V. P. Dudkevich

Thermodynamics of Epitaxial Ferroelectric Films.

The problem of phase transitions and physical properties of the BaTiO{sub 3}-type films on the (001) single-crystal substrates of the cubic syngony was solved in the limits of the Landau-Devonshire thermodynamics. The thermoelastic film-substrate interaction caused by the difference between thermal expansion coefficients was strictly taken into consideration. The model was based on the following assumptions: (1) the film is closely conjugated with the substrate; (2) the film is sufficiently thick to find itself unstrained at the growth temperature T{sub s} (growth stresses were compensated by misfit dislocations), and (3) the film is sufficiently thin, and the stresses arising at the temperatures T > T{sub s} may be considered to be uniform.

The structure and the piezoelectric properties of thin Pb(Zr0.53Ti0.45W0.01Cd0.01)O3 films

Abstract Thin ferroelectric films with thicknesses of (0.6–4.1) × 10−6m have been grown by single-target r.f. sputtering. Powdered lead zirconate-titanate (PZT) type ceramics were used as a target. Microstructure and both dielectric and piezoelectric properties of a thin film depend on its thickness. When the thickness increases, the thermoelastic stresses increase and the influence of the oxide transition layer in the metallic substrate-thin ferroelectric film interface decreases. Thin PZT-type ferroelectric films are characterized by high values of the piezoelectric modulus d33 and weak temperature dependences. All these create an opportunity for their application to electromechanical transducers (e.g. in electroacoustics).

The growth process and certain ferroelectric properties of heteroepitaxial (Ba1−xSrx)TiO3/MgO(001) thin films

Abstract Heteroepitaxial (Ba 0.85 Sr 0.15 )TiO 3 and (Ba 0.6 Sr 0.4 )TiO 3 thin films of thickness from 20 to 1200 nm were obtained on the (001) planes of MgO single crystals of thickness 0.5 mm by the method of r.f. sputtering of stoichiometric targets. Depending on the sputtering conditions, insular or layer-by-layer growth of the heteroepitaxial films was observed. Large planar mechanical stresses ( σ 11 = σ 22 ) act in these thin films owing to the misfit of lattice parameters of the substrate ( a s ) and the thin film ( a f a s ; σ 11 ° = σ 22 ° = σ ° > 0) and also to the difference in coefficients of thermal expansion of the substrate (λ s ) and the thin film ( λ f λ s ; σ 11 t = σ 22 t = σ t d f ⩽ 20 nm tensile stresses are found ( σ ° > 0), while in films of thickness d f > 20 nm compressive stresses occur ( σ t

Phase transitions and domain structure in heteroepitaxial ferroelectric (Ba1−xSrx)TiO3//(100)MgO and PbTiO3//(100)MgO thin films

Abstract Heteroepitaxial PbTiO3 and (Ba1−xSrx)TiO3 thin films were obtained by the r.f. sputtering method. The (100) surface cuts of MgO single crystals served as substrates. The films obtained exhibited ferroelectric properties closely similar to those of the ceramic targets. Depending on substrate temperature (Ts) with other deposition parameters constant, heteroepitaxial films of various degrees of perfection of the crystal structure were obtained. Films deposited at a temperature slightly higher than critical temperature (Tcr) for the heteroepitaxy process exhibited an insular growth mechanism while for Ts ⩾ Tcr layer-by-layer growth was found. At room temperature the crystal structure of the PbTiO3//(100)MgO films and of the (Ba1−xSrx)TiO3//(100)MgO films for × ⩽ 0,3 exhibit symmetry of the tetragonal system P4mm. Phase transitions in the (Ba1−xSrx)TiO3//(100)MgO films unlike those in the PbTiO3//(100)MgO films exhibited marked diffusion. The domain structure of the heteroepitaxial films, in comparis...

Ferroelectric Film Self-Polarization

In the present paper three mechanisms of self-polarization of ferroelectric crystals are discussed: polarization by the crystal bending, that by the “organized” Phase transition and that by the internal field. It is shown that these mechanisms operate also in the case of films. However, the using of cathode sputtering leads to the appearance of two new mechanisms: polarization by the field biasing the substrate with respect to the gas discharge at the film deposition temperature Ts below the Curie point temperature Tc (Ts Tc).

Thin ferroelectric films of the lead zirconate-titanate type obtained by r.f. sputtering

Abstract Using the method of r.f. sputtering, polycrystalline ferroelectric Pb(Zr0.53Ti0.45W0.01Cd0.01)O3 thin films were obtained with a thickness df = (0.13–11.2) × 10−6m. Study of the crystal structure and microstructure as a function of thickness showed that these thin films have a two-phase structure (phase I of perovskite-type structure and phase II of pyrochlore structure). The concentration of phase II and dimensions of phase I grains and also the degree of perfection of their structure govern the electrical properties of these thin films. The ferroelectric thin films obtained were analysed with respect to their suitability for the construction of memory elements. It was ascertained that this application is feasible but only after subjecting the thin films to annealing in an oxygen atmosphere.

Dynamical deformation sensors based on thin ferroelectric PZT films

Abstract The conditions of preparation of thin polycrystalline ferroelectric PZT films of Pb(Zr0.53Ti0.45W0.01Cd0.01)O3 chemical constitution obtained by r.f. sputtering are presented. Two variants of the technique are demonstrated, namely (1) sputtering of a powdered ceramic target in a continuous r.f. discharge and (2) sputtering of a hot-pressed target in a pulsed r.f. discharge. On the basis of thin films deposited on stainless steel, isotropic piezoelectric sensors of dynamical deformation have been constructed. The sensors have been calibrated in the range of low frequencies and their properties investigated under both laboratory and industrial conditions. On the basis of thin PZT-type films deposited on ceramic substrates (polycor), anisotropic piezoelectric sensors of dynamical deformation have been built. Investigations performed under laboratory conditions have shown that one can use such anisotropic sensors for measuring the main components of the deformation tensor of the surface of the sample under investigation and for determining the angle between the sensor axis and the main axis of the deformation tensor.

Memory effects in the structure silicon single crystal-ferroelecltric film

Abstract The memory effects in the structure: (Ba Sr) TiO3 film-silicon single crystal have been studied, It is shown that for explaining them it is necessary to take into account both the natural unipolarity of (Ba, Sr) TiO3 film and the injection of carriers from Si. In terms of the results obtained a conclusion has been made on the possibility of using such structures as currentless cells memory for long-term storage of information.

Heteroepitaxial films of (Ba,Sr)TiO3

Abstract Experimental data about certain peculiarities of ferroelectric phase transition revealed by the temperature dependences of unit cell parameters and domain structure specificity are presented.

The surface layer of oxide ferroelectric crystals

An analysis of the existing hypotheses on the origin of the surface layer in ferroelectric crystals has been carried out based on the experimental data obtained from an x-ray structural study of BaTiO3 crystals. It has been shown that the surface layer of these crystals is due to the capture of basic charge carriers (holes) by the extrinsic surface states.