The smallest magnetic-memory bit ever made—an aggregation of just 12
iron atoms created by researchers at IBM—shows the ultimate limits of
future data-storage systems.
The magnetic memory elements don't work in the same way that today's
hard drives work, and, in theory, they can be much smaller without
becoming unstable. Data-storage arrays made from these atomic bits would
be about 100 times denser than anything that can be built today. But
the 12 atoms making up each bit must be painstakingly assembled using an
expensive and complex microscope, and the bits can hold data for only a
few hours and at low temperatures approaching absolute zero, so the
miniscule memory elements won't be found in consumer devices anytime
soon.
Let's get small: This scanning tunneling microscope image shows a group of 12 iron atoms, the smallest magnetic memory bit ever made.
As the semiconductor industry bumps up against the limits of scaling
by making memory and computation devices ever smaller, the IBM Almaden
research group, led by Andreas Heinrich, is working from the other end, building computing elements atom-by-atom in the lab.
The necessary technology for large-scale manufacturing at the
single-atom scale doesn't exist yet. Today, says Heinrich, the question
is, "What is it you would want to build on the scale of atoms for data
storage and computation, in the distant future?"
As engineers miniaturize conventional devices, they're finding that
quantum physics, which never had to be accounted for in the past, makes
devices less stable. As conventional magnetic memory bits are
miniaturized, for example, each bit's magnetic field begins to affect
its neighbors', weakening each bit's ability to hold on to a 1 or a 0.
The IBM researchers found that it was possible to sidestep this
problem by using groups of atoms that display a different kind of
magnetism. The key, says Heinrich, is the magnetic spin of each
individual atom.
In conventional magnets, whether they're found holding up a note on
the refrigerator or in a data-storage array, the magnetic spins of the
atoms are aligned. It's this alignment that leads to instability when
magnetic-memory elements are miniaturized. The IBM researchers made
their tiny memory elements by lining up iron atoms whose spins were
counter-aligned.
The researchers both constructed and wrote data to the tiny memory
elements using a scanning tunneling microscope, a device developed at
IBM Zürich in 1981. This microscope has a very thin conducting probe
that can be used to image a surface and push individual atoms around.
Heinrich says his team found it could make antiferromagnetic memory
using fewer than 12 atoms, but these were less stable. With 12 atoms,
the memory elements obey classical physics, and the read-and-write
pulses applied through the microscope probe are similar to those used in
today's hard drives. This research is described today in the journal Science.
Any realistic nonvolatile data storage technology has to be able to
hold onto the data for 10 years at temperatures well over room
temperature, says Victor Zhirnov,
a research scientist at the Semiconductor Research Corporation, who was
not involved with the work. The IBM bits can hold onto a 1 or a 0 for
just a few hours, and only at very low temperatures, but Heinrich says
it should be possible to increase their stability for operation at more
realistic temperatures by using 150 atoms per bit rather than 12—still a
miniscule number compared to existing forms of memory.
However, making a realistic technology was not the aim of the current
work, says Heinrich. His aim is to explore whether other kinds of
computing elements can be made from a few atoms, perhaps by embracing
quantum. "We have to have the foresight not to worry about the next
step, but to jump to something potentially revolutionary," he says.
By Katherine Bourzac
From Technology Review
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