Crystal Structure Modification and Dielectric Properties of Sr- and La-Containing A 2 B 2 O 7 Thin Films for High-Temperature Operational Film Capacitors.

In order to obtain thermally stable thin-film materials with high dielectric constant, A 2 B 2 O 7 thin films (Sr 2 Ta 2 O 7 , Sr 2 Nb 2 O 7 , La 2 Zr 2 O 7 , and La 2 Ti 2 O 7 ) containing Sr or La and their solid solutions were grown on Pt/Ti/SiO 2 /Si substrates by RF sputtering and their crystal structures and dielectric properties were investigated. The Sr 2 Ta 2 O 7 and La 2 Ti 2 O 7 films exhibit highly oriented crystal structures. By contrast, the Sr 2 Nb 2 O 7 and La 2 Zr 2 O 7 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 Sr 2 Ta 2 O 7 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 x Sr 2 Ta 2 O 7 -(1- x )La 2 Ti 2 O 7 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 A 2 B 2 O 7 ferroelectric thin films have potential applications as high-temperature film capacitors that can operate at temperatures as high as 300 °C.