Proposal Numbers: #1140953 / #1140121 P.I.'s: Costas Grigoropoulos / Renkun Chen Institution: University of California-Berkeley / University of California-San Diego
Thermal interface materials play a critical role in thermal management of electronic devices. Current materials, such as greases and solders would be insufficient for cooling the devices with increasingly higher power dissipation level. The objective of this research is to develop a high performance thermal interface material based on copper nanowire array. The new material will have one order of magnitude lower thermal contact resistance compared to the existing ones. To achieve this goal, vertically aligned, dense arrays of single crystalline copper nanowires with well-controlled diameters, spacing and packing density will be synthesized by electroplating through porous anodic alumina membranes. Fundamental studies on mechanical, thermal and electrical properties of individual nanowires will be carried out by using micro-fabricated devices. Interfacial and bulk thermal resistances of copper nanowire arrays will be characterized using a sensitive transient thermo-reflectance technique.
Intellectual Merit: Copper nanowires simultaneously possess two important features that make them a unique candidate for high performance thermal interface materials: high thermal conductivity and high mechanical compliance. Because of the high thermal conductivity and the high packing density of approximately 50%, copper nanowire array has a lower thermal contact resistance compared to the state of the art thermal interface materials. Moreover, the large aspect ratio of the nanowires (> 200:1) makes them highly compliant when subjected to thermal stress, hence the high thermal performance can be retained after thermal cycling. The proposed topics of investigation will advance the understanding of mechanical and electro-thermal properties of copper nanowires pertaining to thermal packaging applications, both individually and collectively as an array, and will lead to the development of a new class of thermal interface materials with superior thermal and mechanical properties.
Broader Impacts: Thermal interface material is one of the key thermal packaging components that are highly demanded by microelectronic industry pursuing increasingly higher clock speed. The proposed copper nanowires based interfaces could become a disruptive enabling technology for developing electronic devices with higher performance, hence can potentially make a tremendous societal impact. Educational and outreach activities will be tightly integrated into the program. By developing new curriculum and recruiting undergraduate students into the research, the program will educate next generation thermal engineers who will be motivated by fascinating nanosciences and the grand technological challenges faced by our society. The proposed outreach programs will leverage the efforts of both the Berkeley and UCSD campuses for promoting diversities, and will benefit K-12 and under-represented students.
Thermal interface materials play a critical role in the thermal management of electronic devices. Current materials, such as greases and solders, will be insufficient for cooling future devices such as smart phones and computers with increasingly higher power dissipation levels. The objective of this research is to develop a high performance thermal interface material based on metal nanowire arrays. The new thermal interface material is expected to posses lower thermal contact resistance compared to existing technologies. In addtion, the nanowire structure also improve the mechanical flexibility of the thermal interface (in another word, nanowires tend to band but do not break when applying a copressive force on the wires). To make nanowire based thermal interface materials, we syntheszed vertically aligned and dense arrays of high quality copper and gold nanowires with well-controlled diameters, spacing, and packing density will be synthesized by electroplating through porous anodic alumina membranes. We have also studied thermal and electrical properties of individual nanowires using novel devices. Thermal conductivity of nanowire arrays was measured using a 3w technique. Copper nanowires simultaneously possess two important metrics that make them a unique candidate for high performance thermal interface materials: high thermal conductivity and high mechanical compliance. Because of the high thermal conductivity and a high packing density of approximately 50%, copper nanowire arrays have a lower thermal contact resistance compared to current state-of-the-art thermal interface materials. Moreover, the large aspect ratio of the nanowires (> 200:1) makes them highly compliant when subjected to thermal and mechanical stresses, hence the high thermal performance can be retained after thermal cycling. The investigated topics advanced the understanding of electrothermal properties of copper nanowires pertaining to thermal packaging applications, both individually and collectively as an array, and pave the way for the development of a new class of thermal interface materials with superior thermal and mechanical properties. More broadly, this study established the correlation between microstructures and mechanical/thermal properties, and also directly probed the thermal resistance of non-ideal interfaces between individual nanowires and substrates. These fundamental insights could advance our understanding on properties of copper, one of the most widely used materials in thermal packaging. From the applicaiton perspective, thermal interface materials are one of the key thermal packaging components that are in high demand in various electronic devices experiencing ever-increasing heat flux. The proposed copper nanowire based interfaces could become a disruptive enabling technology for developing electronic devices with higher performance and, hence, could potentially make a tremendous societal impact in communication and computing. Educational and outreach activities are also tightly integrated into the program. By developing new curricula and recruiting under-represented groups and K-12 and undergraduate students into the research, the program help recruit and train next generation thermal engineers with a deep understanding of thermal physics. The proposed outreach programs leveraged the efforts of both the Berkeley and UCSD campuses for promoting diversity, and will benefit K-12, undergraduate and under-represented students.
