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)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
/ε
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.