Soliton Transistor

A transistor based not on the customary sandwich of semiconductor layers but on a Josephson junction (itself a sandwich consisting of two superconducting layers separated by a thin film of insulating material) architecture, and involving not the gated flow of electrons or holes (the empty spaces left behind by electrons) but the controllable flow of tiny magnetic vortices, has been built and tested by Farshid Raissi, a scientist at the Toosi University of Technology in Tehran.

The vortices, set in motion in the form of solitons (pulses that do not lose energy or their shape as they travel) travel at the speed of light and therefore are much faster than the electrons in ordinary transistors, possibly leading, Raissi argues, to quicker switching speeds (raissi@kntu.ac.ir). In his experimental transistor setup, which is about 800 microns long, trains of vortex solitons, created by applying small applied magnetic fields to the junction and set in motion by a applying a brief current into the junction, are used to control the flow of a separate soliton train.

Part of the reason solitons can be used in this controllable way (and controlling flow---turning a component on or off---is one of the hallmarks of transistors) is the fact that solitons can be made to annihilate with anti-solitons (solitons consisting of vortices established with a contrary magnetic orientation). With his vortex-soliton transistor Raissi has observed switching speeds of 8 GHz, as fast or faster than the best existing transistors.

Raissi expects no insurmountable problems in shrinking and mass producing his soliton device, and expects to achieve speeds of 200 GHz, which would make this transistor architecture quite attractive for use in supercomputers. (Applied Physics Letters, 27 June 2005; lab website, www.ee.kntu.ac.ir )