Compositional change of MgO barrier and interface in CoFeB∕MgO∕CoFeB tunnel junction after annealing

Abstract

Recent experiments have demonstrated high tunneling magnetoresistance (TMR) ratios in magnetic tunnel junctions (MTJs) with the MgO barrier. The CoFeB∕MgO∕CoFeB junctions showed better properties than the CoFe∕MgO∕CoFe junctions because the MgO layer had a good crystalline structure with (001) texture and smooth and sharp interface between CoFeB∕MgO. In this work, the compositional changes in the MgO barrier and at the interface of CoFeB∕MgO∕CoFeB after the CoFeB crystallization were studied in annealed MTJs. X-ray photoelectron spectroscopy depth profiles were utilized for the as-deposited and 340°C annealed specimens. Transmission electron microscope analyses showed that the MgO barrier had (100) texture on CoFeB in the junctions and CoFeB was crystallized in the annealed junctions. B in the bottom CoFeB layer diffused into the MgO barrier and B–oxide was formed at the interface of CoFeB∕MgO∕CoFeB after the CoFeB crystallization. The B behavior will be discussed.