Single electrons perform logic

The ultimate in transistors, which turn on and off in response to a flow of electricity, is a device that can be tripped by a single electron.

Researchers from Hokkaido University have put together an AND logic circuit made from four single-electron tunneling transistors.

The devices draw little power and are very small, which opens the way for making computers that are more powerful than is possible with ordinary transistors.

An AND circuit ordinarily contains two inputs and one output. When both the inputs are on, the output turns on, when one or both of the outputs are off, the output is off.

The researchers device is made from a self-organized network of gallium arsenide quantum dots, or bits of semiconductor material that can trap single electrons. The circuit works differently from those made from transistors in today's computer chips. The architecture, dubbed binary decision diagram, sends a single electron through a series of transistors, and its path determines the outcome of a logic operation.

The researchers' are working to form more complicated circuits, and to make the devices practical. The researchers prototypes operate at very cold temperatures -- around 4 degrees above absolute zero.

Single electron transistor logic in memory devices could be used in small practical systems within ten years, according to the researchers. The work appeared in the September 29, 2003 issue of Applied Physics Letters.