Inorganic aerogels have exhibited many superior characteristics with extensive applications, but are still plagued by a nearly century-old tradeoff between their mechanical and thermal properties. When reducing thermal conductivity by ultralow density, inorganic aerogels generally suffer from large fragility due to their brittle nature or weak joint crosslinking, while enhancing the mechanical robustness by material design and structural engineering, they easily sacrifice thermal insulation and stability. Here, we report a chemically bonded multi-nanolayer design and synthesis of a graphene/amorphous boron nitride aerogel to address this typical tradeoff to further enhance mechanical and thermal properties. Attributed to the chemically bonded interface and coupled toughening effect, our aerogels display a low density of 0.8 mg cm⁻³ with ultrahigh flexibility (elastic compressive strain up to 99% and bending strain up to 90%), and exceptional thermostability (strength degradation <3% after sharp thermal shocks), as well as the lowest thermal conductivities in a vacuum (only 1.57 mW m⁻¹ K⁻¹ at room temperature and 10.39 mW m⁻¹ K⁻¹ at 500°C) among solid materials to date. This unique combination of mechanical and thermal properties offers an attractive material system for thermal superinsulation at extreme conditions.

Thermal contact resistance at mechanically assembled interfaces can substantially limit the performance of graphite- and graphene-based thermal interface materials despite their high intrinsic thermal conductivity. Here, we introduce finger-joint mating surfaces for laterally oriented graphite films and vertically aligned graphene pads. Steady-state thermal-resistance measurements are used to quantify the geometry-induced reduction in total interfacial resistance and isolate the corresponding enhancement in thermal contact conductance. Contact-state and as-fabricated finger-profile characterizations are then performed to reveal the underlying geometric mechanism. The finger-joint configuration increases the thermal contact conductance by approximately 109%–128% across the graphitic thermal interface materials (TIMs) examined. Interfacial characterization reveals indentations localized near the finger peaks, while reconstruction of the as-fabricated finger geometry provides a quantitative explanation for the observed enhancement. In an LED assembly, the finger-joint interface reduces the chip temperature by more than 50 °C relative to the corresponding planar interface. These findings demonstrate finger-joint interface architecture as a robust design strategy for enhancing thermal conductance across TIM assemblies with anisotropic as well as isotropic transport characteristics. More broadly, they highlight geometric regulation of mechanical contact as a general route for unlocking the intrinsic thermal potential of high-conductivity TIMs in advanced packaging.

Thermal pads are widely used for heat dissipation in electronic devices, but their performance can be limited by incomplete contact with the adjoining surfaces. In this study, a double-sided finger-joint interface was introduced to improve thermal contact without modifying the composition of the thermal pad. Two commercial thermal pads were assembled between either planar or finger-structured brass substrates and tested under pressures ranging from 0.1 to 1.0 MPa. For both pads, the finger-joint interface reduced the thermal contact resistance to approximately one-third of that measured with the corresponding planar interface. Surface morphology characterization and mechanical analysis indicated that the finger geometry increased the local normal contact force and promoted more effective contact between the pads and substrates. In a bolt-clamped LED assembly, the finger-joint interface reduced the chip temperature by 49.6 °C at 1.0 A, corresponding to a 45.3% reduction in chip temperature rise. This improvement was retained after 100 heating and cooling cycles. These findings demonstrate that surface geometry provides a practical approach for improving the effective thermal contact performance of thermal pads.