Growth characteristics of Al oxide formed by ozone in magnetic tunnel junctions

Abstract

Magnetic tunnel junctions with Al2O3 barrier layer oxidized by ozone and oxygen mixture gas (ozone atmosphere) were fabricated and Al oxidation characteristics were investigated. The tunneling magnetoresonance ratio and junction resistance of ozone oxidized junctions were 33% and several kΩ μm2. In this study, oxidation kinetics and its chemistry were investigated using transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). To study the growth characteristics of Al oxide in ozone atmosphere, the Al layers were oxidized under zero, positive, and negative bias conditions. The results of cross sectional TEM showed that the oxide thickness exposed to the ozone gas for 70 min is 3.2, 3.75, and 3.47 nm at 0, +100, and −100 V bias conditions, respectively. Both positive and negative bias accelerated aluminum oxidation. This result indicates that both electron tunneling and ion migration are rate controlling steps in this oxidation process. From the results of the angle resolved XPS, the O/Al ratio was not uniform through the oxide layer grown under positive bias condition. The oxygen content at the top side of the AlOx barrier was richer than other positions.