Integration of Epitaxial LiNbO3thin 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 degrees Y-X and 30 degrees X-Y LiNbO3 films by direct liquid injection chemical vapour deposition on Si substrates by using epitaxial SrTiO3 layers, grown by molecular beam epitaxy, has been demonstrated. The stability of the interfaces and chemical interactions between SrTiO3, LiNbO3 and Si were studied experimentally and by thermodynamical calculations. The experimental conditions for pure 36 degrees Y-X orientation growth have been optimized. The piezoelectricity of epitaxial 36 degrees Y-X LiNbO3/SrTiO3/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 LiNbO3. According to the theoretical calculations, 36 degrees Y-X LiNbO3 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 PbZr1-xTixO3 films.