Patent ID: 7579042

Claim:
A method for making a magnetic tunnel junction comprising a layer of metal oxide or semiconductor oxide on a first ferromagnetic layer, the method comprising: (a) selecting a temperature and an O 2 partial pressure at which the oxidation of the metal or semiconductor is thermodynamically favored while the oxidation of the first ferromagnetic layer is not; and (b) exposing a layer of the metal or the semiconductor deposited on the first ferromagnetic layer to a gas comprising a mixture of CO 2 and CO or a mixture of H 2 and H 2 O to oxidize the metal or semiconductor and provide a tunnel barrier oxide layer on the first ferromagnetic layer; wherein (pCO/pCO 2 ) or (pH 2/ pH 2 O)≧(1/(pO 2 *K)) 1/2 , where pCO is the partial pressure of CO in the gas mixture; pCO 2 is the partial pressure of CO 2 in the gas mixture; pH 2 is the partial pressure of H 2 in the gas mixture; pH 2 O is the partial pressure of H 2 O in the gas mixture; pO 2 is the selected O 2 partial pressure; and K is an equilibrium constant calculated from exp(−ΔG° r×n /R*T), where R is the gas constant, T is the selected temperature, and −ΔG° r×n is the free energy of formation of CO 2 from CO and O 2 or the free energy of formation of H 2 O from H 2 and O 2 ; further wherein the selected O 2 partial pressure is no greater than 10 −20 torr, and the free energy for the production of an oxide in the metal or semiconductor is less than the free energy for the production of an oxide in the ferromagnetic layer at the selected temperature and O 2 partial pressure; and further wherein the first ferromaanetic layer comprises a Co—Fe alloy or a Ni—Fe alloy.