Preparation conditions investigation on high-quality lithium niobate thin films on SiO2 substrates

Lithium niobate (LiNbO₃, LN) is a dielectric material with excellent ferroelectric, electro-optic, nonlinear-optic, and acoustic-optic properties. Although the thin film LN-on-insulator (LNOI) wafers are widely used in integrated photonics, it is very difficult to prepare high-quality LN thin film for thin film LN-on-insulator (LNOI) wafers with integrated functions and good performance. Currently, the most common preparation method for LNOI is crystal-ion-slicing (CIS). In addition, several techniques, including chemical vapor deposition, RF sputtering, pulsed laser deposition, sol-gel, and molecular beam epitaxy, have been developed to produce high-quality films. However, these methods cannot produce highly crystalline materials. This situation severely limits the choice of substrate in LNOI preparation. The main purpose of this study is to explore the influence of different sputtering power and annealing conditions on the optical properties of LN thin films prepared by RF sputtering. The LN thin films were prepared by RF sputtering on SiO₂ substrates under different powers for 1 h, and the fastest sputtering power was selected. Using this power, thicker LN thin films were prepared within 2 h and annealed rapidly at 500, 600, and 700 °C. By analyzing the properties of crystal orientation, refractive index, extinction coefficient, film thickness, and surface morphology, we found the obvious changes in these properties of LN thin films under different sputtering and annealing conditions, and the optimal sputtering conditions to fabricate high-quality LN thin film has been developed. Among all the prepared samples, the sample annealed at 700 °C for 20 min had the best quality.