"These nanoscale oscillators could potentially replace much bulkier and expensive components in microwave circuits," explained Matthew Pufall of NIST. "This is a significant advance in demonstrating the potential utility of these devices."
The devices, which were 50 nm in diameter, consisted of two magnetic layers separated by a 5 nm-thick layer of copper. The first magnetic layer was a 20 nm coating of Co90Fe10 while the second magnetic layer consisted of 5 nm thick Ni80Fe20.
In response to a DC electrical current, the devices emitted microwave radiation with a frequency typically in the range of 1–40 GHz. The researchers were able to lock the phase of two devices 500 nm apart by altering the currents applied to each device, making their frequencies approach one another.
Once the oscillators were phase locked with each other, they produced microwaves with a narrower signal linewidth and greater power. They were also less susceptible to external noise. The researchers predict that a phase-locked array of N devices would produce power that scaled with N2.
A single spin torque nano-oscillator device produces microwave power typically less than 1 nW. But the researchers reckon they could produce microwatts of microwave power by building an array of phase-coherent nano-oscillator devices.
Such devices could have applications in wireless chip-to-chip or intra-chip communications. The devices are also compatible with standard semiconductor manufacturing techniques, which the researchers believe should make them cheap to produce.
The researchers believe the nano-oscillators may phase lock as a result of the "spin waves" that they emit.
A team from Freescale Semiconductor, US, reported similar results at the same time. They synchronized the phase of nano-oscillators 80 nm in diameter situated roughly 200 nm apart. The synchronized devices emitted frequencies of roughly 10–24 GHz.
The researchers reported their results in Nature.