Curie Temperature, Biaxial Elastic Modulus, and Thermal Expansion Coefficient of (K,Na)NbO₃Piezoelectric Thin Films

We investigated fundamental parameters such as the Curie temperature, biaxial elastic modulus, and thermal expansion coefficient of (K,Na)NbO 3 (KNN) films on Pt/Ti/SiO 2 /Si substrates. From the temperature dependence of the dielectric constant of the KNN films, their Curie temperature was approximately 360 °C; this value was confirmed from critical changes in the lattice parameters of the films and the stress induced in the films at approximately this temperature. By using the optical lever method, the biaxial elastic modulus and thermal expansion coefficient of the KNN films were found to be 92 GPa and 8.0 × 10 -6 (1/°C), respectively. The fundamental properties of the KNN films were similar to those of widely used Pb(Zr,Ti)O 3 films, indicating that KNN films are potential candidates for lead-free piezoelectric thin films in micro-electro-mechanical system (MEMS) applications.