AVS 47th International Symposium
    Magnetic Interfaces and Nanostructures Thursday Sessions
       Session MI-ThA

Paper MI-ThA9
Analysis of Tunneling Magnetoresistance Structures by Low Energy Electron Nanoscale Luminescence Spectroscopy

Thursday, October 5, 2000, 4:40 pm, Room 206

Session: Magnetic Devices: GMR & Tunneling
Presenter: S.H. Goss, The Ohio State University
Authors: S.H. Goss, The Ohio State University
S.S.P. Parkin, IBM Almaden Research Center
L.J. Brillson, The Ohio State University
Correspondent: Click to Email
The performance of state-of-the-art tunneling magnetoresistive (TMR) heads depends sensitively on the thickness of insulating layers less than a few nanometers thick which separate two magnetic films. We have used low energy electron nanoscale luminescence (LEEN) spectroscopy to observe optical emission from TMR test structures with buried insulating oxides less than a few nm thick. TMR structures grown by DC magnetron sputtering consisted of a 0.8 - 3 nm Al oxide layer on a 2.4 nm CoFe alloy (84:16) sandwiched between a multilayer metal-on-Si substrate and a 4.4 nm CoFe plus Pt overlayer. LEEN excitation energies ranging from 0.5-3 keV enabled us to distinguish between emissions from the buried oxide layers vs. the free surface. We used different compositions, thicknesses, and oxidation exposures to separate Al oxide from transition metal oxide emissions, as well as from the ambient-exposed Pt surface. A broad peak centered at 2.7 eV increased with increasing oxygen plasma exposure at constant Al thickness. It also increased with increasing Al thickness and commensurate oxygen exposure. Emission from oxidized CoFe without Al consists of a featureless emission extending from 1.5 - 3.7eV. Common to all these spectra is emission at 1.8 eV, which energy-dependent LEEN demonstrates is due to the ambient-exposed Pt. Finally, spectral changes of the buried, oxidized Al/CoFe sandwich layers as a function of thickness and oxygen exposure reveal the regime separating oxidation of the Al layer alone from over-oxidation that extends into the CoFe base layer. These results suggest that optical emission from nanometer - thick tunnel layers within TMR structures can be used to assess the extent of oxidation as well as to optimize deposition and process conditions.