Patent ID: 8202572

Claim:
A method of forming a tunnel barrier in a magnetic tunnel junction (MTJ), comprising: (a) providing a substrate and subjecting said substrate to a natural oxidation process or to a plasma treatment with an inert gas; (b) depositing a first metal layer having a first thickness that forms a continuous film on the substrate; (c) performing a natural oxidation (NOX) process to convert said first metal layer to a first metal oxide (M OX1 ) layer; (d) repeating the metal deposition and NOX process one or more times to form a stack including one or more metal oxide layers on the M OX1 layer wherein a second metal layer that is oxidized to a second metal oxide layer (M OX2 ), and contacts a surface of the M OX1 layer has a thickness less than the first thickness; (e) depositing an uppermost metal layer on the stack of one or more metal oxide layers wherein the uppermost metal layer has a thickness less than the thickness of the second metal layer; and (f) performing an annealing process that causes oxygen from the metal oxide layers to diffuse into the uppermost metal layer thereby fully oxidizing the uppermost M layer to an uppermost M OX layer and forming a tunnel barrier having a stack of at least three metal oxide layers.