Microstructure analysis of porous lead zirconate-titanate films

Porous ferroelectric lead zirconate-titanate (PZT) films with different internal structures are synthesized using a sol-gel technique and spin-on deposition on platinized silicon substrates. The films' porosity is engineered using various structure-directing agents: polyvinylpyrrolidone with a molecular weight of 360 000 (1-6.6 wt.%) and block copolymer surfactants Brij 30 and Brij 76 (30-60 wt.%). The films' structures are characterized by transmission electron microscopy. The PVP-based films contain large, elongated pores with diameters as large as 100 nm. By contrast, the films prepared from solutions with block copolymers exhibit a small pore size depending on the surfactant molecular weight (10-19 nm for Brij 30 and 20-27 nm for Brij 76), with a mostly uniform distribution of channel-like pores within the film volume. Despite their highly porous structures, all of the films show a columnar-grain perovskite structure with grains as large as several micrometers and curved grain boundaries. The films demonstrate ferroelectric behavior with dielectric hysteresis, and their permittivity decreases with increasing porosity. Thus, the Brij 30 and Brij 76 copolymer surfactants can be used to engineer fine porous structures in PZT films for various applications in electronics.