Scientists have long known about the electronic properties of VO₂ but haven't been able to explain them until know. It turns out that its atomic structure changes as the temperature rises, transitioning from a crystalline structure at room temperature to a metallic one at temperatures above 68°C. And this transition happens in less than a nanosecond - a real advantage for electronics applications. "VO₂ is also sensitive to other factors that could cause it to change phases, such as by injecting electrical power, optically, or by applying a THz radiation pulse," says Adrian Ionescu, the EPFL professor who heads the school's Nanoelectronic Devices Laboratory (Nanolab) and also serves as the Phase-Change Switch project coordinator.


The challenge: reaching higher temperatures

However, unlocking the full potential of VO₂ has always been tricky because its transition temperature of 68°C is too low for modern electronic devices, where circuits must be able to run flawlessly at 100°C. But two EPFL researchers - Ionescu from the School of Engineering (STI) and Andreas Schüler from the School of Architecture, Civil and Environmental Engineering (ENAC) - may have found a solution to this problem, according to their joint research published in Applied Physics Letters in July 2017. They found that adding germanium to VO₂ film can lift the material's phase change temperature to over 100°C.

Even more interesting findings from the Nanolab - especially for radiofrequency applications - were published in IEEE Access on 2 February 2018. For the first time ever, scientists were able to make ultra-compact, modulable frequency filters. Their technology also uses VO₂ and phase-change switches, and is particularly effective in the frequency range crucial for space communication systems (the Ka band, with programmable frequency modulation between 28.2 and 35 GHz).


Neuromorphic processors and autonomous vehicles

These promising discoveries are likely to spur further research into applications for VO₂ in ultra-low-power electronic devices. In addition to space communications, other fields could include neuromorphic computing and high-frequency radars for self-driving cars.

Ecole Polytechnique Fédérale de Lausanne. Posted: Feb 05, 2018.

Nota do Scientific Editor: E. A. Casu, A. A. Muller, M. Fernandez-Bolanos, A. Fumarola, A. Krammer, A. Schuler and A. M. Ionescu. Vanadium Oxide bandstop tunable filter for Ka frequency bands based on a novel reconfigurable spiral shape defected ground plane CPW. IEEE Access, 2018, 1, DOI: 10.1109/ACCESS.2018.2795463.

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