Transmission electron microscopy study on the crystallizationand boron distribution of CoFeB/MgO/CoFeB magnetic tunnel junctions with various capping layers

High-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS) were used to study the microstructural properties of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with various capping layers. Crystallization of CoFeB layers was strongly dependent on the capping mater...

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Published in:Applied physics letters 2009-03, Vol.94 (12), p.122501-122501-3
Main Authors: Miyajima, Toyoo, Ibusuki, Takahiro, Umehara, Shinjiro, Sato, Masashige, Eguchi, Shin, Tsukada, Mineharu, Kataoka, Yuji
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Summary:High-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS) were used to study the microstructural properties of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with various capping layers. Crystallization of CoFeB layers was strongly dependent on the capping materials, and was affected by B diffusion. With NiFe-cap MTJs, CoFeB crystallized from the cap interface and formed a fcc structure; on the other hand, with Ta- and Ti-cap MTJs, CoFeB crystallized from the MgO interface and formed a bcc structure. EELS analysis showed that B mainly diffused to the capping layers and rarely to the MgO layers with increasing temperature. With Ti-cap MTJs, B diffusion caused hcp-Ti crystals to form an amorphous structure and CoFeB crystallized at lower temperature.
ISSN:0003-6951
1077-3118
DOI:10.1063/1.3106624