View Full Version : One-Atom-Tall Wires Could Extend Life of Moore's Law

Ron Czapala
01-05-2012, 10:55 PM

Scientific American

There may be a bit more room at the bottom, after all.
In 1959 physicist Richard Feynman issued a famed address at a meeting of the American Physical Society, a talk entitled "There's Plenty of Room at the Bottom." It was an invitation to push the boundaries of the miniature, a nanotech call to arms that many physicists heeded to great effect. But more than 50 years since his challenge (pdf), researchers have begun to run up against a few hurdles that could slow the progression toward ever-tinier devices. Someday soon those hurdles could threaten Moore's Law, which describes the semiconductor industry's steady, decades-long progression toward smaller, faster, cheaper circuits.

One issue is that as wires shrink to just nanometers in diameter, their resistivity tends to grow, curbing their usefulness as current carriers. Now a team of researchers has shown that it is possible to fabricate low-resistivity nanowires at the smallest scales imaginable by stringing together individual atoms in silicon.

The group, from the University of New South Wales (U.N.S.W.) and the University of Melbourne in Australia, and from Purdue University in Indiana, constructed their wires from chains of phosphorus atoms. The wires, described in the January 6 issue of Science, were as small as four atoms (about 1.5 nanometers) wide and a single atom tall. Each wire was prepared by lithographically writing lines onto a silicon sample with microscopy techniques and then depositing phosphorus along that line. By packing the phosphorus atoms close together and encasing the nanowires in silicon, the researchers were able to scale down without sacrificing conductivity, at least at low temperatures.

"What people typically find is that below about 10 nanometers the resistivity increases exponentially in these [silicon] wires," says Michelle Simmons, a U.N.S.W. physicist and a study co-author. But that appears not to be a problem with the new wires. "As we change the width of the wire, the resistivity remains the same," she says.

Phosphorus is often introduced into silicon because each phosphorus atom donates an electron to the silicon crystal, which promotes electrical conduction or even can serve as bits in quantum computation schemes. But those conduction electrons can easily be pulled away from duty, especially in tiny wires where the wire's exposed surface is large compared with its volume. By encasing the nanowires entirely in silicon, Simmons and her colleagues made the conduction electrons more immune to outside influence. "That moves the wires away from the surfaces and away from other interfaces," Simmons says. "That allows the electron to stay conducting and not get caught up in other interfaces."

Demonstrating electric transport in a wire so small "is quite an accomplishment," says Volker Schmidt, a researcher at the Max Planck Institute of Microstructure Physics in Halle, Germany. "And being able to fabricate metallic wires of such dimensions, by this theoretically microelectronics-compatible approach, could be a potentially interesting route for silicon-based electronics."

The wires, the researchers say, have the carrying capacity of copper, indicating that the technique might help microchips continue their steady shrinkage over time. The new finding might even extend the life of Moore's Law, Arizona State University in Tempe electrical engineer David Ferry wrote in a commentary in Science accompanying the research.

But don't expect to find atom-scale nanowires in your next gadget purchase. The technology is still in its early phase, with wire formation requiring atom-scale lithography with a scanning tunneling microscope. "It's not an industry-compatible tool at the moment," Simmons says.

01-06-2012, 12:24 AM
Gee. I had not realised that 1.5nm is 4 atoms. We are at 20nm now, so Moores Law doesnt have long to go before thay cannot scale down any more. Of course there is 3D, so that will permit continuation of the increase in transistors.

BTW Did you see Intel & Micron have a 128Gb flash memory chip? There are either 2 or 4 transistors per bit, so either 256 billion or 512 billion transistors (plus control transistors) per chip!!!

01-06-2012, 01:30 AM
When is Moore's law expected to slow or come to a halt?

03-20-2014, 04:52 PM
When is Moore's law expected to slow or come to a halt?

Apparently now! Just as well, SMT soldering is hard enough on these old eyes. Soldering one-atom wire connections might prove even more frustrating.


Loopy Byteloose
03-20-2014, 05:06 PM
You can't get electrons attached to sub-atom particles (they orbit a nucleus), so a one-atom wire is likely the limit.

Of course the size of the nucleus might get a wee bit smaller.

Beau Schwabe
03-20-2014, 05:14 PM
My concern would be with metal migration.... passing DC is one thing but applying a signal to a wire that small would be analogous to fabricating a jump rope out of play-dough. With 'fewer' atoms in the 'rope' it would tend to self-destruct in a shorter amount of time with any electro-mechanical stress either externally induced or electrically induced through the wires themselves.


03-20-2014, 05:21 PM
No worries Erco, We just have to use the transistors we have more efficiently. Doug Burger from MicroSoft has a plan already: http://www.youtube.com/watch?v=dkIuIIp6bl0#t=11

User Name
03-20-2014, 08:51 PM
Doug Burger from MicroSoft has a plan already: http://www.youtube.com/watch?v=dkIuIIp6bl0#t=11

Compelling presentation! I was a bit cynical at the start because the talking head was from MS. But putting that aside, the talk got pretty interesting. Thanks, Heater, for some grist on which to grind.

Still, the best thing MS could do in the short-term is to rewrite Windows from the ground up, and not rely on hardware to supercharge their barge.

User Name
03-20-2014, 09:05 PM
... a one-atom wire is likely the limit.

At cryogenic temperatures perhaps, but at RT one atom is too flaky to be a reliable wire.

03-20-2014, 11:40 PM
I'm not sure "tall" is the correct word, "thick" would be grammatically more correct, but "thin" seems
more appropriate.

Metal migration wouldn't necessarily apply to a non-metal crystal, its a property of irregular grain-boundaries
in polycrystalline metals I believe.

Clock Loop
03-21-2014, 02:27 AM
Funny humans...

http://www.youtube.com/watch?v=3S9oDPGaqpw&feature=player_detailpage#t=6770 (http://www.youtube.com/watch?v=3S9oDPGaqpw&feature=player_detailpage#t=6770)

p.s.s..thereisnoelectron (http://www.thereisnoelectron.com)