Polaritons: Empowering Semiconductor Technology through Miniature Powerhouses

Quantum particles known as phonons are responsible for the movement of thermal energy in a process termed heat transfer. However, with the advent of increasingly sophisticated nanoscale semiconductors, phonons alone are not sufficient in dissipating heat. This conundrum has motivated researchers at Purdue University to explore a new aspect of nanoscale heat transfer utilizing hybrid quasiparticles known as “polaritons.”

Heat transfer is a particular fascination for Thomas Beechem, the associate professor of mechanical engineering at Purdue University. He likens phonons and photons, which are particles that are representative of energy as opposed to physical entities, to the components of a hybrid Prius. The novelty of the “polariton” lies in its composition: a combination of both photon and phonon, embodying the characteristics of each but also possessing distinct attributes of its own.

Despite their role in optical applications ranging from stained-glass art to health testing kits, the heat transferring abilities of polaritons had largely been overlooked due to their significance in materials of a nanoscale size. Jacob Minyard, a Ph.D. student working under Beechem, explains that it was the unchecked miniaturization of semiconductors, which seemingly hindered the efficiency of phonons in heat dispersion, that led them to consider polaritons as an alternative means of heat transfer. Minyard suggests that polaritons could make a more significant contribution to the thermal conductivity of these small-scale semiconductors.

This suggestion was brought forth in their research which was featured in the Journal of Applied Physics. Beechem speaks of how the heat transfer community has been looking at the impact of polaritons in a segmented manner, focusing on their effects on different materials or interfaces. However, their research sheds light on the dominant role of polaritons in heat transfer for surfaces thinner than 10 nanometers, which according to Beechem, are twice the size of the transistors found in an iPhone 15.

Beechem’s excitement is palpable as he speaks of the opportunities that polariton heat transfer could bring to the semiconductor industry, especially in terms of design that incorporates both phonons and polaritons. As to how this could be done in the real world, Minyard acknowledges that their findings have barely scratched the surface, and more research needs to be done to understand how the multiple materials used in chipmaking could be optimized for more efficient heat conduction.

In light of this, both researchers are keen on assisting chip manufacturers to incorporate their theoretical research findings into the actual design of semiconductor chips. They emphasize that the incorporation should aim for the efficient use of polaritons in transferring heat from the very inception of the design, including the choice of materials and the configuration of the chip layers. In their eyes, the challenge of translating theory into practice is an exciting one, and they are eager to proceed with physical experimentation within the supportive environment of Purdue University.

“The heat transfer community here at Purdue is so robust,” Beechem said. “We can literally go upstairs and talk to Xianfan Xu, who had one of the first experimental realizations of this effect. Then we can walk over to Flex Lab and ask Xiulin Ruan about his pioneering work in phonon scattering. And we have the facilities here at Birck Nanotechnology Center to build nanoscale experiments, and use one-of-a-kind measurement tools to confirm our findings. It’s really a researcher’s dream.”