Evaluation of acoustic properties of (K,Na)NbO 3 film

Currently, it is required to develop lead-free piezoelectric thin film materials such as (K,Na)NbO 3 (KNN) for a substitute of Pb(Zr,Ti)O 3 (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; s 11 E = 9.27 pm 2 /N, s 12 E = −3.06 pm 2 /N, s 66 E = 24.7 pm 2 /N, c 33 E = 2.89 GPa, k 31 2 = 0.06%, k t 2 = 2.08%, d 31 = −78.9 pC/N, Poison ratio σ E = 0.33, and e 33 T /e 0 = 1.27×10 3 . 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 (A 0 ) and symmetric (S 0 ) modes of leaky Lamb wave, respectively. This is an important step to the determination of full material constants of the KNN film.