We develop a phenomenological model of electro-mechanical ferroelectric fatigue based on a ferroelectric cohesive law that couples mechanical displacement and electric-potential discontinuity to mechanical tractions and surface-charge density. The ferroelectric cohesive law exhibits a monotonic envelope and loading-unloading hysteresis. The model is applicable whenever the changes in properties leading to fatigue are localized in one or more planar-like regions, modelled by the cohesive surfaces. We validate the model against experimental data for a simple test configuration consisting of an infinite slab acted upon by an oscillatory voltage differential across the slab and otherwise stress free. The model captures salient features of the experimental record including: the existence of a threshold nominal field for the onset of fatigue; the dependence of the threshold on the applied-field frequency; the dependence of fatigue life on the amplitude of the nominal field; and the size effect on the coercive field. Our results, although not conclusive, indicate that planar-like regions affected by cycling may lead to the observed fatigue in tetragonal PZT. A particularly appealing feature of the model is that it can be incorporated in a very natural and convenient way into a general finite element analysis of structures and devices for fatigue life assessment.

The dielectric constant of a material is strongly dependent on both the polarizability and the density of the material through the Clausius Mossotti equation. While the atomic polarizability depends on the stoichiometry of the constituent atoms, the molecular polarizability is a function of the atoms’ short range bonding structure and hence can be strongly dependent on processing conditions. Since the density of the material also depends on the thermally activated diffusivity of atoms during processing, varying the processing temperatures has an effect on both the molecular polarizability and the density. The dielectric constant of Zr0.2Sn0.2Ti0.6O2 is shown to be a strong function of the substrate temperature during sputter deposition with the highest value ∼55 at 200 °C and lower values at both higher and lower process temperatures. We have investigated the bonding structure and density of the oxide dielectric deposited at a variety of substrate temperatures in order to elucidate the relative effects of each.

Ba0.5Sr0.5TiO3 (BSTO) thin films were grown on (001) MgO using pulsed-laser deposition (PLD). The microstructures of in-situ and ex-situ annealed BSTO films were studied by X-ray diffraction and transmission electron microscopy (TEM). The films showed a cube on cube epitaxial relationship with <100> BSTO // <100> MgO. They were essentially single crystals with a columnar structure and possessed smooth surfaces. The interfaces of the BSTO films and substrates were atomically sharp, with misfit dislocations. Better crystallinity and full strain relaxation was obtained in films grown in 10-1 mbar oxygen and annealed ex-situ. A 30% increase in dielectric tuneability was achieved compared with in-situ annealing and deposition at 10-4 mbar. Threading dislocations are the dominant defects in the films grown in 10-1 mbar oxygen and annealed ex-situ, while the films with in-situ annealing show columnar structures with low angle boundaries.

Sub-100nm-Thick Polycrystalline Bi4-xLaxTi3O12 (BLT) thin films have been formed on silicon substrates by sol-gel and spin-coating techniques. The analysis of X-ray reflectivity for the BLT/Si structure showed that the BLT film density was slightly lower than the ideal value and the interfacial layer was formed. By Fourier transform infrared spectroscopy (FT-IR) it is confirmed that the formation of the interfacial layer was due to oxidation of Si. Clockwise hysteresis was observed in capacitance-voltage (C-V) characteristics for Au/BLT/p-Si structures at a frequency range between 1 MHz – 1 kHz. The frequency dispersion of the C-V curve was caused by a large amount of interface states at BLT/Si interface. As the film was crystallized at 550°C for 2 h the maximum interface state density was ∼3.4×1011 cm-2ev-1 at 1 kHz. Also, the negative gate-voltage shift of the C-V curve from the ideal curve and the gate-bias dependence of the flat-band voltage were observed, resulting in the presence of undesirable positive charges in the film and the electron injection to the traps near the BLT/Si interface. By post-annealing of the device at 400 °C in oxygen atmosphere the interface states (fast sates) were successfully reduced to a third of the initial value and also the positive charges were significantly diminished.

We demonstrate transparent thin film transistors (TFTs) with nonvolatile memory operation using Bi4-xLaxTi3O12 (BLT) as a gate insulator and indium tin oxide (ITO) as a channel. ITO is also used for the gate, source and drain electrodes. Drain current-drain voltage (ID-VD) characteristics of transparent ITO/BLT ferroelectric-gate TFTs exhibit excellent n-channel transistor operations. On current of 0.35 mA was obtained when the applied gate voltage is 6V. On the other hand, the off current of the device is as low as 10-10A, which indicates that the ITO channel is sufficiently depleted by the ferroelectric polarization. In addition, drain current-gate voltage (ID-VG) characteristics demonstrate clear counterclockwise hysteresis loop due to the ferroelectric gate insulator. Optical transmittance of the fabricated device is greater than 60% including the quartz substrate.

The polarization change invoked by bipolar pulse cycling stress (voltage cycling) was investigated in detail for a Pt/PZT/Pt ferroelectric capacitor. The remnant polarization increased after voltage cycling, then, it decreased during storage and approached to the initial value. The estimated activation energy of the decay of the gained-polarization during the storage was 0.52eV. This value suggests that the valence change between Ti3+ and Ti4+ is the key of this phenomenon. The model where Ti-related defects pin the polarization was introduced to explain the result. Based on the findings and the model, a combination of voltage cycling and storage is useful to characterize internal defects. We propose this characterization method, named voltage cycling method, as an effective way to analyze internal defects in a ferroelectric capacitor.

c-axis-oriented epitaxial SrBi2Ta2O9 ultra-thin films were grown by pulse-gas-introduced metalorganic chemical vapor deposition (pulsed-MOCVD) on (100)SrTiO3 single crystal substrates with atomic scale step structure and their growth behavior was investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Minimum growth unit was found to be “ghalf-unit-cell” of SrBi2Ta2O9. Height of steps and width of terraces observed at SrBi2Ta2O9 film surface were in good agreement with those at SrTiO3 substrate surface. This shape transfer was induced by lattice displacement of SrBi2Ta2O9 along c-direction formed at atomic step on SrTiO3 substrate. In-plane growth of half-unit-cell SrBi2Ta2O9 2D-islands striding across the step walls was observed. It was considered to be a special phenomenon for c-axis-oriented films of layer-structured compounds due to their large crystal anisotropy and/or several times larger half-unit-cell height than single step one of SrTiO3.

In this study lead zirkonat titanate (PZT) thin films were deposited using direct liquid injection metal organic chemical vapor deposition (DLI-MOCVD).

The chemical states and the stoichiometry of PZT-films were characterized using X-ray photoelectron spectroscopy (XPS). The crystal structure of the films was investigated by X-ray diffraction (XRD).

The surface composition of the films was Pb : Zr : Ti = 1.05 : 0.52 : 0.48, which indicates that the deposited films had a stoichiometric PZT composition. 130 nm thick PZT films deposited on Ir showed <110> preferred orientation.

The main role for formation of the perovsktive PZT films plays the content of the lead in the deposited films. Lead deficiency causes the formation of the pyrochlore phase with poor electrical properties. In films with a significant excess of lead a second PbO phase appeared that can be observed even with naked eyes. Negligible excess of lead can be reduced by post-deposition annealing at 500-600 °C.

The Ir/PZT/Ir capacitor showed large values of the remanent polarisation of about 60μC/cm2 at an applied voltage of 3 V. So high value of the remanent polarisation can be induced by structural stress in the films. After ten switch impulses the values of the remanent polarisation have significantly decreased. This is probably due to a relaxation of crystal cells.

We have observed novel terahertz (THz) radiation characteristics of multiferroic BiFeO3 thin films upon illumination of femtosecond laser pulses. The radiated THz pulses from BiFeO3 thin films were shown to originate from an ultrafast modulation of spontaneous polarization, which was introduced by the photoexcited charge carriers. Based on our findings, we briefly present new approaches to nondestructive readout for nonvolatile memory devices and ferroelectric domain imaging microscopy using THz radiation as a sensitive probe.

Ferroelectrics are expected to become one of the next generation ultra-high density data storage media. The requirements for pulse amplitude and the duration to switch the domain were both markedly decreased by using a new domain stabilizing method; offset voltage application method. Additionally, with this method it became possible to invert a smaller domain with a diameter of less than 10 nm. Finally, significant progress was made regarding the memory density for ferroelectric data storage, and an area density of 10.1 Tera-bit/inch2 was successfully achieved. This represents the highest memory density for rewritable data storage reported to date.

We report on microstructure and ferroelectric properties of ultrathin PbTiO3 films epitaxially grown on SrTiO3(100), La-doped SrTiO3(100) and SrRuO3/SrTiO3(100) by MOCVD. High angle annular dark field scanning transmission electron microscopy, atomic force microscopy, x-ray diffraction and x-ray reflectivity measurements demonstrated that 1-20 monolayer (ML)-thick epitaxial PbTiO3 films had high-crystallinity, atomically flat surface and sharp interface at an atomic scale. The epitaxial relationship and thickness were also confirmed by these methods. Kelvin force probe microscopy and contact resonance piezoresponse force microscopy revealed that a 7ML (2.7nm)-thick PbTiO3 film grown on SrRuO3/SrTiO3 had the ferroelectric polarization.

In the present study, we comparatively investigate the distribution of electronic interface states of three different perovskite oxide interfaces, formed by epitaxial thin films of La0.7Sr0.3MnO3 (LSMO), La0.7Ca0.3MnO3 (LCMO), and La0.7Ce0.3MnO3 (LCeMO) on SrTiO3(100) substrates, in the as-prepared state as well as after an annealing procedure. We find that annealing significantly reduces the number and density of interface trap states. Two different experimental realizations of the surface photovoltage spectroscopy (SPS) technique were employed: an approach based on X-ray photoelectron spectroscopy (XPS), as well as a capacitive method. The advantages and limitations of both methods are critically discussed.

The Hysteresis characteristics of below 400 nm- thick Pb(Zr0.52Ti0.48)O3 (PZT) thin films grown on Pt (111) /Ti/SiO2/Si substrates have showed very poor with remanent polarization of 1∼3 μC/cm2 in our previous research. To study the further scaling-down, we introduced the method of our previous research that the (Pb0.72La0.28)Ti0.94O3 (PLT) buffer layers play an important role in enhancing the ferroelectric properties of the PZT thin films. As a result, the remanent polarization of 300 nm-thick PZT thin films with the 10 nm-thick PLT buffer layers have showed 32 μC/cm2 at applied voltage of 8 V and 24 μC/cm2 at applied voltage of 5 V. Inserted the PLT seed layers between the PZT thin films and substrate, the hysteresis characteristics of PZT thin films were improved a lot. The dielectric and leakage current properties of PZT thin films were also investigated.

Micro-machined piezoelectric film devices are usually fabricated onto substrates, so that the displacement response of the film is clamped with the substrate. To investigate the longitudinal displacement behavior of 10-μm-thick lead zirconate titanate (PZT) films deposited onto Si substrates, disk shape structures with diameters of 20 to 80-μm were fabricated by an reactive ion etching (RIE) process. The polarization-field (P-E) hysteresis curves did not show a remarkable difference with decreasing the PZT disk diameter. On the other hand, unipolar driven longitudinal displacement increased, and the amount of the displacement was saturated at a diameter of 30 and 20 μm. The AFM measured longitudinal piezoelectric constants, AFM d33, were estimated in the case of before poling and after poling at 100V for 10 min. The AFM d33 for the before and after poling process were 65 and 94 pm/V for 80-μm-diameter film disk, and 153 and 315 pm/V for 20-μm-diameter film disk, respectively. The value of poled AFM d33 for 20-μm-diameter film disk was comparable to bulk PZT ceramics. These results suggest that the decrease of the disk diameter reduces the Si substrate bending related with the clamping effect between the film and substrate, and facilitates domain reorientation in the poling process. It seems that the actual piezoelectric constant of films can be estimated from the longitudinal displacement when the ratio of the PZT disk diameter, d, to the PZT film thickness, t, shows d/t < 3 for 10-μm-thick PZT films.

Three-dimensional domain configuration of multi-domain LiTaO3 is revealed by Scanning Nonlinear Dielectric Microscopy (SNDM). SNDM can measure the polarization components both perpendicular and parallel to the surface of the specimen. These techniques are applied to the both congruent and stoichiometric LiTaO3 crystals. The images obtained by SNDM measurements allow us to confirm the various domain features of LiTaO3 and to understand both similarities and differences between the congruent and stoichiometric compositions.

An epitaxial ferroelectric thin film can be modeled by a two-dimensional array of dipoles. The orientation of each dipole is assigned to one of the four possible states which are mutually perpendicular to each other. Consequently, the whole film can be divided into domains with both 90° and 180° domain walls. The dominant switching mechanism for individual dipole is implemented by a 90° rotation. Two different conditions have been considered. For the first one (model A), every dipole inside the film is allowed to rotate, provided that it is thermally activated. For the second (model B), only the dipole rotation is restricted to those at the domain walls. The phase transition temperatures under these two models have been evaluated. Furthermore, the effects of sample size and boundary condition are discussed.

Highly (100) oriented Pb(Zr,Ti)O3 [PZT] films were fabricated using lanthanum nitrate/nickel acetate double layers as a buffer layer, regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature, and heating rate. The buffer layer was also acted as a very effective barrier against Pb-Si interdiffusion, thus allowing for the direct deposition of PZT films on Si, SiO2/Si, and glass substrates. The strong orientation was attributed to the formation of a crystalline intermediate phase between the PZT and lanthanum nitrate during annealing. The lanthanum nitrate/nickel acetate double layers became a lanthanum nickel oxide (LaNiO3), which shows good electrical conductivity, after an annealing process at 650°C. The nature and the role of lanthanum nitrate buffer as a layer for the growth of highly (100) oriented PZT films have been studied. The dielectric, ferroelectric, piezoelectric and electrooptic properties of the highly (100) oriented PZT films with a lanthanum nitrate/nickel acetate buffer layer were measured and compared with the values measured from the (111) and (100) oriented PZT films deposited without buffer layer.

Temperature dependency of the dielectric property of c-axis-oriented SrBi4Ti4O15 films was investigated in a temperature range from 80 to 400 K. c-axis-oriented epitaxial films with the film thickness of 30 and 140 nm were grown on (100)cSrRuO3//(100)SrTiO3 substrates by metal organic chemical vapor deposition (MOCVD). Increasing lattice distortions along the a- and c-axes with decreasing film thickness was ascertained by XRD reciprocal space mapping. However, capacitance change normalized by the capacitance data at 300 K for with temperature was independent of the film thickness; it increased from 80 to 230 K and contrary decreased with increasing the temperature. Especially, the temperature coefficient of capacitance from 230 to 330 K was almost the same. It indicates that dielectric characteristics of these films for the temperature are independent of the film thickness in the actual use. Moreover, the same mesurement for the 120 nm-thick fiber-textured c-axis-oriented SrBi4Ti4O15 film deposited on the (100)cLaNiO3/(111)Pt/TiO2/SiO2/(100)Si substrate was also investigated. Resultant capacitance change with the temperature was basically the same with that of the epitaxial one, even though the temperature at maximum capacitance value was slightly shifted to lower temperature of 200 K. These data suggest that of capacitance change with the temperature was almost independent of the film thickness and the in-plane orientation.

Thin iridium films are required as electrode material for ferroelectric capacitors. SBT or PZT are often used as ferroelectric material in such capacitors. The PZT based non-volatile ferroelectric random access memories show better fatigue characteristics if platinum is replaced by iridium as electrode material. Metalorganic chemical vapor deposition (MOCVD) was used for the deposition because of the superior step coverage on three-dimensional structures compared to the conventional physical vapor deposition processes of metal layers. Particularly, in memory fabrication, good step coverage is essential. The iridium films were deposited on different substrates at temperatures of 300 – 500 °C by liquid-delivery MOCVD. The precursor Ir(EtCp)(1,5COD) [iridium(ethylcyclopentadienyl)(1,5-cyclooctadiene)] was diluted in toluene (0.1 M concentration) for the deposition experiments. The iridium films were deposited onto TiO2/SiO2/Si-, SiO2/Si-, and Si-substrates to compare the iridium film properties on different substrates. The growth conditions like oxygen flow, growth temperature, and reactor pressure were varied. The growth rates were in a range between 0.05 and 4.6 nm per minute. We found that the growth rates were highly influenced by the oxygen flow and the substrate material. Oxygen assisted the decomposition of the precursor, and carbon and hydrogen of the organic source were oxidized, which suppressed its incorporation into the iridium layer. Annealing in an oxidizing ambient at temperatures above 700 °C resulted in an increased oxidation of the films as proved by XRD analyses. The resistivity of the films was determined by the Van-der-Pauw method. Low resistivities of 7 – 70 µΩcm were obtained for the as-deposited iridium films.

High quality Pb(Zr,Ti)O3 [PZT] and (Pb1-xBax)(ZryTi1-y)O3 (x ≤ 0.15, 0.25 ≤ y ≤ 0.50) [PBZT] thin films were grown on Pt (111) and Ir (111) coated silicon substrates by means of a pulsed liquid injection metal organic chemical vapor deposition (MOCVD) technique. The precursor solutions of Pb(DPM)2, Ba(DPM)2, Zr(IBPM)4, and Ti(OiPr)2(DPM)2 dissolved in butylacetate were separately injected into an AIX-200 reactor using a TriJet™ vaporizer. Stoichiometric films (0.98 ≤ A/B ≤ 1.06) with thickness between 80 nm and 150 nm were deposited at a susceptor temperature of 615 °C to 660 °C. Pure PZT films grown on platinum coated substrates show a randomly oriented perovskite structure accompanied with formation of a PbPtx alloy at the PZT/Pt interface. On the Ir(111) coated substrates the pure PZT films also exhibit a random orientation possibly due to oxidation of the Ir surface layer during the deposition process. Ferroelectric properties of Pr = 35 µC/cm2 and Ec = 90 kV/cm were obtained for a PZT (30/70) film of 150 nm thickness grown on Ir/Si. In contrast, PBZT films with a Ba content of about 5 to 15% show lower tendency for formation of a PbPtx interfacial layer, and a preferred (111) texture was observed for PBZT films grown on the Ir (111) substrates under optimized process conditions. Tetragonal and rhombohedral PBZT films with 15% Ba and a Zr-content of about 0.35 and 0.50, respectively, show an orientation dependence of the ferroelectric properties in the way that Ec is highest for <111> textured films in comparison to Ec determined for <110> textured films. The remanent polarization of 85 nm thick tetragonal PBZT films changes from 17 µC/cm2 for <111> orientation to 13.5 µC/cm2 for <110> texture. The relative permittivity changes in the same way from 600 to 540, respectively. The rhombohedral films exhibit a nearly independent Pr value of about 11 µC/cm2 while the switching field changes from 75 kV/cm for an <111> textured film to 46 kV/cm for an (110) textured one. The relative permittivity values of both films are 890 and 715 for the (110) and the (111) textured films, respectively. The trends observed for the textured PBZT films grown on Si substrates reflect the behaviour reported for epitaxial films [2]