Influence of convective heat transfer on the AC temperature amplitude of a microheater on glass or polyimide substrate

In this study, we address the impact of convective heat transfer on the measured thermal conductivity of a substrate when using the 3ω method. The conventional approach assumes negligible convective heat transfer by performing measurements in a vacuum chamber or by regarding the surface as adiabatic. However, if the 3ω sensor is exposed to air during the measurement, the convective heat transfer in the air can significantly affect the measured thermal conductivity of the sample. The measurement error is known to depend on the ratio of thermal resistance of substrate conduction and surface convective heat transfer. To quantify this effect, we perform a computational fluid dynamic simulation. An Eagle XG glass or a polyimide substrate is considered as the substrate of the 3ω sensor. Temperature oscillation at the microheater is calculated depending on the frequency and amplitude of the convective heat transfer coefficient. By comparing the calculated results with the theoretical model considering only one-dimensional conduction heat transfer, we assess the differences and analyse the measurement error of the substrate's thermal conductivity when neglecting the surface convective heat transfer.