Low Dielectric and High Thermal Conductive Phononic Crystal Nanofiber Metamaterial Film

The rapid advancement of 3D heterogeneous integration technology has created stringent requirements for the thermal conductivity of low dielectric materials. However, common low dielectric materials generally have low thermal conductivity, which hinders the ability to simultaneously optimize signal transmission and heat dissipation in integrated systems. Here, a crystallization control strategy is proposed to tackle the challenge of balancing high thermal conductivity with a low dielectric constant. Through precise control of synthesis parameters, a phononic crystal nanofiber (NF) metamaterial film composed of boron nitride nanosheets (BNNS) and crystalline polyimide (PI) bridges has been successfully developed. The crystalline PI bridging structure and BNNS synergistically form a phononic crystal-like metamaterial inside the fiber, enhancing lattice vibration and facilitating heat transfer. Meanwhile, the PI around the fiber maintains a long-range disordered structure, hindering the arrangement of dipoles. The synergistic effect enables the phononic crystal NF film to achieve a high thermal conductivity of up to 6.51 W/(m·k) and a relatively low dielectric constant of 2.63, thereby enhancing the energy efficiency of 3D integrated systems.