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Using electron paramagnetic resonance (EPR) we have followed the microstructural evolution with temperature of lead zirconate titanate (PZT) ceramics from the amorphous to the perovskite phase. A number of paramagnetic point defects were identified (Carbon, Pb+3, and Ti+3) while traversing the evolution of these ceramics during various heat treatments both before and after optical illumination. Perhaps the most important finding is that the Pb+3 and Ti+3 centers can only be optically created in the perovskite materials, thereby, showing that they are not associated with the amorphous or the pyrochlore phases. It is also found that EPR signals attributed to carbon radicals are present in fairly high concentrations (4 × 1017/cm3) if the solution chemistry derived PZT materials are annealed in an oxygen deficient ambient (0.1% O2) at 650°C.
We have studied oxygen diffusion in thin films of Pb(Zr,Ti)O3 on Pt/Ti/SiO2/Si <100> multilayer substrates using 18O as a tracer. The PZT films were synthesized using the sol-gel technique and crystallized in air at 650° C for 30 minutes. Diffusion experiments were conducted in one atmosphere of 18O2 at tmipertures between 400-600°C, the extent of exchange was monitored using secondary ion mass spectromentry. Exchange profiles were modeled using solutions of the diffusion equation with boundary conditions for a layer with finite thickness. Significant exchange (>60%) of 16O by 18O was measured after treatment under conditions similar to those used for crystallization. At low levels of exchange, oxygen diffusion does not follow a simple Fickian profile and differences exist between nominally identical films. These results suggest that oxygen exchange is sensitive to the film's microstructure.
Through systematic variation of film processing temperature and time, we have characterized the pyrochlore to perovskite crystallization process of solution-derived PZT 20/80 thin films. The ≈3000 Å thick films were prepared by spin deposition using <100> single crystal MgO as the film substrate. By controlled rapid thermal processing, films at different stages in the perovskite crystallization process were prepared with the tetragonal PZT 20/80 phase being <100>/<001> oriented relative to the MgO surface. An activation energy for the conversion process of 326 kJ/mole was determined by use of an Arrhenius expression using rate constants found by application of the method of Avrami. The activation energy for formation of the PZT 20/80 perovskite phase of the solution-derived films compared favorably with that calculated from data by Kwok and Desu  for sputter-deposited 3500 Å thick PZT 55/45 films. The similarity in activation energies indicates that the energetics of the conversion process is not strongly dependent on the method used for film deposition.
Lead zirconate titanate thin films were deposited on Pt/TiN/BPSG/Si structures by sputtering an oxide target of nominal composition (Pb(Zr0.55,Ti0.45)O3 or PZT) in argon plasma. The PZT films were deposited at different pressures and different substrate temperatures ranging from floating temperature to 400°; the thicknesses of the sputtered films were in the 15-720 nm range. The absolute and relative cation and oxygen compositions of the thin films were determined by a new method based on the simultaneous use of Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA) induced by a deuteron beam. The total deposition rate and atomic ones are observed as a function of the substrate temperature and pressure. Therefore the dependence of fil composition on pressure and substrate temperature is discussed.
Post-deposition annealing studies and ferroelectric properties are presented. The values of the remanent polarization, Pr, were in the range 5-7 µC/cm2, the coercitive field, Ec, between 15 and 25 kV/cm and the dielectric constant, µr, evaluated from capacitance measurements around 1200, depending on the process parameters.
The application of synchrotron white beam X-ray topography to the study of ferroelectric domain structures in hydrothermally grown potassium titanyl phosphate (KTiOPO4: KTP) single crystals is reported. The domain walls can be exclusively imaged on topographs with selected diffraction vectors and X-ray wavelengths, while images of other defects, such as dislocations, inclusions and surface scratches, can be simultaneously made very diffuse. The topographic images correspond well with electrostatic toning images. X-ray topography readily reveals the three dimensional shapes of the domain walls. There are two contributions to domain wall contrast: one is fringe-like which can be interpreted in terms of the dynamical theory of X-ray diffraction, and the other is diffuse strain contrast arising from long range strain associated with the wall. These two contributions can be observed simultaneously or separately depending on the diffraction conditions. The long range strain is thought to be associated with the curvature of the domain walls. It appears that the main components of the displacement field associated with this strain are directed approximately perpendicular to the domain wall.
Ultrasonic transducers, microactuators and resonators using sol gel PZT films, polymer membranes and silicon machining techniques can take the form of cantilevers, membranes, and array sensors. Static deflections in simple electrode configurations for PZT films supported on silicon or silicon nitride membranes are of the order of 1 μm, while larger deflections can be developed under ac and resonant excitation. High frequency acoustic actuators using capacitative excitation of polymer films have been used to evaluate the performance of piezoelectric sensors.
Ferroelectric relaxor thin films Pb[(Mg1/3Nb2/3)0.9Ti0.1]O3 (90PMNIOPT) have been fabricated by the sol-gel technique. The dielectric, piezoelectric and electrostrictive characteristics have been investigated. Experimental results show that the dielectric permittivity and effective piezoelectric coefficients of the films can be tuned by varying dc bias fields which offers the useful features in designing smart micro transducer and actuator systems. Dielectric constants of the films are in the range of 5000 to 6000. The electric field induced strain is on the order of 10−3, and the maximum effective d33 coefficient of 90PMINI0PT films is as large as 265 pC/N at 31 kV/cm. The electrostrictive coefficient Q11 is on the order of 1.2 c×10−2 m4/C2 and M11 is 3.5 c×10−16 m2/V2.
Lead based thin ferroelectric films have been prepared using both sol-gel and dual ion beam sputtering (DIBS) processes. Material compositions within the PbTiO3 and PLZT system have been deposited by both techniques onto metallised silicon. By using a standard sol-gel prepared solution, modified with acetylacetone and spin-coating, lµm thick fully perovskite layers, were obtained at low temperature (450°) with some preferred orientation. The grain size was in the range 0.2-0.4µm. A dielectric constant of 400 and a reversible pyroelectric coefficient of 1.2 × 10−4Cm−2K−1 were obtained. In contrast, a range of capping layers (SiO2, A12O3, BPSG) on silicon have been investigated using the DIBS process. Highly crystalline (100) and (111) films were readily produced at temperatures in excess of 550°, at a growth rate of 0.3µm/hour. Control of stoichiometry has also been studied in detail, by sputtering of a composite metal-ceramic target with a high energy Kr beam and by bombarding the growing film with a low energy oxygen ion-beam. Dielectric constants of 200-300, losses below 0.015 and resistivities above 1010Ωm have been achieved. A pyroelectric coefficient of the order of 2.5 × 10−4Cm−2K-1, pre-poled for a La-doped film on BPSG capped Si was obtained, which did not increase significantly on poling.
The successful development of PZT thin films for decoupling capacitor devices places stringent requirements on the dielectric and leakage properties of the films. We have characterized these properties for PZT thin films with compositions near the morphotropic phase boundary prepared by a sol-gel process. Capacitors were fabricated from films with thicknesses varying from 0.4 to 1.2 µm. For zero applied bias, the dielectric constants of these films were in the range of 800 to 1200. The room temperature dielectric constant was observed to decrease by ∼ 25% with the application of a 5 V bias. We have also characterized the interrelationships between temperature, applied bias, and dielectric constant. The capacitors exhibited asymmetry in their leakage and breakdown characteristics with bias sign, as well as non-linear I-V behavior. Breakdown fields for undoped PZT 53/47 films were typically in the range of 750 kV/cm.
We have also studied the effects of La and Nb donor doping on the leakage behavior of PZT 50/50 thin films. Doping with 2 to 5 mol % of either La or Nb resulted in a reduction in film leakage current by a factor of 103. Leakage currents of the highly doped materials were approximately 2 × 10−9 A/cm2 under an applied field of ∼ 65 kV/cm at a temperature of 125×C.
A fiber optic phase and polarization modulator is presented in which a thin transparent piezoelectric polyvinylidene fluoride film with indium tin oxide electrode metallization is placed directly in the path of the output of a single mode fiber. Experimental characterization is presented in terms of the linearity of response, phase shifting coefficient, and frequency response for two arrangements differing in the boundary clamping conditions. Many applications to fiber optic switches, intensity modulators and demultiplexers are indicated.
Prototype ferroelectric thin film, nonvolatile memory, nondestructive readout (NDRO), semiconductor devices have been fabricated. The “1” and “0” logic states of these prototype devices are in principle determined by the modulation of the conductivity of a semiconductor film channel by the polarization state of the underlying ferroelectric thin film layer. Programmed resistance ratios of the two logic states of 5:1 are demonstrated. While the best performance to date has been achieved for devices that have a 40 nm ln2O3 film covering a 300 nm thick PZT 20/80 layer, we also develop criteria for selecting semiconductor films that will improve performance for this NDRO device design. Among the other semiconductor films that are characterized with respect to this criteria are boron doped Ge, ZnO and aluminum doped ZnO. It is demonstrated that by appropriate donor doping of ZnO films the effects of intrinsic defects are masked and that process temperatures can be extended by 300×C.
A pyroelectric infrared sensor using a poly(vinylidene fluoride) (PVDF) thin film has been integrated with a read-out circuit on a silicon substrate. The PVDF thin film with a thickness of 1-2 µm was deposited on the sensing area by an electro-spray (ESP) method. A form I crystal and a large pyroelectric coefficient of 4 nCcm−2K−1 were observed just after the deposition without any poling treatments. The fabrication process of the sensor was based on a standard MOS LSI process and a polysilicon sacrificial layer etching technique. In order to reduce the heat capacitance and the thermal conduction, the PVDF thin film was supported on a thin Si3N4 membrane structure formed by etching a part of the silicon substrate under the sensing area. The sensor with a sensing area of 400x400 µm2 had a responsivity of 98 V/W, a detectivity of l.4× 107 cmHz1/2W−1, an NEP of 2.9× 10−99 Hz1/2W at a frequency of 100 Hz and a time constant of 1.3 msec.
Photo-induced changes in the hysteresis behavior of sol-gel derived Pb(Zr,Ti)O3 (PZT) and (Pb,La)(Zr,Ti)03 (PLZT) films have been characterized. The film photosensitivity has been evaluated with respect to the magnitude of the effects, the time response and the spectral dependence. Photo-induced hysteresis changes exhibit a stretched-exponential time dependence, which implies a dispersive mechanism. The spectral dependence is strongly peaked at the band edge (∼3.4 eV), which indicates that generation of electron-hole pairs in the material is critical. The photo-induced hysteresis changes are reproducible and stable, which indicates that the controlling charge traps are stable. However, improvements in film photosensitivity will be required to develop these materials for optical memory applications.
A study is reported of field-induced effects in ferroelectric materials using optical interferometry. One of the techniques used is based on the use of a WYKO TOPO3 system and provides a three dimensional representation of field-induced displacement. The information provided is supplemented by optical transmission measurements on thin sections of material fabricated to allow interference fringing to be seen. Initial work has centred on the characterisation of ceramic PLZT material. Both transverse and longitudinal electrode configurations have been studied and have highlighted the magnitude of the effects possible and the importance of electrostrictive processes in determining the direction of deformation. These can result in anomalously high strain gradients over distances of the order of 50-100µm. This behaviour is compared with that found for preliminary samples of thin film ferroelectric materials.
The pyroelectric and photogalvanic effects have been studied extensively in epitaxial Pb(Zr0.52Ti0.48)O3 (PZT) thin films. For the first time, photo-induced currents, which were completely reversible by electrical voltage, were observed in ferroelectric thin films. The photo-induced currents exhibited transient and steady state components. The transient component, in turn, consisted of two components with fast (<1 µs) and slow (∼hours) relaxation times. The mechanisms of the photo-induced currents in PZT films and their possible application in non-destructive readout ferroelectric memory are discussed.
Discoveries within the last two years have created possibilities for the fabrication of epitaxial oxide heterostructures on GaAs substrates. In particular, magnesium oxide, MgO, may have broad applications, including its use as a cladding layer in optical waveguides. This report expands upon earlier work by revealing additional epitaxial structures involving lithium niobate which have been grown. There are now five known variants of Z-lithium niobate on GaAs: direct Z-cut growth on GaAs (111)A or B, Z-cut growth on MgO (111)/GaAs (111)A or B, and Z-cut growth on MgO (111)/GaAs (001). Broad in-plane misalignment (about 15°) characterizes the latter structure, whereas the former posses a textural width of 3° to 5° in the plane. All structures contain internal boundaries resulting from 180° rotations about the Zaxis. A critical issue for any ferroelectric heterostructure is its integrity in the presence of thermally induced tensile strain. Approaches to the mitigation of thin fim fracture are discussed and a novel approach to strain relief via ridge waveguide fabrication is reported.
Ferroelectric materials such as BaTiO3 are notable for their nonlinear optical and electrical properties. Optical frequency doubling in thin films integrated with compact semiconductor laser pumped solid state lasers is an attractive candidate for high efficiency generation of blue light. Chemical vapor deposition (CVD) using a single liquid source has been used to grow BaTiO3 films on MgO. X-ray diffraction in the pole figure configuration indicates the films to be epitaxial, and rocking curves had FWHM ≈ 0.7°. An optical scatterometer (λ = 633 nm.) has been used to identify deposition conditions that result in the lowest scatter losses. This paper describes these results as well as waveguide designs to enhance the second harmonic generation efficiency in epitaxial BaTiO3 films on MgO.
Dry etching of a Pt/PbZrxTi1−xO3/Pt (Pt/PZT/Pt) ferroelectric capacitor stack with CF4/Ar plasmas with a reactive ion etching process for the fabrication of micrometer-sized integrated ferroelectric capacitors is described. The etch rate for both Pt and PZT is determined as a function of the process settings: Power, pressure and CF4-Ar gas flow ratio. A chemical enhancement of the etch rate is found for PZT. It is shown that it is possible to etch the Pt/PZT/Pt ferroelectric capacitor stack in a CF4/Ar plasma in a single lithographic process using patterning by photoresist masking. Redeposition processes occurring during etching are described.
In this work, we have identified a suitable etch gas (CCI2,F2 ) for Reactive Ion Etching (RIE) of PZT thin films on RuO2 electrodes. The etch rate and anisotropy have been studied as a function of etching conditions. The effect of gas pressure, RF power and O2 concentration on the etch rate have been determined. It was found that ion bombardment effects are primarily responsible for the etching of both PZT and RuO2 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 PbO is the limiting factor in the etch process. For RuO2 thin films, etch rates of the order of 8-10 nm/min were obtained when O2 was added to the etch gas.
Wet chemical, reactive ion etching and reactive ion-beam etching of sol-gel prepared PZT (54/46) [Pb(Zr,Ti)O3], Lanthanum doped PZT [PLZT (9/65/35)] and LiTaO3 have been investigated. Wet chemical etching using an HCI-HF solution, reactive-ion etching using a SF6 plasma and chemically assisted ion-beam etching (CAIBE) using a xenon plasma and chlorine reactive gas were used. Etch rates for each method were determined and the ability to define small features in the thin film ferroelectric was investigated. It was found that for structures smaller than approximately 20 × 20 μm2, chemically assisted ion beam etching provided by far the best results. 3 × 3 μm2 capacitor and 2 μm wide optical waveguide structures in PZT, PLZT respectively, were successfully fabricated using a CAIBE system. An etch depth monitor enabled accurate in-situ etch rate monitoring of the PLZT and PZT thin films.