Role of TiO₂ Seed Layer Thickness on the Nanostructure Evolution and Phase Transformation Behavior of Sputtered PZT Thin Films During Post‐Deposition Air‐Annealing

Abstract

An optimum TiO2 seed layer is said to facilitate nucleation and subsequent growth of perovskite phase in Pb(Zr,Ti)O3 (PZT) films during annealing. The actual causes that prevent perovskite growth, particularly in sputtered PZT films on thick TiO2 seed layers are not yet understood clearly. Herein, based on the results of X‐ray diffractometry (XRD), field‐emission scanning electron microscopy (FESEM), and analytical scanning/transmission electron microscopy (S/TEM) with semi‐quantitative elemental mapping using energy dispersive X‐ray (EDX) spectrum imaging, the post‐annealing crystallization trend of r.f. magnetron sputter‐deposited amorphous PZT films has been scrutinized as a function of TiO2 seed layer thickness. Upon annealing, PZT films on thin TiO2 layers (~20–100 nm) partially crystallize into perovskite PZT via a transient pyrochlore/fluorite phase. However, no perovskite phase forms on thicker (~550 nm) TiO2 layer. Thickness of underlying TiO2 seed layer strongly influences the crystallization, phase formation, texture, and surface morphology of the PZT films. During crystallization, Pb diffuses away from the PZT film to form solid solution with TiO2 seed layer. Perovskite PZT phase transformation requires a minimum Pb‐concentration within the transient pyrochlore/fluorite phase. During the growth of perovskite grains, Zr gets segregated, resulting in Zr‐concentration build‐up within the surrounding disordered fcc fluorite phase.

Integration of epitaxial Pb(Zr0.52Ti0.48)O3 films on GaN/AlGaN/GaN/Si(111) substrates using rutile TiO2 buffer layers

“…It has been previously shown that the preferred orientation of the PZT films can be maintained using relatively thick buffer layers [39]. Moreover, the thickness of the TiO 2 buffer layer between PZT and a substrate has been shown to be an important parameter to control the amount of diffused Pb into the substrate [40] as well as reducing leakage. Therefore, in the following experiments, in order to prevent the diffusion of Pb into GaN/Si during the PZT deposition, a 20 nm R-TiO 2 buffer layer was used.…”

Structural and Electrical Characteristics of Metal-Ferroelectric Pb1.1(Zr0.40Ti0.60)O3-Insulator (ZnO)-Silicon Capacitors for Nonvolatile Applications

“…roughness of the film surface is 13.11 nm and observed well-defined grain growth of PZT/ZnO structure. As can be seen from Figure 3(b), after nucleation, circular rosettes grow at right corner of the film along perpendicular direction to the substrate [15]. Figure 4(a) shows a typical C-V characteristic at room temperature for an Au/ZnO/Si (MIS) diode measured at 1 MHz with a small signal voltage of 200 mV, and the sweep rate of the bias voltage was 0.2 V/s.…”

Bottom-up micromachined PZT film-based ultrasonic microphone with compressible parylene tube

“…The annealing process of titanium allows us to obtain a thin titanium dioxide film as the seed layer. This seed layer between PZT film and titanium substrate could not only prevent the formation of the pyrochlore/fluorite phase, but also improve the crystal quality of PZT films grown on lattice-incompatible substrates [28,29]. The process substrate was placed in a vacuum furnace, and air inside the furnace was drawn to reach a pressure of 20 mtorr.…”