Thermal conductivity measurements of bulk materials and thin films by the 3o method

An experimental apparatus was assembled based on a four-wire 3o method to determine the thermal conductivity of bulk and thin film materials. By driving a current of angular frequency o through a thin heating wire deposited on a specimen surface, a localized thermal wave with a frequency 2o is created. Due to the change of the metal line's resistance with increasing temperature the imposed temperature oscillation can be estimated by measuring the voltage drop at a frequency 3o. The 3o measurements were performed in a frequency range covering five orders of magnitude (1 Hz--300 kHz).; Bulk materials with a low thermal conductivity (soda lime with 1.15 W/(m·K) and Pyrex with 1.33 W/(m·K)) as well as silicon that possesses a much higher thermal conductivity (130 W/(m·K)) were measured by the 3o method. In addition, the thermal conductivities of silica films of thicknesses between 0.3 mum to 3.2 mum were measured. The determined thermal conductivity of those silica films (1.55 W/(m·K)) was independent of film thickness. Finally, the possibility of measuring the thermal conductivity of thin diamond films is discussed.