Russell A. Lipeles

Effects of Hydrolysis On Metallo-Organic Solution Deposition of PZT FILMS

The effects of hydrolysis on the degree of polymerization during metallo-organic solution deposition of lead zirconate titanate (PZT) films have been investigated. The reaction of lead 2-ethylhexanoate, zirconium n-tetrapropoxide, and titanium tetrabutoxide in isopropanol with water were studied using thermogravimetry, specular reflectance Fourier transform infrared spectroscopy (FTIR) and optical and electron microscopy. Films prepared from coating solutions having varying amounts of water exhibited dramatic differences in morphology. The films were spin-coated on platinum coated fused silica substrates and annealed at 525°C for 30 minutes. Unhydrolyzed coating solutions and solutions with a mole ratio of water to total metal of 0.5 yielded perovskite films with 0.5–5μm grains. A mole ratio of 1.5 (the amount of water required to completely hydrolyze the metallo–organics in the solution) formed amorphous, porous films. The stability of the prepolymerized films inhibits crystallization and densification at moderate temperatures.

Deposition and Characterization of Photoconductive PZT Thin Films

Deposition by the aqueous acetate solution (DAAS) technique was used to synthesize highly crystalline thin films of undoped and 2% iron-doped Pb(Zr{sub 0.53}Ti{sub 0.47})O{sub 3} [PZT (53,47)] perovskites on sapphire and Pt substrates at 600 C. Fe ions were added either at the precursor stage or diffused thermally. The crystallization of the films was measured by X-ray diffraction. The ferroelectric activity was examined by polarization-voltage hysteresis (P-E) loops. The electro-optical properties of ferroelectric/photoconductive PZT thin films were investigated by excitation photocurrent spectroscopy (EPS) and 77 K emission spectroscopy. The photoconductivity measured at visible wavelengths was enhanced for the thermally diffused, but not the precursor-processed doped materials. This, together with lattice parameters obtained from X-ray data and P-E hysteresis loop measurements, suggested that the precursor-processed doped ions are strongly bonded in the perovskite lattice, whereas the thermally diffused ions are bound more weakly in the grain boundaries.

Photoconductivity of extrinsic ion-dopedPLZT ceramics

Abstract Photocurrent action spectra of Fe-doped PLZT ceramics showed that iron defects enhanced the visible light photoconductivity of PLZT. Long thermal diffusion times increased the dark conductivity. Photocurrent action spectra were used to separate the photocurrent, photovoltaic, dark current, and space charge contributions to the total photocurrent.

Reduction of lattice defects in proton-exchanged lithium niobate waveguides

It is shown that the formation of water at the surface of protonated LiNbO3 can lead to the precipitation of disordered phases, causing undesirable degradation of the electro-optic properties of the material. These structural defects are observed to increase the conductivity, which leads to a slow build-up of space charges, believed to be a key reason for voltage bias drifts in LiNbO3 electro-optic devices. Annealing under a controlled partial pressure of water vapor is shown to minimize such damage to the crystal lattice. An additional reverse exchange process is proposed that further improves the stability of the crystal and its electro-optic properties.

Effects of laser radiation on photoconductivity in PZT thin films

Abstract Excitation photocurrent spectroscopy (EPS) was used to record photoconductivity from 200 to 600 nm for a Pb(Zr0.53Ti0.47)O3 (PZT) thin film. Four spectral bands at 262, 338, and 428/472 nm were observed and assigned tentatively to originate from Pb3+, O+ +(vacancy center) and Fe3+ (impurity and/or ion-doped) centers, respectively. When the band at 262 nm in the PZT film was excited using a KrF laser (248 nm), the photoconductivity at 262 nm enhances as observed in EPS. The resistivity decreases by a factor of 7 as compared to the unexposed sample that caused the P-E hysteresis loop to broaden along the polarization axis. When the band at 338 nm was pumped by a N2 laser (337 nm), the P-E hysteresis loop shows a reduction in the polarization and a 26-fold increase in the resistivity. The results are consistent with the generation of shallow trapping states that dominated the production of dark current in EPS. It is suggested that KrF laser creates the conductive Pb3+ hole traps and N2 laser mainly ...

Metalloorganic solution deposition of ferroelectric PZT films

The metallo-organic solution deposition (MOSD or sol-gel) technique can be used for preparing lead zirconate titanate (PZT) ceramics with a wide range of compositions and crystal structures for electrooptical applications. Film morphology is affected by the stoichiometry of the film, hydrolysis and polymerization of the sol-gel solution, and thermal treatment of the deposited material. The lattice parameter decreases with the amount of titanium in the PZT, in agreement with ceramic data. A slight initial excess of lead in the coating solution is found to improve film morphology. Unlike traditional powder ceramic processing techniques, MOSD permits the growth of small uniform grains that are conducive to achieving consistent electronic and optical properties. Results show that the properties of films prepared by the MOSD process can be tailored to meet the needs of device applications.<<ETX>>

Characterization of PZT films fatigued at low frequency

We report a method using SEM, EDX, SIMS, and polarization-voltage hysteresis data to investigate changes that occur in PZT thin films fatigued using low (below 100 kHz) frequency square waves. Fatigue in PZT capacitors can limit the lifetime of destructive readout ferroelectric memories. Identification of physical and electronic changes that occur during fatigue will lead to understanding fatigue mechanisms and the development of improved electrode-ferroelectric interfaces.

Photoconductivity of ceramic PLZT thermally diffused with iron

Increased spectral sensitivity was observed in lead lanthanum zirconate titanate ceramic thermally diffused with iron. The magnitude of the photocurrent and dark current was found to depend on whether the diffusion atmosphere was oxidizing (air or oxygen) or was reducing (argon). The oxygen atmosphere was more efficient in enhancing the photocurrent than was diffusion in air. Samples annealed in argon showed a higher dark current than the samples diffused under oxidizing conditions and no photocurrent. The lowest dark current observed needs to be decreased further for use as a photosensitive layer in spatial light modulators.<<ETX>>

Barium diffusion in metallo-organic solution deposited barrier layers and Y1Ba2Cu3O7-x films

Barium silicate and barium aluminate films were studied for use as chemical reaction and diffusion barrier layers for Y1Ba2Cu3O7 (YBC) deposited on sapphire and fused silica substrates by the sol-gel technique. Depth profiling by secondary ion mass spectrometry (SIMS) was used to characterize the abruptness of the interfaces between the barrier layer and the YBC film as well as the barrier layer and the substrate. We found that barium aluminate films reacted with fused silica substrates forming a coarse-grained barium silicate phase. Barium silicate, BaSiO3, also reacted with silica substrates forming a broad, amorphous reaction zone containing some BaSi2O5. Although barium silicate and barium aluminate deposited on sapphire formed a BaA112O19 phase, they provided a barrier to barium diffusion from sol-gel deposited YBC. Crystalline barium aluminate grown on c-cut sapphire was the most effective barrier layer for the growth of YBC films; compositionally uniform YBC films were made similar to that grown on strontium titanate substrates. These data show that chemically stable, crystalline films are more effective barrier layers than amorphous films.

DAAS technique for synthesizing doped PZT and PLZT thin films

The deposition by aqueous acetate solution (DAAS) technique has been developed for the preparation of 5% Fe-doped Pb(Zr/sub 0.53/Ti/sub 0.47/)O/sub 3/ (PZT) and (Pb/sub 0.93/La/sub 0.07/)(Zr/sub 0.65/Ti/sub 0.35/)/sub 0.983/O /sub 3/ (PLZT) thin films on Pt[111]/Ti/SiO/sub 2//Si substrates. PZT films, crystallized at 600 degrees C for 10 min, display good electrical properties and fatigue characteristics. Iron doping suppressed the crystallization of the films as measured by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. When 5% of the zirconium and titanium were replaced by iron in the stoichiometric precursor solution, the film crystallized predominantly in the [110] orientation. When 5% excess iron was added to the precursor solution, the film crystallized in the [100] orientation. The electronic states and charge species responsible for photoconductivity were investigated by emission/excitation and photocurrent action spectroscopy. The low photoemission at 77 K and high photoconductivity at 298 K in the doped thin films, as compared with thermally iron-doped ceramics, are attributed to surface energy quenching and low trapping state density.<<ETX>>