Scientific News  Computers, Internet, Software, Household and Office Equipment New computer technologies SCIENTISTS DEVELOP ATOMIC-SCALE MEMORY
SCIENTISTS DEVELOP ATOMIC-SCALE MEMORY
 In 1959, physics icon Richard Feynman, in a
characteristic back-of-the-envelope calculation, predicted that all the words
written in the history of the world could be contained in a cube of material one
two-hundredths of an inch wide - provided those words were written with atoms.
Now, a little more than 40 years after Feynman's
prescient estimate, scientists at the University of Wisconsin-Madison have
created an atomic-scale memory using atoms of silicon in place of the 1s and 0s
that computers use to store data.
The feat, reported in the journal Nanotechnology,
represents a first crude step toward a practical atomic-scale memory where atoms
would represent the bits of information that make up the words, pictures and
codes read by computers.
"This is proof of concept of what Feynman
was saying 40 years ago," says Franz Himpsel, a UW-Madison professor of
physics and the senior author of the Nanotechnology paper.
Although the memory created by Himpsel and his
colleagues is in two dimensions rather than the three-dimensional cube
envisioned by Feynman, it provides a storage density a million times greater
than a CD-ROM, today's conventional means of storing data.
The atom, says Himpsel, represents the "hard
wall" of technological miniaturization. "We seem to be at a natural
limit."
Although divisible, the atom is a fundamental
unit of nature. They are the smallest particles of an element and a single grain
of sand, for example, can contain 10 million billion atoms.
The new memory was constructed on a silicon
surface that automatically forms furrows within which rows of silicon atoms are
aligned and rest like tennis balls in a gutter. By lifting out single silicon
atoms with the tip of a scanning tunneling microscope, the Wisconsin team
created gaps that represent the 0s of data storage while atoms left in place
represent the1s.
Like conventional memory, the atomic-scale device
can be initialized, formatted, written and read at room temperature.
By manipulating individual atoms at room
temperature to create memory, Himpsel and his colleagues are treading a middle
ground between atom manipulation at very low temperatures and conventional data
storage, which operates at room temperature but uses millions of atoms per bit.
It is far easier to manipulate atoms one at a time and keep them stable at very
low temperatures, Himpsel says.
The new memory was made without the use of
lithography. To make conventional memory chips, light is used to etch patterns
on a chemically treated silicon surface. To use lithography to make chips that
are denser than the best available chips is prohibitively expensive and
difficult.
The new atomic-scale memory was made by
evaporating gold onto a silicon wafer, which results in a precise track
structure. By subsequently evaporating silicon onto the treated wafer, the
Wisconsin team was able to diffuse silicon atoms across the structure where they
line up and sit within the tracks like eggs in a carton. These silicon atoms
represent the bits of information.
Importantly, the atoms line up in such a way that
there are atomically precise gaps between individual atoms, permitting
scientists to pluck the particles out using the superfine tip of a scanning
tunneling microscope without disturbing neighboring atoms and possibly creating
unwanted chemical bonds.
While the Wisconsin work proves the feasibility
of atomic-scale memory and provides a platform for exploring the fundamental
limits of data storage, the technology will require years, if not decades, of
refinement to achieve a practical working memory that could be mass produced,
Himpsel says. Obvious drawbacks, he notes, are the fact the memory was
constructed and manipulated in a vacuum, and that a scanning tunneling
microscope is needed to write memory which makes the writing process very time
consuming.
Moreover, there is a tradeoff between memory
density and speed, Himpsel says. "As density increases, your ability to
read the memory comes down because you get less and less of a signal. As you
make things smaller, it's going to get slower."
An intriguing aspect of the Wisconsin work is
that memory density is comparable to the way nature stores data in DNA molecules.
The Wisconsin atomic-scale silicon memory uses 20 atoms to store one bit of
information, including the space around the single atom bits. DNA uses 32 atoms
to store information in one half of the chemical base pair that is the
fundamental unit that makes up genetic information.
"Compared to conventional storage media,
both DNA and the silicon surface excel by their storage density," says
Himpsel.
Co-authors of the Nanotechnology paper, published
in the July 4, 2002 issue of Nanotechnology, include R. Bennewitz, J.N. Crain, A.
Kirakosian, J-L. Lin, J.L. McChesney and D.Y. Petrovykh.
For more information, visit: http://uw.physics.wisc.edu/~himpsel/memory.html
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Publishing date: September 10, 2002
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