Structural, electrical and piezoelectric properties of LiNbO3 thin films for surface acoustic wave resonators applications

In this work, 0.30 μm thick LiNbO3 layers have been deposited by sputtering on nanocrystalline diamond/Si and platinised Si substrates. The films were then analyzed in terms of their structural and optical properties. Crystalline orientations along the (0 1 2), (1 0 4) and (1 1 0) axes have been detected after thermal treatment at 500 °C in air. The films were near-stoichiometric and did not reveal strong losses or diffusion in lithium during deposition or after thermal annealing. Pronounced decrease of the roughness on top of the LiNbO3 layer and at the interface between LiNbO3 and diamond was also observed after annealing, compared to the bare nanocrystalline diamond on Si substrate. Furthermore, ellipsometry analysis showed a better density and a reduced thickness of the surface layer after post-deposition annealing. The dielectric constant and losses have been measured to 50 and less than 3.5%, respectively, for metal/insulator/metal structures with 0.30 μm thick LiNbO3 layer. The piezoelectric coefficient d33 was found to be 7.1 pm/V. Finally, we succeeded in switching local domain under various positive and negative voltages.