Crystalline Structure of Highly Piezoelectric (K,Na)NbO₃ Films Deposited by RF Magnetron Sputtering

Abstract

We have previously reported (K,Na)NbO 3 (KNN) films, whose piezoelectric properties are the highest reported thus far. In this study, we investigate the detailed crystalline structures of these KNN films after deposition on Pt/MgO and Pt/Ti/SiO 2 / Si substrates by RF magnetron sputtering. The KNN film on Pt/MgO was epitaxially grown on the Pt lower electrode with a perfect h001i orientation in the perovskite structure. The KNN film on Pt/Ti/SiO 2 /Si was polycrystalline with a preferential h001i orientation in the perovskite structure having dense columnar grains. X-ray diffraction measurements revealed that the KNN films grown on Pt/MgO and Pt/Ti/SiO 2 /Si were tetragonal; the lattice parameters c and a were related as c=a > 1. The KNN film on Pt/MgO had a higher c=a value than the KNN film on Pt/Ti/SiO 2 /Si, indicating that the former had more compressed strain. We conclude that this difference in compressed strain may contribute to the difference in piezoelectric properties of the KNN films on Pt/MgO and Pt/Ti/SiO 2 /Si.

High electromechanical strain and enhanced temperature characteristics in lead-free (Na,Bi)TiO3–BaTiO3 thin films on Si substrates

“…In this study, to alleviate the tensile thermal stress loaded to the film from the substrate and to obtain c -axis oriented NBT–BT thin film on Si, we precisely controlled the sputtering conditions. Sputtered films are commonly under compression due to energetic particle bombardment 54–56 , the degree of which is controllable by tailoring the sputtering conditions such as gas pressure, supplied power, and substrate bias 54,55,57,58 . Poling process was not carried out for the obtained film.…”

Phase transitions and electrical behavior of lead-free (K0.50Na0.50)NbO3 thin film

“…2͑b͒, which is undoubtedly a contributing parameter for the enhanced dielectric behavior. 14 The P-E curves of the KNN thin film and bulk ceramic are shown in Figs. 3͑a͒ and 3͑b͒.…”

Development of KNN-Based Piezoelectric Materials

“…Radio-frequency (RF) magnetron sputtering onto Pt 0.8 Ir 0.2 substrate is shown to provide single phase perovskite films with about 30% deficiency of the alkali metal elements [106]. Processing under reduced pressure and temperature suggested that the deficiency is not a consequence of volatilization due to heat treatment but as a result of different sputtering rates.…”