The Emerging Carbon (Computing) Age

By Kurt Cagle
July 14, 2008 | Comments: 1
In the early 1970s, the integrated circuit came of age, marking the ascention of what could best be described as the silicon era. Silicon, the most common material in the Earth's crust, proved to be remarkably useful for its ability to create computational gates by establishing semi-conductors that allowed the flow of electrons only in the presence or absence of other elecrtical currents.

Many science fiction writers over the last forty years have concentrated on the rise of "silicon" life forms - robots and computer AIs - yet there are indications that the next major "age" in computing will be dictated not by the presence of sand, but the presence of soot.

Carbon and silicon are in the same family in the periodic table, and both are capable of surprisingly sophisticated structures. However, there is a reason that organic chemistry is the chemistry of carbon rather than silicon. For all of silicon's potential, silicon forms relatively few compounds, and the ones that it does form are invariably marked by rigidity.

Carbon, on the other hand, is the foundation of tens of thousands of organic molecules. Yet perhaps one of the most intriguing of these molecules from a computing standpoint is benzene. Friedrich August Kekulé, a German chemist, published a paper in 1865 describing benzene as a ring of six carbon atoms, attached in turn to various other carbon, hydrogen or nitrogen atoms at each terminus. He first came to the realization about this structure in a dream, when he imagined the giant snake Ouroboros, the world snake of Norse culture which formed a ring by swallowing its own tail.

If you take each "attachment" of a benzene ring and place a carbon atom at the other end - then repeat the process over and over again, what you end up with is a honeycomb like sheet of carbon rings called graphene.  It turns out that graphene has a number of very unusual properties that have caused chip designers among other resarchers to look very hard at the molecule.

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Graphene is unique in that it is the only known two-dimensional crystal. One effect of this is that when an electron moves across a graphene surface, it effectively encounters nearly no resistance, which in turn mimics the characteristics of low temperature semi-conductors. It's also ideal for controlling and reading the spin characteristic of electrons, which points to its potential use within spintronics based computing systems.

If you take a sheet of graphene and roll it up, this creates carbon nanotubes, which apply similar superconducting characteristics to wirelike filaments. Moreover, by removing an atom from each "ring" (making the structures pentagonal) it becomes possible to "cap" the tubes. It also becomes possible by working in the same manner to induce folding of such five and six -rings into a ball that bears a high degree of similarity to Buckminster Fuller's geodesic domes. This fact, not lost on the researchers, accounts for the name of ball-like molecules known formally as Fullerenes and informally as Bucky Balls

While the physical and materials properties of these carbon super-molecules have begun being exploited on a regular basis, the computing properties are only just now beginning to be tested. Fullerenes, for instance, can act like cages to hold in both tiny molecules and a surprisingly high mount of charge - meaning that bucky balls could very well end up serving as nano-level capacitors. By doping graphene sheets, the resulting characteristics can also be utilized to turn superconductors into semiconductors.

While graphene occurs naturally - indeed, any time you write with a pencil on a paper you are in fact leaving behind wadded clumps of graphene sheets - normally it is very difficult to keep such sheets from twisting and turning on themselves (in essence forming three dimensional compounds). Indeed, it was only in 2004 that researchers from the University of Manchester in England were able to isolate graphene, ironically by shaving graphite using a silicon molecular "blade".

More recently graphene has been created by using a silicon substrate to lay down a thin layer of carbon into graphene sheets, then peeling away the graphene from the silicon. Such sheets are still quite small - the largest one to date has been on the order of 100 microns, and as such barely visible to the naked eye, but the particular technique holds promise for larger scale commercial manufacture.

For instance, DARPA recently awarded IBM a $2.4 million dollar contract to explore Wafer-Scale Graphene RF Nanoelectronics , looking at a combination of doped graphene sheets and carbon nano-tubes (which are essentially graphene hollow "wires") in order to create electronics that have far less resistance (and hence generate far less heat) than the corresponding silicon structures. This potential is not insignificant - Moore's Law is facing major limits within silicon-based material because the heat generated by electrons moving through the ever thinner wave-guides is reaching a point where it is burning through the integrated circuitry.

It is perhaps inevitable that computing is taking its first tentative steps towards an "organic" basis. The versatility of carbon as the foundation of living chemistry, coupled with the growing realization that near-term nanotechnology is likely to be far more dominated by chemical processes rather than mechanical ones, makes carbon an inviting medium for exploration of computing and electronics - and makes the barrier between computation and life just that much thinner.

Kurt Cagle is an online editor for O'Reilly Media, and lives in Victoria, British Columbia.

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FYI, Rep. Culberson mentioned nanotubes is his interview with O'Reilly News. He touted the conductivity of C nanotubes as being something that could help solve the energy crisis.

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