Dependence of Giant Tunnel Magnetoresistance of Sputtered   CoFeB/MgO/CoFeB Magnetic Tunnel Junctions on MgO Barrier Thickness and   Annealing Temperatur
  We investigated the dependence of giant tunnel magnetoresistance (TMR) on the thickness of an MgO barrier and on the annealing temperature of sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions deposited on SiO2/Si wafers. The resistance-area product exponentially increases with MgO thickness, indicating that the quality of MgO barriers is high in the investigated thickness range of 1.15-2.4 nm. High-resolution transmission electron microscope images show that annealing at 375 C results in the formation of crystalline CoFeB/MgO/CoFeB structures, even though CoFeB electrodes are amorphous in the as-sputtered state. The TMR ratio increases with annealing temperature and is as high as 260% at room temperature and 403% at 5 K. 
Jun Hayakawa, Shoji Ikeda, Fumihiro Matsukura, Hiromasa Takahashi and   Hideo Ohno