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Nanoscale Microwave Oscillators Generate Close to 1 Microwatt at UCLA

Consumer electronic manufacturers are looking at microwave frequencies from 2.4 GHz to 60 GHz and higher to meet the ever-increasing demand for higher speed data connectivity. These efforts could be helped by a high-performance nanoscale microwave oscillator developed by a UCLA-led research team. Unlike current silicon-based oscillators that use the charge of an electron to create microwaves, the UCLA-developed oscillators use the spin of an electron, as in the case of magnetism, to gain “several orders-of-magnitude advantages over oscillators commonly in use today.” 

The 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) looking into spin-transfer torque magnetoresistive random access memory (STT-RAM). Principal investigator and research co-author Kang L. Wang, UCLA Engineering's Raytheon Professor of Electrical Engineering, explains, “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.”

The spin-transfer nano-oscillators are composed of two distinct magnetic layers, one with a fixed magnetic polar direction and the other layer with a magnetic direction that can be made to gyrate by passing an electric current through it. This design allows the structure to produce a very precise microwave signal. 

Pedram Khalili, project manager for the UCLA–DARPA research programs in STT-RAM and non-volatile logic, said, “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. We have realized both these requirements in a single structure.”

The spin-based nanoscale oscillators have an output of a bit less than one microwatt and, what the UCLA news release, said was “a record narrow signal line width of 25 megahertz.” While this power output may not sound impressive, it is accomplished by a device that about 10,000 times smaller than the silicon-based oscillators used today.

Details on the research were published in the article High-Power Coherent Microwave Emission from Magnetic Tunnel Junction Nano-oscillators with Perpendicular Anisotropy, available to ACS Publications subscribers.