What comes after silicon?

Companies are now producing chips based on 45 nm devices, but as transistors get smaller and smaller, the laws of physics loom larger and larger. Sander points out that at the scales chipmakers are now working, objects that we consider to be infinitesimally small start to become significant factors.

“All of the physical features that form transistors or the connections between transistors are made up of atoms and molecules,” he says. “These atoms and molecules are the fundamental building blocks and their dimensions just cannot be reduced. As transistors or their components continue to get smaller, we will reach a point where the placement of individual atoms will affect their behavior.”

Chipmakers at Intel have already had to face this problem, says Mr. Bohr. For a chip to work correctly, the thickness of its silicon layers needs to shrink proportionally to the length and width. For example, at the 90 and 65 nm horizontal sizes, the “gate oxide” layer, which acts as an electrical insulator between conductive layers, is only 1.2 nm thick (about 2 inches in our Colorado-size version). This is roughly the thickness of five individual atoms, according to Bohr.

The problem was that at 45 nm, the gate oxide would have to be even thinner – so thin that electrons would start tunneling through it, ruining its properties as an insulator. Intel worked around this problem by using a new layer based on the element hafnium.

Looking beyond silicon
There have been recent discussions that more esoteric forms of computing technologies might provide a breakthrough to keep Moore’s Law alive.

Optical computing, which would use photons rather than electrons, is one idea. But both Bohr and Sander agree that optical technology works best to connect processors together over a distance, rather than inside the chips themselves.

Another contender is quantum computing, which uses the attributes of elementary particles such as electrons as the basis for calculation.

As opposed to traditional digital computing, where a bit of data is either a 1 or a 0, in quantum computing it can be both at once. Again, neither Bohr or Sander sees quantum computing having much utility except in some specialized areas such as cryptography, at least in the short term.

The good news for Moore’s Law is that it seems healthy for at least another decade. Intel’s Bohr expects at least another 10 years of biannual doubling, while Sander sees innovations on the horizon that could keep the trend on track through 2020. AMD is already developing new technology needed for 16 nm transistors, which is on their road map for 2014.

And beyond that? “The industry is now looking for some new physics,” says Sander. “We have used what we call ‘charge-based physics’ since the days of vacuum tubes. Now the Nanoelectronics Research Initiative, of which AMD is a member, is sponsoring ... university research to find new physical-switching mechanisms that don’t require the movement of [an] electronic charge. It is too soon to tell, but this is the kind of work that could allow Moore’s Law to continue well beyond 2020.”

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