28-09-2018 | | By Rob Coppinger
A heat sink more than three times better than copper could be commercially available in a couple of years after engineers found a way to make the semiconductor boron-arsenide virtually defect free.
Researchers are speaking to potential commercial partners for commercialising the boron-arsenide and examining how to scale up manufacture now centimetre sized wafers can be produced in the laboratory. Copper and silicon carbide are often used as heat sinks, but boron-arsenide offers a thermal conductivity more than three times better with a heat flow rate to its surface of 1,300 Watts per metre-Kelvin. But, it is not any old boron-arsenide that has this thermal conductivity rate, its internal crystalline structure must be virtually defect free.
“This material is not that common in nature, so we need to use chemical process to synthesise it, so we spent time testing the different conditions, temperature and pressure,” says Yongjie Hu, an assistant professor of mechanical and aerospace engineering at University of California Los Angeles (UCLA). This could potentially revolutionize thermal management designs for computer processors and other electronics, or for light-based devices like light emitting diodes.
Illustration showing a schematic of a computer chip with a hotspot (bottom); an electron microscope image of defect-free boron arsenide (middle); and an image showing electron diffraction patterns in boron arsenide.
Credit: Hu Research Lab/UCLA Samueli
Boron-arsenide without careful control of the synthesis process can have a conductivity rate as low as 200 Watts per metre-Kelvin. Hu and his team have worked on this material for three years. During the first 18 months they were able to steadily raise the conductivity up to 1,300 through a very careful control of all the factors in the manufacturing process, such as temperature gradient flow. “For thermal conductivity any kind of defect or imperfection of the crystal lattice will destroy the thermal conductivity and reduce the numbers [of Watts per metre-Kelvin,” says Hu.
This initially was a disappointment as the theoretical prediction for boron-arsenide more than 2,000 Watts per metre-Kelvin. This led Hu and his team to spend a year trying to get the conductivity up to 2,000 Watts, but 1,300 was the most they could achieve. Theoretical papers since that first born-arsenide prediction have revised down the maximum conductivity of a structural defect free boron-arsenide to 1,300. “We don’t claim 100% zero defects,” adds Hu, “but from the macroscopic properties it looks like we have no defects.”
As boron-arsenide is a semiconductor, Hu expects that it can be more easily integrated into existing electronics manufacturing processes. “Maybe a couple of years it could be used in commercial applications if everything goes smoothly,” he says. The first product could be a very small heat sink for hot spots on microchips or something larger providing the sort of circuit board-wide relief from the build-up of heat.
The research was funded by the United States government’s National Science Foundation, the US Air Force Office of Scientific Research, the American Chemical Society’s Petroleum Research Fund, UCLA’s Sustainable LA Grand Challenge, and the Anthony and Jeanne Pritzker Family Foundation.
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