Thickness dependent stresses and thermal expansion of epitaxial LiNbO3 thin films on C-sapphire

LiNbO3 films of high epitaxial quality and with thicknesses of 120-500 nm were deposited at 650 °C on C-sapphire by atmospheric pressure metal-organic chemical vapour deposition. Li nonstoichiometry, residual stresses, twinning, and thermal expansion of the films as a function of the film thickness were investigated by means of Raman spectroscopy and X-ray diffraction. The relaxation of residual stresses, Li2O loss, inelastic deformation and elastic hysteresis during cycles of heating up to 860 °C and cooling down to room temperature were studied, as well. The residual stresses and thermal expansion of films were highly thickness dependent. It was shown that the {011¯2} twinning contributed to the stress relaxation in the thick LiNbO3 films.