Novel gate dielectric materials: perfection is not enough
Date: Thursday, October 18, 2007 @ 21:34:05 UTC Topic: Science
For the first time theoretical modeling has provided a glimpse into how
promising dielectric materials are able to trap charges, something
which may affect the performance of advanced electronic devices. This
is revealed in a paper published on the 12th October in Physical Review
Letters by researchers at the London Centre for Nanotechnology and
SEMATECH, a company in Austin, Texas.
Through the constant quest for
miniaturization, transistors and all their components continue to
decrease in size. A similar reduction has resulted in the thickness of
a component material known as the gate dielectric – typically a thin
layer of silicon dioxide, which has now been in use for decades.
Unfortunately, as the thickness of the gate dielectric decreases,
silicon dioxide begins to leak current, leading to unwieldy power
consumption and reduced reliability. Scientists
hope that this material can be replaced with others, known as
high-dielectric constant (or high-k) dielectrics, which mitigate the
leakage effects at these tiny scales.
Metal oxides with high-k have attracted tremendous interest due to
their application as novel materials in the latest generation of
devices. The impetus for their practical introduction would be further
helped if their ability to capture and trap charges and subsequent
impact on instability of device performance was better understood.
It has long been believed that these charge-trapping properties
originate from structural imperfections in materials themselves.
However, as is theoretically demonstrated in this publication, even if
the structure of the high k dielectric material is perfect, the charges
(either electrons or the absence of electrons – known as holes) may
experience ‘self trapping’.
They do so by forming polarons
– a polarizing interaction of an electron or hole with the perfect
surrounding lattice. Professor Alexander Shluger of the London Centre
for Nanotechnology and the Department of Physics & Astronomy
at UCL says: “This creates an energy well which traps the charge, just
like a deformation of a thin rubber film traps a billiard ball.”
The resulting prediction is that at low temperatures electrons and
holes in these materials can move by hopping between trapping sites
rather than propagating more conventionally as a wave. This can have
important practical implications for the materials’ electrical
properties. In summary, this new understanding of the polaron formation
properties of the transition metal oxides may open the way to
suppressing undesirable characteristics in these materials.
Source: University College London Via: http://www.physorg.com/news111759778.html ----------
PROBING QUESTION: WHAT IS A NEUTRINO?, October 16
Neutrinos are tiny -- really, really tiny -- particles of matter. They are so small, in fact, that they pass between, and even through, atoms without interacting at all. Neutrinos are everywhere: If you start counting now, more than 10 quintillion (that's 10 trillion billions) of them will have passed through your body by the time you finish this article. Yet only one of those 10 quintillion neutrinos will likely interact with an atom in your body. The rest will go merrily on their way.
Full story at http://www.physorg.com/news111769019.html
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