Abstract
MgO-based magnetic tunneling junctions (MTJs) with CoFeB ferromagnetic layers were fabricated in this study. The structural, magnetic and electrotransport properties of both as-deposited and annealed samples were well discussed. The pattern process was also set up to fabricate small size MTJs, which can avoid the geometric effect and improve the reliability of measured MR ratio, especially for low RA samples. Both pseudo spin-valve and spin-valve type samples were prepared. The magnetic properties of these samples were well examined. The parallel and antiparallel states can also be well distinguished. We also investigated the dependence of MgO thickness on interlayer coupling between free layer and pinned layer. In the top pinned spin-valve structure, we observed a monotonic decay with increasing MgO thickness. However, some oscillation of interlayer coupling strength with the MgO thickness was observed in the bottom pinned structure. The structural properties of MgO prepared with various sputtering powers and working pressures during deposition process were studied by using the XRD measurement. We found that different buffer layer can induce different MgO structure. The crystalline MgO with (111) preferred orientation was successfully fabricated in this study. Photolithography and dry etching were both used in our pattern process, which worked well for our previous AlOx-based MTJs. But there were some problems in the MgO-based MTJs. Only nonlinear I-V curve can be observed, which means the existence of the tunneling effect.