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

Photosensitive ferroelectric materials exhibit various photoferroelectric phenomena due to the strong influence of nonequilibrium charge carriers on polarization and phase transition. These phenomena are essential for a number of applications including photodriven actuators and sensitive photodetectors. In this work, the effect of UV illumination on dielectric and piezoelectric properties is investigated in lead zirconate titanate (PZT) thin films, which are currently the most promising material for microactuator applications. The effective piezoelectric coefficient (d(33)) and dielectric permittivity (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 attributed to the reduction of average remanent polarization under the UV light. Thus a direct effect of the photoactive light on ferroelectric polarization is observed under essentially nondestructive (weak-field) conditions. The origin of the observed effect is discussed along with the possible implications for thin-film devices. (C) 2001 American Institute of Physics.