Integration of epitaxial LiNbO 3 thin films with silicon technology.

Development of bulk acoustic wave filters with ultra-wide pass bands and operating at high frequencies for 5 th and 6 th generation telecommunication applications and micro-scale actuators, energy harvesters and sensors requires lead-free piezoelectric thin films with high electromechanical coupling and compatible with Si technology. In this paper, the epitaxial growth of 36°Y-X and 30°X-Y LiNbO 3 films by direct liquid injection chemical vapour deposition on Si substrates by using epitaxial SrTiO 3 layers, grown by molecular beam epitaxy, has been demonstrated. The stability of the interfaces and chemical interactions between SrTiO 3 , LiNbO 3 and Si were studied experimentally and by thermodynamical calculations. The experimental conditions for pure 36°Y-X orientation growth have been optimized. The piezoelectricity of epitaxial 36°Y-X LiNbO 3 /SrTiO 3 /Si films was confirmed by means of piezoelectric force microscopy measurements and the ferroelectric domain inversion was attained at 85 kV.cm -1 as expected for the nearly stoichiometric LiNbO 3 . According to the theoretical calculations, 36°Y-X LiNbO 3 films on Si could offer an electromechanical coupling of 24.4% for thickness extension excitation of bulk acoustic waves and a comparable figure of merit of actuators and vibrational energy harvesters to that of standard PbZr 1- x Ti x O 3 films.