Mechanical Nanocomputer Proposed

Scientists at the University of Wisconsin-Madison, including Prof. Robert Blick, have proposed building a nanocomputer that works on a purely mechanical basis. Instead of shuffling electrons through circuits, it would physically move its atoms, with components pushing and pulling on each other to do computations. The molecular manufacturing community has been proposing a similar approach for at least two decades.

The news stories compare the proposal to Babbage's mechanical computer designs. However, I haven't yet found a description of exactly how the mechanisms would work. Babbage's machines, of course, used gears and cams -- lots of sliding interfaces between parts. And sliding is something that MEMS (micro-electro-mechanical systems) aren't very good at. The researchers have already built one component, using MEMS techniques, and expect their work to be commercially relevant in just a few years. So it's not clear how close the current designs are to Babbage's designs.

Eric Drexler proposed as far back as the mid-1980's that nanoscale mechanical computers could be built via molecular manufacturing. Drexler's designs used rods sliding in housings, with bumps that would interfere with the motion of other rods. This is not something that could be built with today's MEMS. So the detail of the designs probably doesn't owe much to Drexler's work. The overall concept -- that scaling laws allow nanoscale mechanisms to work at gigahertz speed -- is of course the same as Drexler's. Scaling laws are underappreciated but straightforward, so it's inevitable that both researchers took the same approach -- once they decided that mechanical nanocomputers were worth looking at.

Ralph Merkle worked on designs for a mechanical nanocomputer that would not require sliding interfaces, and published some in 1993. Without knowing the details of Blick's designs, it's impossible to say whether Blick owes anything to Merkle's work.

As Drexler pointed out, mechanical nanocomputers may be the most compact way to do computation; atoms don't tunnel nearly as easily as electrons do. This also means they may work at higher temperatures than electronic computers. And, because atoms tend to stay where you put them, it may be possible to spend less energy on avoiding errors. So as MEMS gets more precise, it may be possible to build useful mechanical nanocomputers with MEMS techniques.

Several of the press stories mentioned diamond as a possible nanocomputer construction material. Some MEMS are now being built out of diamond, so this should not be seen as a nod to Drexler's diamondoid proposals. In fact, it would have been nice if the press stories had acknowledged the conceptual leadership of the molecular manufacturing community (though I'm not surprised that they didn't). But the mention of diamond nanocomputers, as well as the more general idea of mechanical nanocomputers, may work to give long-overdue recognition to the basic soundness of Drexler's nanocomputer proposals.

Chris Phoenix

Tags: nanotechnology nanotech nano science technology ethics weblog blog

Comments

[Brian Wang]

They still seem to be using DC current for the computer. But the current is controlled by a nanomechanical nanoscale pillar.

http://advancednano.blogspot.com/2007/07/nanomechanical-computer-project.html

The 9 page paper is here
http://www.iop.org/EJ/article/-search=25210907.1/1367-2630/9/7/241/njp7_7_241.pdf

It has to be clearly stated that current operating speeds of nano-electromechanical single electron transistors (NEMSETs) are of the order of 1 GHz [3], which is not competitive with standard complimentary metal oxide semiconductors (CMOS

As we have found in recent measurements [4] self-excitation can be exploited to generate
mechanical oscillations without any ac excitation. Hence, dc voltages are sufficient to operate the NMC. Basically, a dc voltage creates an electric field to support mechanical oscillations of the nanopillars. A classical example is straightforward to construct [5]. It has to be noted that onset of the mechanical oscillations is induced by a thermal fluctuation, which is found to be
enhanced, if the electrical field is inhomogeneous.

[Ray Phoenix]

From the paper:

"The scaling of the power of the nanomechanical circuits we find by applying the standard relation for CMOS dynamic power consumption P = CV2f . Assuming an operating frequency of f = 1 GHz, a typical operating voltage of V = 1 V and a NEMSET total capacitance of C = 10 aF, we find a total dynamic power of P = 10nW. This value can be further reduced by lowering the gating voltage to some 100mV and the overall capacitance to below 10 aF. Under the assumption that the gate is switched at a speed of 1 GHz the total power corresponds to an energy of E = 10 aJ per switching event for nanomechanical transistors. At this stage this is only two orders of magnitude above the thermal energy limit Eth = kBT for 300 K. A computing architecture made from nanomechanical transistors thus is competitive with 45 nm CMOS technology, while taking a step towards enabling reversible computing.

In summary, we have shown how to construct a computational device purely based on nanomechanical elements—the NMC. Single nanomechanical switches are operational and simulation shows that the concept is feasible for circuit integration."

10 attojoules, if I read correctly. That's good, I think. The authors point out that high temperature operation is a strong point. The technology has relatively low clock speed, which the authors acknowledge.

Clearly nothing slides, and the transistors should suffer absolutely no wear, so properly shielded from radiation, the device should last indefinitely.

Note the comment on reversible computing, as well.

[Chris Phoenix, CRN]

Yes, Drexler's and Merkle's computers were also designed for reversibility.

I wouldn't call this computer totally mechanical, since it transports electrons. The design is really not much at all like the mechanical nanocomputers proposed by MM researchers. In which case it's interesting that the news stories make it sound so similar in some respects.

Chris