The inner workings of high-power electronic devices must remain cool to operate reliably. High internal temperatures can make programs run slower, freeze, or shut down. To address this issue, researchers have optimized the crystal-growing process of boron arsenide — a material that has excellent thermal properties and can effectively dissipate the heat generated in electronic devices.
The result of this optimization marks the realization of a previously predicted class of ultra-high-thermal-conductivity materials. Boron arsenide is not a naturally occurring material, so it must be synthesized in the lab. It also needs to have a very specific structure and low defect density for it to have peak thermal conductivity, so its growth happens in a very controlled way.
Most of today's high-performance computer chips and high-power electronic devices are made of silicon, a crystalline semiconducting material that does an adequate job of dissipating heat. But in combination with other cooling technology incorporated into devices, silicon can handle only so much. Diamond has the highest known thermal conductivity — about 15 times that of silicon — but there are problems when it comes to using it for thermal management of electronics. The cost of natural diamonds and structural defects in man-made diamond films make the material impractical for widespread use in electronics.
The boron arsenide crystals were synthesized using a technique called chemical vapor transport. Elemental boron and arsenic are combined while in the vapor phase, and then cool and condense into small crystals. Materials characterization and trial-and-error synthesis were combined to find the conditions that produce crystals of high enough quality.
Electron microscopy and a technique called time-domain thermoreflectance were used to determine if the lab-grown crystals were free of the types of defects that cause a reduction in thermal conductivity.
Dozens of the boron arsenide crystals were tested. It was found that the thermal conductivity of the material can be three times higher than that of the best materials being used as heat spreaders today.