Nanoscale Barrier Layers to Enable the Use of Gallium-Based Thermal Interface Materials with Aluminum

Performance of thermal interface materials (TIMs), such as thermal pastes and mats, hinders the advance of integrated circuit (IC) devices. Current state-of-the-art TIMs suffer from low thermal conductivity, thick cross sections, and poor long-term performance. Gallium (Ga) and gallium-based alloys and amalgamations, in liquid and solid form, have demonstrated up to three times greater thermal conductivity than conventional TIMs, but rapidly alloy with and destroy aluminum (Al) components, which are commonly found in IC devices. In this work, we investigate the use of thin-film barrier layers on Al to prevent Ga alloying and characterize their performance through accelerated Ga exposure experiments and scanning electron microscopy. It is found that 100-nm-thick layers of the common passivation materials niobium and 304 stainless steel do not sufficiently prohibit Ga migration, but a 100 nm layer of titanium (Ti) does. No alloying is evident in Ti-coated Al samples after exposure to a liquid Ga alloy droplet at 300 °C for 168 h, 250 thermal cycles from room temperature to 150 °C with 30-min dwell, or 50 thermal cycles from room temperature to 300 °C with 2-min dwell. The results present a clear and direct path to the use of Ga and Ga alloys as TIMs through the addition of a thin inexpensive barrier layer on Al components and may enable future IC device technologies.