Longitudinal Electrooptic Effects and Photosensitivities of Lead Zirconate Titanate Thin Films

Abstract

The feasibility of storing and reading high‐density optical information in lead zirconate titanate (PZT) and in lead lanthanum zirconate titanate (PLZT) thin films depends on both the longitudinal electrooptic coefficients and the photosensitivities of the films. This paper describes the methods used to measure the longitudinal electrooptic effects and the photosensitivities of the films. The results of these measurements were used to evaluate a longitudinal quadratic electrooptic R coefficient, a longitudinal linear electrooptic rc coefficient, and the wavelength dependence of the photosensitivity of a composition of PZT polycrystalline thin film. The longitudinal electrooptic R and rc coefficients are about an order of magnitude less than the transverse R and rc coefficients of bulk ceramics of similar compositions. This is attributed to clamping of the film by the rigid substrate. The large birefringence of the films after poling (>10−2) suggests that the optic axes of the films are preferentially oriented normal to the film surface. The techniques used in this paper for evaluating the photosensitivities of thin films are based on measuring the photocurrent generated rather than the reduction in coercive voltage (as in bulk ceramics) when the film is exposed to light. The thin film photosensitivities appear to be significantly higher than those of bulk ceramics of similar compositions. The high photosensitivities coupled with the substantial longitudinal electrooptic coefficients combine to establish the feasibility of using PZT or PLZT thin films for optical information storage applications.