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


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.

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    • "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. "
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