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°C for 1h, 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°C for 40min, 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.