Efficient characterization of ultrathin AlOx insulating barriers in magnetic tunnel junctions fabricated by masked rf plasma oxidation technique

AlOx insulating barriers in magnetic tunnel junctions were prepared by a masked rf plasma oxidation process to reduce direct ion-bombardment effect on the barrier. In our method, the root-mean-square value of 2.1 A in the barrier and the magnetic resistance ratio up to 32% were observed. In addition, the surface plasmon resonance spectroscopy (SPRS) measurement was performed to efficiently determine optimum oxidation time, dielectric properties, and oxidation states inside thin barrier. The SPRS results revealed that the dielectric value and thickness of the optimum barrier were found to be 1.3576+i1.4488 and 16.3 A, respectively, with a thickness confirmation by a high resolving transmission electron microscope measurement.