Simultaneous Reduction of Bulk and Contact Thermal Resistance in High-Loading Thermal Interface Materials Using Self-Assembled Monolayers

Abstract

Thermal interface materials (TIMs) play a pivotal role in the transfer of heat from high-temperature sources, such as CPUs, to heat sinks in power electronics. The effectiveness of grease-type TIMs is determined by their effective thermal impedance (R_EFF), which hinges on optimizing both the specific bulk (R_B) and contact (R_C) thermal resistances. Achieving concurrent optimization of these resistances poses a significant challenge, especially in high filler loading TIMs, typically above 76 vol%. This research leverages interface engineering through Self-Assembled Monolayers (SAMs) to address this challenge. A substantial decrease in R_EFF is realized to 0.169 K cm² W⁻¹, a tenfold enhancement compared to non-SAM treated TIMs, which exhibit R_EFF values of 2.265 K cm² W⁻¹. This leap in performance is primarily ascribed to the reduced surface energy of SAM treated Al₂O₃, leading to lower particle-to-particle Van der Waals forces, thereby improving particle dispersion and strengthening interfacial bonds. Furthermore, longer carbon chains in SAMs result in increased R_B, yet a decrease in R_C, due to the chains' capacity for enhanced energy absorption and molecular entanglement. The investigation underscores the significance of shorter-chain SAMs in fine-tuning thermal resistance, highlighting the crucial role of molecular architecture in the design of advanced TIMs.