Sixty years after the transistor began a technological revolution that transformed nearly every aspect of our daily lives, a new transistor brings innovations that may help to do so again. Developed at RIKEN, the device uses the electrostatic accumulation of electrical charge on the surface of a strongly-correlated material to trigger bulk switching of electronic state. Functional at room temperature and triggered by a potential of only 1 V, the switching mechanism provides a novel building block for ultra low power devices, non-volatile memory and optical switches based on a new device concept.

After shrinking for many decades, conventional electronics is approaching quantum scaling limits, motivating the search for alternative technologies to take its place. Among these, strongly-correlated materials, whose electrons interact with each other to produce unusual and often useful properties, have attracted growing attention. One of these properties is triggered in phase transitions: applying a small external voltage can induce a very large change in electric resistance, a mechanism akin to a switch that has many potential applications.

Now, researchers at the RIKEN Advanced Science Institute have created the world's first transistor that harnesses this unique property. Described in a paper in Nature, the device uses an electric-double layer to tune the charge density on the surface of vanadium dioxide (VO₂), a well-known classical strongly-correlated material. Thanks to the strong correlation of electrons and electron-lattice coupling in VO₂, this surface charge in turn drives localized electrons within the bulk to delocalize, greatly magnifying the change of electronic phase. A potential of only 1 V, they show, is enough to switch the material from an insulator to a metal and trigger an astounding thousand-fold drop in resistance.

The electronic phase, however, is not the only thing that changes in this insulator-to-metal transition: using synchrotron radiation from RIKEN's SPring-8 facility in Harima, the research group analyzed the crystal structure of the VO₂, showing that it, too, undergoes a transformation, from monoclinic to tetragonal structure. Electric-field induced bulk transformation of this kind is impossible using conventional semiconductor-based electronics and suggests a wide range of potential applications.

First released over sixty years ago to little fanfare, the transistor has had a dramatic impact on our daily lives, powering the electronic devices we use every day. The new switching mechanism takes this first discovery to a new level, demonstrating that a very small electric potential is enough to control macroscopic electronic states and offering a new route to controlling the state of matter.

Reference

• M. Nakano, K. Shibuya, D. Okuyama, T. Hatano, S. Ono, M. Kawasaki, Y. Iwasa and Y. Tokura, “Collective bulk carrier delocalization driven by electrostatic surface charge accumulation” Nature , (2012). doi: 10.1038/nature11296

Contact

Masaki Nakano (Postdoctoral researcher)
Strong-Correlation Hybrid Materials Research Team
RIKEN Advanced Science Institute

Yoshihiro Iwasa (Team Leader and Professor)
Strong-Correlation Hybrid Materials Research Team
RIKEN Advanced Science Institute
Quantum-Phase Electronics Center and Department of Applied Physics
University of Tokyo

Jens Wilkinson
RIKEN Global Relations and Research Coordination Office
Tel: +81-(0)48-462-1225 / Fax: +81-(0)48-463-3687
Email: pr@riken.jp