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 di odes. Recent data illustrated the strong anisotropy in the thermal conducti vity of polyimide films of thickness near 1 mu m, with the in-plane value l arger by a factor of approximately six. This manuscript extends previous th eoretical work on heat conduction in stretched bulk polymers to model the c onductivity anisotropy in spin-coated polymer films. Predictions are based on the standard deviation of the angle of molecular orientation with respec t to the film in-plane direction, which can be investigated using birefring ence data, and the expected conductivity anisotropy in a material with perf ectly aligned chains. The modeling and previous data indicate that the anis otropy factor could increase to a value larger than 10 for polyimide films much thinner than 1 mu m. (C) 1999 American Institute of Physics. [S0021-89 79(99)04516-8].