Abstract: Sintered metals serving as thermal interface materials (TIMs) with superior thermal conductivities show the most promise in meeting the heat dissipation requirements of next-generation wide bandgap applications. Nevertheless, their thermal stabilities during high-temperature service provide significant challenges. Herein, a facile approach was developed for one-step synthesis of single-phase Ag-Cu supersaturated solid-solution nanoparticle (Ag-Cu SS-NP) pastes with adjustable Cu contents (up to 37.7 at.%), and they exhibited ultrahigh resistance to oxidation and excellent sinterability. A paste composed of Ag-Cu SS-NPs was sintered in air at 250 °C for 20 min, and this resulted in a dense supersaturated structure with an impressive thermal conductivity of 157.8 W/(m K) and a room-temperature shear strength of 133.4 MPa. Microstructural analyses demonstrated that Cu had precipitated from the Ag lattice to form Cu nanoprecipitates, which refined the grain sizes and induced high-density dislocations during sintering. For the pinning effect of dislocations and grain boundaries by the Cu nanoprecipitates and coherent twins, the high-temperature (400 °C) shear strength of sintered Ag-Cu SS-NP joints was significantly improved by 67 % (58.6 MPa), meanwhile the shear strength after long-term aging at 200 and 300 °C for 960 h were increased by 123 % (140.3 MPa) and 80 % (82.4 MPa) compared to those of sintered Ag NP joints, respectively. The remarkable thermal stability is far superior to traditional TIMs, so the Ag-Cu SS-NP paste exhibits excellent potential as a TIM for high-temperature power device applications.

Key words: Ag-Cu nanoparticles, Supersaturated, Low-temperature sintering, Ultrahigh thermal stability