Ｃｕ‐ＡｌＯｘ ＮＯＬ（Ｎａｎｏ‐Ｏｘｉｄｅ‐Ｌａｙｅｒ）形成過程の考察

Abstract

Current-perpendicular-to-plane giant-magnetoresistance spinvalve with Cu-AlOx NOL (nano-oxide layer) spacer has attracted much attention for its relatively high RA and high MR ratio, which are due to the current-confined metal path in the oxide insulator. To clarify the mechanism for the formation of an NOL, we studied the surface structure of an inhomogeneous AlOx layer on Cu by in-situ conductive-AFM observations in various oxidation conditions. The current intensity images obtained show that different Cu metal paths appear at a Cu surface surrounded by AlOx grains, where the AlOx structure of each NOL is different. The AlOx structure, i. e., the NOL structure, can be controlled by pre-annealing of the Al layer before oxidation. It was found that a thin Al layer on Cu (111) was changed remarkably to fine particles by annealing. The fine particles moved from the Cu (111) terrace to the terrace edge. Therefore, the Al movement from a terrace, where a metal path appears, is caused by a decrease in the Cu surface energy.