Nanotube memory scheme is magnetic
Technology Research News
carbon nanotubes are so small -- the size of molecules -- if each could
store one bit of information, devices made from nanotubes could potentially
hold colossal amounts of information. With this in mind, many researchers
are working to build memory devices from the tiny tubes.
Researchers from Texas A&M University and Rensselaer Polytechnic
Institute have designed a type of nanotube flash memory that has a potential
capacity of 40 gigabits per square centimeter and 1,000 terabits per cubic
A terabit is 1,000 gigabits, or the contents of about 26 DVDs.
Each memory element is made from a pair of crossed carbon nanotubes
filled with iron or embedded in a ferromagnetic medium. Carbon nanotubes
are rolled up sheets of carbon atoms that have useful electrical properties
and can be narrower than a nanometer.
The researchers' design calls for storing information using magnetization
to control electrical current -- the same principle behind magnetic disk
drive read heads.
In an array of crossed nanotubes, each junction could store a bit
of information -- a 1 or a 0. "If you crossed the same number of nanotubes
as the number of transistors in today's microprocessors, then you get about
1015 bits... that is one million gigabits," said Laszlo Kish,
an associate professor of electrical engineering at Texas A&M University.
The amount of current that flows through a pair of magnetic layers
sandwiching a non-magnetic layer depends on the magnetic orientations of
the layers. Each electron has a magnetic orientation. Layers that are magnetically
parallel will allow electrons that are magnetically aligned with the layers
to pass through while layers with opposite magnetic orientations will block
A pair of magnetic nanotubes crossed at other than a right angle
acts like the magnetic layers in disk read heads. Writing a bit to the crossed
pair involves sending a positive or negative electric pulse to set the magnetic
orientation of the two sides of the junction. Reading the bit is accomplished
by sending a weaker pulse, which is always either positive or negative.
If the readout pulse has the opposite clarity from the write pulse, the
current in the circuit is diminished. The high current and low current states
represent the 1s and 0s of computer information.
Because nanotubes are so small, a storage device based on the researchers'
design would also be extraordinarily fast, according to Kish. Data rates
of 1,000 gigabytes per second are conceivable, he said. Such devices would
also use relatively little power, he said.
The design would also yield more durable devices than other schemes
using crossed nanotubes to build storage systems because they require the
nanotubes to bend into and out of proximity with each other, said Pulickel
Ajayan, a professor of materials science and engineering at Rensselaer Polytechnic
Institute and Kish's colleague.
The researchers' next step is to build a single memory element and
test its properties in various conditions to find the optimal composition
and electrical properties for this type of memory. Then they must figure
out how to integrate the simple memory junctions in a three-dimensional
structure in order to make memory device from them.
A prototype device could be developed in five years, said Ajayan.
The crossed-nanotube memory elements could eventually be used to
build magnetic memory devices with "extraordinary storage capacity," but
it will take time to make practical memory elements from nanotubes, said
It took 15 years of development after Nobel laureate Jack Kilby
came up with the idea of integrating transistors into computer chips for
the idea to become practical, said Kish. Researchers working to make electronics
from nanotubes are only at the stage of imagining the first transistor,
The work appeared in the February 28, 2005 issue of Applied Physics
Timeline: 5 years
TRN Categories: Data Storage Technology; Nanotechnology
Story Type: News
Related Elements: Technical paper, "TerraByte flash memory
with carbon nanotubes," Applied Physics Letters, February 28, 2005
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