Characteristics of lead zirconate titanate (PZT) films deposited by the sol-gel method using platinum and reactive sputtered RuOx electrodes

Abstract

Pb(Zr0.52, Ti0.48)O3 (PZT) thin-film capacitors with sputtered platinum (Pt) and reactive sputtered ruthenium oxide (RuOx) electrodes were fabricated. We have studied the effect of pyrolysis temperatures between 300 C and 600 C on the materials and the ferroelectric characteristics of PZT films deposited by the sol-gel method. When using Pt electrodes, the X-ray Diffraction (XRD) patterns showed that the texture of the PZT films was mainly [111] orientation for pyrolysis temperatures below 400 C, but changed to [100] orientation for pyrolysis temperatures at or above 400 C. With RuOx electrodes, the films were [110] preferred orientated. The [110] peak intensity dropped significantly for the pyrolysis temperatures at or above 450 C. At a final annealing temperature of 700 C for 10 minutes, the remanent polarization Pr of the films with Pt electrodes has a maximum value of 34uCcm-2 at 400 C of pyrolysis temperature. However, there is no considerable effect of pyrolysis temperature on the texture of the PZT films. The PZT capacitors with RuOx electrodes have the values of Pr about 24uCcm-2 for pyrolysis temperatures between 300 C and 400 C. In both cases, pyrochlore phase also existed in the films pyrolyzed at temperatures above 400 C and hence the remanent polarization and dielectric constant dropped considerably for the pyrolysis temperatures at or above 450 C. Applying the optimised pyrolysis temperature of 400 C from previous studies, the RuOx/PZT/RuOx capacitors were fabricated for the ferroelectric and fatigue measurement. The ferroelectric and fatigue properties of the PZT capacitors were investigated with different oxygen content in the RuOx electrodes and different electrode thickness. Increase in oxygen content in the electrodes would improve the fatigue properties of the capacitors but the remanent polarization has maximum value at a relative oxygen partial pressure of 10%. Our fatigue result is consistent with the oxygen vacancy model. Considerable degradation in ferroelectric and fatigue properties of the capacitors was observed when the electrode thickness was below 230nm. Oxygen deficiency in the thin electrodes was detected through Auger Electron Spectroscopy (AES) measurement. It was testified that the effect of electrode thickness is attributed to the oxygen diffusion in the bottom electrode layers. The I-V characteristics of the PZT capacitors with Pt and RuOx electrodes were also investigated. For the RuO2/PZT/RuO2 capacitors, increase in electrode oxygen content lowered the leakage current density when the applied electric field was below l2OkVcm-1. The leakage current density of Pt/PZT/Pt capacitors was confirmed to be lower than that of RuO2/PZT/RuO2 capacitors. It was found that, in the high E-field region, Pt/PZT/Pt capacitors obey the Frenkel Poole Emission conduction model.