Evaluation of acoustic properties of (K,Na)NbO3 film

Currently, it is required to develop lead-free piezoelectric thin film materials such as (K,Na)NbO₃ (KNN) for a substitute of Pb(Zr,Ti)O₃ (PZT). However, the material constants of a KNN film have not been reported yet. In this paper, some material constants of a KNN film are presented for the first time. We fabricated some piezoelectric resonators using a blanket KNN film by MEMS (micro electro mechanical systems) technology, and obtained the following material constants and related values; s₁₁^E = 9.27 pm²/N, s₁₂^E = -3.06 pm²/N, s₆₆^E = 24.7 pm²/N, c₃₃^E = 2.89 GPa, k₃₁² = 0.06%, k_t² = 2.08%, d₃₁ = -78.9 pC/N, Poison ratio σ^E = 0.33, and e₃₃^T/ε₀ = 1.27×10³. We also measured the velocities of leaky Lamb wave in a KNN diaphragm covered with Al using a line-focus-beam ultrasonic material characterization (LFB-UMC) system. Phase velocities of 1491 m/s and 5370-5180 m/s were measured for antisymmetric (A₀) and symmetric (S₀) modes of leaky Lamb wave, respectively. This is an important step to the determination of full material constants of the KNN film.