Heat Capacity, Thermal Conductivity, and Interface Resistance Extraction for Single-Walled Carbon Nanotube Films Using Frequency-Domain Thermoreflectance

Thermal interface materials (TIMs) based on vertically aligned carbon nanotube (VACNT) films promise the unusual combination of high thermal conductance and low elastic modulus, properties that are critical for TIM performance and reliability. This paper reports through-plane thermal conductivity, heat capacity, and boundary resistances measured using frequency domain thermoreflectance for seven VACNT films. The films are composed of single-walled carbon nanotubes grown using chemical vapor deposition on Si substrates and have thicknesses from 5.3 to 81 μm. The top surfaces of the films are coated with 100-nm Ti and 100-nm Ag as a transducer layer for the thermoreflectance measurement. The roughness of the top surface of each sample is measured using atomic force microscopy. The average thermal conductivity of the films ranges from 2.1 to 3.5 W m^-1 K^-1 and the average heat capacity ranges from 5.5 to 9.3 J cm^-3 K^-1. The heat capacity of the films is used to calculate the volume fraction of tubes that contributes to thermal conduction. The CNT-metal boundary resistances are below 1 m² K MW^-1 and the CNT-substrate resistance ranges from 3 to 80 m² K MW^-1. Variations of the nanotube alignment and morphology throughout the film are also examined using scanning electron micrographs to provide a comprehensive analysis of these films.