Enhanced dielectric and piezoelectric response in PZT superlattice-like films by leveraging spontaneous Zr/Ti gradient formation

Spontaneous Zr/Ti gradient formation during crystallization in sol–gel-processed Pb(ZrxTi1−x)O3 films is used to prepare superlattice-like (SL), highly (1 0 0)-oriented thin films on Pt/Ti/SiO2/Si substrates. SLs with stacking periodicity ranging from 13 up to 60 nm are synthesized with compositional gradient normal to the film surface and composition centered at x ≈ 0.53. X-ray diffraction (XRD) shows high order satellite peaks and no secondary phases. XRD structural refinement, along with XPS depth profile chemical analysis, reveals that the crystal structure alternates between rhombohedral and in-plane polarized tetragonal phases, effectively corresponding to "artificially created" phase boundaries. SL films have ∼45% and ∼20% higher d33,f piezoelectric coefficient and dielectric permittivity, respectively, with respect to compositional-gradient-free films of similar thickness, possibly due to enhanced reorientation of electrical dipoles and higher extrinsic contributions due to the motion of the "artificially created" phase boundaries in SL films. Dielectric nonlinear studies indicate a higher amount of extrinsic contributions to the dielectric response in SL and gradient-enhanced films than in conventional films of similar average composition. This processing method provides a simple chemical route to create thin ferroelectric films with enhanced dielectric and piezoelectric properties suitable for a range of miniaturized applications.