demos terabit storage
Technology Research News
Cramming lots of information into very
small spaces means making and measuring infinitesimal containers for each
bit of data.
Researchers from Tohoku University, the Japanese National Institute for
Materials Science, and Pioneer Corporation in Japan have found a way to
store huge amounts of data after figuring out how to make many tiny, inverted
dots in a thin film of metal and determining how to sense the state of
The dots are as small as 10 nanometers in diameter and store one bit of
information each. A nanometer is one millionth of a millimeter, or the
equivalent of a line of 10 hydrogen atoms.
The researchers' prototype storage device packs 1.5 trillion dots per
square inch, and so could store 1.5 terabits in one square inch of material,
said Yasuo Cho, an associate professor of electrical engineering at Tohoku
University in Japan. That's the equivalent of 48 million 250-page books,
or 47 DVDs.
The storage material, a thin film of single-crystal lithium tantalate,
is ferroelectric, meaning its atoms are aligned electrically, or polarized.
Atoms in small sections, or domains, of the material can be polarized
opposite to neighboring domains, and these two polarization states can
represent the 1s and 0s of computing.
In contrast, today's disk drives are made from ferromagnetic materials,
whose polarization is magnetic. The domains in ferromagnetic materials
are sensitive to temperature, making very small domains unstable even
at room temperature.
Domain size is not affected by temperature in the researchers' ferroelectric
material, and the domain wall of a typical ferroelectric material can
be as thin as one or a few lattice segments of the crystal, which is much
smaller than is possible using ferromagnetic domains, said Cho.
In order to use these infinitesimal domains to store information, however,
there must be a way to change the polarization states to write data to
the media, and sense the state without affecting it to read the data.
Other research teams have used ferroelectric materials' piezoelectric
behavior to read domains. Piezoelectric materials generate electricity
when they vibrate and vibrate when they are subjected to an electric current;
piezoimaging measures domains using the vibrations of a microscopic probe
tip. But this measurement technique limits the size of the bits that can
be measured and the speed at which they can be sensed, said Cho.
The researchers' measuring device, dubbed scanning nonlinear dialectic
microscope (SNDM), overcomes these limitations, said Cho. The device uses
an alternating electric field to measure the change in capacitance, or
ability to store an electric charge, between domains, which reveals the
different polarizations. "SNDM has sub-nanometer resolution, and is a
purely electrical method," he said.
Using the prototype, the researchers were able to read 25 kilobytes, or
thousand bytes, of data per second, said Cho. This is relatively slow
-- it would take 10 seconds to retrieve a 250-page book at that speed,
assuming 1,000 characters per page. It is possible to increase the read
speed to 3.75 megabytes per second, said Cho. This would make it possible
to retrieve the information contained in about 150 books in 10 seconds.
Current disk drives have read speeds of about 20 to 50 megabytes, or million
bytes, per second.
The researchers' prototype stores information 100 times faster than it
can read it; the prototype has a write speed of 2.5 megabytes per second,
said Cho. This could be increased to 125 megabytes per second, he added.
Today's disk drives write data at about 10 to 35 megabytes per second.
The researchers are ultimately aiming to increase the amount of information
they can store in the material to 4 thousand trillion bits, or 4 petabits,
per square inch -- the equivalent of 125,000 DVDs worth of information.
This assumes a domain size of 0.4 nanometers, which is an individual atom
within the crystal lattice.
The researchers' scheme and the use of lithium tantalate are good ideas,
said Rainer Waser, a professor of materials science and engineering at
Aachen University in Germany. There are many questions, however, including
how the researchers will increase the write speed, he said.
It is also much more difficult to come up with a new technology than to
improve an existing one. "[Magnetic] hard drives are highly developed
systems," said Waser. "Nevertheless, it is interesting to think along
this road," he said.
The researchers current prototype is not accurate enough for practical
applications, but further refinements should solve the problem, according
to Cho. The system could be used in practical applications in five years,
Cho's research colleagues were Kenjiro Fujimoto,Yoshiomi Hiranaga and
Yasuo Wagatsuma from Tohoku University in Japan, Atsushi Onoe from Pioneer
Corporation in Japan, and Kazuya Terabe and Kenji Kitamura from the National
Institute for Materials Science in Japan. They published the research
in the December 2, 2002 issue of Applied Physics Letters. The research
was funded by the Japan Society for the Promotion of Science (JSPS).
Timeline: 5 years
TRN Categories: Data Storage Technology; Materials Science
Story Type: News
Related Elements: Technical paper, "Tbit/inch2, Ferroelectric
Data Storage Based on Scanning Nonlinear Dialectic Microscopy," Applied
Physics Letters, December 2, 2002.
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