Manufacturing Bits: Oct. 11

Space elevators; diamond power semis; more 5G.


Space elevators
Last year, Pennsylvania State University disclosed a technology called benzene-derived carbon nanothreads or sometimes called diamond nanothreads (DNTs).

DNTs resemble carbon nanotubes. They are tiny hollow cylindrical tubes that are stronger than steel, but they are also brittle. Basically, DNTs are 1D structures with poly-benzene sections, which are connected by Stone–Wales (SW) transformation defects, according to Queensland University of Technology (QUT).

Now, QUT is exploring DNTs in an effort to find uses for the technology. Combined with other materials, DNTs could be used to make ultra-strong, light-weight composites and components, such as plane fuselages. As a two-dimensional technology, DNTs could be used in flexible electronics. And in the distant future, DNTs might be the best candidate for use in building space elevators.

In a simulation test, researchers from QUT found that bonded DNT can transition from a brittle to a ductile behavior. This is done by varying the length of the poly-benzene sections, according to researchers. All told, DNTs have different mechanical responses, as compared to other 1D carbon allotropes, according to researchers.

The key to DNTs are the SW defects. The defects behave like grain boundary structures. They interrupt with the consistency of the poly-benzene sections. “DNT, by comparison (to carbon nanotubes), is even thinner, incorporating kinks of hydrogen in the carbon’s hollow structure, called Stone-Wale (SW) transformation defects, which I’ve discovered reduces brittleness and adds flexibility,” said Haifei Zhan from QUT’s School of Chemistry, Physics and Mechanical Engineering.

“The SW defects give DNT a flexibility that rigid carbon nanotubes can’t replicate – think of it as the difference between sewing with uncooked spaghetti and cooked spaghetti,” Zhan said. “My simulations have shown that the SW defects act like hinges, connecting straight sections of DNT. And by changing the spacing of those defects, we can change – or tune – the flexibility of the DNT.”

There are some near- and far-term apps for the technology. “There’s already talk in the global carbon community of DNT being the best candidate yet for building a space elevator,” Zhan said.

A space elevator, a proposed space transportation system, would consist of a cable. It would be anchored to the surface and extending into space. “A space elevator (SE) can be thought of as a vertical railroad into space. A cable (tether) stretches from the ground to a counterweight 100,000 km up/out in space. Elevator cars (climbers), powered by electricity travel up and down the tether and carry cargo and eventually humans to and from space,” according to the International Space Elevator Consortium (ISEC), which promotes the development, construction and operation of a space elevator.

However, many say it’s nearly impossible to build futuristic space elevators with today’s material.

A space elevator. Climbers carry cargo up and down the cable. (Source: Wikipedia)

A space elevator. Climbers carry cargo up and down the cable. (Source: Wikipedia)

Diamond power semis
Power semiconductors are used in the field of power electronics.

The mainstream technology is silicon-based MOSFETs and IGBTs. But two wide-bandgap materials—gallium nitride (GaN) and silicon carbide (SiC)—are moving into the sector. GaN-based power semis are capable of handling high voltages with more power density. But heat can build up on tiny areas of the device, creating several hotspots.

Singapore’s A*STAR Institute of Microelectronics has found a solution. A layer of diamond can be implemented on a GaN-based power device. It can spread the heat and improve the thermal performance.

Researchers created a GaN-based test chip. It had eight tiny hotspots, each 0.45 by 0.3 millimeters. Then, they fabricated a layer of diamond using chemical vapor deposition (CVD). The diamond heat spreader and test chip were bonded. The device was then connected to a microcooler, “a device consisting of a series of micrometer-wide channels and a micro-jet impingement array,” according to researchers.

A test sample comprised of a thermal chip, a heat spreader and a microcooler (Source: A*STAR)

A test sample comprised of a thermal chip, a heat spreader and a microcooler (Source: A*STAR)

Researchers exposed the device with 10 to 120 Watts of power. The device maintained its structure at 160 degrees Celsius. In total, the maximum chip temperature was 27.3% lower than another device using copper as the heat spreading layer.

“We next hope to develop a novel micro-fluid cooler of higher and more uniform cooling capability, and to achieve thermal management using a diamond layer of high thermal conductivity near an electronic gate,” said Yong Han from the A*STAR Institute of Microelectronics, on the organization’s Web site.

More 5G
Leti, an institute of CEA Tech, and the Institute for Information Industry of Taiwan (III) announced an agreement for mutual exploration of a wide range of information and communications technology related to the Internet of Things (IoT) and 5G wireless connectivity.

The five-year collaboration will include, but is not limited to, joint development and implementation of IoT and 5G based Smart ICT solutions for the EU and Taiwan, and scientific information exchanges. Also envisioned are cross-invitations to scientific events, joint implementation of international collaborative projects and partnerships, and work on experimental platforms and test beds that can be used to provide real-world validation of solutions.

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