Comparison of oxidation methods for magnetic tunnel junction material

Advances in reducing the resistance and enhancing the magnetoresistance (MR %) of the magnetic tunnel junction (MTJ) material has made it useful for ma gnetoresistive random access memory as well as magnetic field sensing appli cations. One of the most important aspects for producing the MTJ material i s the method used for forming the tunnel barrier, and its impact on the pro perties of MTJ such as resistance and area product (RA), MR%, and RA unifor mity across a large area. We have explored forming the aluminum oxide tunne l barrier with air; reactive sputtering; plasma oxidation with plasma sourc e; plasma oxidation with power introduced from the target side; and plasma oxidation with power introduced from the substrate side. Our results show t hat all techniques can be made to work. Plasma oxidation is favored due to its simplicity and manufacturing compatibility. It was also discovered that different oxidation methods used in this study caused little difference in MTJ resistance uniformity. The latter is mainly determined by the Al metal -thickness uniformity. Modeling based on Simmons' theory supports our exper imental finding. This illustrates the importance in improving Al metal-film uniformity for producing MTJ with ultra-uniform resistance. (C) 2000 Ameri can Institute of Physics. [S0021-8979(00)43008-2].