Liquid metal particles enabled ultrahigh isotropic thermal conductivity in soft thermal interface materials for biochips packaging

Abstract

Semiconductor bioelectronics increasingly integrate on-device AI, the resulting power density however demands thermal interface materials (TIMs) that are simultaneously soft, electrically insulating, thermally conductive, and biocompatible. Conventional epoxy filler TIMs rarely satisfy all of these requirements because of limited biocompatibility, high stiffness, and relatively low through plane heat transport. Here we report a liquid metal particles (LMPs)-based epoxy (LPE) composite in which amine functionalized gallium based LMPs initiate epoxy curing on their own surfaces, forming conformal insulating shells and a controllable nano insulating gap between neighboring LMPs. By treating this shell as excluded volume, we derive a packing with shells model that sets a practical upper limit of approximately 60 vol% for LMPs loading, which we validate by visual measurements. At this optimum, LPE60 reaches nearly isotropic thermal conductivities (7.49 W m−1 K−1 in plane and 4.38 W m−1 K−1 through plane) while maintaining electrical insulation and tissue like softness (Young's modulus 7.96 kPa). LPE60 also shows approximately 100% cell viability at 72 h, less than 10% stress decay after 1000-time tensile cycles, and strong adhesion. Device level tests on an LED module and on a flexible PI heater platform show that LPE60 lowers steady state operating temperatures more effectively than a commercial thermal epoxy and keeps this performance under thermal cycling and bending. These results identify LPE60 as a versatile TIM platform for soft, biocompatible, high-power biochips and flexible semiconductor packaging.