pulses could speed memory
Technology Research News
Researchers from the Research Institute
for Materials in the Netherlands and Siemens AG in Germany have found
a way to switch a magnetic bit more quickly. The potential payoff is faster
The key is a method to precisely shape incredibly fast magnetic pulses.
In today's magnetic random access memory (MRAM) chips, electric pulses
switch microscopic bits of magnetic material that represent the 1s and
0s of computer information. And it takes a certain amount of time -- the
rise time -- for a given electric pulse to impart the intensity needed
to switch a bit from the magnetic orientation that represents a 0 to the
magnetic orientation that represents a 1. MRAM is a relatively new type
of memory that retains data even when the power is turned off.
This rise time is like the upward curve of a graph. The steeper the curve,
the faster the rise time; and the faster the rise time, the faster the
The researchers' device produces magnetic pulses with curves so steep
the pulses are essentially square, according to Thomas Gerrits, a researcher
at the Research Institute for Materials in the Netherlands (NSRIM). The
researchers make a square pulse by hitting the two tines of a fork-shaped
piece of semiconductor material with ultrafast laser pulses timed slightly
apart. The laser pulses produce electric pulses that overlap as the semiconductor
tines come together. The overlapping electric pulses, in turn, produce
the square magnetic pulse.
The laser pulses used to shape the switching pulse last only 150 femtoseconds,
or million billionths of a second, and their paths are only a few microns,
or thousands of a millimeter apart, according to Gerrits. The resulting
switching pulses showed a rise time of about 10 picoseconds, or trillionths
of a second, which means they are capable of switching a bit within 200
picoseconds, according to Gerrits. This is about seven times faster than
today's commercial MRAM.
The switching rate of today's MRAM depends on accommodating the relaxation
time of the system, or the time it takes to complete a pulse cycle including
a longer a rise time, which is on the order of 1.5 nanoseconds, or billionths
of a second, said Gerrits.
The researchers' method works because the shaped magnetic pulse matches
the intrinsic properties of the magnetic elements, according to Gerrits.
"This shaping method is used to control the precessional response of a
magnetic system, which can only be achieved by short-rise-time magnetic
field pulses," he said. The processional response is the way a bit's magnetic
field rotates as it shifts from the 0 orientation to the 1 orientation
and vice versa.
A major logistical problem remains in adapting the pulse-shaping method
for practical use, said Gerrits. The pump-laser pulses, which last only
150 femtoseconds, are not easy to produce. "There are shoe-box size systems
on the market," but the miniaturized versions required for a practical
memory chip do not exist yet, he said. "A combination of these laser systems
and semiconductors is up to industry," he said.
The researchers' experiment is well designed, said Caroline Ross, an associate
professor of materials science and engineering at the Massachusetts Institute
of Technology. "This is useful because it would ideally allow you to make
a very fast MRAM with precise switching," she said.
The experiment has provided useful information about the way a small magnetic
structure switches, said Ross. Using the method in a real device will
be difficult, however, she said. "The problem with the method from a device
standpoint is that you need to apply a very carefully shaped [magnetic]
The thin metal interconnects that connect components in real devices have
higher resistance to electrical current than the researchers' experimental
equipment, said Ross. "Making very sharp and fast current pulses to generate
a very sharp field pulse," using standard equipment might be tricky, she
said. If it can be done, however, it would significantly improve the future
performance of devices like MRAMs, Ross said.
Developing a practical system and integrating it into a working computer
would take somewhere between 2 and 10 years, said Gerrits.
Gerrits' research colleagues were Hugo A. M. van den Berg, Julius Hohlfeld,
O. Gielkens and Theo Rasing from the Research Institute for Materials
and Ludwig Bär from Siemens AG in Germany. They published the research
in the August 1, 2002 issue of the journal Nature. The research was funded
by the Netherlands Organization for Scientific Research (NWO), Philips
Research, and the European Union.
Timeline: < 10 years
Funding: Corporate, Government
TRN Categories: Data Storage Technology; Physics
Story Type: News
Related Elements: Technical paper, "Ultrafast Precessional
Magnetization Reversal by Picosecond Magnetic Field Pulse Shaping," Nature,
August 1, 2002.
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