We investigated the effects of exposure to active ammonia (NH3) gas generated by catalytic chemical vapor deposition (Cat-CVD) apparatus on ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) capacitors. It is very important to know these effects in order to apply Cat-CVD SiNx films to passivation films for ferroelectric FRAMs. The exposure to active NH3 was carried out for PZT film capacitors with two types of bottom electrodes on Si wafer at various substrate temperatures. The capacitor with Pt/IrO2 bottom electrode peeled off from substrate during exposure over 200°C. On the other hand, the ferroelectricity of the capacitors with IrO2 bottom electrodes gradually degraded from 200°C to 300°C. As a result, it is found that no degradation of the ferroelectricity is detected for exposure below 200°C. It is concluded that the Cat-CVD method is a promising candidate for preparation of the SiNx passivation film on ferroelectrics, since it is a low stressed film with low hydrogen content.

Sputtered Pb(Zr, Ti)O3 thin films with superior ferroelectric properties were successfully obtained by controlling the grain structure and the film compositions. We found that amorphous PbTiO3 buffer layers are effective in forming PZT thin films with fine dense grains. The sputtered PZT thin films with Ti-rich phase showed excellent ferroelectric properties. The polarization retention properties of PZT capacitors with Ti-rich phase are remarkable, and the value of the retained polarization density after 10 years is expected to be larger than 40 μC/cm2. Further, 150-nm-thick PZT capacitors with Zr/Ti=30/70 showed 2P, at 1.5 V of more than 30 μC/cm2, and good retention property. These results indicate the potential of the lower voltage operation of sputtered PZT capacitors by optimizing the film composition and thickness.

It is shown that high-quality La-doped PZT-films, (Pb,La)(Zr,Ti)O3, can be deposited by pulsed laser deposition (PLD) directly onto stainless steel substrates resulting in a very simple bicomponental system with high potential for sensor applications. This is an astonishing result, since there is quite a substantial lattice mismatch between the substrate and the PZT-film. Careful investigations revealed the existence of a thin oriented nickeloxide layer at the surface of the stainless steel. The formation of this interface layer leads to a reduction of the lattice mismatch thus affecting the subsequent phase formation of the perovskite PZT. The interface was examined by RBS, XRD, TEM / X-TEM studies and SIMS depth profiling. The phase formation and stoichiometry of the PZT films were investigated by XRD and EDX and their microstructure and texture by SEM and XRD pole figure measurements.

Recent progress in the measuring techniques based on a combination of a quasistatic P-V analysis, conventional dynamic hysteresis measurements, and fast pulse characterization allows to determine the coercive voltage as a function of the frequency over a range of more than seven orders of magnitude. In this review, we explain the experimental techniques and present the results for the thin film systems of SrBi2Ta2O9 (SBT) and Pb(ZrTi)O3 (PZT). Theoretical models of the correlation between the ferroelectric relaxation and the coercive voltage are discussed in the light of the new data.

In this paper the temperature dependence of reversible and irreversible polarization contributions in the temperature range between 223 K and 473 K is investigated to elucidate the microscopic mechanism responsible for reversible and irreversible changes of the ferroelectric polarization. Small signal capacitance measurements under dc-bias are used to measure the reversible contributions. Quasi-static hysteresis measurements are used to obtain the total polarization, i.e. the sum of the reversible and irreversible contributions. The combination of both measurements allows the separation of the reversible and irreversible parts. The reversible and irreversible contributions are demonstrated for SrBi2Ta2O9 (SBT), SrBi2Ta2-xNbxO9 (SBTN) thin films and compared to tetragonal PbZr0.3Ti0.7O3 (PZT) thin film capacitors.

A pulsing technique was used for more detailed investigation of the switching process in ferroelectric PZT films. This technique allows for the separation of the switching and reversible parts of the polarization and an estimation of the impact of the different effects in the hysteresis loop such as domain structure, depolarizing field and space charge distribution. It is shown that it is possible to provide nondestructive readout of the information stored as the polarization state by measuring the nonlinearity of the reversible polarization. Theoretical limit for the nondestructive readout signal is 20% of the remanent polarization in the differential regime and 12% in the direct regime. The experimental value of the signal is 10% in the both regimes and does not depend on time or the number of readings.

The effects of grain boundaries on the characteristics of the PZT thin films using single-grained PZT array by selective nucleation and growth method were investigated by locating the upper Pt electrode of 8 μm× 8 μm sized square directly on the single grains, 1 grain boundary and 4 grain boundaries in a controlled manner. It turned out that when there was no grain boundary, the best ferroelectric and electrical performance were obtained as expected. However, serious degradation was observed in polarization, leakage current, breakdown field and fatigue characteristics when grain boundary was contained in the area measured. This is the first qualitative investigation about the effects of the grain boundaries on the ferroelectric and electrical performance of the PZT thin films. It was found that degradation of the PZT thin films was accelerated with increasing the length of the grain boundaries within the top electrode and the main source of degradation in PZT thin films is grain boundary.

Domain structure and growth mechanism of PbTiO3 thin films were investigated using a transmission electron microscopy(TEM) from the viewpoint of size effects. At initial growth stage of (111)-oriented PbTiO3 films prepared by metalorganic chemical vapor deposition(MOCVD), triangle-shaped islands were grown on Pt(111)/SiO2/Si before becoming a continuous film. Triangular islands grew gradually in a lateral dimension. This means that PbTiO3 films grew two-dimensionally at initial growth stage. In cross-sectional TEM photomicrographs, (101)-twin boundaries (90° domain walls) and inclination of {110} or {101}-plane were observed in PbTiO3 islands. This result indicates that such small PbTiO3 islands have a tetragonal structure and could have spontaneous polarization. The minimum island which had 90° domain walls was 10nm high and 18nm wide.

Variable temperature atomic force microscopy (AFM), scanning surface potential microscopy (SSPM) and piezoresponse imaging were applied to the characterization of a model BaTiO3(100) surface. The influence of the domain structure on surface topography, surface potential and piezoresponse image is discussed. The domain induced surface corrugations and piezoelectric response were found to disappear above the Curie temperature in full agreement with theoretical expectations. Relaxation of apparent surface potential after the transition to paraelectric state on heating and during the transition to ferroelectric state on cooling was observed. The kinetics of potential relaxation was orders of magnitude slower than that of the transition.

Near-field second harmonic microscopy is ideally suited for studies of local nonlinearity and poling of ferroelectric materials at the microscopic level. Its main advantages in comparison with other scanning probe techniques are the possibility of fast time-resolved measurements, and substantially smaller perturbation of the sample under investigation caused by the optical probe. We report second harmonic imaging of the surface of thin BaTiO3 films obtained in a near-field microscopy setup using a Ti:sapphire laser system consisting of an oscillator and a regenerative amplifier operating at 810 nm. Optical resolution on the order of 80 nm has been achieved.

We report results on domain retention in preferentially oriented Pb(Zr,Ti)O3 (PZT) thin films on Pt and on LaNiO3 (LNO) electrodes. Effects of bottom electrodes on domain images and retention properties have been explored by detecting an electrostatic force exerted on the biased conductive probe. It was demonstrated that polarization loss of PZT crystallites on LNO appears to be less than that of PZT grains on Pt. Moreover, charge retention was controlled by a reverse-poling protocol during electrostatic force microscopy (EFM) measurements. The surface charge density of the PZT films was observed as a function of time in a selected area where a region is single-poled and another region is reverse-poled. The retention behavior of the regions is very different; the single-poled region shows a declined response and the reverse-poled region reveals a retained characteristic. Decay and retention mechanisms are explained by space-charge redistribution and trapping of defects in the films.

A fundamental issue in the physics of ferroelectric memories and piezoelectric devices is to study how their properties scale with the size of the ferroelectric structure. In this work we present results concerning the ferroelectric behavior of structures with lateral sizes in the range 100 nm to 1 μm. The ferroelectric characterization was achieved using the piezoresponse mode of a scanning force microscope. 100 nm patterned PZT polycrystalline structures as well as 200 nm epitaxial SrBi2Ta2O9 grains exhibit distinct ferroelectric hysteresis loops. Fatigue measurements on 500 nm structures of PZT were also performed and are discussed.

Rare earth (Gd+3 and Ce+3) substitution on La+3 sites of the sol-gel prepared Pb0.85La0.15TiO3 films is studied using x-ray diffraction, atomic force microscopy, Raman scattering, and electrical characterization techniques. With increasing content of rare earths an increase in the lattice tetragonality was evidenced from x-ray data. Raman spectra obtained form Pb0.85La0.15-xCexTiO3 (x=0.0–0.07) and Pb0.85La0.15-xGdxTiO3 (x=0.0–0.15) films show features characteristics of PbTiO3 perovskite. Frequency variations of the lowest soft mode as a function of the composition x and temperature corraborate the increased tetragonality in these films. The ferroelectric transition temperature, dielectric constant, and coercive field was found to increase with Gd content. The phase transition temperature and polarization values increase up to 5 at.% Ce doping while they decrease above that composition due to the reduced domain wall mobility caused by Ce precipitation. A slight increase in the surface roughness was observed with increasing rare earth content in these films.

A powder x-ray diffraction method has been developed to quantify textured volume fractions in thin films. It has been applied to {111}, {100} and randomly oriented PbZrxTi1-xO3 in 200 nm thick films used for ferroelectric random access memory applications. The integrated and peak intensities of 100, 110, 200 and 222 Bragg peaks from an untextured PZT film were determined by applying a thickness correction to a θ–2θ scan obtained from random powder of the same composition as the film. X-ray scans were made on the same peaks from the PZT film specimens. The distributions of grain orientation for the {111} and {100} populations in the films were determined from ω scans which were obtained from the films using 100, 200 and 222 scattering angles and corrected for defocussing and absorption. To determine the total volume fraction of each population of grains, the ratios of the integrated film peak intensities to the corrected powder integrated peak intensities were multiplied by the integrals of the corrected ω scans.

We have been successful in the fabrication of (001) oriented epitaxial PZT films on YBCO/SrTiO3/MgO/TiN/Si heterostructures by pulsed laser deposition. The films were observed to be single phase by X-ray diffraction. The deposition parameters were varied to obtain the best epitaxial layer for each of the compounds. Transmission electron microscopy was employed for understanding of the structure, crystallinity and interfaces for each of these epilayers. Dielectric and P-E hysteresis loop measurements were carried out with evaporated Ag electrodes. The dielectric constant for the films was found to be around 380–400. The value of saturation polarization Ps was between 40–50 μC/cm2 and the coercive field Ec varied from 45–55 kV/cm. Integration of PZT films with silicon will be useful for future memory and micromechanical devices.

In the present work we have studied the characteristics of Pb1.05-xLaxTil-x/4O3 ( x= 0 to 30 at%) thin films prepared by acetic acid and methoxy-ethanol based sol-gel techniques. We have found that higher intermediate temperature fired films (x=0.15), prepared by acetic acid modified technique yielded (100) textured growth with improved dielectric properties. It has been argued that homogeneous mixing of the film constituents in the sol is influenced by the choice of the precursor materials and preparation methodology which in turn controls the growth characteristics and electrical properties. Lanthanum as a dopant has a pronounced influence on the structure, microstructure and electrical properties of the deposited films. In the Raman spectra, the soft E(1TO) phonon shifts towards the lower frequency with a sharp decrease in its intensity and a tetragonal to cubic structural transformation (for 26.5 at % La) was observed at room temperature. In the ferroelectric composition range (up to 15 at % La doping), we have observed a significant improvement of ferroelectric properties with the La addition.

Stress development in thin layers of PbZr0.53Ti0.47O3 (PZT) and PbTiO3 (PT) prepared by sol-gel processing was monitored by in situ laser reflectance measurements. Layers were spin coated onto silicon substrates and thermally cycled to 600°C and 650°C. The shrinkage normal to the film plane was determined by in situ ellipsometry and scanning electron microscopy. Both PZT and PT multilayers showed a similar stress behavior on heating, but quite different behavior on cooling. As the film became dense at high temperatures, total stress was dominated by the thermal expansion mismatch between the oxide layer and the substrate. On cooling, the PT multilayers, which already crystallized into the perovskite structure, ended nearly stress free at room temperature, whereas mostly amorphous PZT multilayers were under a high tensile stress. Densification in PZT layers appeared to occur between 370°C and 520°C. At near 370°C the shrinkage mode for a single PZT layer was also observed to change substantially. A two-stage sintering process employing 450°C-sintering and 650°C-crystallization was found to be as effective as direct furnace insertion method in producing a dense film.

It is suggested that the processes of charge injection and entrapment at the interfacial layer of Pb(Zr,Ti)O3 (PZT) film capacitors are responsible for both polarization fatigue and size effects on ferroelectric switching. The study of the charge injection by analyzing the dependence of coercive field on maximum polarization shows that there is a direct relationship between the charge injection properties and fatigue performance. Based on our results, we conclude that enhancement of charge relaxation at the interfaces of PZT capacitors results in two positive effects: improvement of polarization fatigue performance and suppression of size effects on ferroelectric switching, which are detrimental for low-voltage PZT film capacitors.

This idea has been implemented experimentally by introducing a thin RuO2 layer into the top-electrode interface of the Pt/PZT/Pt capacitor. PZT film capacitors of 100–170 nm thickness prepared in this way exhibited substantially improved fatigue in combination with weak size effects, which allows reduction of the operation voltage down to 0.8 V without degradation of the hysteresis properties. Our results show that the control of charge relaxation at the interface is a key issue for development of the low-voltage ferroelectric capacitors.

Vacancy type defects in La0.5 Sr0.5CoO3/Pb0.9La0.1Zr0.2 Ti0.8/La0.5Sr0.5CoO3 capacitors were investigated by positron depth profiling. Post-growth annealing of the capacitor structure in oxygen deficient atmosphere exhibits the formation of vacancy type defects in all layers. A significant increase in open volume defects was found in the top and bottom electrode. The changes in the bottom electrode were studied more closely by etching off the top layer.

Compositional depth profiles have been obtained on chemical solution deposited lead zirconate titanate (PZT) thin films using radio-frequency glow discharge atomic emission spectroscopy. The technique is very rapid, requiring less than one minute for complete multi-element depth profiling of films and multilayer substrates. In the present study, the method was employed to obtain compositional profiles of the various metallic (Pb, Zr, Ti, Si) and organic-related (C, H, O) species that are present in the films and underlying device. Preliminary results using this relatively new technique are reported for PZT films deposited by an aqueous acetate process and heat treated at temperatures ranging from 300 and 700°C. The initial results from these investigations suggest that Pb volatilization occurs at temperatures as low as those typically encountered during the pyrolysis step. Significant interdiffusion of the Pb into the underlying Pt electrode at this temperature is also suggested. Effects of modifying ligand on film thickness and organic decomposition behavior were also observed.