A new “sandwich” nanostructure is contributing to electronic cooling

With the increasing complexity and performance of electronic devices, effective heat management has become essential to ensure their optimal operation and longevity. Traditional solutions such as thermal greases, lubricants, and epoxies have limitations when it comes to thermal conductivity, durability, and reliability. To overcome these limitations, scientists are actively researching alternative thermal interface materials and structures. Their goal is to develop innovative cooling methods that surpass conventional techniques and meet the evolving needs of modern electronic devices. By exploring new materials, scientists hope to tackle the challenges associated with heat management and enhance the overall performance and durability of electronic systems. One approach involves searching for substances with higher thermal conductivity to enable more efficient heat transfer.

In a recent study published in the peer-reviewed journal ACS Nano, Dr. Lin Jing, Dr. Rui Cheng, Dr. Raghav Garg, Dr. Wei Gong, Mr. Inkyu Lee, Associate Professor Tzahi Cohen-Karni, Assistant Professor Xu Zhang and led by Professor Sheng Shen from Carnegie Mellon University, and Dr. Aaron Schmit from the Massachusetts Institute of Technology introduced a groundbreaking method for creating a 3D graphene-nanowire “sandwich” thermal interface technology. This technology offers exceptional mechanical compliance and high thermal conductivity. The synthesis process involved sputtering a copper thin film onto an anodic aluminum oxide template and electroplating copper nanowires onto the template. The anodic aluminum oxide template was then dissolved, and the resulting structure underwent plasma enhanced chemical vapor deposition of 3D graphene flakes. Then, this “sandwich” is completed by electroplating another continuous thin copper layer around the nanowire tips. The assembly process included electroplating thin layers of tin on both its upper and lower surfaces, placing the thermal interface material between two substrates, applying pressure, and heating it to the point of tin’s melting for a short duration. The melted tin  filled into the  gap at the interface, creating a strong bond upon cooling. The resulting sandwich material was flexible, soft, and fully free-standing, with a thickness of less than 40 μm.

To assess the mechanical properties of the 3D “sandwich” thermal interface material, the researchers conducted nanoindentation and scratch tests. These tests revealed that the structure possessed low stiffness, similar to foams and polymers. Thermal transport properties were evaluated using the frequency-domain thermoreflectance method. The measurements demonstrated a remarkable increase in thermal conductivity when 3D graphene is present (97 W/mK), compared to pure copper nanowires (65 W/mK). The overall thermal resistance of the structure was less than 0.27 mm²K/W,  which is about one order of magnitude lower than traditional solder. In the thermal mapping demo, when compared to thermal paste, the 3D graphene-nanowire “sandwich” material exhibited lower thermal resistance , indicating superior thermal management capabilities. Furthermore, the material displayed outstanding stability during thermal cycling tests spanning a temperature range of -55 °C to 125 °C over more than a thousand cycles.

In summary, Professor Sheng Shen and his team successfully developed a flexible 3D graphene-nanowire “sandwich” thermal interface material that possesses low stiffness, high thermal conductivity, and superior thermal management capabilities compared to traditional thermal paste. The material exhibited remarkable stability over a thousand temperature cycles and holds potential for enhanced thermal management, energy conversion, and energy harvesting on various flexible and curved electronic surfaces.