A team of University
of California, Los Angeles (UCLA) researchers has created
the most powerful high-performance nanoscale microwave oscillators in the
world, a development that could lead to cheaper, more energy-efficient mobile
communication devices that deliver much better signal quality.
Today’s cell phones, WiFi–enabled tablets,
and other electronic gadgets all use microwave oscillators, tiny devices that
generate the electrical signals used in communications. In a cell phone, for
example, the transmitter and receiver circuits contain oscillators that produce
radio-frequency signals, which are then converted by the phone’s antenna into
incoming and outgoing electromagnetic waves.
Current oscillators are silicon-based and
use the charge of an electron to create microwaves. The UCLA-developed
oscillators, however, use the spin of an electron, as in the case of
magnetism, and carry several orders-of-magnitude advantages over the oscillators
commonly in use today.
UCLA’s electron spin–based oscillators grew
out of research at the UCLA Henry Samueli School of Engineering and Applied
Science sponsored by the Defense Advanced Research Projects Agency (DARPA).
This research focused on STT-RAM, or spin-transfer torque magnetoresistive
random access memory, which has great potential over other types of memory in
terms of both speed and power efficiency.
“We realized that the layered nanoscale
structures that make STT-RAM such a great candidate for memory could also be
developed for microwave oscillators for communications,” said principal
investigator and research co-author Kang L. Wang, UCLA Engineering’s Raytheon
Professor of Electrical Engineering and director of the Western Institute of
Nanoelectronics (WIN).
The structures, called spin-transfer
nano-oscillators, or STNOs, are composed of two distinct magnetic layers. One
layer has a fixed magnetic polar direction, while the other layer’s magnetic
direction can be manipulated to gyrate by passing an electric current through
it. This allows the structure to produce very precise oscillating microwaves.
“Previously, there had been no
demonstration of a spin-transfer oscillator with sufficiently high output power
and simultaneously good signal quality, which are the two main metrics of an
oscillator—hence preventing practical applications,” said co-author Pedram
Khalili, project manager for the UCLA–DARPA research programs in STT-RAM and non-volatile
logic. “We have realized both these requirements in a single
structure.”
The SNTO was tested to show a record-high
output power of close to 1 micro-watt, with a record narrow signal linewidth of
25 megahertz. Output power refers to the strength of the signal, and 1
micro-watt is the desired level for STNOs to be practical for applications.
Also, a narrow signal linewidth corresponds to a higher quality signal at a
given frequency. This means less noise and interference, for a cleaner voice
and video signal. It also means more users can be accommodated onto a given
frequency band.
In addition, the new nanoscale system is
about 10,000-times smaller than the silicon-based oscillators used today. The
nano-oscillators can easily be incorporated into existing integrated circuits
(computer chips), as they are compatible with current design and manufacturing
standards in the computer and electronic device industries. And the oscillators
can be used in both analog (voice) and digital (data) communications, which
means smart phones could take full advantage of them.
“For the past decade, we have been
working to realize a new paradigm in nanoelectronics and
nanoarchitectures,” said Wang, who is also a member of the California
NanoSystems Institute at UCLA. “This has led to tremendous progress in
memory research. And along those same lines, we believe these new STNOs are
excellent candidates to succeed today’s oscillators.”
The paper, “High-Power Coherent
Microwave Emission from Magnetic Tunnel Junction Nano-oscillators with Perpendicular
Anisotropy,” has been published online in ACS Nano.
