Electrode Effect on Ferroelectricity in Free-Standing Membranes of PbZr_0.2Ti_0.8O₃

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.