Depolarization Characteristics of Sol-Gel Pb_1.05(Zr_0.53Ti_0.47)O₃ Thin Films

Abstract

Thin films of composition Pb_1.05(Zr_0.53Ti_0.47)O₃ in the thickness range 0.8–1.25 μm deposited on Pt substrates using a sol-gel method have been used for depolarization studies. The measurement sequence consisted of (i) polarizing the sample to the desired polarization state, (ii) switching or reinforcing the polarization state by applying a square voltage pulse of height 15–20 volts and duration 3–30 s, and (iii) monitoring the polarization as a function of time. The hysteresis loops were recorded after various steps.

The hysteresis loops exhibited asymmetry along the field axis, indicating the presence of an internal bias. It is shown that the internal bias can be changed by applying an external voltage pulse and that there exists a definite relationship between the achieved polarization state and the final orientation of the internal bias E _i .

A technique called time analyzed transient spectroscopy (TATS) has been used to analyze the polarization decay curves. The decay of polarization is exponential with the time constants varying from sample to sample indicating that the species producing the depolarization field are distributed inhomogeneously. Exponential decay indicates that the value of the opposing depolarizing field remains constant in the absence of external voltage. A model based on the depolarizing field arising from the asymmetry of the charge distribution in the interfacial space charge regions due to trapping or detrapping of the charge carriers while applying an external voltage pulse, is proposed.

Keywords:

• Depolarization
• PZT
• thin film