A novel magnetic tunnel junction structure using the edge of a magnetic film

We propose and demonstrate an edge magnetic tunnel junction (MTJ) structure that uses the edge part of the magnetic thin film and the barrier layer parallel to the edge surface. The shape of an edge MTJ becomes a rectangle whose area is defined as the product of the thickness of one magnetic thin film and the line width of another magnetic film. The thickness of a thin film is reduced in a controlled manner so that the edge junction structure can have a smaller area as well as a smaller variation in area. In the case of the edge junction, a rectangular aspect ratio is enlarged without increasing the area of the cell. An in situ ion milling etching apparatus is connected to the sputtering system in order to avoid the oxidation of the edge surface. In our fabrication process of the edge MTJs, magnetic electrodes are not exposed to water, oxygen plasma, or organic solvent. The edge MTJs consist of CoFeB/MgO/CoFeB. We obtain both a high magnetoresistance ratio (MR) of 71% and a small area of 0.3×0.04 μm in the edge MTJ.