Abstract: Currently, Al₂O₃-based thermal interface materials (TIMs) have the most extensive industrial application for the thermal management of modern electronic devices. These TIMs are characterized by their low cost, ease of processing, high electrical insulation, but are limited by their thermal conductivity. The thermal performance bottleneck of Al₂O₃-based TIMs primarily stems from the extremely high interfacial thermal resistance at the micro/nano-scale interfaces between adjoining alumina fillers, a phenomenon resulting from the “point to point” dry contact established by the nature of solid spherical particles. To address this issue, herein, we have successfully developed a well-designed hybrid filler system, utilizing Al₂O₃ as the main thermally conductive filler and incorporating hexagonal boron nitride (h-BN) flakes and gallium-based liquid metal (LM), to significantly improve the through-plane thermal conductivity of the targeted TIMs. Specifically, a mechanochemical grinding process was utilized to promote the anchoring and spreading of LM on the Al₂O₃ surface, followed by a vertical compression that forced the h-BN flakes into good coverage and tight adhesion on the LM-modified alumina. As a result, not only did the contact mode between the fillers change from “point-to-point” to “face-to-face,” but the “dry” contact also evolved into “liquid-solid" interface configurations with extremely low contact thermal resistance, thanks to the surface-anchored LM. Moreover, the h-BN flakes can also form a highly oriented arrangement during the pressing, thereby creating additional thermal conductive pathways that boast high heat transfer efficiency. Compared to the pure Al₂O₃-based composite, the TIM comprising 50 wt% Al₂O₃, 20 wt% h-BN, and 10 wt% LM, with soft polydimethylsiloxane (PDMS) as the matrix, demonstrates an impressive through-plane thermal conductivity of 7.2 ± 0.30 W m^-1 K^-1, marking a significant improvement of 133 %. In the TIM performance test, the cooling efficiency of our sample is ∼1.67 times that of the advanced commercial thermal pad. Additionally, it possesses a high volume resistivity of 5.6 × 10¹¹ Ω cm, a low dielectric constant of 2.15 at 10⁶ Hz, and a low dielectric loss tangent of 0.0058 at 10⁶ Hz. Our finding is believed to inspire others to prepare advanced TIMs with comprehensive properties via purposeful filler hybridization.

Key words: Alumina, Hexagonal boron nitride, Liquid metal, Thermal interface material, Thermal management