Talk-Polywell.org

28 August 2009

Graphene nanoribbons cut power use, cooler than copper

R. Colin Johnson
EE Times
August 3, 2009 (9:52 AM EST)

PORTLAND, Ore. — Graphene could carry nearly 1,000 times more current and operate at temperatures more than 10 times cooler than conventional copper interconnects below 22-nanometer line widths, according to researchers at the Georgia Institute of Technology.

The speed (electron mobility) of graphene has been touted as better than copper, but the Georgia Tech data on nanoribbons as small as 16 nm quantifies just how superior carbon is compated to copper. Graphene nanoribbons tested could carry as much as 10 billion amps/CM, or nearly 1,000 times greater than copper.

"No one had measured graphene's current carrying capacity before this," claimed Raghunath Murali, a senior research engineer in Georgia Tech's Nanotechnology Research Center. "One possible reason that this property of graphene was not touted before is that there were no experimental results until our work."

The superior current-carrying capability of carbon integrated into graphene nanoribbons also showed less heat build up since carbon's thermal conductivity is much higher than copper. Nanoribbons have a thermal conductivity of 1,000-5,000 watts per meter Kelvin--ten times greater than copper. The Georgia Tech researchers also claimed that graphene nanoribbons will mitigate electromigration, a growing problem for copper as line widths descend to the nanoscale.

"If the current carried through a wire is close to the current-carrying capacity of the wire, then the chances of electromigration are greater than if the current in the wire is much smaller than the current-carrying capacity," said Murali. "Graphene has over two orders of magnitude greater capacity than copper, thus, if a graphene wire is compared to a copper wire carrying the same current, then the graphene wire will better resist electromigration."

Three hurdles remain to commercialization of carbon interrconnects, according to the researchers: perfecting methods of growing monolayers of graphene over entire wafers (since only centimeter-sized areas can be easiliy grown in monolayers); fabricating vias to interrconnect graphene nanowires; and integration of carbon into the back-end of the CMOS manufacturing process.

While I'm not positive on this, My Gut (tm) reaction is that graphene won't work for bulk power transport the power lines work. Thinking it through I'd say it's probably the voltages involved. It would run roughshod with that dainty configuration of carbon nuclei. Good for circuit boards, bad for power lines and polywell's.

Professor Science wrote:While I'm not positive on this, My Gut (tm) reaction is that graphene won't work for bulk power transport the power lines work. Thinking it through I'd say it's probably the voltages involved. It would run roughshod with that dainty configuration of carbon nuclei. Good for circuit boards, bad for power lines and polywell's.

I don't know about Polywells, The voltages used to drive the electromagnets only need to be perhaps 10-20 volts (car battery range) with alot of amps. Also, with high conductivity and good heat extraction the conducting wires/ribbons can be much smaller in crossection, which means there could be alot more windings for proportionatly stronger magnetic fields with the same current. A win- win situation. Now if only the graphine actually works near the levels advertised and can be drawn into usefull lengths. The thickness of insulation needed and space for cooling liquid may end up being the limiting factor for the possible turns that can be packed into a given volume.


Dan Tibbets

How does graphene stack up against silver for electrical conductivity, or mono-isotopic diamond for heat ??

Okay, I'm being a tad facetious here, as one is outrageously expensive in industrial quantities, and the other requires nano-g orbital industry...

Nik wrote:How does graphene stack up against silver for electrical conductivity, or mono-isotopic diamond for heat ??

Okay, I'm being a tad facetious here, as one is outrageously expensive in industrial quantities, and the other requires nano-g orbital industry...

The conductivity of silver at room temperature is only slightly greater than copper.
http://www.newworldencyclopedia.org/ent ... nductivity

Incidentally aluminum has a smaller conductivity per unit cross section, but due to its lighter weight it is actually a superior conductor than copper on a weight basis. That is why aluminum alloys are used in power lines (also, probably cheaper).

I don't know the heat conductivity, but I suspect it is similar to diamonds.

Dan Tibbets

Breakthrough in Developing Super-Material Graphene

Until now graphene of sufficient quality has only been produced in the form of small flakes of tiny fractions of a millimeter, using painstaking methods such as peeling layers off graphite crystals with sticky tape. Producing useable electronics requires much larger areas of material to be grown. This project saw researchers, for the first time, produce and successfully operate a large number of electronic devices from a sizable area of graphene layers (approximately 50 mm2).

http://ttp.northwestern.edu/abstracts/v ... 73&cat=179
http://www.youtube.com/watch?v=1cfZ1DQI ... re=related

"We discuss the possibility of a superconducting state in metal coated graphene."

http://nanoscience.bu.edu/papers/Castro ... 202007.pdf

Note how the material in the youtube video curls up after being flashed. Maybe it could be bonded to a metal foil prior to flashing, and if the right foil was used...

Just daydreaming.

Professor Science wrote:While I'm not positive on this, My Gut (tm) reaction is that graphene won't work for bulk power transport the power lines work. Thinking it through I'd say it's probably the voltages involved. It would run roughshod with that dainty configuration of carbon nuclei. Good for circuit boards, bad for power lines and polywell's.

For bulk power carbon nanotubes are about 5X better than copper.

Part of the higher current carrying ability of graphene is due to its higher melting point.

[quote="MSimon"]Part of the higher current carrying ability of graphene is due to its higher melting point.[/quote]

Graphene has another property which makes it a better conductor: electrons lose their mass and move within it at a substantial fraction of the speed of light (10^6 metres per second---only about 300 times slower than the speed of light in a vacuum). In a normal conductor such as copper, electrons move only a few centimeters per second. Electrons in most conductors can be described by non-relativistic quantum mechanics, whereas the electrons in graphene need to be treated as relativistic particles called massless Dirac fermions.

Minor nitpick: that's not 300 times slower, but one 300th of the speed.

Bob Carver wrote:Graphene [...] electrons lose their mass and move within it at a substantial fraction of the speed of light (10^6 metres per second [...]). In a normal conductor such as copper, electrons move only a few centimeters per second.

That would appear to indicate that graphene will provide a greater benefit for DC over AC ? This would seem to be extra useful for direct conversion Polywell.

BenTC wrote:That would appear to indicate that graphene will provide a greater benefit for DC over AC ? This would seem to be extra useful for direct conversion Polywell.

I think so. Another thing to consider is that if a graphene conductor could be made with no defects, it would be a superconductor. The only joule heating in graphene occurs when electrons collide with impurities in the structure. And, this would happen at temperatures far higher than any other superconductor.

BenTC wrote:

Bob Carver wrote:Graphene [...] electrons lose their mass and move within it at a substantial fraction of the speed of light (10^6 metres per second [...]). In a normal conductor such as copper, electrons move only a few centimeters per second.

That would appear to indicate that graphene will provide a greater benefit for DC over AC ? This would seem to be extra useful for direct conversion Polywell.

The first stirrings in that direction are carbon nanotube semiconductors.

http://nanotechweb.org/cws/article/tech/16432

Electron mobility is about 10X of silicon. Which means that a power transistor should be able to run at 10X the speed. And the larger band gap means higher voltages per transistor should be possible. Also higher temperature operation easing cooling problems.

http://www.thaindian.com/newsportal/hea ... 04747.html

Also silicon carbide which is already in production:

http://en.wikipedia.org/wiki/Silicon_ca ... t_elements

http://powerelectronics.com/news/silico ... ansistors/

http://www.aist.go.jp/aist_e/latest_res ... 50407.html

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SiC diodes are quite good with 1200 V 50 A devices available. I haven't seen much re: practical transistors.

http://www.cree.com/products/power_docs2.asp

SiC RF transistors:

http://dkc1.digikey.com/us/en/techzone/ ... z_wireless