Annealing effects on structural and transport properties of rf-sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions

Annealing effects on the structural and transport properties of sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions deposited on SiO2/Si were investigated. At the as-deposited state, the CoFeB was amorphous at the CoFeB/MgO interface. High-resolution transmission electron microscope image clearly shows that after annealing at 270 degrees C for 1 h, crystallization of amorphous CoFeB (three to four monolayers) with lattice matching to MgO (100) occurred locally at the interface between MgO and CoFeB, producing a magnetoresistance (MR) around 35%-40%. After annealing at 360 degrees C for 40 min, the MR increased to 102%. The increase in the MR with annealing is attributed to the complete formation of (100) crystalline structure of CoFeB well lattice matched with the (100)-oriented MgO barrier. The bias voltage dependence of the MR shows a consistent correlation with each CoFeB/MgO interface. (C) 2006 American Institute of Physics.