'Ballistic' nanotransistors?

Computer designers at the University of Rochester (UR) say they've invented the next generation of transistors. Their ballistic deflection transistors could lead to terahertz-speed computers. So, is this the end of the semiconductor industry as we know it? Not so fast...
Written by Roland Piquepaille, Inactive

Computer designers at the University of Rochester (UR) say they've invented the next generation of transistors. In a short article, ZDNet UK writes that these ballistic deflection transistors (BDT) could lead to terahertz-speed computers. We are far away from real chips manufactured with this technique, but it's interesting to note that this "ballistic design bounces individual electrons off deflectors as if playing a game of atomic billiards." And such nanotransistors would use less power and create a tiny fraction of the heat generated by current transistors. So, is this the end of the semiconductor industry as we know it? Not so fast...

Before going further, why this BDT is 'ballistic'? Here is an explanation picked from this UR news release.

The BDT is "ballistic" because it is made from a sheet of semiconductor material called a "2D electron gas," which allows the electrons to travel without hitting impurities, which would impede the transistor's performance.

This 'imprecise' definition of 'ballistic' was intriguing, as was this introduction from the UR news release.

"Everyone has been trying to make better transistors by modifying current designs, but what we really need is the next paradigm," says Quentin Diduck, a graduate student at the University who thought up the radical new design.

So I decided to investigate and this led me to another news release from Bell Labs -- but dating from December 1999, "Ballistic Transistor Has Virtually Unimpeded Current Flow." Here is a short excerpt -- which mentioned 'pinball' instead of 'billiard.'

"The electrons going through the channel are like a ball going through a pinball game," said Bell Labs researcher Greg Timp, who presented his research findings today at the International Electron Devices Meeting. "In our device, we not only made the channel very short to minimize the channel resistance, but we also removed nearly all the 'pinball bumpers' by making the insulating layer smoother than it is in conventional transistors. This results in 85 percent of the current being transmitted from the source to the drain, which yields the ballistic transport."

The name of the game has changed between 1999 and 2006, but has the design changed? And by the way, how these ballistic nanotransistors are working? Here is the answer from UR -- in 2006.

The Ballistic Deflection Transistor (BDT) should produce far less heat and run far faster than standard transistors because it does not start and stop the flow of its electrons the way conventional designs do. It resembles a roadway intersection, except in the middle of the intersection sits a triangular block. From the "south" an electron is fired, as it approaches the crossroads, it passes through an electrical field that pushes the electron slightly east or west.
When the electron reaches the middle of the intersection, it bounces off one side of the triangle block and is deflected straight along either the east or west roads. In this way, if the electron current travels along the east road, it may be counted as a zero, and as a one if it travels down the west road.

Below is an image of an electron going from South to West, meaning it accounts for a "one" value (Credit: University of Rochester). You also can watch this short animation for slightly more details (Windows Media Player format, 26 seconds, 3.14 MB).

A 'ballistic' nanotransistor

There is another interesting fact in the UR news release: the team who developed the prototype is truly multidisciplinary.

"We've assembled a unique team to take on this chip," says Marc Feldman, professor of computer engineering at the University. "In addition to myself and Quentin, we have a theoretical physicist, a circuit designer, and an expert in computer architecture. We're not just designing a new transistor, but a new archetype as well, and as far as I know, this is the first time an architect has been involved in the actual design of the transistor on which the entire architecture is built."

This might be true, but 'ballistic' nanotransistors are not completely new, as you can see by visiting a site designed by Richard Taylor, an Associate Professor of Physics, Psychology, and Art at the University of Oregon, "Electronic and Optical Billiards."

So will this 'ballistic computing' concept work? Is it new or not? Please tell me what you think.

Sources: Graeme Wearden, ZDNet UK, August 17, 2006; University of Rochester news release, August 16, 2006; and various web sites

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