Electrode Effect on Ferroelectricity in Free-Standing Membranes of PbZr0.2Ti0.8O3

Abstract

We report the effects of screening capacity, surface roughness, and interfacial epitaxy of the bottom electrodes on the polarization switching, domain wall (DW) roughness, and ferroelectric Curie temperature (T_C) of PbZr_0.2Ti_0.8O₃ (PZT)-based free-standing membranes. Singe crystalline 10–50 nm (001) PZT and PZT/La_0.67Sr_0.33MnO₃ (LSMO) membranes are prepared on Au, correlated oxide LSMO, and two-dimensional (2D) semiconductor MoS₂ base layers. Switching the polarization of PZT yields nonvolatile current modulation in the MoS₂ channel at room temperature, with an on/off ratio of up to 2 × 10⁵ and no apparent decay for more than 3 days. Piezoresponse force microscopy studies show that the coercive field E_c for the PZT membranes varies from 0.75 to 3.0 MV cm^–1 on different base layers and exhibits strong polarization asymmetry. The PZT/LSMO membranes exhibit significantly smaller E_c, with the samples transferred on LSMO showing symmetric E_c of about −0.26/+0.28 MV cm^–1, smaller than that of epitaxial PZT films. The DW roughness exponent ζ points to 2D random bond disorder dominated DW roughening (ζ = 0.31) at room temperature. Upon thermal quench at progressively higher temperatures, ζ values for PZT membranes on Au and LSMO approach the theoretical value for 1D random bond disorder (ζ = 2/3), while samples on MoS₂ exhibits thermal roughening (ζ = 1/2). The PZT membranes on Au, LSMO, and MoS₂ show T_C of about 763 ± 12, 725 ± 25, and 588 ± 12 °C, respectively, well exceeding the bulk value. Our study reveals the complex interplay between the electrostatic and mechanical boundary conditions in determining ferroelectricity in free-standing PZT membranes, providing important material parameters for the functional design of PZT-based flexible nanoelectronics.