We examined the Raman spectra of the tetragonal Pb(Zr, Ti)O3 (PZT) films between FeRAM cells with a micro-Raman apparatus. We found that a Raman light peaked at 600cm−1 polarized linearly perpendicular to the polarization of the exciting light had a different intensity for each of the film.

We showed that the difference in the intensities can be explained by the differing distributions of grain orientations in the films. Based on this knowledge, we estimated the volume fraction of 90° domains as well as the average spontaneous polarization of the grains.

Investigations of pure and chemically substituted tantalate and niobate members of the Pb(Mg1/3 Nb2/3)O3 (PMN) family of perovskite relaxors demonstrate that the degree of cation ordering and size of the chemically ordered domains can be extensively modified by thermal treatment. These observations and refinements of the cation occupancies in well ordered samples conflict with the predictions of the widely accepted “space charge model”, and instead support a “random site” model for the 1:1 B-site ordering. In this model one of the positions in the ordered structure is occupied by Ta (or Nb) and the other contains a random distribution of Mg and the remaining Ta cations. The stability of the order and magnitude of the domain growth can be enhanced by relatively small concentrations of selected solid solution additives (e.g. Zr in Pb(Mg1/3Ta2/3)O3 (PMT); Th or Sc in PMN). Correlations between the stability of the 1:1 order and the size of the solid solution additive can be used to understand the different responses of the cation order in PMN and PMT to thermal treatment. Results are also presented for the dielectric response of fully ordered relaxors in the (l–x) Pb(Mg1/3Ta2/3)O3 – (x) Pb(Sc1/2 Ta1/2)O3 system. While large domain samples of PMT-rich compositions exhibit a relaxor response, a crossover to normal ferroelectric behavior is observed for x = 0.5. The change in the dielectric response can be rationalized in terms of the effect of the chemistry of the random site sub-lattice on the correlation length of the ferroelectric coupling.

Bismuth-based-layer-structured ferroelectric films have been formed epitaxially on Nb-doped SrTiO3 substrates by pulsed laser deposition (PLD). These films show an atomically smooth surface with a wide terrace of 100 nm∼200 nm, as observed by atomic force microscopy (AFM) which is ideal for measuring such properties. Thin films of (Bi0.7, Ba0.) (Fe0.7, Ti0.3)O3 exhibit both ferroelectric and ferromagnetic (weak ferromagnetism) properties at room temperature. In these samples, a size effect is discussed at the same time.

Schottky barrier heights of various metals on tantalum pentoxide, barium strontium titanate, lead zirconate-titanate and strontium bismuth tantalate have been calculated as a function of metal work function. These oxides have a dimensionless Schottky barrier pinning factor, S, of 0.28 – 0.4 and not close to 1, because S is controlled by the Ti-O type bonds not Sr-O type bonds, as assumed previously. Band offsets on silicon are asymmetric with much smaller offset at the conduction band, so that Ta2O5 and barium strontium titanate (BST) are relatively poor barriers to electrons on Si.

Films of (111) oriented self-polarized, tetragonal ferroelectric PZT crystallites on (100)Si/SiO2(250 nm)/(111) Pt (50 nm) have been investigated by STM, AFM and SAXS. After metallization of the PZT surface with a Cr-Ni film (5.2 nm thickness) or a Ti film (5.0 nm thickness), single domains were visible on the metal surface by STM measurements as parallel stripes. The lamellar stripes had a width of 10.5 – 25.2 nm and a vertical corrugation of 0.9 – 3.0 nm at the intersection line of the domain walls with the crystallite surface.

High resolution AFM with EBD supertips on unmetallized samples revealed areas of typically several µm in diameter showing crystallites with perfectly parallel aligned (90°) domains of 10 - 15 nm width with their boundaries along {110} planes. Single domain walls were visible as a trace on the surface by a negative corrugation effect of 1.0 – 1.5 nm. This corrugation is assumed to be a reflection of the strain distribution normal to the surface. Furthermore, coherency (oxygen) defects are accumulated at the interface between 90 ° twin domains.

SAXS investigations allowed to estimate a mean value of domain thickness of 17.5 nm. Exertion of stress (5.1 104Nm−2) to the film resulted in an increase of domain width by ∼1%.

It is widely reported that the dielectric permittivity of ferroelectric films decreases with decreasing film thickness, and understanding and controlling these size effects are very important for charge storage application of these films. By combining phenomenological theory with careful experimental work, we have shown that the form of the boundary condition for the polarization plays a decisive role in the manifestation of size effects in ferroelectric films. We have taken two extreme boundary conditions to prove our point. For the case normal electrodes, it is assumed that the boundary condition for the component of polarization vector at the ferroelectric/electrode interface is P = 0. This case corresponds to the presence of a strong edge field, resulting in “freezing out” of the ferroelectric polarization at the interface and thus exhibiting severe size effects. However, if one utilizes conductive oxide electrodes that are ferroelectric in nature the polarization would not vanish at the ferroelectric/electrode interface and therefore the size effects are largely suppressed. To prove our point and to eliminate grain size, stress, and compositional effects, epitaxial SrTiO3 thin films with stoichiometric composition on SrTiO3 single crystal substrates were investigated. In fact, the experimental data also indicates that the use of ferroelectric electrodes indeed suppress the size effects.

The imprint characteristics of chemical solution deposited Pb(Zr,Ti)O3 (PZT) and SrBi2Ta2O9(SBT) thin films have been investigated. The imprint properties were evaluated by polarization-electric field hysteresis measurements. Imprint was measured at the elevated temperatures to accelerate imprint rate. Several parametric variables such as voltage and DC bias were also used to investigate possible imprint mechanisms. To quantify imprint, two different standards for evaluation of ferroelectric capacitors were compared: voltage shift and asymmetric polarization shift. Two types of PZT thin films with the same Zr/Ti composition were prepared to investigate the influence of loop shape on the rate of imprint. In addition, the imprint behavior of SBT was also investigated. It is shown that the imprint rate is strongly dependent upon the method of evaluation as well as the loop shape.

We have conducted in-situ transmission electron microscopy (TEM) experiments on thinned single crystal barium titanate in order to study the effects of applied electric field, temperature, electron beam irradiation and UV irradiation on domain nucleation and propagation. We observe two basic modes of domain wall motion; (i) a lateral motion which uniformly widens or narrows the total domain width; (ii) a “zipping” motion in which one end of a domain narrows to a point, which then propagates lengthwise, widening (or narrowing) the domain behind it. Both domain creation and destruction can occur by this latter process. When cooling from above Tc, domain growth usually occurs by the “zipping” motion. We believe that both the lateral and “zipping” modes of motion are related. The “zipping” mode tends to occur in the presence of inhomogeneous long-range strain fields, or when trapped charges are present locally. In some instances, the trapped charge is strong enough to show significant image contrast in bright-field. Domain motion, initiated by heat, electric fields or UV irradiation, moves such charges. A model of domain motion is presented which shows how displacement charge can be injected into the ferroelectric, and which may contribute to the fatigue of these materials.

Pyroelectric effect on ferroelectricity was examined for PZT capacitors with diodes in series. It was observed that the magnitude of the polarization reversal increases as heating rate increases. The polarization reversal begins to decrease as heating rate becomes very high, which may stem from the fact that pyroelectric charges flow through the PZT film at high temperature as the film loses its resistance at the elevated temperature. A pure remanent polarization reversal model is suggested for the polarization reversal caused by pyroelectric charges. Based on the above results, a thermal shock test method is proposed for quality control of FRAM products. The thermal shock test reveals that pyroelectric effect can be minimized by controlling process for 1T-1C FRAM. It was also observed, by the thermal shock test, that imprint dominates pyroelectric effect in 1Tr cell with MFIS structure.

The microstrain in epitaxial BaTiO3 thin films has been investigated using x-ray diffraction. The full width half maximum of the (001) diffraction peaks ranged from 0.12 to 0.49 deg. From the analysis of the angular dependence of the diffraction peak broadening, it is concluded that the broadening is due predominantly to strain. The magnitude of the microstrain decreases sharply with increasing film thickness.

Ferroelectric BaTiO 3 thin films with perovskite structure were grown by sol-gel spin-on processing onto (111)Pt/Ti/SiO2/Si substrates. In order to investigate the effects of space charge in BaTiO3 thin films, we measured the relative dielectric constant and the ac conductivity of the films as a function of frequency, ac oscillation amplitude and temperature. Dielectric constant and dielectric loss were 147 and 0.03 at 100 kHz, respectively. Also, BaTiO3 thin films exhibited marked dielectric relaxation above the Curie temperature and in the low frequency region below 100 Hz. This low frequency dielectric relaxation is attributed to the ionized space charge carriers such as oxygen vacancies and defects in BaTiO3 film and the interfaical polarization. The thermal activation energy for the relaxation process of the ionized space charge carriers was 0.72 eV.

SrTiO3/BaTiO3 superlattices were deposited using injection MOCVD. The films obtained on LaAlO3(LAO), Al2O3, SrTiO3(STO) and SrTiO3:Nb(STO:Nb) were charcterized using X-ray diffraction. While the films on LaAlO3 (012), SrTiO3(100) and SrTiO3:Nb (100) were epitaxial, the multilayers deposited on Al2O3(0001)were highly oriented, but displaying two different in-plane orientations. To our knowledge, this is the first time that BTO/STO superlattices were deposited by MOCVD.

Thin film PbZr0.55Ti0.45O3 (PZT) capacitors were observed to develop a dc voltage offset when driven with an ac applied electric field. This voltage offset displayed a strong dependence on the ambient oxygen partial pressure, PO2, of the atmosphere above the film, in addition to applied electric field and temperature dependencies. A scenario is proposed wherein a chemical potential gradient is established in the film, the magnitude of which is determined by the ambient PO2. The subsequent redistribution of oxygen vacancies is thought to create the observed voltage offset. This hypothesis was supported by the observation of similar voltage offsets in compositionally graded PZT films. This effect shows promise for novel low-temperature oxygen sensing applications.

Lead zirconate, PbZrO3, is antiferroelectric at room temperature and has a first-order phase transition to the paraelectric state at 230°C in bulk crystals. At room temperature, the antiferroelectric Pb displacements along [110] directions produce a superstructure at the (h+¼ k+¼, 1) positions (referenced to pseudo-tetragonal unit cell). The Pb displacements occur perpendicular to the shorter c axis. In this study, the behavior of thin films was compared to the bulk. Films of lead zirconate were deposited onto electroded silicon wafers via the sol gel method. By varying the deposition conditions of the Pt substrate, films with both {111} and {100} preferred orientation were grown. The crystalline film consisted of columnar grains which were not completely aligned with each other, but had a random orientation with respect to the film's perpendicular axis. Measurements of superstructure peak intensities vs. temperature show that the thin films exhibit a much more gradual phase transition to the paraelectric state compared to the bulk. Furthermore, comparison of a and c vs. temperature show this effect, as well as a strain of about 0.5% in c. In the {100} oriented films, we found that the c-axis was oriented perpendicular to the film's surface, meaning they should be classified as (001).

Thin films of Li-doped ZnO of different compositions (Zn1−xLix)O, x=0.1, 0.17 and 0.3 have been prepared on Si(100) substrate for the first time by pulsed laser deposition. These films are characterized for their structural, surface morphology and ferroelectric nature. A memory window of 1.2V has been observed in capacitance-voltage measurement.

Structural and ferroelectric properties of stoichiometric SrBi2Ta2O9 and Sr-deficient-and-Bi-excess Sr0.8Bi2.2Ta2O9 bulk ceramics materials are studied. The ferroelectric Curie temperatures for SrBi2Ta2O9 and Sr0.8Bi2.2Ta2O9 are 300 and 400°C, respectively. Structure analysis by neutron powder diffraction reveals that Bi2O2 layer and TaO6 octahedra are considerably distorted and that atomic displacement along the a-axis causes ferroelectric spontaneous polarization. In Sro8Bi22Ta2O9, both Bi-substitution and cation-vacancies exist at the Sr-site. The calculated polarization of Sr0.8Bi2.2Ta2O9 is higher than that of the stoichiometric sample, which is consistent with observations of remanent polarization in thin-film capacitors. The Bi-substitution and the cation-vacancies at the Sr site enhance structural distortion in the TaO6 octahedron and lead to the higher Curie temperature and the higher ferroelectric spontaneous polarization.

The crystallographic texture of PZT thin films has been proven to play a critical role in the electrical performance of PZT used in non-volatile FRAM. During both development and production of FRAM, PZT texture must be monitored to assure ferroelectric performance. A common method for monitoring texture is to use normalized intensities collected from X-ray diffraction 2-theta scans. Although this method can reveal thin film texture, it does not give a quantitative measure of the volume of textured and/or random material. In addition, this method can only be used to compare films with constant thickness since differences in X-ray absorption are not taken into account. A new method for calculating the volume fractions of textured and randomly oriented material in PZT thin films has been developed. This new method for calculating textured volume fractions still utilizes integrated intensities from 2-theta scans, but the calculations include corrections for film thickness and geometrical factors. The calculated volume fractions obtained from this new method of data analysis can be used directly for physical evaluation of PZT thin film ferroelectric performance.

The substrate dependence of the ferroelectric properties of sol-gel derived BaTiO3 thin films was investigated. Thin (0.35 µm) films were deposited on Si substrates of various orientations and doping. Films deposited on p+ Si (1020 cm−3 B, 2% Ge) (110) were self-poled. The poling direction is self-restoring even after being reversed by an external bias or heated above the Curie temperature. The pyroelectric coefficient was not zero above the Curie point, which indicated that the films were permanently subjected to an electric field, which originates from the contact potential between the film and the substrate. Thisconclusion was confirmed by surface photo voltage spectroscopy. The possibility of a paraelectric to ferroelectric transition driven by an electric field due to the contact potential difference must be taken into account for dynamic random access memory (DRAM) applications.

We have fabricated metal/ferroelectric/insulator/semiconductor (MEFIS) capacitors of Pt/SrBi2Ta2O9(SBT)/CeO2/Si and Pt/SBT/Ce-Si-O/Si. The cerium silicate (Ce-Si-O) layer is formed by reaction between CeO2 thin film and SiO2/Si substrate at 1100 °C. The SBT film on the cerium silicate layer is smoother than the SBT/CeO2. The memory window of the SBT/Ce-Si-O increases to 1.4 V at a sweep voltage of ±5 V, whereas the memory window of the SBT/CeO2 is 0.8 V at the same sweep voltage.

Pb5Ge3O11 is a new promising candidate for nonvolatile memory such as one-transistor memory applications because of its moderate polarization and relative low dielectric constant. But this material is a low symmetry ferroelectric material and it is said the spontaneous polarization exists only along the c-axis. Furthermore, in the PbO- GeO 2 system, the stability range for the Pb5Ge3O11 phase is very limited and that even a relatively small deviation in composition or in growth temperature could lead to the formation of other lead germanate compounds. Many methods have been used to grow Pb5Ge3O11 film. This is the first time the Pb5Ge3O1 thin film has been successfully grown by advanced MOCVD technique with a liquid delivery system. This paper will discuss the MOCVD process for growing Pb5Ge3O11 thin films on different electrodes (Pt, Ir and Pt/Ir). The properties of these electrodes, the microstructures of the Pb5Ge3O11 thin films on these electrodes and their ferroelectric properties will be discussed. The advanced two-step deposition technique has been used to improve the uniformity of the Pb5Ge3O11 film. Pure c-axis oriented Pb5Ge3O11 thin film and polycrystalline Pb5Ge3O11 thin film with preferred c-axis orientation and some Pb3GeO5 secondary phase have been successfully grown on these electrodes with good ferroelectric properties.