Improvement in Ferroelectric Properties of Chemically Synthesized Lead-Free Piezoelectric (K,Na)(Nb,Ta)O3 Thin Films by Mn Doping

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Lead-free piezoelectric (K,Na)(Nb,Ta)O3 thin films were prepared by chemical solution deposition. Perovskite single-phase (K0.5Na0.5)(Nb0.8Ta0.2)O3 and Mn-doped (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films were successfully fabricated at 600 °C on Pt/TiOx/SiO2/Si substrates by controlling the excess amounts of K and Na, and Mn by doping. The (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films showed poor ferroelectric polarizations due to the insufficient insulating resistance at room temperature. The leakage current density of the (K0.5Na0.5)(Nb0.8Ta0.2)O3 films, especially in the high-applied-field region, was markedly reduced by doping with a small amount of Mn. Also, the ferroelectric properties of the (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films were markedly improved by Mn doping. 0.5 and 1.0 mol % Mn-doped (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films exhibited well-shaped ferroelectric polarization–electric field ($P$–$E$) hysteresis loops at room temperature. The remanent polarization ($P_{\text{r}}$) and coercive field ($E_{\text{c}}$) values of the 0.5 and 1.0 mol % Mn-doped (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films at 1 kHz were approximately 14 and 21 μC/cm2, and 111 and 86 kV/cm, respectively. Furthermore, these films showed a typical field-induced butterfly loop, and the estimated effective $d_{33}$ values were 58 pm/V for the 0.5 mol % Mn-doped (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films and 41 pm/V for the 1.0 mol % Mn-doped (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films.
2010-09-25