Dielectric properties of PZT thin films under a low AC-electric field at different bias fields
Résumé
Functional ferroelectric thin films present a great interest for telecommunication applications. In particular, the tunability of the dielectric constant under an applied electric field allows realizing of intelligent devices. The non linear variation of the permittivity is attributed to domain wall motion. The movement of domain walls under the influence of a low ac electric field corresponds either to a vibration around the equilibrium position (pinning center) or to a jump towards another equilibrium state. The first mechanism corresponds to a reversible process whereas the second is related to an irreversible modification of the local polarization. This results in the “hyperbolic law” for the description of the permittivity which is an improvement of the Raleight law. We present here a study of the parameters of the hyperbolic law as a function of the bias field, i.e. at different points of the hysteresis cycle. We are in particular interested by the ratio between the reversible and the irreversible contribution to the permittivity. Experiments concern the real part of the permittivity but also the imaginary part which is related to the dielectric losses phenomena.