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Graphene and Carbon Nanotubes Together Produce a Digital Switch

Hybrid material produces a switch ratio orders of magnitude higher than graphene alone

2 min read
Graphene and Carbon Nanotubes Together Produce a Digital Switch
Illustration: Michigan Technological University

The two darlings of carbon nanomaterials, carbon nanotubes and graphene, increasingly are joining forces even as they are having  their obituaries read while still hardly out of the lab. We’ve seen them being used in hybrid energy storage applications and for supercapacitors.

Now researchers at the Michigan Technological University (MTU) have combined these two nanomaterials to tackle a far more difficult application field: electronics. Specifically, the researchers have created digital switches by making a sandwich of carbon nanotubes and graphene.

The carbon nanotubes in question are of the boron nitride variety, which serve as pretty effective insulators. Strictly speaking, boron nitride is a semiconductor, however, its band gap is so wide it effectively serves as an insulator. The boron nitride nanotubes’ large band gap makes up for the fact that graphene doesn’t have any band gap.

The trick for the researchers was to find a way to bring these two materials together so that their attractive electronic properties could be leveraged in one device that would allow the speedy movement of electrons and then completely shut down that movement.

In research published in the journal Scientific Reports, the MTU researchers exfoliated the graphene and modified its surface so that it was made of small holes. The researchers then coaxed the carbon nanotubes to grow out of these holes.

“When we put these two aliens together, we create something better,” said Yoke Khin Yap, a professor at MTU, in a press release. “When we put them together, you form a band gap mismatch—that creates a so-called ‘potential barrier’ that stops electrons.”

The electrons are able to move smoothly along the graphene but when they come up to the hair-like sprouts of boron nitride carbon nanotubes they are slowed way down. It is at these points of where the graphene meets the carbon nanotubes, known as heterojunctions, that digital switches are made possible.

“Imagine the electrons are like cars driving across a smooth track,” Yap said in the release. “They circle around and around, but then they come to a staircase and are forced to stop.”

The researchers claim that the switch ratio—how fast the material can turn on and off the flow of electrons—is very high, measuring several orders of magnitude faster than current graphene switches.

In addition to having a relatively high switch ratio compared to current graphene switches, the hybrid material also avoids the issue of electron scattering in which electrons are dispersed in directions you don’t want them to go. The hybrid material gets around this issue because the two materials that make it up have the same atomic arrangement pattern.

“You want to control the direction of the electrons,” Yap added. “This is difficult in high speed environments, and the electron scattering reduces the number and speed of electrons.”

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3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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