TEM investigation of MgO thin films for magnetic tunnel junction application

Abstract

TEM analysis of sputter-deposited MgO has been performed using a plan view and cross-section approach. The influence of the sputtering parameters including target to substrate distance (TSD), sputtering power and Ar pressure on the structure and composition of deposited films has been investigated by analysing in plan view. Optimum deposition conditions have been identified and MgO layers deposited under these are partly crystalline within an amorphous matrix. Cross-sectional TEM imaging of MgO deposited under optimum conditions onto CoFeB in a basic MTJ structure (CoFeB/MgO/CoFeB trilayer), shows that in the initial deposition, at the bottom interface of the trilayer, amorphous MgO forms and this then becomes partly crystalline (but with no preferred texture) with continued deposition, towards the top interface of the layer. TEM- energy dispersive X-ray (EDX) and electron energy loss spectroscopy (EELS) composition analyses suggest that the inhomogeneous oxide film structure could be caused by the deposition of disordered, non-stoichiometric MgO. © 2010 IOP Publishing Ltd.