MgO barrier-perpendicular magnetic tunnel junctions with CoFe/Pd multilayers and ferromagnetic insertion layers

Applied Physics Letters (Impact Factor: 3.3). 10/2009; 95(23). DOI: 10.1063/1.3265740
Source: arXiv

ABSTRACT The authors studied an effect of ferromagnetic (Co20Fe60B20 or Fe) layer
insertion on tunnel magnetoresistance (TMR) properties of MgO-barrier magnetic
tunnel junctions (MTJs) with CoFe/Pd multilayer electrodes. TMR ratio in MTJs
with CoFeB/MgO/Fe stack reached 67% at an-nealing temperature (Ta) of 200
degree C and then decreased rapidly at Ta over 250 degree C. The degradation of
the TMR ratio may be related to crystallization of CoFe(B) into fcc(111) or
bcc(011) texture result-ing from diffusion of B into Pd layers. MTJs which were
in-situ annealed at 350oC just after depo-siting bottom CoFe/Pd multilayer
showed TMR ratio of 78% by post annealing at Ta =200 degree C.

34 Reads
  • Source
    • "Usually the thermal stability issue is more critical in the free layer, since the thickness of the free layer is thinner than that of the reference layer. PMA materials directly deposited on the CoFeB layer, resulting in a high TMR in the MTJ with an MgO tunnel barrier, are rare-earth transition-metal alloys [1]–[3], and [Co-based alloy/Pd] multilayers [4]. Unfortunately, the PMA of these materials can be deteriorated at an annealing temperature higher than 300 C during the MRAM fabrication process. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We have fabricated perpendicular magnetic tunnel junctions consisting of hcp Ru underlayer/hcp CoPt alloy/CoFeB/MgO/CoFeB/ CoPt alloy (or Co)/Pt capping layer. By inserting the CoPt alloy (or Co) between the CoFeB and Pt capping layers, it is possible to increase a perpendicular magnetic anisotropy of the top electrode. Using a top electrode of Co 40 Fe 40 B 20 (0 4 nm) Co 72 Pt 28 (1 6 nm) Pt, we have obtained an effective magnetic anisotropy of 3 3 10 6 erg/cm 3 and a tunnel magnetoresistance (TMR) of 9.4%. The analysis of the crystal structure reveals that the low TMR is a consequence of the fcc (111) texture of CoFeB layers. Index Terms—Magnetic tunnel junctions (MTJs), perpendicular magnetic anisotropy (PMA), tunnel magnetoresistance (TMR).
    IEEE Transactions on Magnetics 11/2011; 48(3):1130. DOI:10.1109/TMAG.2011.2176744 · 1.39 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Magnetic CoFeB/MgO/CoFeB-based tunnel junctions with perpendicular magnetic anisotropy Co/M multilayers (M=Ni, Pd, Pt) have been investigated as a function of structural and magnetic properties. Magnetometry, ferromagnetic resonance, x-ray diffraction, stress tests, and local electrode atom probe tomography were carried out primarily on Co/Ni multilayers. A statistical design of experiments was conducted to optimize the perpendicular magnetic anisotropy and damping parameter α of these multilayers. Seed layers, thickness, and thickness ratios are all critical to achieve perpendicular behavior. Perpendicular MgO-based magnetic tunnel junctions with Co/Ni and Co/Pd reference and free layers were fabricated and tested. Sharp MR-H switching characteristics were observed for the Co/Pd multilayers, and a somewhat softer transition was observed for the Co/Ni multilayer with a Cu seed, which did not have as high a perpendicular anisotropy. Tunneling magnetoresistance (TMR) values were limited to about 10%, primarily because the fcc-bcc-fcc transition does not promote the “MgO giant TMR” symmetry filtering effect.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 07/2010; 28(4). DOI:10.1116/1.3430549 · 2.32 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In magnetic tunnel junctions (MTJ), synthetic antiferromagnets (SAF) are usually used as reference layer to minimize dipolar interactions induced between this layer and the free layer (FL). We show here that the use of SAF allows us to reduce the asymmetry of the FL reversal due to stray fields in nanosized MTJs with perpendicular magnetic anisotropy.
    IEEE Magnetics Letters 02/2010; 1(1):3000204 - 3000204. DOI:10.1109/LMAG.2010.2052238 · 1.69 Impact Factor
Show more