Effect of Lattice Strain and Improvement of the Piezoelectric Properties of (K,Na)NbO 3 Lead-Free Film

• Published in: Japanese Journal of Applied Physics 2010-09, Vol.49 (9S), p.9
• Main Authors: Suenaga, Kazufumi, Shibata, Kenji, Watanabe, Kazutoshi, Nomoto, Akira, Horikiri, Fumimasa, Mishima, Tomoyoshi
• Format: Article
• Language: English
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/JJAP.49.09MA05

(K,Na)NbO 3 (KNN) films with very high transverse piezoelectric coefficient d 31 , which attained values comparable to those of Pb(Zr,Ti)O 3 (PZT) films for the first time, were successfully deposited on Pt/Ti/SiO 2 /Si φ 4-in. substrates by RF magnetron sputtering. These films were polycrystalline and had pseudo-cubic perovskite structure with a 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 (∼-100 pm/V) that can be uniformized on φ 4-in. substrates and with a standard deviation that decreases to about 4 pm/V.