Intrinsic stress of bismuth oxide thin films: effect of vapour chopping and air ageing

Bismuth oxide thin films of thickness 1000 A⁰ have been prepared by thermal oxidation (in air) of vacuum evaporated bismuth thin films (on glass substrate) at different oxidation temperatures and duration. Both the vapour chopped and nonchopped bismuth oxide thin films showed polycrystalline and polymorphic structure. The monoclinic bismuth oxide was found to be predominant in both the cases. The effect of vapour chopping and air exposure for 40 days on the intrinsic stress of bismuth oxide thin films has been studied. The vapour chopped films showed low (3.92 − 4.80 × 10⁹ N/m²) intrinsic stress than those of nonchopped bismuth oxide thin films (5.77 − 6.74 × 10⁹ N/m²). Intrinsic stress was found to increase due to air ageing. The effect of air ageing on the vapour chopped films was found low. The vapour chopped films showed higher packing density. Higher the packing density, lower the film will age. The process of chopping vapour flow creates films with less inhomogenety i.e. a low concentration of flaws and non-planar defects which results in lower intrinsic stress.