L. P. Nesterenko

Fatigue of Lead Titanate and Lead Zirconate Titanate Thin Films

The fatigue of lead titanate and lead zirconate titanate ferroelectric thin films, i.e., a change in the polarization as a function of the number of switching cycles in an external electric field, is investigated experimentally. The threshold numbers of switching cycles are determined to be 1010–1011 for the lead titanate films and 109–1010 for the lead zirconate titanate films. It is shown that a change in the temperature does not substantially affect the threshold number of switching cycles at which the switched polarization decreases drastically. However, an increase in the external field strength leads to a noticeable decrease in the threshold number of switching cycles. The process of fatigue is accompanied by an increase in the coercive field and the internal bias field. It is established that, as the number of switching cycles increases, the internal bias field changes more significantly as compared to the coercive field. The absence of a change in the phase composition in repeatedly switched samples indicates that the fatigue processes have a nonchemical nature. The anomaly observed in the frequency dependence of the permittivity in the frequency range 106–107 Hz due to the domain structure disappears after multiple switching cycles. This suggests that the observed fatigue phenomenon has a domain nature.

Dielectric properties of lead titanate thin films on corundum substrates

Ferroelectric films of lead titanate were synthesized on corundum (Al2O3) substrates. The main parameters that characterize the dielectric hysteresis, such as the spontaneous polarization, coercive force, internal bias field, and the phase-transition temperature, were determined. The dispersion of the permittivity was studied using impedance spectroscopy in wide temperature and frequency ranges. An anomaly in the frequency dependence of the complex permittivity was revealed at frequencies of the order of 107 Hz.

Processes of ageing and fatigue in lead titanate thin films

Processes of ageing and fatigue in lead titanate thin films are experimentally investigated. The films under discussion were synthesized by plasma-enhanced magnetron sputtering of titanium and lead on titanium, silicon and polycor substrates in an argon environment, and subsequent annealing in an oxygen atmosphere. High temperature resistance, long shelf ageing and repolarization stability of lead titanate films on polycor substrates was shown. Reduction of polarization under cyclic switching in sine wave electric field to the minimal value happens after 10 11 cycles. Partial recovery of the basic dielectric characteristics of lead titanate thin films was observed during relaxation without external influences.

Internal field in ferroelectric films with different electrodes

It has been shown that a difference between the binding energies of electrons in different electrodes induces an electric field in the bulk of a ferroelectric film, which can be interpreted as a kind of internal bias field. The values of the internal bias field in films of different thicknesses have been found and compared with the theoretical calculations.

Influence of fatigue processes on the switching currents in lead titanate and lead zirconate-titanate films

The processes of polarization fatigue in PbTiO3 and Pb(Zr0.5Ti0.5)O3 films on silicon substrates have been studied by the method of switching in rectangular pulsed fields. Dependences of the switchable polarization, the maximum switching current imax, and the switching time τs on the number of switching cycles have been obtained from the data on the switching currents. It has been shown that the mobility of domain walls is retained in the fatigue processes and the observed fatigue is connected with switching off a fraction of the switchable volume due to pinning of reverse domain nuclei by charged defects.

Frequency dependence of the coercive field and the internal bias field in ferroelectric thin films

The dependences of the coercive field and the internal bias field on the switching field frequency for lead zirconate titanate and lead titanate thin films are experimentally studied over a wide temperature range. It is shown that, as the frequency increases, the coercive field and the bias field in these films increase at the rate dependent on the temperature and the substrate used.

Influence of electric field on fatigue processes of thin ferroelectric films

The field and frequency dependences of the remanent polarization, coercive field, and internal bias field on the number of switching cycles have been studied experimentally in thin ferroelectric lead titanate and lead zirconate titanate films. A model is proposed to describe the features of fatigue effect in these films.

Evolution of the switching current during the accumulation of fatigue in lead titanate and lead zirconate titanate thin films

The fatigue processes caused by repeated cyclic switching of polarization in lead titanate and lead zirconate titanate thin films on silicon substrates by applying rectangular pulse and sine wave fields are investigated. Upon an increase in the cycling number, an increase in the coercive and internal bias fields is observed, along with a reduction in the switching current maximum, the switching time, and the switchable polarization. At the same time, no change in the mobility of domain boundaries is observed.

Domain Walls Creep in Thin Ferroelectric Films

The switching processes in lead titanate thin films in subcritical rectangular pulsed fields have been investigated. Based on the obtained results, the dynamic exponent factor in the dependence of the domain wall velocity on the value of external field has been evaluated. It was shown that the value of the exponent factor increases as the film thickness decreases. The growth of the dynamic factor is associated with an increase in the crystallite axes orientation, when the thickness of polycrystalline films decreases.

Parameters of Domain Boundaries in Thin PbTiO3 Films

Features of polarization switching processes in lead titanate thin films were investigated. The films under discussion were synthesized by plasma-enhanced magnetron sputtering of titanium and lead on Al 2 O 3 substrates in an argon medium, and subsequent annealing in an oxygen atmosphere. In terms of theory of lateral motion of domain boundaries the main parameters of domain walls, characterizing kinetics of domain structure in thin polycrystalline lead titanate films, were determined.