Zirconate Titanate Thin Film Capacitors Research Articles

Domain behavior in lead zirconate titanate (PZT) thin film capacitors

Abstract Domain behavior based on surface energy and volumetric free energy was discussed in relation to imprint. Surface enery and volumetric free energy result in net free energy, which determines the critical size for domain growth. If a domain size is greater than the critical size, they will grow spontaneously under a constant electric field or even under zero electric field. Sometimes, they can grow to the extent that they dominate reverse domains. This phenomenon appears to be polarization reversal under zero voltage bias. Spontaneous domain growth either under zero electric field or a constant electric field was demonstratred. This phenomenon can be partly a source of asymmetric imprint mechanism.

Effect of ultraviolet light on fatigue of lead zirconate titanate thin-film capacitors

Fatigue of Pb(Zr0.52Ti0.48)O3 (PZT) thin-film capacitors was studied under UV light (He-Cd laser, λ=325 nm). The remanent polarization of the PZT film capacitors increased upon light illumination. Fatigue resistance was also improved under UV light. During fatigue test, the change in polarization of PZT films upon UV light illumination increased gradually with cycling. These results were examined within the framework of the polarization screening model, which is suggested as an essential process for fatigue. This leads to a conclusion that more charged defects are involved in the fatigue process through internal screening of polarization.

High speed optoelectronic response from the edges of lead zirconate titanate thin film capacitors

This letter reports on a high speed (∼10 ns), nondestructive, polarization-dependent photoresponse from lead zirconate titanate (PZT) thin films, when illuminated with λ=532 nm, at ∼mW/μm2 of incident optical power. This photoresponse emerges primarily from the edges of the sandwich ferroelectric capacitors, consisting of PZT films with predominant c-axis orientation. This response, in contrast with the thermally triggered effect, is unipolar in nature and occurs at an order of magnitude lower power level, and therefore offers a greater application potential. Its dependence on the crystal orientation and remanent polarization in the PZT film, and therefore its ability to track the built-in E fields within the film, may offer such photoresponse as a high speed nondestructive evaluation tool.

Reactive Ion Etching of Lead Zirconate Titanate (PZT) Thin Film Capacitors

One of the key processing concerns in the integration of thin film capacitors into the existing VLSI for ferroelectric or dynamic random access memory applications is the patterning of these films and the electrodes. In this work, we have identified a suitable etch gas for dry etching of PZT thin films on electrodes. The etch rate and anisotropy have been studied as a function of etching conditions. The trends in the effect on the etch rate of the gas pressure, RF power and additions to the etch gas have been determined and an etching mechanism has been proposed. It was found that ion bombardment effects are primarily responsible for the etching of both PZT and thin films. Etch rates of the order of 20–30 nm/min were obtained for PZT thin films under low gas pressure and high RF power conditions. The etch residues and the relative etch rates of the components of the PZT solid solution were determined using XPS. The results show that the etching of is the limiting factor in the etch process.

Correlations Among Degradations in Lead Zirconate Titanate thin Film Capacitors

AbstractMany attempts have been made to reduce degradation properties of Lead Zirconate Titanate (PZT) thin film capacitors. Although each degradation property has been studied extensively for the sake of material improvement, it is desired that they be understood in a unified manner in order to reduce degradation properties simultaneously. This can be achieved if a common source(s) of degradations is identified and controlled. In the past it was noticed that oxygen vacancies play a key role in fatigue, leakage current, and electrical degradation/breakdown of PZT films. It is now known that space charges (oxygen vacancies, mainly) affect ageing, too. Therefore, a quantitative ageing mechanism is proposed based on oxygen vacancy migration under internal field generated by either remanent polarization or spontaneous polarization. Fatigue, leakage current, electrical degradation, and polarization reversal mechanisms are correlated with the ageing mechanism in order to establish guidelines for simultaneous degradation control of PZT thin film capacitors. In addition, the current pitfalls in the ferroelectric test circuit is discussed, which may cause false retention, imprint, and ageing.

Effects of post-deposition annealing ambient on the electrical characteristics and phase transformation kinetics of sputtered lead zirconate titanate (65/35) thin film capacitors

The fabrication of high dielectric constant lead zirconate titanate thin films for dynamic random access memory application involves post-deposition annealing to convert the low dielectric constant pyrochlore phase to the desired high dielectric constant perovskite phase. The results of our experiments detailing the dielectric characteristics such as degradation field (the electric field at which a sudden increase in leakage takes place), leakage current density, time-dependent dielectric breakdown characteristics, charge storage density, coercive field, and charge storage density are reported. The charge storage density was measured using both double-bipolar pulses and quasistatic capacitance-voltage techniques. The results of these two measurement techniques are discussed for oxygen and nitrogen annealed films. Additionally, a comparative study of the phase transformation kinetics when the post-deposition annealing is carried out in a nonoxidizing ambient such as nitrogen, as against an oxidizing ambient (pure oxygen), is detailed.

Fatigue modeling of lead zirconate titanate thin films

Abstract Polarization of ferroelectrics decreases as the number of polarization reversals increase. This phenomenon is known as fatigue. Understanding fatigue mechanisms is important for improving the reliability of ferroelectric thin films. A quantitative fatigue model is proposed for lead zirconate titanate (PZT) thin film capacitors on the basis of effective one-directional movement of defects, defect intrapment at electrode-PZT interfaces (and/or at grain and domain boundaries) and the resultant polarization loss at those surfaces under an alternating pulse. An asymmetric polarization may occur on alternating polarity because of asymmetry in electrode-ferroelectric interfaces, and/or non-uniform defect distribution in the bulk. The internal field difference owing to the asymmetric polarization causes an effective one-directional movement of defects such as oxygen vacancies, lead vacancies, mobile impurity ions, etc. These defects can be trapped at electrode-PZT interfaces, grain boundaries, and/or domain boundaries because of their lower potential energies at those sites than those in PZT bulk. This entrapment in turn results in the loss of polarization. In accordance with this fatigue source, a fatigue equation is derived which consists of three constants: initial saturation polarization, piling constant, and decay constant. The predicted values from the model agree very well with the experimental data.

Comparative study of the perovskite phase microstructure evolution and electrical properties of lead zirconate titanate thin-film capacitors annealed in oxygen and nitrogen ambients

Lead zirconate titanate [PZT, Pb(ZrxTi1−x)O3, x=0.65, 400 nm] thin-film capacitors with very low leakage current and large stored charge densities (Q′c=Pmax–Pr) for ultralarge scale integration dynamic random access memory (ULSI DRAM) memory applications have been fabricated by reactive dc magnetron sputtering followed by an annealing step. In this letter, we present a comparative study of the significant influence of the use of an oxidizing (O2) as against a nonoxidizing annealing ambient (N2) on the evolution of the perovskite phase microstructure and the electrical properties of PZT capacitors. The phase transformation kinetics are faster in a N2 annealing ambient at low temperatures, yielding capacitors with a large Q′c at low annealing thermal budgets. However, N2 annealed films exhibit a lower breakdown field and time to breakdown which is in agreement with a degradation model based on the field-induced concentration polarization of oxygen vacancies.