Engineers find a simple yet clever way to boost chip speeds

Phys.Org ^ | 06-17-2015 | Provided by Stanford University

[Red Badger]

A typical computer chip includes millions of transistors connected with an extensive network of copper wires. Although chip wires are unimaginably short and thin compared to household wires both have one thing in common: in each case the copper is wrapped within a protective sheath.

For years a material called tantalum nitride has formed protective layer in chip wires.

Now Stanford-led experiments demonstrate that a different sheathing material, graphene, can help electrons scoot through tiny copper wires in chips more quickly.

Graphene is a single layer of carbon atoms arranged in a strong yet thin lattice. Stanford electrical engineer H.-S. Philip Wong says this modest fix, using graphene to wrap wires, could allow transistors to exchange data faster than is currently possible. And the advantages of using graphene would become greater in the future as transistors continue to shrink.

"Researchers have made tremendous advances on all of the other components in chips but recently, there hasn't been much progress on improving the performance of the wires," he said.

Wong led a team of six researchers, including two from the University of Wisconsin-Madison, who will present their findings at the Symposia of VLSI Technology and Circuits in Kyoto, a leading venue for the electronics industry.

Ling Li, a graduate student in electrical engineering at Stanford and first author of the research paper, explained why changing the exterior wrapper on connecting wires can have such a big impact on chip performance.

It begins with understanding the dual role of this protective layer: it isolates the copper from the silicon on the chip and also serve to conduct electricity.

On silicon chips, the transistors act like tiny gates to switch electrons on or off. That switching function is how transistors process data.

The copper wires between the transistors transport this data once it is processed.

The isolating material—currently tantalum nitride—keeps the copper from migrating into the silicon transistors and rendering them non-functional.

Why switch to graphene?

Two reasons, starting with the ceaseless desire to keep making electronic components smaller.

When the Stanford team used the thinnest possible layer of tantalum nitride needed to perform this isolating function, they found that the industry-standard was eight times thicker than the graphene layer that did the same work.

Graphene had a second advantage as a protective sheathing and here it's important to differentiate how this outer layer functions in chip wires versus a household wires.

In house wires the outer layer insulates the copper to prevent electrocution or fires.

In a chip the layer around the wires is a barrier to prevent copper atoms from infiltrating the silicon. Were that to happen the transistors would cease to function. So the protective layer isolates the copper from the silicon

The Stanford experiment showed that graphene could perform this isolating role while also serving as an auxiliary conductor of electrons. Its lattice structure allows electrons to leap from carbon atom to carbon atom straight down the wire, while effectively containing the copper atoms within the copper wire.

These benefits—the thinness of the graphene layer and its dual role as isolator and auxiliary conductor—allow this new wire technology to carry more data between transistors, speeding up overall chip performance in the process.

In today's chips the benefits are modest; a graphene isolator would boost wire speeds from four percent to 17 percent, depending on the length of the wire.

But as transistors and wires continue to shrink in size, the benefits of the ultrathin yet conductive graphene isolator become greater. The Stanford engineers estimate that their technology could increase wire speeds by 30 percent in the next two generations

The Stanford researchers think the promise of faster computing will induce other researchers to get interested in wires, and help to overcome some of the hurdles needed to take this proof of principle into common practice.

This would include techniques to grow graphene, especially growing it directly onto wires while chips are being mass-produced. In addition to his University of Wisconsin collaborator Professor Michael Arnold, Wong cited Purdue University Professor Zhihong Chen. Wong noted that the idea of using graphene as an isolator was inspired by Cornell University Professor Paul McEuen and his pioneering research on the basic properties of this marvelous material. Alexander Balandin of the University of California-Riverside has also made contributions to using graphene in chips.

"Graphene has been promised to benefit the electronics industry for a long time, and using it as a copper barrier is perhaps the first realization of this promise," Wong said.

Scanning tunnelling microscopy (STM) image of graphene on Ir(111). The image size is 15 nm × 15 nm. Credit: ESRF

[HandyDandy]

Red Badger explained above that it is the two conductors (copper and graphene) in parallel that reduce the resistance and hence provide the benefit of more speed. I still don’t get how you can use a conductive sheathing and not damage the silicone and yet be isolated from the silicone. I do know that the “magic property” of the material gortex is that it allows perspiration droplets to escape, but does not allow water-sized droplets to penetrate. So, you stay warm AND dry. Perhaps graphene works somewhat like that.

[az_gila]

Sounds promising. If it really is a revolutionary technology then the environmentalists will need to start their demonization campaign right away.

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“Graphene is a single layer of carbon atoms arranged in a strong yet thin lattice”

Have the researchers work on a way to get the carbon atoms out of CO2 and they can get all the money they want for research.

In practice, it doesn't matter how much energy it will take to convert that CO2 used as an input since the greenies never look at the big picture...:^)

[T-Bone Texan]

It saddens me that whenever I see news about cutting edge developments like this, it's always a foreigner doing the work. We used to be so awesome - as a people, and as a culture.

Now we just provide an environment for other people to be awesome, and that's just sad.

[Spaulding]

I expect that you are on the right track Red Badger. The solid state physicists at FR are probably too busy designing to weigh in, but there are likely many issues at work, and probably being considered by semiconductor designers before this Graphene layer can become deployed. My guess, given that the performance number given is about 30%, that this is another design rules shrink. Shrinking design rules are constrained by interconnect limitations. The “wires” inside a processor with over 1 1/2 billion transistors, and probably double that number of simple gates, is enormous, probably over 40 billion. The delay through the wires connecting all those devices limits frequencies, since 64 bit registers must have 64 bits all loaded before those registers can be read. When data arrive irregularly it is called “skew”. I’m guessing that Graphene is more important for its thinness and to minimize contamination, since the silicon substrate is an insulator unless it is “contaminated”, accidentally, or intentionally, as in “doped”, the process used to create semiconductors.

Perhaps we have an expert who can correct me or illuminate the issue? Few understand what a wonder our semiconductors are. To add what little else I have encountered measuring electrical signals, the dielectric constant of the insulator has a significant effect upon the velocity of electrical signals through a conductor. We used to estimate electrical pulse velocity at 7 inches/nanoseconds or about 60% of the velocity of light in a vacuum. Today’s semiconductors behave like waveguides, only they are built of millions of waveguides, yes, radio frequencies. These waveguides behave just like those pipes inside radar transmitters and receivers, but carry much less power. If they didn’t, a 4 Gigahertz processor couldn’t work since there would be no way to pass bits between logical units, or even to differentiate ones from zeros.

[tophat9000]

If the graphite is an auxiliary conductor.. resistance should be lower in the wire.. so less heat and less power used also...so win,win

[Herosmith]

With the faster speed, wouldn’t this also make more heat? So with one enhancement, we may have created another problem.

[mbj]

https://en.wikipedia.org/wiki/Graphene

[Lurkina.n.Learnin]

The title makes it sound a lot simpler than I think it would be.

[Red Badger]

Not really, considering the processes involved are not ‘new’ to the industry....................

[Red Badger]

Not necessarily so, since the graphene makes the connections less resistance, so less heat generated.........................

[Red Badger]

We’ll ask one..................

[Red Badger]

Now we just provide an environment for other people to be awesome..........

That's what we've always done, since 1776!......................

[novemberslady]

bkmk

[Red Badger]

I’m guessing that Graphene is more important for its thinness and to minimize contamination, since the silicon substrate is an insulator unless it is “contaminated”, accidentally, or intentionally, as in “doped”, the process used to create semiconductors.

The Stanford experiment showed that graphene could perform this isolating role while also serving as an auxiliary conductor of electrons. Its lattice structure allows electrons to leap from carbon atom to carbon atom straight down the wire, while effectively containing the copper atoms within the copper wire.

I'm guessing that the copper 'wires' are functioning really like just a skeletal substructure to hold the graphene's carbon atoms in place. The graphene is really the true conductor, while the copper fills in any 'holes' that may be present in the graphene. With copper atoms being larger than carbon atoms, they cannot migrate thru the holes into the silicon.......................