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From superconductors to microelectronics: How will the key role of thermal interfaces affect future technologies?
With the rapid development of science and technology, the study of thermal interfaces has become increasingly important because they directly affect the thermal conductivity of materials, especially in the fields of superconductivity and microelectronics. Thermal interface resistance, also commonly referred to as thermal boundary impedance or Kapitzer impedance, is a measure of the resistance to heat flow between two materials. This thermal resistance exists not only at the point of contact of the materials, but also at atomically perfect interfaces, because the physical properties of the different materials cause energy carriers (such as phonons or electrons) to scatter at the interface.
This interfacial thermal resistance results in a limited difference in temperature at the interface when a constant heat flux is applied, which is critical for thermal management of future high-performance devices.
Interfacial thermal resistance is particularly critical in nanoscale systems where interface characteristics can significantly affect performance compared to bulk materials. For example, in the development of microelectronic semiconductor devices, it is expected that a device with an 8 nm feature size will generate up to 100,000 W/cm² of thermal simulation during operation, so more efficient heat dissipation mechanisms are needed to handle the expected 1000 W/cm². Heat flow. This makes interfaces with low thermal resistance technologically very important.
On the other hand, applications that require good thermal isolation, such as jet engine turbines, require interfaces with high thermal resistance to ensure stable operation at extremely high temperatures.
Currently, metal-ceramic composites are being used in these high thermal resistance applications. High thermal resistance can also be achieved with multi-layer systems. Since thermal boundary impedance is caused by scattering of carriers at the interface, its type depends on the material of the interface. For example, in a metal-metal interface, the scattering effect of electrons will dominate the thermal boundary impedance because electrons are the main heat carriers in metals.
Two commonly used prediction models for thermal boundary impedance are the phonon acoustic mismatch model (AMM) and the diffusion mismatch model (DMM). The former assumes a geometrically perfect interface and that phonon transport across it is completely elastic, whereas the latter assumes that scattering at the interface is diffusive, which is particularly accurate for rough interfaces at high temperatures. The application of these models can be further explored in molecular dynamics (MD) simulations, providing a powerful tool for studying interfacial thermal resistance.
Recent MD studies have shown that the thermal resistance of the solid-liquid interface on nanostructured solid surfaces can be reduced by enhancing the solid-liquid interaction energy, which opens up a new direction for heat conduction research.
Historically, when the concept of thermal interface impedance was first proposed in 1936, research on liquid helium had already proven the existence of this phenomenon. However, it was not until 1941 that Pyotr Kapitsa conducted a systematic study of the thermal behavior of liquid helium interfaces. The main theoretical model in this field is the acoustic mismatch model (AMM), but this model fails by as much as two orders of magnitude in predicting the thermal conductivity of liquid helium interfaces. More interestingly, the behavior of thermal resistance under pressure changes is almost unaffected, which means that other mechanisms play a more important role in dominating the heat transfer process.
Exploring the thermal interface properties of materials is the key to future technological progress, especially in the fields of superconductivity, microelectronics and cutting-edge materials science. As our understanding of the properties of these interfaces improves, entirely new technologies and applications may emerge. But we can’t help but ask, can we completely overcome the challenge of interface thermal resistance in the future and achieve a more efficient thermal management system?
