Abstract
Polyimide films whose refractive indices in the film plane show anisotropy (in-plane birefringence, Δn) were prepared by a novel method based on the anisotropy of thermal expansion coefficients (Δα) of single crystal substrates. Polyimide molecular chains were oriented along the crystal axis having a larger thermal expansion coefficient. The Δn of polyimide films increases as the Δα and the larger thermal expansion coefficient of the substrates increase.