Growth of ATiO3 (A = Ba,Sr) dielectric thin film by a hydrothermal–electrochemical method

Abstract

The hydrothermal–electrochemical growth ofATiO3 (A = Ba, Sr) dielectric thin films on Ti substrates inA(OH)2 solutions is reviewed. The film thickness increased monotonically with increase in the quantityof electricity passed through the Ti substrate, and could be controlled coulometrically by thisfactor. The current efficiency for the film growth was in the range from about 0.6% to 3.0%.(Ba,Sr)TiO3 solid-solution films could be grown with control of the Ba/Sr composition.ATiO3 thin films could also be grown uniformly on porous Ti bodiesusing cyclic electrolysis. A tracer experiment revealed that theATiO3 film grew at the film/substrate interface by transport of both A-site and oxygen atomsfrom the solution to the interface. The films grown were composed of a thin surface layerhaving an isotropic polycrystalline structure and an inner layer having a columnarstructure. Nanopores were found at the boundaries of columnar grains constituting theinner layer. The observed pores are considered to act as short-circuit paths for masstransport from the film surface to the film/substrate interface. The resistivity of theBaTiO3 thin film wasas high as 1012 Ω cm in the voltage range up to 2 V. The breakdown field was higher than30 MV m−1. The dielectric constant and dielectric loss were about 340–350 and 7%–10%, respectively, at 1 kHzand 0.1 Vrms. The polarization–voltage hysteresis loops were those of a paraelectric phase.