Nanoscale "memristive" RF switches enable on-the-fly IC reconfiguration

Superfast nanoscale (RF) switches crafted by a team of University of Massachusetts, Amherst researchers are boasting reprogrammable features akin to those involved in interneuron communication.

Reconfigurable RF systems in use by the military today depend upon the availability of tiny switches that can be integrated into chips and easily reprogrammed to serve different RF functions. So far, though, the use of reconfigurable has been severely limited by performance drawbacks such as added noise, size, power consumption, functional instability, and a lack of durability.

Now, new nanoscale RF switches based on memristor technology can overcome these challenges, thanks to a collaboration that combined the expertise of two assistant professors within UMass Amherst’s Electrical and Computer Engineering department, Joseph Bardin and Qiangfei Xia.

Professor Bardin’s main area of expertise is RF devices, circuits, and systems, while Professor Xia is an expert in nanoscale memristive devices.

Both Bardin and Xia received the U.S. Defense Advanced Research Projects Agency (DARPA) Young Faculty Award (YFA). “Our collaboration was encouraged by DARPA’s Microsystems Technology Office Director Bill Chappell, who served as our mentor within the YFA program,” Bardin says.

So, what exactly is a memristor and its role in the “nanoscale memristive RF switches” invented by the duo? “It’s essentially a nonvolatile device whose resistance depends on the history of the current/voltage applied to the device,” Bardin explains. “By using appropriate programming protocols, the DC resistance of these devices can be switched over ten orders of magnitude. There are many flavors of memristors, but the device that we demonstrated is specifically tailored for RF applications by minimizing OFF-state capacitance and ON-state resistance.”

Reconfigurable RF systems are desirable for reducing the parts count in communications and systems. “A typical cellphone has several front-end chips, for example, each of which serves to receive a specific communications band,” Bardin says. “Emerging reconfigurable RF technologies promise to enable the development of single-chip solutions where the front end can be reconfigured on the fly for the desired functionality.”

What’s in Xia and Bardin’s switches? Just two conductive elements – a pair of gold and silver electrodes – separated by an air gap of 35 nanometers. Specific changes in voltages or currents within these switches trigger the formation of disintegration of conductive silver filaments between the elements, resembling a neuron firing, in which tiny gaps are briefly and reversibly bridged by chemical neurotransmitters to allow electro-chemical signals to move from one neuron to the next.

The key significance of this work is that “compared to other RF switches, our memristive RF switch is orders of magnitude smaller in device size, but nonetheless achieves quite promising performance, even outperforming some of the metrics of other state-of-the-art technologies,” Bardin notes.

The biggest tech surprise along the way for Bardin and Xia? Simply that the switches worked as well as they did.

They expect the key application of their work to be “the integration of large numbers of switches directly into an to enable highly reconfigurable architectures that aren’t feasible today because of the large physical dimensions of today’s state-of-the-art RF switches,” Bardin explains.

The switches’ ability to enable on-the-fly IC reconfiguration, could allow the military “to reconfigure a device to act as either a satellite receiver or a radar,” he points out. This means users can make the device behave like a cellphone signal emitter, for example, then quickly reprogram it to serve as a collision-avoidance radar component or local radio jammer.

“The nanoscale dimensions of these switches, their performance, and the relative simplicity with which they can be integrated into existing chip technology bodes well for their inclusion within a new generation of reconfigurable RF chips,” says DARPA’s Chappell. “These switches can change from one type of radio to a completely different type, all without a hardware change. We can even use one chip set to switch from a communications system to a radar, which are traditionally very different designs.”

The timeline for this technology? Still at least several years out. “There are open issues that we need to resolve,” Bardin says. “We plan to work on improving the endurance – number of times the device can be reconfigured – and RF power-handling capabilities.”

DARPA’s YFA program (www.darpa.mil/work-with-us/for-universities/young-faculty-award) identifies and engages rising research stars in junior-faculty positions at U.S. academic institutions and introduces them to Department of Defense (DoD) needs and DARPA’s program-development process. YFA awardees receive a $500,000 grant for a two-year period, with an opportunity to be considered for another $500,000 under the DARPA Director’s Award.

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