Metallic perovskite contact layers enable fatigue-resistant ferroelectric memory capacitors to be obtained. LaNiO3 films atop (100) LaAlO3 substrates exhibit metallic resistivity over a wide range of temperature and oxygen partial pressure. Subsequent deposition of PZT and LaNiO3 thin films atop LaNiO3/LaAlO3 provides parallel-plate ferroelectric capacitor structures. However, the quality of the PZT thin films cannot be reliably indicated by conventional means such as x-ray diffraction. Optical properties of the PZT layers were examined to discern differences in otherwise similar films. The suitability of Au/LaNiO3/PZT/LaNiO3/LaAlO3 devices for nonvolatile memory applications was surveyed through pulsed voltage testing. Observed 1-second remanent polarization (PR [1 sec]) exceeded 35μC/cm2. Long-term memory was demonstrated for up to sixteen hours. No decrease in remanent polarization was apparent after more than 2 × 1010 switching cycles.

Optical losses are a barrier to use of ferroelectric waveguide thin films. Losses of about 2 dB/cm will reduce the efficiency of a frequency doubler by over 50%. Achieving losses on this order in conjunction with other essential film properties is difficult. The optical loss has several origins, including absorption, mode leakage, internal scattering and surface scattering. When the film surface morphology is accurately known, it is possible to estimate the surface scattering component of the loss. We have employed atomic force microscopy and computer modeling to compute, and correlate the optical loss as a function of film thickness and wavelength. The results suggest upper limits to the morphological roughness for various device applications. For lithium niobate films on sapphire which are intended to frequency double into the blue part of the spectrum, the optimal film thickness is about 400 nm and the RMS roughness is constrained below about 1.0 nm, with some weak dependence on grain size. Although present growth techniques do not appear to achieve this level of surface flatness intrinsically, an understanding of the morphological development of the film structure may lead to improvements.

Single phase, highly textured strontium barium niobate (SBN) thin films were deposited by low pressure metal-organic chemical vapor deposition on both crystalline and amorphous substrates. The metal precursors employed were niobium pentaethoxide as well as barium and strontium (hexafluoroacetylacetonate)2•tetraglyme. SBN thin films with compositions across the entire solid solution range were deposited. The nonlinear optical properties of the SBN films were also measured. Nonlinear optical coefficients approaching bulk values were obtained for as-deposited oriented films. The room temperature, effective second-order nonlinear coefficient was 3.0 pm/V. Films with the highest degree of crystalline perfection had the largest effective nonlinear coefficient. The second harmonic intensity was strongly temperature dependent with a maximum at the ferroelectric transition.

We report the epitaxial growth of Sr0.6iBa0.39Nb2O6 (SBN) thin films on MgO substrates by pulsed laser deposition. Rutherford backscattering analysis shows that the films have stoichiometric composition, identical to the target, and thicknesses in the range 200–400 nm. X-ray diffraction 2θ-scans indicate layers with the (001) orientation perpendicular to the substrate plane, and phi scans on the (221) plane reveal that the films have two pairs of in-plane orientations. The orientations correspond to a rotation of the SBN unit cell relative to the MgO unit cell of ± 18.6° and ± 30.9° respectively. Waveguide characterization shows waveguides supporting up to four modes and film refractive indices which compare well with those of bulk SBN.

Lithium niobáte (LiNDO3) in single crystal form is useful for the fabrication of acoustooptic and active waveguide devices. In this paper, the feasibility of integrating LiNbO3 thin layers on sapphire is reported. The performance of signal modulators, surface acoustic wave devices, and second harmonic generators relies on control of crystallographic orientation, so a thin-layer deposition method must meet high standards of crystallographic perfection and optical quality. Solution deposition of lithium niobium ethoxide was evaluated on (110) and (006) sapphire substrates for heteroepitaxy. Atomic force microscopy was used to determine the development of microstructure during the transition from the amorphous to crystalline state. Slab waveguides were formed and evaluated for optical quality and loss. Optical losses in the TEo mode of 500nm (110) LiNbO3 thin layers were determined to be 6 dB/cm. Preliminary results are given for the heteroepitaxial growth of α-Ga2O3 buffer layers.

A set of fatigue measurements has been performed on RF-sputtered PZT films of about 2 urn in thickness. Polarization switching characteristics with the sinusoidal ac electric field applied were studied both with sandwich and planar electrodes. Planar structure has allowed one to study the influence of the free charge carriers induced by UV -illumination in the planar capacitor gap. The fatigue became noticeable after 106 switching cycles for a sandwich structure and after 109 cycles for the films with planar electrodes. Illuminating the film during polarization switching greatly accelerates the fatigue process. The additional fatigue induced by the photoactive light was completely reversible.

Thin films of PbTiO3 were prepared by sol-gel method on platinum-coated-Si and Al2O3 and annealed at 600°C. The annealing time of the films, deposited on Si, were 6 and 12 hours, respectively. Micro-Raman spectra show high background in the low frequency region and the bands are broader with respect to the single crystal work, which indicates the polycrystalline nature of the samples. The film annealed for 12 hours showed more pronounced peaks in the spectra when compared to the film annealed for 6 hours. Micro-Raman measurements on different spots in the film indicate that the PT film on platinum-coated silicon substrate is highly inhomogeneous. In the case of PT/Al2O3 such studies show a homogeneous film. The frequencies of most of the modes are decreased, which is associated to grains under stress. The nature of the stress is discussed. Although film stress may not be homogeneous, a stress value around 1.2 GPa is estimated from Raman data. XRD and SEM techniques were used for structural characterization.

Optical properties of La2Ti2O7 thin films were investigated by spectroscopie ellipsometry and compared to those of bulk sintered ceramics. Thin films were prepared by pulsed laser deposition (PLD) from bulk targets. To separate the effects of thickness, porosity, and index of refraction on observed Ψ and δspectra in thin films, a Cauchy model for n vs. λ was developed from sintered samples, with known porosity. Assuming the effective bulk index of refraction followed the rule of mixtures, corrected models for La2Ti2O7 without porosity were used to determine thickness and porosity of thin films as a function of fabrication parameters such as laser energy, substrate material and temperature. Ellipsometry models were tested and refined through XRD, EDX, ESCA, and SEM.

Tne present paper is devoted to the experimental study and the analysis of photoferroelectric phenomena in ferroelectric-semiconductor Sn2P2S6 crystals and films. These photoactive light-induced phenomena observed in polarized Sn2P2S6 samples are described by the model of screening the depoling field of remanent polarisation by free charge carriers fixed at the deep energy levels.

Deposition by aqueous acetate solution (DAAS) technique was used to synthesize undoped and 5 wt% Cr-, Mn-, Eu-, or Pr-doped Pb(Zr0.53Ti0.47O3 [PZT] thin films. The dopant was incorporated into PZT either in the precursor coating solution or via thermal diffusion into undoped PZT. X-ray diffraction shows that ion-doped PZT thin films on Pt<l 1 l>/Ti/SiO2/Si<100> (in particular, the Mn- and Eu- doped samples) display better crystallinity and smaller lattice parameters than those on sapphire substrates. The enhancement of photoconductivity at visible wavelengths measured by excitation photocurrent spectroscopy (EPS) goes as Cr-doped∼Mn-doped > Eu-doped ∼ Pr-doped. Only Mn-doped PZT perovskites have the band gap energy red-shifted to 360 nm from 330 nm. The space charge (or photovoltaic) field was estimated to be < 8 v when about 100 v was applied to ion-doped PZT thin films with 260 or 320 nm light. By using laser irradiation at selected wavelengths and switching the polarity of applied bias voltage, the expected changes in resistance (Ry) and remanent polarization (±Pr) states were observed in the P-E hysteresis loops. The possible applications of extrinsic ion-doped PZT thin films in optical memory devices are discussed.

Photoelectrical properties of the p-n junctions on the base of Pb1−xGexTe were investigated. A number of anomalous phenomena below Tc such as: the change of the photovoltage sign, low frequency maximum in the temperature dependence of the junction capacitance and feature near the edge of the spectral dependence were observed.

To explain the obtained results a model considering screening of spontaneous polarization outside the junction was proposed. This work gave for the first time experimental evidence concerning the model of polarization switching in ferroelectric with p-n junction.

A five-factor, full-factorial experiment on process sensitivity of non-volatile polarization, Pnv for Pt/PZT/Pt capacitors shows the most dramatic factor is the use, or not, of a Ti adhesion layer for the bottom electrode. With the Ti layer, Pnv is generally lower and is sensitive to several factors and interactions involving the crystallization anneal, sol-gel synthesis, and Pt thickness and deposition temperature. A possible cause is Ti diffusion through the Pt as observed in Auger and XPS depth profiles of oxygen annealed Pt/Ti electrodes.

Thin films of pb(Zr0.53Ti0.47)O3 (PZT) grown in our laboratory on RuO2 electrodes by the sol-gel process are characterized by high leakage currents and by the presence of a pyrochlore-type second phase. We have used a thin Pt interlayer between the PZT film and RuO2 bottom electrode to produce RuO2/PZT/100ÅPt/RuO2/SiO2/Si capacitor structures. It is found that use of such a Pt interlayer significantly reduces or eliminates the second phase in the PZT films, and lowers their leakage currents by more than four orders of magnitude. At the same time, the excellent resistance to polarization fatigue characteristic of the RuO2/PZT/RuO2 capacitors is maintained. The microstructures of PZT films grown on RuO2 electrodes with and without the 100Å Pt interlayer are compared. In addition, the voltage, temperature, and polarity dependence of the leakage current in these samples was measured. The data suggest that leakage current in these samples is most likely Schottky emission controlled. The barrier heights are determined to be about 0.80 and 0.73 eV for the top and bottom interfaces, respectively.

The selection of a suitable electrode and barrier layer is important in the integration of lead zirconate titanate (PZT) into memory circuits. Processing at elevated temperatures of up to 800°C can give rise to diffusion processes and therefore to formation of poor quality layers.

In this paper we used Rutherford Backscattering Spectrometry (RBS), Auger Electron Spectrometry (AES), and X-ray Diffraction (XRD) to study the effects of annealings on the interdiffusion of Pt/TiN/Ti trilayers deposited on BPSG/Si substrates. The wafers were annealed in Ar, N2 or O2 ambients with temperatures ranging from 550 to 700°C for 60 min, 30 min or 30 sec. Drastic changes occur when the as deposited Pt/TiN/Ti layers on BPSG/Si structures are exposed to classical heat treatment: oxidation induces diffusion of Ti into Pt and oxidation of Ti is also observed. Regardeless of annealing proceedure used, significant improvement in the interdiffusion of Pt, Ti and O have been achieved when the TiN/Ti/BPSG/Si structure was heated up to 450°C in vacuum. Platinum films deposited on such a structure seem to be a promising barrier layer for PZT film elements as there was no indication of Pb diffusion into the underlying layers and furthermore the desired crystal structure was obtained.

The degradation (fatigue) of dielectric properties of ferroelectric PZT (Lead Zirconate Titanate) thin films during cycling was investigated. PZT thin films were fabricated by metal-organic decomposition (MOD). Samples with electrodes of platinum (Pt) and ruthenium oxide (RuO2) were studied. The interfacial capacitance (if any) at the Pt/PZT and RuO2/PZT interfaces was determined from the thickness dependence of low-field dielectric permittivity (εr) measurements. It was observed that a low εrlayer existed at the Pt/PZT interface but not at the RuO2/PZT interface. The dielectric permittivity of this interfacial layer degrades with increasing fatigue while the εrof the bulk PZT film remains constant. This indicates that fatigue increases the interfacial layer thickness but does not change the bulk properties. For the capacitors with RuO2/PZT/RuO2 structure, however, the εdoes not change with thickness and fatigue cycling. This implies no interfacial layer exists between RuO2/PZT and, therefore, no fatigue was observed. Additionally, an impedance spectroscopie technique has been proposed for possible use in analyzing the nature of the interfacial layer during the fatigue process.

The ferroelectric properties of PZT on RuO2 electrodes were compared to those on RuOStudy on Multilayered Electrodes for Ferroelectric Thin Film Capacitors. It seems that the microstructure of PZT film plays an important role in the improvement of electrical properties. In particular, the change in the grain size of PZT film is responsible for the enhancement of the electrical properties. It was found in this study that films with smaller grain size had larger coercive fields. The exact dependence of the grain size on the hysteretic property is not fully understood at present. However, it is believed that the grain size affects both domain formation and domain pinning because of the influence of grain boundaries. The change in physical properties of PZT films due to the bottom electrode is understood in terms of interfacial modifications. Here we report on a method to modify physical properties of PZT films utilizing interfacial engineering.

The formation of Pt hillocks during high temperature processing is a problem when using Pt as a bottom electrode for high dielectric constant materials. The hillock height is frequently larger than the dielectric thickness, degrading the leakage current of the device. In this work, Pt was deposited by electron beam evaporation on in-situ formed 40 nm ZrO2 coated SiO2 / Si substrates. The samples were then annealed at temperatures between 400°C and 700°C for times ranging from 2 min to 40 min. The surface roughness was measured by atomic force microscopy (AFM). The surface was characterized using Ra, RMS and Zmax over 5 μm × 5μm regions. Zmax is sensitive to hillock formation and Ra is sensitive to changes in general surface roughness. Analysis of Zmax indicates that 100 nm Pt / ZrO2 deposited at 315°C forms hillocks above 450°C during initial heatup. Subsequently, the hillocks decay for temperatures of 600°C and above such that they are almost gone after a 30 min air anneal. In-situ wafer stress measurements of Pt / ZrO2 were performed in O2 at temperatures up to 650°C. The Pt relaxes above 500°C in O2.

A PZT thin film capacitor displays a reduction in the charge storage density (Qc') after the device has undergone pulsed electrical stress. This changes the charge-voltage relationship for the devices. The effect of this change in the Q-V relationship on the DRAM READ time is described. Measurements of the charge and voltage decay rates have been previously identified as ideal techniques for characterizing signal loss. For the first time the effects of electrical stress on these rates have been studied. While the charge decay rate decreases with an increase in the number of stress cycles for both the bipolar and unipolar stress, the voltage decay rate decreases after unipolar stress but it increases for bipolar stress at lower stress voltages. The implications of these results on the DRAM performance shall be discussed.

The kinetics of BST thin film grain nucleation and growth caused by rapid thermal annealing have been investigated. A series of Ba0.67Sr0.33Tii0.5O3 films were deposited on Pt electrodes using a metal-organic decomposition process. The effects of anneal time and temperature on BST grain sizes were studied by altering the processing conditions during RTA. A series of films were annealed by RTA at temperatures ranging from 550°C to 950°C for times ranging from 30 to 120 seconds. Crystallographic and microstructural characterization were done using XRD and TEM. The XRD results indicated that BST grain size increased with increasing anneal temperature, but was not affected by anneal time. Plan-view TEM indicated that BST grains were imbedded in an amorphous matrix. The average grain size was on the order of 200 Å.

Thin film barium strontium titanate, Ba1−xSrxTiO3 (BST), has been deposited on Pt bottom electrodes using metal-organic decomposition (MOD). Optimization of BST electric properties, including capacitance density and leakage current, can be achieved by altering the chemical and microstructural attribute of the films. Dielectric properties of BST are strongly dependent on processing temperature, film thickness, composition, and microstructure, which are closely correlated with each other. Nucleation temperatures of BST range from 580°C – 650°C depending on film thicknesses. The chemical composition giving the highest dielectric constant is explained in terms of microstructure; capacitance increases with increasing grain size for the BST films in this study. Capacitance density of 50 fF/μ m2 and leakage current density < 100 nA/cm2 at 1.6 V can be achieved by optimizing BST materials properties. In addition, leakage conduction through the Pt/BST/Pt capacitor is shown to consist of polarization current resulting from Debye relaxation and true leakage current attributed to Schottky electron emission.