Space-charge influenced-injection model for conduction in Pb(ZrxTi1−x)O3 thin films

Abstract

A comprehensive study of leakage conduction in $\mathrm{Pb}({\mathrm{Zr}}_x{\mathrm{Ti}}_{\text{1−x}}){\mathrm{O}}_{\mathrm{3}}$ films with Pt electrodes is carried out. The conduction properties of films prepared in different ways (sol–gel coating, metalorganic chemical vapor deposition, sputtering) were studied by using different experimental techniques including variation of the applied voltage profile, photoassisted measurements, measurements at elevated temperatures, and variation of the prehistory of the samples. Based on the collective data, it is concluded that two different regimes of carrier injection (with the critical electric field of the crossover between these regimes being independent of the measuring technique) are responsible for true leakage conduction in $\mathrm{Pt–Pb}({\mathrm{Zr}}_x{\mathrm{Ti}}_{\text{1−x}}){\mathrm{O}}_{\mathrm{3}}\mathrm{–Pt}$ films. A space-charge influenced-injection model is proposed for the interpretation of the experimental results obtained. This model describes well the main features of the observed current–voltage characteristics and provides a reasonable fit for the current–voltage curves measured at elevated temperatures, the values of the fitting parameters being in good agreement with the results of other studies. The true leakage current in the $\mathrm{Pt–Pb}({\mathrm{Zr}}_x{\mathrm{Ti}}_{\text{1−x}}){\mathrm{O}}_{\mathrm{3}}\mathrm{–Pt}$ system is shown to be time dependent because of the influence of the injected charge entrapment during measurement. According to the present results, an activation energy of about 0.9 eV describes the temperature dependence of conduction in the range of $\text{70–200\hspace{0.17em}°}\mathrm{C}.$ It is shown that a possible origin of the crossover in the activation energy at the temperature range $\text{120–140\hspace{0.17em}°}\mathrm{C}$ widely reported in the literature can be a consequence of the measuring procedure.