Microstructure and texture development in single layered and heterolayered PZT thin films

Single-layered Pb(Zr0.7Ti0.3)O3 and Pb(Zr0.3Ti0.7)O3 thin films and heterolayered Pb(Zr1−xTix)O3 thin films consisting of alternating Pb(Zr0.7Ti0.3)O3 and Pb(Zr0.3Ti0.7)O3 layers were studied for their microstructure and texture development. The texture in the single-layered PZT films is affected by the Zr/Ti ratio as they have different crystallization behavior depending on the Zr/Ti ratio. With increasing film thickness, the average grain size of Pb(Zr1−xTix)O3 increases. An unusually large grain size of 1–3 μm together with a strong (001)/(100) preferred orientation were observed for the heterolayered PZ70T30, whereby Pb(Zr0.7Ti0.3)O3 was used as the seeding layer, for film as thin as 150 nm. The film microstructure is refined drastically when the stacking sequence is changed, i.e., when Pb(Zr0.3Ti0.7)O3 is employed as the seeding layer. Thermal treatment of the PZ70T30 seeding layer also plays an important function in the microstructure development of the heterolayered PZ70T30 film. The formation of the large-grained film is correlated to the lowered nucleation energy of crystallizing Pb(Zr0.7Ti0.3)O3 by the top Pb(Zr0.3Ti0.7)O3. The Pb(Zr0.3Ti0.7)O3 layer facilitated the nucleation and crystallization of the Pb(Zr0.7Ti0.3)O3 amorphous seeding layer, whereby the overall microstructure of the heterolayered thin film was dictated by the Pb(Zr0.7Ti0.3)O3 seeding layer leading to the growth of larger PZT grains.