High-Order Lamb Wave Mode of 128°Y-cut LiNbO₃/SiO₂ Resonator Covered with AlN Film Exhibiting Higher Electromechanical Coupling

In this work, A method was adopted to improve the electromechanical coupling coefficient (k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) of high-order Lamb Wave Resonator (LWR) by covering with Aluminum Nitride (AlN) film. The AlN film with higher acoustic-velocity is deposited on Lithium Niobate (LN or LiNibO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>) and Silicon oxide (SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>) to form a tri-layer structure LWR. Compared with the traditional bi-layer structure LWR composed of LN/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>, both the S2 and A3 mode LWRs in this tri-layer structure exhibit higher k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. As the mode order of the Lamb wave increases, the improvement of k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> gradually slows down. The proposed design has great application potential in the field of high-frequency and large-bandwidth wireless communications.