We developed a fully epitaxial magnetic tunnel junction on an 8″ silicon wafer by using a mass-production sputtering apparatus and achieved a high magnetoresistance ratio exceeding 240% at room temperature. One of the key factors in this achievement is the use of a B2-type Ni-Al seed layer on the wafer as a (001)-oriented and an atomically smooth template. Another is the insertion of a thin Al layer prior to MgO sputtering as protection from plasma damage, resulting in the formation of a spinel-type single-crystal Mg-Al-O tunnel barrier after in situ annealing. This epitaxial technology for transition metals on large wafers will lead to advanced practical spintronics devices incorporating high-performance single-crystalline materials such as chemical-ordered alloys and tunnel barriers.
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