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Ern Worthman,
Editorial Director |
One thing I want to do before I die is see an atom. I know that objective pales in comparison to having a lifelong goal of finding a cure for Alzheimer’s, or walking on the moon as a civilian. But still... for an eternal techno-geek like me, that is something that excites me.
When I say "see an atom, " I mean "SEE an atom. " Not a mathematical representation, not an electronically-generated image, not using Avogadro’s number but the real McCoy! And, I may just get that chance.
In a study published in the August 1 issue of Applied Physics Letters, John Booske, a UW-Madison professor of electrical and computer engineering, and Keith Thompson, David Larson and Tom Kelly of the Madison-based company Imago Scientific Instruments, used Imago’s local electrode atom probe microscope to pinpoint individual atoms of boron — a common additive, or dopant, in semiconductors — within a sea of silicon atoms.
Now that’s exciting. But I still want to really see an atom — live, in real-time, as a camera would capture it. That way, I’ll know all that I’ve been told and taught over the last 30 or so years is true.
Boron is a decent sized atom. Hydrogen has a covalent radius of about 37 pm. Boron has a covalent radius of about 85 pm, about 2.5 times that of hydrogen. Silicon has a covalent radius of 117, germanium, 122. Well, OK, I’d be happy to see a germanium atom.
Realistically speaking, the technique used by Kelly doesn’t really "photograph" or capture a movie of atoms the way a techno-plebe would call "seeing" it. Rather, the image is one of clusters of "dots" on an electron microscope image (see the figure below).
But it’s a start. At least we can recognize the dots as atoms. And once the atoms are identified, they can be counted; quite a feat, and very significant for developmental technologies.
This is a breakthrough, as Booske, Thompson, Larson and Kelly point out. Actually being able to see how atoms, in this case dopant atoms, but theoretically any atoms, precipitate though semiconductor material has far reaching implications.
As we are all well aware, the transistor has taken on the characteristics of the amazing shrinking person (had to be politically correct). We’re talking real devices less than 100 nm in all three dimensions.
As these devices shrink, close enough isn’t good enough anymore. In large-footprint, power-insensitive devices, all that really mattered was that a reasonable electron flow across the junction and through the semiconductor material was achieved. Molecular count wasn’t particularly critical and tolerances weren’t nearly so critical.
However, as we approach single electron device junctions, what was once error margin is now critical margin. As the team so aptly presents, the functionality really does come down to the atomic level. Too many or too few dopants (or too many or too few of anything at this level, really) will introduce significant errors.
Tomorrow’s atomic-scale semiconductor devices will have to be held to tolerances at an order of magnitude smaller than just the error margin of their predecessors. For example, where the dopants diffuse in the silicon, "how many" and "how deep" are parameters that will have to be extremly tightly controlled at this level. And this is only one set of parameters. Junction parameters are another critical element of these micro-scale devices and there are tens more.
Now, understand that this team has only found a way to render images of such devices. Not a way to develop and construct them.
However, knowledge is power and the ability to see what is going wrong (or right) is the first step in fixing it.
Virtually every sector of the electronics industry can benefit from smaller and lower-powered devices that raise the bar for functionality. But sometimes we hit the wall (as is the case with computer µPC densities). Reality is that we are hitting the wall in many areas. Things just can’t get any faster, smaller, more functional or denser with much of today’s mainstream technologies and platforms. And we really don’t have a lot of functional options on the immediate horizon. We have a lot of emerging technologies, with a lot of potential, but these are exactly that — emerging technologies.
What is promising is that innovations such as the LEAP microscope will hasten the development curve, and on a personal level, make it so I can die fulfilled.
Wireless Design & Development
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