Enhanced tunnel magnetoresistance by Hf layer insertion in the tunnel barriers

Summary form only given. Magnetic tunnel junctions consist of two ferromagnetic electrodes separated by an insulating barrier. The tunnel magnetoresistance(TMR) and junction resistance critically depend on the insulating layer quality. The defects in tunnel barrier or at the interfaces between barrier and metal electrodes could degrade MR ratio by introducing spin flip scattering. In this study, we have introduced the artificial modification of the oxide barrier by forming Hf oxide in the middle of the Al/sub 2/O/sub 3/ barrier. As Hf oxide has higher heat of formation (-268kcal/mole of Hf) than Al oxide (-202kcal/mole), the inserted Hf layer could act as oxide stabilizer and decrease the degree of disorder and defects in the barrier. Magnetic tunnel junctions of Hf(5nm)/NiFe(8nm)/IrMn(20nm)/CoFe(4nm)/Al oxide or Al-HfAl oxide/CoFe(3nm)/NiFe(15nm) were deposited by magnetron sputtering system. Tunnel barriers were formed by exposing the Al(1.4nm) layer or Al-Hf-Al(0.6/0.2/0.6nm) layer to ozone and oxygen mixture gas for tens of minutes.