New "Leakage-Free" Nanotube, Quantum Dot Transistor Uses No Semiconductors
June 25, 2013 3:30 PM
comment(s) - last by
Device operates at room temperature; feature with is currently 20 nm, could be shrunk smaller
Michigan Technological University
(Michigan Tech/MTU) physics professor
Yoke Khin Yap
is concerned that the
current route of semiconductor development
extending Moore's Law
[press release], "At the rate the current technology is progressing, in 10 or 20 years, they won’t be able to get any smaller. Also, semiconductors have another disadvantage: they waste a lot of energy in the form of heat."
He believed the solution to this challenge lay in
new, novel materials
He began testing designs using
tiny globs of metal called "quantum dots" (QDs)
sprinkled on a nanoinsulator. For the insulator substrate he chose boron nitride
, known as BNNTs. For the quantum dots he used gold, an ideal material for making regular, precisely-sized QDs.
The team needed a way to position the dots in atomic space on the nanotube, so they turned to using a laser. Using this method, they were able to positions gold QDs that were a mere 3 nanometers in diameter -- or roughly 1/7th the size of transistors produced at current circuit manufacturing nodes.
An artist's rendering of the nanotube transistor [Image Source: MTU]
Testing the design in collaboration with
Oak Ridge National Laboratory
(ORNL), they hooked an electrode up to each end of the construct and tested it at room temperature. They observed quantum tunneling -- the hallmark phenomena necessary to construct a non-semiconductor transistor. Electrons "jump" (or tunnel) from one gold QD to the next, as current is applied.
The researchers were able to control the voltage to switch this conduction on and off, forming a transistor. Professor Yap describes, "Imagine that the nanotubes are a river, with an electrode on each bank. Now imagine some very tiny stepping stones across the river. The electrons hopped between the gold stepping stones. The stones are so small, you can only get one electron on the stone at a time. Every electron is passing the same way, so the device is always stable."
Past transistors made from materials other than semiconductor typically had to be cooled with liquid helium to operate well; by contrast Professor Yap's design performs well at room temperature.
Currently each nanotube is 1 micron long and 20 nm wide -- making these transistors on par with current designs. But the researchers expect these transistors to scale better than semiconductor sizes as tube diameter and lengths are shrunk. The team already has
to deposit aligned substrate "carpets" so now all that remains is developing methods to mass-position the nanodots (as individual laser positioning is prohibitively slow for making the billions of transistors in a modern IC).
Electron micrographs of nanotube "carpets" grown by Prof. Yap's team back in 2011.
[Image Source: MTU]
Professor Yap, who has filed for a patent on the design and manufacturing process, comments, "Theoretically, these tunneling channels can be miniaturized into virtually zero dimension when the distance between electrodes is reduced to a small fraction of a micron."
The best feature of the transistors is that there's no electrons (according to the authors) lost between gold nanodot and no gold nanodot -- a heat generating phenomena known as "leakage". By contrast,
leakage is a massive problem
for nanoscale silicon-based transistors, limiting clock speeds and circuit density.
In addition to the patent his work was
[abstract] in a peer-reviewed journal article in the
journal from publisher Wiley.
Advanced Materials [abstract]
MTU [press release]
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RE: HEat is one issue...
6/25/2013 6:13:58 PM
you're mixing up things there a bit
electromigration - transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms.
so the metal in the conductor traces and stuff moves about beacause of high current densities, causing open circuits and/or shorts (the redeposited metal forms hillocks and stuff that can make contact with nearby traces or physically crack things open). And as things get smaller the current densities tend to go up, and of course a lot less metal needs to be moved for the trace to fail.
what you're talking about sounds more like tunneling. :)
RE: HEat is one issue...
6/25/2013 9:16:47 PM
No, although the 2 terms are similar, they're very different. Electromigration, as you've noted, is actually a change in the material itself - grossly, like you broke a chunk of silicon off and moved it around inside the semiconductor.
Electron migration in general refers to the movement of electrons from one location to another, based on understood particle physics. In and of itself, "electron migration" isn't a bad thing (and actually, generally speaking, is a good thing...electrically speaking)...and perhaps I should have been more clear originally, but with reference to semiconductor designs, "electron migration" is brought up as a problem in that the electrons find places to migrate to that you didn't intend for them to go.
RE: HEat is one issue...
6/26/2013 8:11:23 AM
Electromigration is movement of atoms caused by momentum of transfer of electrons(current and wind force). I don't normally hear people use electron migration, they prefer using "current".
RE: HEat is one issue...
6/26/2013 11:08:44 AM
If you google up the term, you find many papers where the phrase is used, especially in relation to semicondutors.
While technically the same thing, "electron migration" seems to get used when you're trying to refer to a singular movement of an electron in a specific instance, as opposed to "current" which of course is the intended large-scale flow of electrons through a given conductive material.
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