Composite materials for effective heat dissipation application

  Bin Xu

  Lecturer，University of Tokyo     

Abstract: 

Rapid advances in electronics demand heat spreaders with high thermal conductivity and suitable mechanical compliance. To address this need, we developed copper-based composites using diamond and graphite, targeting enhanced heat dissipation through two complementary strategies: interfacial engineering and thermal routing.

For Cu/diamond composites, the main challenge is the low thermal boundary conductance (TBC) caused by weak interfacial bonding and poor vibrational density of states (vDOS) matching between copper and diamond. We introduced a self-assembled monolayer (SAM) as a controllable interfacial layer and first investigated its morphology, including thickness and binding strength, in a planar Cu/SAM/diamond model using time-domain thermoreflectance (TDTR). The results showed that improving vDOS overlap is more effective than simply strengthening interfacial bonding for enhancing TBC in highly mismatched systems. Guided by this understanding, we optimized the SAM structure and applied it to Cu/diamond composites fabricated by plasma sintering. The resulting composite achieved a thermal conductivity of 711 W m⁻¹ K⁻¹, representing a record value among studies using diamond fillers with similar size and volume fraction.

As a lower-cost alternative, we also explored graphite/Cu composites. Although graphite has excellent in-plane thermal conductivity, its low cross-plane conductivity limits its use in heat spreaders. To overcome this anisotropy, we designed three-dimensional graphite layouts to route heat effectively. Finite element modeling identified a double-decker structure, consisting of two graphite blocks with mutually perpendicular c-axes, as the optimal design. This structure was fabricated using a high-temperature process with a Cu microparticle interlayer containing 1 wt% Cr to bond the graphite blocks. Laser flash measurements and device-level tests confirmed that the composite dissipates heat nearly isotropically and performs similarly to an isotropic conductor with an effective thermal conductivity of 900 W m⁻¹ K⁻¹.

These results demonstrate that interfacial engineering and thermal routing are effective strategies for developing high-performance heat spreader composites, providing both fundamental insights and practical solutions for advanced thermal management.

Speaker Biography:

Bin Xu received his PhD in Electrical Engineering from Tohoku University in 2018. He is currently a lecturer at the University of Tokyo, where his research centers on thermal energy engineering. His work covers thermal management for electronic devices, thermoelectric energy harvesting based on phonon-engineering strategies, and the fundamental physics of phonon transport in low-dimensional material systems. These studies have been published in leading journals, including Science Advances, Advanced Functional Materials, and Acta Materialia. He has also received awards on these works, such as the Outstanding Young Researcher Award, the Young Researcher Award from the Heat Transfer Society of Japan, and the Osawa Young Researcher Award from the FNTG Society.