Extrinsic contributions to the apparent thickness dependence of the dielectric constant in epitaxialPb(Zr,Ti)O3thin films

Abstract

The problem of the thickness dependence of the dielectric constant, as well as the extrinsic contributions to its value, is analyzed for the case of epitaxial Pb͑Zr, Ti͒O 3 ͑PZT͒ thin films. It is shown that the frequency dependence of the measured capacitance is best simulated by an equivalent circuit incorporating the trapcontaining capacitance of a Schottky contact. The thickness dependence of the dielectric constant, calculated using the formula of a plane capacitor, appears to be an extrinsic effect due to the interface phenomena in the metal-ferroelectric-metal structure. The intrinsic dielectric constant of the PZT material seems to be thickness independent and of low value of about 30-40. This is closer to the values estimated from Raman measurements or from quantum theories of ferroelectricity. The thickness independence is also proven by piezoresponse force microscopy measurements. The presence of traps is evidenced by the presence of a photovoltaic effect at subgap wavelengths.

Dielectric response of ferroelectric thin films with full and partial depletion

“…Our findings imply that the thickness effect observed in stability of polarization in charge free films can be inverted for films with moderate-to-high depletion charges where thicker films have a smeared and possibly reduced Curie temperature contrary to what one would expect under the BCs used for polarization. The predicted increase in the dielectric constant for thicker films in this work is also in qualitative agreement with previously published experimental results in the thickness regime where elastic domains are absent [9].…”

General equivalent circuit derived from capacitance and impedance measurements performed on epitaxial ferroelectric thin films

“…There are only few studies dedicated to investigation of dielectric properties of epitaxial BTO or PZT films, but without special emphasis on the deduction of the associated equivalent circuit in this case. [31][32][33] The classical equivalent circuit for an ideal ferroelectric capacitor is a parallel R-C connection. 18 In the case of ferroelectric ceramics and polycrystalline films, the equivalent circuit includes several such parallel R-C connections associated with the electrode interfaces, grain boundaries, or grain bulk.…”

Tackling Polar Response in Oxygen Deficient KTaO3Thin Films

“…The low values of ρ and λ corroborates the existence of oxygen vacancies in the as-processed films, as also revealed to above by the Poole-Frenkel formalism. Figure 5 shows the temperature dependence of ε and f rel = 1/τ obtained through the fitting procedure, where it is observed that ε(T ) reveals a defined maximum close to 367 • C. Contrarily, the relaxation frequency shows a broad maximum close to 250 • C. This behavior evidences the existence of a complex relaxation process occurring in the films [ [28][29][30]. The value of ε(∞) obtained is rather low (∼5), which is similar to the one for the optical dielectric constant, obtained from the Poole-Frenkel formalism.…”