 |
 |
Materials Science Division |
HighlightsNanoscale Studies of Metal/Oxide/Metal Tunnel Junction Structures: Development of Novel Characterization ToolsNanoscale Studies of Metal/Oxide/Metal Tunnel Junction Structures: Development of Novel Characterization Tools Scientific Achievement We have developed a novel technique for in-situ TEM characterization of the local transport properties of multilayer thin films, including new sample preparation methodologies for fabricating suitable TEM samples from sheet wafers. This method represents a significant development in the field of in-situ TEM experiments, as it is the first time that local nanometer-scale transport properties of multilayer thin films can be correlated directly to the microstructure at the actual measurement site, enabling the role of the interfaces to be determined. We have successfully demonstrated the ability to obtain in-situ 4-point DC measurements of the I-V characteristics of magnetic tunnel junctions (MTJs) using a point-contact (diameter down to ~40 nm) whilst simultaneously imaging the local tunneling site at high magnification. As an example, we applied this technique to as-grown and annealed CoFe/MgO/CoFe MTJs: the I-V curves for the as-grown specimen are asymmetric with respect to voltage, and a layer of mixed Fe,Co oxide at the bottom interface is responsible for this effect. On annealing at 340 °C for 1 hour in high vacuum, the conductance across the specimens becomes more symmetric with respect to voltage: diffusion of the ferromagnetic elements into the barrier makes it more homogeneous. Significance This
work is a
significant development in the fundamental understanding of
microstructure/magnetotransport correlations in multilayer films. It
represents
the first time that transport behavior is correlated with directly
interpretable high-resolution images from the exact measurement site.
We have
first demonstrated this technique on model MTJs, which represent an
active area
of fundamental scientific research. Although MTJs are commercially used
in hard
disk drive read heads and solid state memory, little is actually known
of their
fundamental properties, particularly the contribution of the
interfaces. This
is reflected in the fact that the performance of the best MTJs reach
only 50%
of that predicted by theory. This work is a significant step forward in
the
study of the fundamental science of these structures. Portions of this
work
have been published in Annu. Rev. Mater.
Res. 38, 559 (2008) (one of the top 10
downloaded papers from ARMR
in 2008); Ultramicrosc. 108,
1529 (2008); Appl. Phys. Lett. 93,
103113 (2008). We are extending our studies to novel MTJs materials such as for example those containing 100% spin polarized materials, as well as to other relevant structures that would benefit from in-situ structure-transport correlation. These will include complex perovskite and related oxides for resistive memory applications as well as ferroelectric and multiferroic multilayers for use in nanocapacitors, switches, and sensors. Performers 
|
|
||||
|
||||
