A theoretical study of an amorphous aluminium oxide layer used as a tunnel barrier in a magnetic tunnel junction

Abstract

An amorphous aluminium oxide layer is assumed to be a condensed gas phase composed of (AlOx)(N) molecules. The total energy and the electron affinity of (AlOx)(N) molecules is calculated by using a DFT program. The effective tunnel barrier height in the MTJ is presumed from a difference between the work function of the ferromagnetic metal and the electron affinity of (AlOx)(N) molecules. By using a quantum-mechanical free electron model the TMR and the RxA product are calculated as a function of the thickness of an amorphous aluminium oxide layer in the F/I/F tunnel junction. It is inferred that the tunnel barrier width determined by subtracting 6 angstrom from the thickness of an amorphous aluminium oxide layer is more suitable to explain an experimental report qualitatively than the tunnel barrier width equivalent to the thickness of an amorphous aluminium oxide layer. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.