Effect of Lattice Strain and Improvement of the Piezoelectric Properties of (K,Na)NbO3 Lead-Free Film

概要

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(K,Na)NbO3 (KNN) films with very high transverse piezoelectric coefficient $d_{31}$, which attained values comparable to those of Pb(Zr,Ti)O3 (PZT) films for the first time, were successfully deposited on Pt/Ti/SiO2/Si $\phi$ 4-in. substrates by RF magnetron sputtering. These films were polycrystalline and had pseudo-cubic perovskite structure with a $\langle 001\rangle$ preferred orientation. Furthermore, we focused on the effect of lattice strain on $d_{31}$ of KNN to clarify the relationship between the piezoelectric properties and structural parameters apart from orientation. We found that $-d_{31}$ increases with decreasing lattice strain $c/a$ ratio of KNN when the in-plane lattice parameter $a$ increases and the out-of-plane lattice parameter $c$ decreases. By controlling the lattice strain $c/a$ ratio strictly and maintaining a homogeneous strain, we achieved a high $d_{31}$ (${\sim}{-}100$ pm/V) that can be uniformized on $\phi$ 4-in. substrates and with a standard deviation that decreases to about 4 pm/V.
2010-09-25