Rare Earth Metal and Cousin of Platinum is Attractive
for Improving Flash Memory Chips
One of the rarest metals on Earth
may be an excellent option for enabling future flash memory chips to continue to
increase in speed and density, according to a group of researchers in Taiwan.
“Incorporating nanocrystals of iridium into the critical floating gate portion
of flash memory designs shows both excellent memory properties as well as
stability in the high temperatures used in processing such semiconductor
devices,” says the research team leader, Wen-Shou Tseng of Taiwan’s Center for
Measurement Standards, Industrial Technology Research Institute. The research
results appears in the journal Applied Physics Letters, which is published by
the American Institute of Physics. His colleagues included students and
professor at the nearby National Chiao Tung University and Chung Hua University.
This team chose iridium -- a hard, dense and corrosion-resistant metal in the
platinum family that is one of the rarest metals found in the earth’s crust --
because unlike most alternatives, it has two desired properties: Iridium holds
its electrons strongly (it has a high “work function”, which is well-known to
correlate with excellent memory properties), and its melting point of nearly
2,500 degrees Celcius is well beyond the 900 C annealing temperature that many
chips must survive during manufacturing. Fortunately only a billionth of a
billionth of a gram of iridium would be needed for each gate.
worldwide are investigating new ways to improve the popular flash memory, which
is the nonvolatile memory chip design used in virtually all digital cameras and
mobile electronics and, increasingly, in solid-state drives for laptop
computers. The easiest way for future flash memories to hold more data and
read/write faster, is to shrink the dimensions of the existing chip design,
including the floating gate. But today’s gate design has already progressed to
the point where it cannot get much smaller before it can no longer retain the
electrical charges that actually store the data. Nanocrystals have been proposed
as a rather simple change that can improve memory chip performance without
changing the tried-and-true floating-gate design.
In recent years, many different metals have been investigated for their
nanocrystal potential. Nickel and tungsten, for example, are attractive for,
respectively, a high work function and thermal stability. But they and other
elements lack both needed properties. It is rare, indeed, that iridium has both
needed qualities, Tseng says.
The article, "Formation of iridium nanocrystals with highly thermal stability
for the applications of nonvolatile memory with excellent trapping ability" by
Terry Tai-Jui Wang, Chang-Lung Chu, Ing-Jar Hsieh, and Wen-Shou Tseng appears in
the journal Applied Physics Letters. See: http://link.aip.org/link/applab/v97/i14/p143507/s1
This work was funded by National Chiao Tung University.
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FUNDERS: National Chiao Tung University.
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