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Title: X-ray absorption spectroscopy studies on magnetic tunnel junctions with AlO and AlN tunnel barriers

Abstract

X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) measurements of the optimized magnetic tunnel junctions (MTJs) with AlO and AlN barriers have been performed to study the chemical structures of the barrier and the underlying layer. These MTJs with AlO and AlN barriers exhibited increased tunneling magnetoresistance (TMR) after annealing at 200 deg. C from 27% to 45% and from 25% to 33%, respectively. Surprisingly, the XPS and XAS measurements confirmed that both the as-grown and the annealed MTJs had metallic Co and Fe at the interface between the barrier and the underlying CoFe layer. After annealing, under-stoichiometric AlO{sub x} and AlN{sub x} phases in MTJs with AlO and AlN barriers partially transformed into stoichiometric Al{sub 2}O{sub 3} and AlN phases, respectively. Thus the increase in TMR after annealing for MTJs with clean interface between the barrier and the underlying layer is believed due to the anion redistribution inside the barrier layer, not from back diffusion from pinned magnetic layer to barrier layer.

Authors:
; ; ; ; ; ;  [1];  [2];  [2];  [2]
  1. Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States)
  2. (Korea, Republic of)
Publication Date:
OSTI Identifier:
20788121
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 99; Journal Issue: 8; Conference: 50. annual conference on magnetism and magnetic materials, San Jose, CA (United States), 30 Oct - 3 Nov 2005; Other Information: DOI: 10.1063/1.2176055; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; ALUMINIUM NITRIDES; ALUMINIUM OXIDES; ANIONS; ANNEALING; COBALT ALLOYS; INTERFACES; IRON ALLOYS; LAYERS; MAGNETORESISTANCE; STOICHIOMETRY; SUPERCONDUCTING JUNCTIONS; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0400-1000 K; TUNNEL EFFECT; X-RAY PHOTOELECTRON SPECTROSCOPY; X-RAY SPECTRA; X-RAY SPECTROSCOPY

Citation Formats

Mun, B. S., Moon, J. C., Hong, S. W., Kang, K. S., Kim, K., Kim, T. W., Ju, H. L., Department of Physics, Yonsei University, Seoul 120-749, Devices Laboratory, Samsung Advanced Institute of Technology, Giheung, Kyunggi-do 449-711, and Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720 and Department of Physics, Yonsei University, Seoul 120-749. X-ray absorption spectroscopy studies on magnetic tunnel junctions with AlO and AlN tunnel barriers. United States: N. p., 2006. Web. doi:10.1063/1.2176055.
Mun, B. S., Moon, J. C., Hong, S. W., Kang, K. S., Kim, K., Kim, T. W., Ju, H. L., Department of Physics, Yonsei University, Seoul 120-749, Devices Laboratory, Samsung Advanced Institute of Technology, Giheung, Kyunggi-do 449-711, & Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720 and Department of Physics, Yonsei University, Seoul 120-749. X-ray absorption spectroscopy studies on magnetic tunnel junctions with AlO and AlN tunnel barriers. United States. doi:10.1063/1.2176055.
Mun, B. S., Moon, J. C., Hong, S. W., Kang, K. S., Kim, K., Kim, T. W., Ju, H. L., Department of Physics, Yonsei University, Seoul 120-749, Devices Laboratory, Samsung Advanced Institute of Technology, Giheung, Kyunggi-do 449-711, and Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720 and Department of Physics, Yonsei University, Seoul 120-749. Sat . "X-ray absorption spectroscopy studies on magnetic tunnel junctions with AlO and AlN tunnel barriers". United States. doi:10.1063/1.2176055.
@article{osti_20788121,
title = {X-ray absorption spectroscopy studies on magnetic tunnel junctions with AlO and AlN tunnel barriers},
author = {Mun, B. S. and Moon, J. C. and Hong, S. W. and Kang, K. S. and Kim, K. and Kim, T. W. and Ju, H. L. and Department of Physics, Yonsei University, Seoul 120-749 and Devices Laboratory, Samsung Advanced Institute of Technology, Giheung, Kyunggi-do 449-711 and Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720 and Department of Physics, Yonsei University, Seoul 120-749},
abstractNote = {X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) measurements of the optimized magnetic tunnel junctions (MTJs) with AlO and AlN barriers have been performed to study the chemical structures of the barrier and the underlying layer. These MTJs with AlO and AlN barriers exhibited increased tunneling magnetoresistance (TMR) after annealing at 200 deg. C from 27% to 45% and from 25% to 33%, respectively. Surprisingly, the XPS and XAS measurements confirmed that both the as-grown and the annealed MTJs had metallic Co and Fe at the interface between the barrier and the underlying CoFe layer. After annealing, under-stoichiometric AlO{sub x} and AlN{sub x} phases in MTJs with AlO and AlN barriers partially transformed into stoichiometric Al{sub 2}O{sub 3} and AlN phases, respectively. Thus the increase in TMR after annealing for MTJs with clean interface between the barrier and the underlying layer is believed due to the anion redistribution inside the barrier layer, not from back diffusion from pinned magnetic layer to barrier layer.},
doi = {10.1063/1.2176055},
journal = {Journal of Applied Physics},
number = 8,
volume = 99,
place = {United States},
year = {Sat Apr 15 00:00:00 EDT 2006},
month = {Sat Apr 15 00:00:00 EDT 2006}
}
  • Nonoxide tunnel barriers such as AlN are of interest for magnetic tunnel junctions to avoid the oxidation of the magnetic electrodes. We have investigated the fabrication and properties of thin AlN-based barriers for use in low resistance magnetic tunnel junctions. Electronic, magnetic and structural data of tunnel valves of the form Ta (100 Aa)/PtMn (300 Aa)/CoFe{sub 20} (20 Aa{endash}25 Aa)/barrier/CoFe{sub 20} (10{endash}20 Aa)/NiFe{sub 16} (35{endash}40 Aa)/Ta (100 Aa) are presented, where the barrier consists of AlN, AlN{sub x}O{sub y} or AlN/AlO{sub x} with total thicknesses between 8 and 15 Aa. The tunnel junctions were sputter deposited and then lithographically patternedmore » down to 2{times}2{mu}m{sup 2} devices. AlN was deposited by reactive sputtering from an Al target with 20%{endash}35% N{sub 2} in the Ar sputter gas at room temperature, resulting in stoichiometric growth of AlN{sub x} (x=0.50{+-}0.05), as determined by RBS. TEM analysis shows that the as-deposited AlN barrier is crystalline. For AlN barriers and AlN followed by natural O{sub 2} oxidation, we obtain tunnel magnetoresistance {gt}10% with specific junction resistance R{sub j} down to 60{Omega}{mu}m{sup 2}. {copyright} 2001 American Institute of Physics.« less
  • Proper as well as under- and over-oxided CoFe-AlO{sub x}-CoFe magnetic tunnel junctions (MTJs) have been systematically investigated in a frequency range from 10{sup 2} to 10{sup 8} Hz by complex capacitance spectroscopy. The dielectric relaxation behavior of the MTJs remarkably disobeys the typical Cole-Cole arc law probably due to the existence of imperfectly blocked Schottky barrier in the metal-insulator interface. The dielectric relaxation response can be successfully modeled on the basis of Debye relaxation by incorporating an interfacial dielectric contribution. In addition, complex capacitance spectroscopy demonstrates significant sensitivity to the oxidation process of metallic Al layers, i.e., almost a fingerprintmore » of under, proper, and over oxidation. This technique provides a fast and simple method to inspect the AlO{sub x} barrier quality of MTJs.« less
  • In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O{sup 2−} migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electricmore » effect, that is, surface electron doping and/or redistribution induced by an external electric field.« less
  • The bulk magnetic moment and the element specific magnetic moment of Co{sub 2}FeAl thin films were examined as a function of annealing temperature by alternating gradient magnetometer (AGM) and X-ray absorption spectroscopy (XAS)/X-ray magnetic circular dichroism (XMCD), respectively. A high magnetic moment can be achieved for all annealing temperatures and the predicted bulk and interface magnetic moment of about 5 {tilde A}{sub B} are reached via heating. We will also present tunnel magnetoresistance (TMR) values of up to 153% at room temperature and 260% at 13 K for MgO based magnetic tunnel junctions (MTJs) with Co{sub 2}FeAl and Co-Fe electrodes.
  • The magnetic and chemical interface properties of Mn-Ir/Co-Fe/Al+oxidation/Ni-Fe magnetic tunnel junctions are investigated for different barrier thickness, oxidation times, and annealing conditions by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. For underoxidized samples the formation of Co-Fe-Al alloy at the lower barrier interface during optimal annealing is observed. For optimally oxidized and overoxidized samples FeO{sub x} is formed during oxidation, which is reduced by Mn diffusing to the barrier during annealing. The reduction of FeO{sub x} is accompanied by an increase of the interfacial magnetic Fe moment, whereas the Co moments hardly change with the postannealing. Comparison of thesemore » results with transport properties of the junctions shows that their polycrystalline structure has to be taken into account to understand the annealing temperature and oxidation state dependence of the tunneling magnetoresistance effect.« less