Determination of barrier oxidation states in spin dependent tunneling structures

X-ray photoelectron spectroscopy (XPS) was used to characterize spin dependent tunneling (SDT) structures using plasma oxidized Ta as the insulating barrier. We are able to determine the relative proportion of the different oxidation states of the insulating barrier material. Information available from this technique includes barrier oxidation states, thickness, and completeness of oxidation. Information on the electrodes is also obtained: specifically, Ta is found to diffuse into NiFe, and oxidation of Ni is observed. XPS is shown to be a powerful tool in characterizing the materials sets that comprise SDT devices. (C) 1999 American Institute of Physics. [S0021-8979(99)04910-5].