Ta thickness dependent oxidation rate has been found. Photoconductance spectra measured on the same junctions indicate changes in the hot-electron transport into the barrier, independent of the barrier asymmetry. These changes further indicate a modification of the junction structure with increasing Ta thickness, which can have a strong adverse effect on the spin polarization of the tunnel current.