Stanford University professor Eric Pop learned a valuable electronics lesson outside of the lab – and inside a DJ booth.

Years before Pop's current gig of training students and leading research in the field of nanotechnology and energy-efficient transistors, the instructor was taking the airwaves at Stanford’s KZSU 90.1 FM.

Pop would talk tunes and play the hits from behind the university studio's thick glass windows. Now, as a radio host-turned-electronics expert, the Stanford researcher thought to use the same sound-proofing principle to cool down electronics.

Pop's team, which included postdoctoral scholar Sam Vaziri, created a super-thin heat shield. The 10-atom-thick material has the potential to protect the temperature-sensitive components of cell phones, laptops, and other gadgets.

"Just like sound, heat is vibrational motion of atoms in materials, but with much higher frequency than sound waves," Vaziri told Tech Briefs.

A New Way of Looking at Heat in Electronics

An electronic device's microprocessor generates plenty of heat. To address the excess temperature, engineers often insulate the part with glass, plastic, or even layers of air.

Researchers have worked to create better heat shields, but a simple "DJ-booth" approach of adding thicker material is not sufficient when many electronics builders want their devices to be smaller, not larger.

Borrowing from a homeowner trick, the Stanford idea is a bit like a multi-paned window, which keeps interiors warmer and quieter by layering air between varying sheets of glass.

The university researchers have shown that a few layers of atomically thin materials, stacked like sheets of paper atop hot spots, can provide the same insulation as a sheet of glass 100 times thicker.

Vaziri and Pop used a layer of graphene and three other sheet-like materials – each three atoms thick – to create a four-layered insulator just 10 atoms deep. Despite the insulator's thinness, the atomic heat vibrations are dampened and lose much of their energy as they pass through each layer.

Topography and SThM thermal maps of graphene (A,B), Gr/MoS2 (C,D), Gr/WSe2 (E,F), and Gr/MoS2/WSe2 (G,H) heterostructures, respectively. These samples were capped with 15 nm of Al2O3 to electrically isolate the thermal probe from the sample when biasing the device. The thermal maps reveal homogenous heating across the channel for the different heterostructures studied with no visible hot spots associated to the multilayer islands. (Image/Caption Credit: Science Advances)

Before nanoscale heat shields find a place in your iPhone, however, the researchers will have to find a way to mass-produce them – perhaps by spraying or depositing the atom-thin layers of materials onto the electronic components during manufacturing; the work is ongoing.

Thinner heat shields, the team hopes, will enable engineers to make electronic devices even more compact than those we have today. In an interview below, Sam Vaziri tells Tech Briefs about his team's sound approach to electronics.

Tech Briefs: In your press release, Professor Pop said, "We’re looking at the heat in electronic devices in an entirely new way." How are you looking at heat in an entirely new way?

Sam Vaziri: Devices such as cell phones and laptops contain high-density electronic components and compact geometries that dissipate large amount of heat in extremely short time scales. This makes the devices hot, which can result in malfunctions in electronic systems.

Considering the trend of electronic miniaturization, this has become a serious design and practical problem. To control the excess heat (or to block or route it), we need nanoscale thermal components to be utilized the same way that we control electricity and light. Such devices do not yet exist because thermal engineering is not as advanced as electronic or optical engineering. Here is how we look at the problem:

Just like sound, heat is vibrational motion of atoms in materials, but with much higher frequency than sound waves. We use quantum mechanical laws to understand the behavior of electrons and, consequently, electronic transport in materials. Electrons carry the elementary electric charge. Similarly, a phonon is the elementary unit (quantum) of atomic vibrations responsible for heat transport.

To control heat (or manipulate phonon transport), we need to design materials atom by atom. This is exactly what we did in this work, with our bottom-up approach of stacking two-dimensional materials layer by layer to achieve engineered thermal properties.

Tech Briefs: In an electronics application, where is this material placed?

Sam Vaziri: This depends on the specific application. This material (or engineering method) can be applied on hot spots, such as on top of CPUs, to isolate the heat, in one direction, and route it away to prevent damaging the surrounding electronics, such as lithium batteries. This method can be also used in micro-and nanoscales to do thermal management within high-density electronics such as CPUs or in energy harvesting modules.

Tech Briefs: How would you characterize the production process? Will it be complicated to produce these shields on a mass scale?

Sam Vaziri: To overcome the challenge of mass-scale production, we will need some technology development. Possible schemes would be automated large area material transfer, sequential material growth on top of one another, inkjet printing, and spray-coating.

Tech Briefs: What’s next regarding this research?

Sam Vaziri: There are several research topics we are pursuing that are related to this work:

  1. Investigating the fundamentally possible methods to scale up the production of these materials.
  2. Using this material to increase the energy efficiency and performance of novel electronic devices. Some devices, such as novel memory devices, need heat to become activated. Heat loss in these devices translates to low performance. Our atomic heat shield can effectively isolate heat within the device and increase the efficiency.
  3. Creating devices such as thermal switches that can be combined with this material to actively control heat transport in electronics.

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