Direct effect of illumination on ferroelectric properties of lead zirconate titanate thin films

Photosensitive ferroelectric materials exhibit various photoferroelectric p henomena due to the strong influence of nonequilibrium charge carriers on p olarization and phase transition. These phenomena are essential for a numbe r of applications including photodriven actuators and sensitive photodetect ors. In this work, the effect of UV illumination on dielectric and piezoele ctric properties is investigated in lead zirconate titanate (PZT) thin film s, which are currently the most promising material for microactuator applic ations. The effective piezoelectric coefficient (d(33)) and dielectric perm ittivity (epsilon) of PZT films are simultaneously measured under a weak ac electric field during illumination with a band gap light (lambda =280-400 nm). It is shown that both d(33) and epsilon decrease under UV illumination . The reduction of permittivity, however, is much smaller than that of d(33 ) and demonstrates a much slower time relaxation. The d(33) decrease is att ributed to the reduction of average remanent polarization under the UV ligh t. Thus a direct effect of the photoactive light on ferroelectric polarizat ion is observed under essentially nondestructive (weak-field) conditions. T he origin of the observed effect is discussed along with the possible impli cations for thin-film devices. (C) 2001 American Institute of Physics.