Characteristics of the Al/sub 2/O/sub 3/ barrier with CoFeB pinned layer in magnetic tunnel junctions

Abstract

Amorphous FM electrode, CoFeB, was used in MTJs to improve the property of the insulating layer interface. The tunnel junctions with a structure of Ta(50 nm)/NiFe(8 nm)/IrMn(10 nm)/pinned layer(4 nm)/Al/sub 2/O/sub 3/(Al 1.1 nm)/CoFeB(3 nm)/NiFe(15 nm) were prepared in a DC magnetron sputtering system. The junctions were made by a photolithographic method and the samples were annealed from 200 /spl deg/C to 340 /spl deg/C. The depth profiles of the insulating barrier before and after annealing were analyzed by XPS and SIMS. MR ratio and junction resistance (RA) products of the MTJs were measured with annealing temperature. The maximum MR ratio were observed at 260 /spl deg/C annealing. RA products increased up to 380 /spl deg/C for CoFeB pinned junctions while it increased up to a 280 /spl deg/C and decreased over this temperature in the tunnel junctions with CoFe pinned layer.