Boron arsenide whisks heat away from electronics

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September 05, 2018

By Sally Cole, Senior Editor

Move over, silicon: Defect-free boron arsenide offers far superior thermal conductivity than other semiconductors and metals, including silicon and copper.

If you haven’t heard of boron arsenide (BAs) yet, you will soon: It’s a new semiconductor “wonder” material that can draw and dissipate waste heat from electronics more effectively than any other known semiconductor or metal materials.

Boron arsenide isn’t a naturally occurring material, so scientists synthesize it within the lab. The material requires a very specific defect-free structure and low density to achieve peak thermal activity, so crystals of it need to be grown in a strictly controlled way.

Defect-free boron arsenide was made for the first time by a team of University of California, Los Angeles (UCLA) engineers, led by Yongjie Hu, an assistant professor of mechanical and aerospace engineering. The material boasts a thermal conductivity that’s more than three times faster at conducting heat than currently used materials such as silicon and copper. Its most promising superpower is that heat that tends to concentrate in hot spots in computer chips instead gets quickly flushed away with boron arsenide. (Figure 1.)

 

Figure 1: This schematic shows a computer chip with a hot spot (bottom), an electron-microscope image of defect-free boron arsenide (middle), and an image showing diffraction patterns in boron arsenide (top). Credit: Hu Research Lab/UCLA Samueli.

This feature is highly desirable, because high-power electronics must remain cool to operate reliably. Materials with high thermal conductivity are necessary to serve as substrates in high-power electronics, because without them the internal temperatures of these devices crank up and can cause programs to run slower, freeze up, or even shut down.

The way the boron arsenide actually dissipates heat is linked to the crystal’s vibrations. This motion creates packets of energy called phonons, which whisk heat away from the crystal.

Boron arsenide “could help greatly improve performance and reduce energy demand in all kinds of electronics, from small devices to the most advanced computer data center equipment,” Hu says. “It has excellent potential to be integrated into current manufacturing processes because of its semiconductor properties and the demonstrated capability to scale up this technology. It could replace current state-of-the-art semiconductor materials for computers and revolutionize the electronics industry.”

The material has the potential to revolutionize thermal-management designs for computer processors and other electronics, or for light-based devices such as light-emitting diodes (LEDs), according to Hu and his graduate students Joonsang Kang, Man Li, Huan Wu, and Huuduy Nguyen; this team has spent years designing and making the materials, as well as doing predictive modeling and taking precision temperature measurements.

As computer processors continue to shrink down to nanometer sizes, it’s not uncommon now to see billions of transistors on single chip. While each smaller generation of chips helps to speed up computers, as well as making them more powerful and capable of doing more work, it also means that the chips are generating more heat.

Today, most high-performance computer chips and high-power electronic devices are made of silicon, a crystalline semiconductor that does a good job of dissipating heat. But even silicon can handle only so much heat.

Diamond still holds the title of the highest known thermal conductivity – about 15 times that of silicon – but it has issues when it comes to thermal management of electronics: It’s super-expensive, and it also happens to be an electrical insulator. When paired with a semiconductor device, diamond expands at a different rate than the device does when it heats up, which is less than desirable.

Beyond its impact on electronic and photonics devices, the UCLA team’s work has also revealed new fundamental insights into the physics of how heat flows through materials.

The work was funded by the National Science Foundation, the 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.

Other researchers around the globe are also currently exploring boron arsenide crystals and announcing advances. A group of researchers from the University of Texas at Dallas and the University of Illinois at Urbana-Champaign recently grew boron arsenide crystals with a thermal conductivity in excess of 1,000 watts per meter-kelvin at room temperature (compared to copper’s 400 watts and diamond’s 2,000 watts) via chemical vapor transport. They’re now working on other processes to improve the growth and properties of the material for large-scale applications.