Determination of the thickness of Al2O3 barriers in magnetic tunnel junctions

Abstract

The barrier thickness in magnetic spin-dependent tunnel junctions with Al2O3 barriers has been measured using grazing incidence x-ray reflectivity and by fitting the tunneling current to the Simmons model. We have studied the effect of glow discharge oxidation time on the barrier structure, revealing a substantial increase in Al2O3 thickness with oxidation. The greater thickness of barrier measured using grazing incidence x-ray reflectivity compared with that obtained by fitting current density–voltage to the Simmons electron tunneling model suggests that electron tunneling is localized to specific regions across the barrier, where the thickness is reduced by fluctuations due to nonconformal roughness.

Observation of fluctuation-induced tunneling conduction in micrometer-sized tunnel junctions

“…As a consequence, electron tunneling would be significantly influenced, causing G(T) to increase exponentially with increasing T. (In the opposite limit of T → 0, G becomes constant, i.e., recovering the elastic tunneling behavior, due to the gradually vanishing V T with T.) Previously, the FITC model has been applied to explain the G(T) behavior observed in a good number of conductor-dielectric composite systems (granular films) 16,17,[23][24][25] and nanowire contacts. 16,17 Surprisingly, although the interfacial roughness must be very common in artificially fabricated MIM tunnel junctions, 11,12,21,22,26 the possible manifestation of the FITC process through hot spots in the oxide layer has never been reported in the literature.…”

Interface sharpening in CoFeB magnetic tunnel junctions

“…The high TMR exhibited by such AlO x MTJs is partially attributed to the excellent quality of the interfaces. Systematic differences between barrier widths determined by x-ray scattering and electrical measurements 4 in devices with a lower TMR have been attributed to the effects of nonconformal roughness, whereby the tunneling begins locally at positions of minimum thickness.…”

Antiferromagnetic interlayer exchange coupling between Fe3O4 layers across a nonmagnetic MgO dielectric layer

“…In earlier investigations, IEC across a nonmagnetic dielectric invariably observed had FM nature. 6,7 Possibly, the fact that antiferromagnetic ͑AF͒ IEC was not observed was related to deficiencies in the control of interface roughness, and thus, orange peel effect, pinholes, and the use of amorphous Al 2 O 3 barrier. Recently, Faure-Vincent et al 8 found a strong AF IEC in a fully epitaxial Fe/ MgO / Fe trilayer structure.…”