Impact of molecular orientation on thermal conduction in spin-coated polyimide films

Polymer films are serving as passive regions in fast logic circuits and as active regions in organic optoelectronic devices, such as light-emitting diodes. Recent data illustrated the strong anisotropy in the thermal conductivity of polyimide films of thickness near 1 μm, with the in-plane value larger by a factor of approximately six. This manuscript extends previous theoretical work on heat conduction in stretched bulk polymers to model the conductivity anisotropy in spin-coated polymer films. Predictions are based on the standard deviation of the angle of molecular orientation with respect to the film in-plane direction, which can be investigated using birefringence data, and the expected conductivity anisotropy in a material with perfectly aligned chains. The modeling and previous data indicate that the anisotropy factor could increase to a value larger than 10 for polyimide films much thinner than 1 μm.