Crystal Structure Modification and Dielectric Properties of Sr- and La-Containing A₂B₂O₇ Thin Films for...

In order to obtain thermally stable thin-film materials with high dielectric constant, A₂B₂O₇ thin films (Sr₂Ta₂O₇, Sr₂Nb₂O₇, La₂Zr₂O₇, and La₂Ti₂O₇) containing Sr or La and their solid solutions were grown on Pt/Ti/SiO₂/Si substrates by RF sputtering and their crystal structures and dielectric properties were investigated. The Sr₂Ta₂O₇ and La₂Ti₂O₇ films exhibit highly oriented crystal structures. By contrast, the Sr₂Nb₂O₇ and La₂Zr₂O₇ films exhibit polycrystalline structures. The leakage properties of the Sr-containing films are lower and more stable in the high-temperature region (up to 300 °C) than those of the La-containing films. Among the investigated films, the Sr₂Ta₂O₇ film grown at 500 °C and annealed at 900 °C shows the most stable dielectric constant with respect to temperature in the temperature range from room temperature to 300 °C. In addition, the xSr₂Ta₂O₇-(1-x)La₂Ti₂O₇ solid solutions exhibit enhanced dielectric properties at x = 0.35. The dielectric constant is greater than 100, and its variation with temperature is less than 10%. The Sr-containing A₂B₂O₇ ferroelectric thin films have potential applications as high-temperature film capacitors that can operate at temperatures as high as 300 °C.