Overheating electrical components is one of the main causes of failure in electronic hardware, and is quickly becoming one of the leading causes of failure in modern mobile devices. While some of the overheating issues are caused by faulty components, the issue is mostly attributed to improper heat displacement and the lack of adequate heat shielding. Often times, engineers will place small aluminum heatsinks and shielding plates on the more egregious thermal offenders and will use air-gaps, cardboard, glass, and plastic to insulate large sections of the design from other heat-producing components like microprocessors, voltage regulators, and memory chips. However, the current reality is that some components are too small to properly shield on an individual basis, but things could be looking up thanks to new research.
A team of engineers at Stanford University have successfully proven that incredibly thin layers of materials, just two to three nanometers thick, could successfully insulate heat-sensitive components with the same level of protection as previous methods using materials 100-times thicker. This is significant because it has become increasingly harder to protect heat-sensitive components as their footprints continue to shrink. In a recently published paper, the researchers unveiled how some outside of the box thinking leads to this new discovery.
This greatly magnified image shows four layers of atomically thin materials that form a heat-shield just two to three nanometers thick, or roughly 50,000 times thinner than a sheet of paper.
Image credit: National Institute of Standards and Technology
Instead of thinking about the heat in the traditional manner, the researchers began thinking about heat as a form of sound. When electrons flow through a conductor, they bounce and rub against its atoms, causing tiny vibrations. As more and more electrons flow past those atoms, the atoms begin to vibrate more vigorously. As well all know from grade school physics when atoms vibrate, they produce tiny soundwaves that are able to propagate through solid materials and create what we perceive as “heat.” If you want to prevent that heat from radiating any further, you have to insulate it with a material that does not transmit these vibrations very well.
Eric Pop, Senior Professor of Electrical Engineering at Stanford took a bit of knowledge from his past as the DJ at Stanford’s KZSU 90.1 FM radio station. While working there as a student, he noted that the sound booths and recording studios utilized thick panes of glass to prevent any sound from escaping. However, designing thick panes of insulating glass into mobile phones is both physically and financially impractical, so his team decided to take a queue from another sound-proofing obsessed industry: construction. You see, most modern windows feature an air-gap that is sandwiched between two panes of glass. The air-gap layer is just that, an airgap, although it is often filled with an inert gas to prevent condensation on the inside of the glass panes. This layer prevents sound and heat energy from passing through from one pane to the other.
Pop’s team realized that they could utilize atomically thin layers of metal separated by very thin airgaps to recreate the same effect at a microscopic level. Up until just under two decades ago, air-gap insulators at this scale were just not possible as no one had yet developed methods to make such thin materials. The insulator that the research team came up with was comprised of just four layers, each about three atoms thick. When combined the total thickness is just over 10-atoms, hundreds of times thinner than anything prior. The layers of material, act as barriers that the sound must pass through, thus reducing the soundwave’s energy each time it passes through a new layer. Think of it as the WiFi in your home. If you have a direct line of sight with the wireless router’s antenna, the signal your device receives is strong. As that signal passes through the walls of your home, it weakens with each subsequent wall it has to pass through. By the time you are outside of your home and several walls later, the signal is very weak, or non-existant altogether.
“We adapted that idea by creating an insulator that used several layers of atomically thin materials instead of a thick mass of glass,” said postdoctoral scholar Sam Vaziri, the lead author on the paper.
“As engineers, we know quite a lot about how to control electricity, and we’re getting better with light, but we’re just starting to understand how to manipulate the high-frequency sound that manifests itself as heat at the atomic scale,” Pop said.
At the moment, mass production of insulators at such a small scale is simply impractical, and new methods have to be developed to reliably produce sheet materials at the atomic level while remaining cost-effective. For now, engineers will continue to study how to effectively control these micro sound waves and hope to one day be able to control and manipulate them much in the same ways we currently can manipulate electricity, and light. In the meantime, this new field of phononics will continue to grow as more research is done.