Exchange-biased magnetic tunnel junctions fabricated with in situ natural oxidation

Exchange-biased magnetic tunnel junctions with a Ta/NiFe/FeMn/NiFe/Al-oxide /NiFe/Ta structure have been fabricated. The tunnel barrier was formed by t he in situ natural oxidation of an Al metal layer under controlled oxygen p ressure. Photolithography and ion milling were used to pattern the multilay er into junction structures of 2 x 2 mu m(2)-20 x 20 mu m(2) dimensions. Ma gnetoresistance (MR) curves show spin-valve-like characteristics, in which an antiparallel configuration of magnetizations in both ferromagnetic layer s is observed between 50 and 240 Oe, and the hysteresis loops for both the free and pinned layers exhibit sufficient separation. An evaluation of the MR curves shows the exchange-bias field to be 340 Oe and coercivity levels in the free layer to become as low as 13 Oe. At room temperature normalized junction resistance is 2 x 10(-5) Omega cm(2), with MR ratios still being maintained at 13%. This resistance value is much lower than previously repo rted values for junctions produced either with plasma oxidation or thermal oxidation in air. Maximum variation in junction resistance is only +/-5% fo r 10 x 10 mu m(2) junctions over a 2 in. wafer. The MR ratio decreases by h alf when the bias voltage is raised from 0 to 440 mV, approximately the sam e ratio of decrease as has been previously reported for other successful ju nctions. (C) 1999 American Institute of Physics. [S0021-8979(99)49108-X].