Homo-epitaxial growth of LiNbO3 thin films by Pulsed Laser deposition

Abstract

With the deployment of the 5th Generation of mobile applications (5G), the performances of radio-frequency (RF) filters are pushed to their limits. Highly crystalline piezoelectric materials with an electromechanical coupling coefficient higher than aluminium nitride are of high interest. Lithium niobate (LiNbO3), with an electromechanical coupling coefficient from 5 % to 45 % for bulk waves, appears to be a promising candidate for a next generation of RF filters. However, despite decades of research, the growth of single-phased, stoichiometric and highly crystalline LiNbO3 thin films is still very challenging.In the present work, 200 nm-thick LiNbO3 films have been grown by pulsed laser deposition on congruent LiNbO3 substrates with various crystalline orientations: X-cut (i.e. (110)), Y-cut (i.e. (100)) and Z-cut (i.e. (001)). The influence of the substrate’s crystal cut on the physical and chemical properties of the LiNbO3 films is investigated. A High-Resolution X-ray Diffraction methodology is developed to characterize the crystalline properties of the homoepitaxial layers. In all cases, single-phased and epitaxial LiNbO3 thin films are obtained. These results indicate that a standard wafer-based PLD system can be used to grow LiNbO3 thin films with a crystalline quality and a stoichiometry very close to a LiNbO3 monocrystalline substrate.