Manufacturing Bits: Sept. 24

LEGO AFM; graphene interconnects; nanotube forests.

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LEGO AFM
Students from the University College London (UCL), Tsinghua University and Peking University have built an atomic force microscope (AFM) or nanoscope using toy LEGOs.

The AFM, dubbed LEGO2NANO, costs less than $500 to make. In contrast, traditional AFMs cost $100,000 or more. The system was made using LEGOs, Arduino controllers, 3D printed parts and consumer electronics.

Source: UCL

Source: UCL

Arduino is an open-source electronics prototyping platform. The most expensive part of the nanoscope are the piezo actuators. With the system, students were able to demonstrate scanning functionality of the AFM in five days.

Now, the goal is to improve the nanoscale resolution of the system. “Low-cost scientific instrumentation is not just useful in high-schools, it can be a huge enabler for hospitals and clinics in developing countries, too,” said Gabriel Aeppli, director of the London Centre for Nanotechnology at UCL, on the university’s Web site. “That’s why novel initiatives like LEGO2NANO are so important.”

Graphene Interconnects
The National Institute of Advanced Industrial Science and Technology (AIST) has developed a new manufacturing technique that will enable multi-layer graphene for interconnect applications.

Today, copper is used for the interconnect in chips. But copper interconnects—the tiny wiring schemes in devices—are becoming more compact at each node, causing an alarming increase in the resistance-capacitance (RC) delay.

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In the future, there are a number of technologies that could replace copper. One technology, graphene, has higher current density and lower resistivity than copper, according to AIST. But the ability to produce multi-layer graphene for the interconnect remains a challenge.

Graphene is produced through the exfoliation of graphite crystals. In AIST’s approach, the production of multi-layer graphene is handled by a chemical vapor deposition (CVD) method using a cobalt epitaxial film as a catalyst.

First, researchers synthesized multi-layer graphene on a sapphire substrate using CVD. The source gas is methane diluted with argon and hydrogen. The catalyst is a cobalt film using a sputtering method. The graphene synthesis temperature is about 1,000° C.

The multi-layer graphene was then transferred onto a silicon substrate. The substrate had an oxide film. The interconnect was made using a typical semiconductor process. With the technology, researchers have achieved the same order of resistivity (9.1 µΩ cm) as that of copper. The resistivity is about one order of magnitude smaller using the conventional CVD method, according to researchers.

Nanotube Forests
Cambridge University claims to have grown the world’s densest array of carbon nanotubes. Researchers have developed a technique that can grow “nanotube forests,” which are five times denser than previous methods, according to the Nanowerk Web site.

Nanotube forests can be used for electronic interconnects and thermal interface materials, according to researchers.

Researchers grew high-density carbon nanotube forests at 450° C on a titanium-coated copper surface. It was also coated using cobalt and molybdenum, which served as the co-catalysts.

In the lab, X-ray photoelectron spectroscopy revealed that molybdenum interacts with titanium and cobalt. This suppressed both the aggregation and lifting off of the cobalt particles, according to researchers.

This, in turn, is the main growth mechanism for the nanotube forest. The forests average a height of 0.38μm and a mass density of 1.6 g cm−3. The forests and copper supports show ohmic conductivity (lowest resistance ∼22 kΩ), according to researchers.

“In microelectronics, this approach to growing high-density carbon nanotube forests on conductors can potentially replace and outperform the current copper-based interconnects in a future generation of devices,” said Cambridge researcher Hisashi Sugime, on the Nanowerk Web site.

—Mark LaPedus