Critical thickness for extrinsic contributions to the dielectric and piezoelectric response in lead zirconate titanate ultrathin films

摘要

Highly (100)-textured Pb(Zr_(0.53)Ti_(0.47))O_3 films (Lotgering factors ≥9O%) with thicknesses ranging from 20 to 260 nm were grown on platinized Si substrates using sol-gel deposition. Ferroelectric hysteresis, low field dielectric permittivity, and nonlinear dielectric response as well as converse longitudinal piezoelectric response (d_(33f)) of the ultrathin films were studied at 1 kHz. The measurements revealed the existence of a critical film thickness, ～50 nm, below which the extrinsic contributions to the dielectric response are almost completely suppressed. Piezoelectric response of the films also showed a significant (～50%) drop at the same critical thickness. Due to the columnar microstructure of these films the critical dimension of the ferroelectric is represented by the thickness rather than the lateral grain size, where the latter is invariant across the samples. The critical thickness led also to a deviation of the thickness dependence of the dielectric permittivity from the in-series capacitors model frequently representing "interfacial dead layers." The critical size is attributed to significant reduction in domain wall population and/or mobility in films thinner than ～50 nm.