Anisotropy Thermal Properties of Electrically Insulating Thin Films and Sheets: A Review

With the growing need for controlling heat dissipation in modern technologies, a comprehensive understanding of thermal transport in electrically insulating materials is essential. Electrically insulating thin films and sheets often exhibit anisotropy thermal conductivity across in-plane and cross-plane directions, either intrinsically, or through structural engineering. This anisotropy enables targeted heat dissipation, such as around sensitive components in modern electronics. This review summarizes the recent progress in enhancing the thermal conductivity of electrically insulating thin films and sheets, in particular, those exhibiting anisotropy in the thermal conductivity. It considers how fabrication strategies impact the structure of the material to control thermal conductivity and thermal conductivity anisotropy, and summarizes the techniques leveraged to measure the thermal conductivity, and evaluates the corresponding electrical parameters. Trends across various material systems, including polymers, ceramics, and composites, are discussed, with additional insights into thickness-dependent behavior, compositing strategies, alignment methods, and trends in filler loadings. Special attention is given to boron nitride (BN)-based composites, where filler alignment, morphology, and loading fraction critically influence anisotropy thermal performance. By analyzing these interrelationships, this review provides a framework for designing next-generation insulating materials with tunable anisotropy thermal properties for advanced thermal management applications.