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70% TMR at room temperature for SDT sandwich junctions with CoFeB as free and reference Layers

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5 Author(s)
Dexin Wang ; NVE Corp., Eden Prairie, MN, USA ; Nordman, C. ; Daughton, J.M. ; Qian, Zhenghong
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Spin dependent tunneling (SDT) wafers were deposited using dc magnetron sputtering. SDT junctions were patterned and connected with one layer of metal lines using photolithography techniques. These junctions have a typical stack structure of Si(100)-Si3N4-Ru-CoFeB-Al2O3-CoFeB-Ru-FeCo-CrMnPt with the antiferromagnet CrMnPt layers for pinning at the top. High-resolution transmission electron microscopy (HRTEM) reveals that the CoFeB has an amorphous structure and a smooth interface with the Al2O3 tunnel barrier. Although it is difficult to pin the amorphous CoFeB directly from the top, the use of a synthetic antiferromagnet (SAF) pinned layer structure allows sufficient rigidity of the reference CoFeB layer. The tunnel junctions were annealed at 250°C for 1 h and tested for magneto-transport properties with tunnel magnetoresistive (TMR) values as high as 70.4% at room temperature, which is the highest value ever reported for such a sandwich structure. This TMR value translates to a spin polarization of 51% for CoFeB, which is likely to be higher at lower temperatures. These junctions also have a low coercivity (Hc) and a low parallel coupling field (Hcoupl). The combination of a high TMR, a low Hc, and a low Hcoupl is ideal for magnetic field sensor applications.

Published in:

Magnetics, IEEE Transactions on  (Volume:40 ,  Issue: 4 )

Date of Publication:

July 2004

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