Improve the response frequency of epitaxial LiNbO₃ film SAW devices by substrate strain gradient

For the traditional surface acoustic wave (SAW) devices, its RF performance is mainly determined by the micro-nano processing technology of the electrode and the physical properties of the piezoelectric material itself. As a ferroelectric material and piezoelectric material, LiNbO₃ has high piezoelectric properties and electromechanical coupling coefficient, which has been widely concerned by researchers. LiNbO₃ films with different thicknesses were epitaxially grown on Al₂O₃ (001) substrates by pulsed laser deposition (PLD). The SAW velocity of the film is increased by stress adjustment, and the SAW device obtains a higher response frequency. The stress on the surface of the film decreases with the increase of the film thickness, which reduces the velocity of the surface acoustic wave. The piezoelectric film prepared by PLD technology has the advantage of epitaxial stress regulation. The SAW velocity of LiNbO₃ film can reach 5701.2 m/s, and the piezoelectric coefficient d₃₃ = 17.6 pm/V. It is an effective way to improve the RF performance of SAW devices. In addition, the SAW device has the best performance when the electrode duty cycle is 50%.