The effect of excess Pb content on the crystallization and electrical properties in sol–gel derived Pb (Zr 0.4Ti 0.6)O 3 thin films

Abstract

The crystallization behavior and electrical properties are closely related to the excess Pb content in PZT (Zr/Ti=40/60) thin films. However, the role of excess Pb in the crystalline growth has not been precisely defined. In this work, the effect of excess Pb content on the crystallization and ferroelectric properties of these films was investigated. To analyze the effect, PZT films containing various amounts of excess Pb, but with same grain size and film orientation, were prepared. In the case of films derived from PZT solutions with a high excess-Pb content, more nuclei formed, but grew into smaller-sized grains than in the case of films with a low Pb content. On the other hand, a conversion from (100)- to (111)-preferred orientation was observed as a result of time-dependent bi-orientational growth. A depth profile analysis using Auger electron spectroscopy revealed that excess Pb enhanced the formation of Ti-rich PZT at the Pt/PZT interface. This Ti-rich PZT seemed to be the origin of the (111) orientation in the film with high excess Pb content. As higher excess Pb was included, the films showed a higher permittivity, a lower distribution of the space charge layer and better resistance against repeating fatigue cycles, due to the inhibition of movement of vacancies. These phenomena could be applied to the formation of a space charge layer via oxygen vacancy accumulation in the case of films with a low Pb content.