Morphological Impact on Thermal Interface Resistance of Self Catalyzing Fecralloy MWNT TIMs

Self catalyzing Fecralloy substrates are investigated as a growth substrate for Multi-walled Carbon Nanotubes (MWNT) Thermal Interface Materials (TIMs). Fecralloy is used without any additional catalyst and with minimal surface preparation to grow double-sided MWNT TIM assemblies. The growth behavior is studied by way of the array morphologies, i.e. array height, density, crystallinity, and diameter distribution. The effects of growth temperature and time are used to observe the growth kinetics, showing a bimodal growth rate with temperature and an optimal growth rate at 725°C with a noticeable onset of amorphous carbon at higher temperatures. The contact resistance of dozens of such samples are evaluated using a DC, 1D reference bar, thermal conductivity measurement system. Temperature and pressure dependent measurements offer insight into the interfacial phonon conduction physics and elastic deformation mechanics of the CNTs tips respectively. Due to the challenges associated with deliberately controlling a single array morphology, a multivariate, statistical approach is used to observe the trends of contact resistance. The contact resistance shows the strongest correlation with array height, following a R ∼= L^−0.5, which contradicts Fourier’s law. However, this is likely a result of the mechanical compliance rather than a ballistic conduction mechanism. Finally, several attempts were made at modeling the relationship between the measured array morphologies and the contact resistance. However, the modeling is relatively unsuccessful, forcing one to rely on the empirical relations found in the exploratory data analysis.