A Plasmonic Revolution For Computer Chips?

By Roland Piquepaille

Today, we're using basically two ways to move data in our computers. Transistors carry small amounts of data and are extremely small, while fiber optic cables can carry huge amounts of data, but are much bigger in size. Now, imagine a single technology combining the advantages of photonics and electronics. This Stanford University report says a new technology can do it: plasnomics. (For more about plasmons, read this Wikipedia article.) Theoretically, it is possible to design plasnomic components with the same materials used today by chipmakers, but with frequencies 100,000 times greater than the ones of current microprocessors. There is still a challenge to solve before getting plasnomic chips. Plasmons can only travel a few millimeters before dying while today's chips are typically about a centimeter across. Read more...

Let's start with some technical explanations.

Surface plasmons are density waves of electrons -- picture bunches of electrons passing a point regularly -- along the surface of a metal. Plasmons have the same frequencies and electromagnetic fields as light, but their sub-wavelength size means they take up less space. Plasmonics, then, is the technology of transmitting these light-like waves along nanoscale wires.

"With every wave you can in principle carry information," says Mark Brongersma, assistant professor of materials science and engineering. [...] "Plasmon waves are interesting because they are at optical frequencies. The higher the frequency of the wave, the more information you can transport." Optical frequencies are about 100,000 times greater than the frequency of today's electronic microprocessors.

But let's get back to the technology.

Plasmons are generated when, under the right conditions, light strikes a metal. The electric field of the light jiggles the electrons in the metal to the light's frequency, setting off density waves of electrons. The process is analogous to how the vibrations of the larynx jiggle molecules in the air into density waves experienced as sound.

Plasmon waves behave on metals much like light waves behave in glass, meaning that plasmonic engineers can employ all the same ingenious tricks -- such as multiplexing, or sending multiple waves -- that photonic engineers use to cram more data down a cable.

This sounds good, but is it possible to use this technology today?

Because plasmonic components can be crafted from the same materials chipmakers use today, Stanford engineers are hopeful they can make all the devices needed to route light around a processor or other kind of chip. These would include plasmon sources, detectors and wires, which the lab already has made, as well as splitters and even transistors.

While an all-plasmonic chip might be feasible someday, Brongersma expects that in the near term, plasmonic wires will act as high-traffic freeways on chips with otherwise conventional electronics.

And even Brongersma recognizes that more research needs to be done before getting plasnomic chips.

The potential of plasmonics right now is mainly limited by the fact that plasmons typically can travel only several millimeters before they peter out. Chips, meanwhile, are typically about a centimeter across, so plasmons can't yet go the whole distance.

The distance a plasmon can travel before dying out is a function of several aspects of the metal. But for optimal transfer through a wire of any metal, the surface of contact with surrounding materials must be as smooth as possible and the metal should not have impurities.

For more information, you can check the following resources.

• "Plasmonic computer chips move closer," an article published by New Scientist on March 17, 2005
  
• The Brongersma Group website and its current research projects
  
• The abstract of a presentation given on May 21, 2005 at the March 2005 Meeting of the American Physical Society, "Sub-wavelength confinement and the diffraction limit for surface plasmon waveguides"
  

Sources: David Orenstein, Stanford University Report, March 16, 2005; and various websites

Related stories can be found in the following categories.

• Chips
  
• Electronics
  
• Future
  
• Materials
  
• Optics
  
• Technology