Microstructure and Dielectric Properties of Thin Polycrystalline PZT Films with Inhomogeneous Distribution of the Composition over Thickness

The RF magnetron sputtering of a PZT ceramic target with a variation in the pressure of the working gas is used to form two two-layer thin-film structures differing in the sequence of layer deposition: structure “A” is deposited at a pressure of 4 and 8 Pa, and structure “B” is deposited at a pressure of 8 and 4 Pa. The total thickness of the structures is ~920 nm. An oxidized silicon wafer and an oxidized silicon wafer with a deposited platinum electrode serve as the substrates. The structures are subjected to high-temperature annealing at 570°C to crystallize the perovskite phase. Their microstructure and elemental composition are investigated with scanning electron microscopy and X-ray microanalysis. The dielectric properties are studied using an E7-20 immittance meter and a modified Sawyer–Tower circuit. The formed thin layers are characterized by a predominant 〈110〉 growth texture. It is shown that the elemental composition and dielectric properties depend on the sequence of deposition of layers. In both structures, the crystallization of the perovskite phase begins in a layer deposited at a pressure of 8 Pa enriched with excess lead, and spreads to the layer with a lower lead content deposited at a pressure of 4 Pa. Structure “B” was characterized by almost complete crystallization into the perovskite phase, the smaller segregation of titanium and zirconium atoms over the structure thickness, a higher dielectric constant, and asymmetry of the dielectric hysteresis loops and reversible dependence of the dielectric constant, which indicate the presence of an internal field and spontaneous polarization. The results obtained make it possible to specify the physical mechanism of the formation of self-polarization in thin PZT films, and also suggest one of the ways to reduce elemental inhomogeneity over thickness, which allows maximization of the dielectric and electromechanical parameters of films, whose composition corresponds to the region of the morphotropic phase boundary.