Thin films of lanthanum-modified lead zirconate-titanate (PLZT) were prepared by rf magnetron sputtering from a single oxide target onto a heated substrate. The target consisted of Pbl-xLaxZryTi1-yO3 with composition close to x=8% and y= 65%, either as a loose powder or a solid sintered disk. Under appropriate conditions, the desired perovskite phase formed in situ without any subsequent post-anneal. Film composition and structure were correlated with deposition parameters, including substrate temperature, target composition, gas pressures, and target aging. For deposition onto MgO or A12O3 crystalline substrates, perovskite PLZT films formed if there was sufficient Pb at the target surface, sufficient oxygen in the sputter gas (≈ 50%), and a substrate temperature >≈600°C. Target heating led to excessive Pb loss from the loose powder target; this was much less significant for the solid target. In addition, it was found that deposition onto an epitaxial perovskite substrate promoted formation of the perovskite phase, leading to an epitaxial film. A prototype ferroelectric capacitor was fabricated by depositing a conducting perovskite film (the high-Tc superconductor YBa2 Cu3O7 ) on a perovskite substrate, sputtering PLZT on top, with Ag for a top electrode. Measurements indicate a remanent polarization of 5 μC/cm2 and a coercive field of 900 V/cm.

X-ray diffraction techniques were used to study the crystallography of PZT thin films prepared by the laser deposition technique. This investigation included identification of phases formed during the annealing process and also the analysis of the profiles of selected diffraction peaks. The PZT films annealed below 800°C typically showed powder x-ray diffraction patterns corresponding to a cubic structure (i.e no peak splitting) instead of the tetragonal patterns characteristic of the target materials. The upper bound contribution of the macro and micro strain to the observed X-ray peak profile and positions was estimated. It was believed that the combined effect of small crystallite size together with residual strain, and possible local inhomogeneity gave rise to the broadening and displacement of the x-ray peaks, which subsequently masked off the splittings. At this stage the physical effect of high temperature annealing is not known. It is possible that as the annealing temperature increased, grain growth took place along with relaxation of residual strain, allowing peak splitting to be observed.

Well crystallized polycrystalline films of cubic BaTiO3 have been synthesized on Ti metal substrates by the hydrothermal reaction of Ti metal with Ba(OH) 2 in the temperature range 80°C-200°C. The films have been synthesized on Ti foil and also on Ti sputtered Si and polymer substrates. The crystallinity, microstructure and electrical properties depend critically on the nature of the substrate.

Thin undoped Pb(ZrxTi1−x)O3 (x=0.2-0.75), BaTiO3, SrTiO3 as well as acceptor (Mn, Ni) and donor (La, Ce) doped films with thicknesses of 0.2-1 μm have been deposited by a modified sol-gel process. The crystal structure and the morphology of the films as a function of the processing and composition were analyzed. The films were characterized with respect to their ferroelectric and dielectric properities e.g. permittivity, remanent polarization, coervice field strength, insulation resistance.

Thin films of antiferroelectric tetragonal (Pb.97 La.02 )(Zr1-x-yTixSny)O3 have been synthesized from acetate and alkoxide precursors via a sol-gel process. A multiple layer spin coating procedure was used to prepare 0.4 gtm films on platinized silicon wafers. Crystallization of the films as confirmed by x-ray diffraction was achieved by rapid thermal annealing at 700°C for 20 seconds. Antiferroelectric to ferroelectric phase switching threshold fields were determined from P-E hysteresis curves. Longitudinal strain is reported as a function of applied electric field, with a maximum strain of 1.6×10-3 measured at an applied dc bias field of 120 kV/cm on a film of composition Pb.97 La.02 (Zr.60Ti.l0Sn.30 )O3. These films show promise for micromechanical actuator applications due to the high strain associated with field forced antiferroelectric to ferroelectric phase switching.

Transmission electron microscopy (TEM) was used to investigate the microstructural evolution of sol-gel derived ferroelectric PZT films. Aggregates of perovskite crystals nucleated and grew out of a pyrochlore matrix at 550°C. A dense, single-phase perovskite PZT film was obtained by fast firing the film at 650°C for 30 minutes. The grain size of this film was approximately 0.2-0.4 μm. Hot-stage TEM observed disappearance of ferroelectric domains as the temperature approaching 325°C.

Spire Corporation has deposited strontium-barium-niobate by chemical vapor deposition at atmospheric pressure using Ba(TMHD), Sr(TMHD), and Nb ethoxide. Deposition temperature as 550°C in an isothermal furnace. Films were deposited upon silicon (precoated with silica), platinum, sapphire, and quartz. Materials were characterized by RBS, X-ray diffraction, EDS, electron, and optical microscopy. Electrical and optical properties were measured at Boston University.

Barium strontium titanate films were deposited onto silicon substrates using pulsed laser ablation deposition. The films were characterized using conventional and high resolution cross-sectional TEM. It was found that the grains were columnar with an average width of approximately 23 nm. An amorphous interfacial layer formed between the Si and BST in all cases. The interfacial layer thickness increased as the sample exposure to O2 increased. TiSi2 was also observed in all the films, although its location at the interface was not directly verified. There are no systematic effects of O2 overpressure on either the film thickness or film microstructure. However, the film which was fabricated with the greatest exposure to O2 may contain TixOy, and contains more equiaxed grains than the other samples. An interfacial layer was also observed at the Au-Pd/BST interface in a metal/ferroelectric/silicon capacitor. The significance of the results is the observation that BST may never come in direct contact with either capacitor electrode, which may explain why the fatigue behavior and electrical characteristics of ferroelectric capacitors depend so strongly on the interfaces.

Thin films of PbZrO3-Pb(Zn0.33Nb0.67)03, with PZN contents of 8- 12%, were fabricated through the sol-gel spin-on technique. The structural, low frequency capacitive, and polarization reversal characteristics were investigated as a function of composition in this solid solution system. The switching of ferroelectric polarization was tested by a sequence of square wave pulses consisting of two positive pulses followed by two negative pulses. Compositions with higher PZN contents are promising for switching applications; the films were typically characterized by a switched charge of 4-14 μC/cm2, coercive field of around 30 kV/cm, and relative permittivity of 400-800.

Ferroelectric PbZr0.2Ti0.8O3/YBa2Cu3O7 heterostructures have been grown on single crystal LaAIO3 and on buffered [100] Si. The cuprate superconductors are used as metal-like bottom electrodes for the subsequent growth of the ferroelectric PZT thin film. Structural studies using x-ray diffraction, and transmission electron microscopy show that the PZT layer is free of large angle grain boundaries (i.e., single crystal-like). Rutherford backscattering studies reveal the composition of the PZT layer to be close to that of the target. Ferroelectric hysteresis measurements using both pulsed measurements and a variable frequency Sawyer-Tower circuit yield remnant polarization values (at 5V) in the range of 15-45μC/cm2 (depending on deposition conditions) with a coercive field in the range of 80-120kV/cm. At a cycling voltage of 5V, these heterostructures exhibit a fatigue lifetime of better than 2x1010 at 40kHz (the polarization decays by only 20% of the initial value). Pulsed poling experiments before and after show that the loss of polarization is reversible. These heterostructures also show excellent aging and logic state retention characteristics.

In this study we report on in-situ growth of lead zirconate titanate (PbZr1-xTixO3, PZT) and strontium titanate (SrTiO3, STO) films by pulsed laser deposition at 248 nm. Films were deposited in an oxygen background at elevated temperatures on a variety of substrates including MgO(l00), Pt(100)/MgO(100), Pt(111)/MgO(111), Pt(110)/MgO(110), Pt(111)/SiO2/Si, and Pt(111)/glass.Deposited films were characterized by Rutherford Backscattering Spectroscopy (RBS), x-ray diffraction (XRD), and electrical (dielectric constant and leakage) measurements. A strong substrate dependence was found for both the fraction of pyrochlore (Pb2Zr2-xTixO7) phase in the PZT films, and the STO film dielectric constants. The origin of the substrate dependence is discussed with regard to nucleation and interface layer cffects, and the chemistry of the relevant materials.

Epitaxial growth of ferroelectric thin films on GaAs (100) by pulsed laser deposition was examined for integrated electro-optic device applications. To promote epitaxy of ferroelectrics and prevent interdiffusion, we have deposited several types of buffer layers. CeO2 reacted strongly with GaAs. Although Y203 9% stabilized-ZrO2 films showed epitaxial growth, YSZ reacted with GaAs at 780°C. MgO grew epitaxially and was stable even at 780°C. HRTEM observation showed a sharp interface between MgO and GaAs. BaTiO3 and SrTiO3 deposited on MgO/GaAs structures showed epitaxial growth. In-plane orientation was BaTiO3 [100 // MgO [100] // GaAs [100]. Epitaxial BaTiO3 films were c-axis oriented tetragonal phase and showed ferroelectric hysteresis.

Lead-zirconate-titanate films were prepared by excimer laser ablation. The coercive field of films deposited on MgO substrates with an electrode was lower than that of films deposited on sapphire substrates. Laser fluence influenced the grain and crystalline size, resulting in a change in the Ec. Film thicknesses were varied over a range from 0.3 to 2.41μm, with the thinnest film showing a large remanent polarization even at an applied effective voltage of 5V.

A modification of the standard Sawyer-Tower circuit method of displaying ferroelectric hysteresis allowed the technique to be extended to sinusoidal switching frequencies of 2 MHz. Using this method, probe station measurements of switched remanent polarization were made for two films: excimer-laser-deposited lead zirconate titanate (PZT) and sol-gel PZT. Switched remanent polarization and dielectric constant were measured as a function of frequency between 100 Hz and 2 MHz and as a function of elapsed switching cycles at the 1-MHz rate. Both films showed decreasing switched remanent polarization and dielectric constant with increasing frequencies. This effect is attributed to limitations in domain wall velocity.

Thin films of BaTiO3 were deposited on platinum-coated silicon substrates using pulsed laser deposition and characterized using electron microscopy, powder x-ray diffraction and electrical measurements. The microstructure consisted of columnar BaTiO3 grains oriented normal to the substrate. Two preferred orientations were observed, with either the (001) or (111) planes of BaTiO3 being parallel to the substrate. The electrical properties of two films were measured and it was found that the (111) film was ferroelectric and the (001) film was not. Possible reasons for this are discussed.

PZT thin films were prepared by pulsed laser deposition on unheated Ptcoated Si substrates. As deposited, the films were amorphous. Films crystallized at 550 - 600 °C to produce predominantly crystalline ferroelectric PZT. Crystallization of the amorphous material was accompanied by a linear shrinkage of ∼2 %, as manifested in development of cracks in the film. Spacing, width and morphology of larger cracks followed a regular progression with decreasing film thickness. For film thicknesses less than 500 runm, much of the shrinkage was taken up by small, closely-spaced cracks of local extent. Implications for measurement of PZT thin film ferroelectric properties and processing are discussed.

A systematic study of the gas phase products observed from the pulsed laser vaporization of a PbZro.54Ti0.46O3 target was performed as a function of laser fluence and ambient gas pressure. At low fluences, ≤0.3 J/cm2, only Pb and PbO were observed, while at higher fluences, between 0.3 - 1.3 J/cm2, neutral atomic species Pb, Zr, and Ti were detected. Small oxide molecules and atomicions were also observed. These regimes are associated with two ejection mechanisms: thermal evaporation and ablation, respectively. No direct evidence of chemical reactions was found over the gas pressure range explored (0-5 mTorr). Within the 25 cm reaction cell distance however, the addition of both inert and reactive gases greatly changed the velocity distributions of the ejected species. The decrease in velocity (energy) as a function of gas pressure was due to physical scattering and could be modeled as a pseudo-first order bimolecular collision process. The scattering rate increased linearly with the physical cross-section of the background gas and was independent of the kinetic energy of the ablated species.

Sol-gel processing is a candidate ferroelectric thin-film deposition method for electronic and electro-optic applications. At Battelle, sol-gel PbTiO3 and Pb(Zr,Ti)O3 films have been prepared on sapphire and single-crystal SrTiO3 substrates. Films deposited and annealed on sapphire substrates are crystalline with the perovksite structure and minimal crystallographic orientation, whereas films deposited on isostructural and lattice-matched SrTiO3 substrates exhibit a high degree of orientation. Guided-mode refractive index measurements were made using a single-prism method and film indices were computed. Refractive index values measured for PbTiO3 films (n = 2.58) and PZT films (n = 2.50) were slightly lower than values expected on the basis of bulk measurements. In double-prism experiments, optical wavcguiding was achieved over distances up to 10 mm in oriented PZT films on [100] SrTiO3substrates. Optical loss of 19 dB/cm was measured on one of these film samples. Such films, given requisite improvement in optical quality, may be suitable for useful optical waveguide devices. An approach is presented for the integration of ferroelectric waveguides onto silicon and/or GaAs substrates.

It is argued that epitaxial films of ionically-bonded materials are more easily achieved than of covalently bonded materials. Good epitaxy can be achieved despite relatively large lattice mismatch with respect to the substrate. However, the strong influence of interfacial energy can result in difficulty in controlling the orientation of epitaxial films.

The crystallographic orientation of ionically-bonded LiNbO3 films was therefore studied. Growth orientation could be controlled by paying attention to the bonding between octahedra in the structure, and to the formation of the octahedra containing lithium and niobium ions. Lithium concentration could be increased by increasing the rf power, 02 partial pressure and total gas pressure, and decreasing the substrate temperature during deposition.

The orientation of the film changed from (012) to (100) via (110) by increasing the Li concentration in the film. The (012) and (100) films were epitaxial with respect to the substrate. In particular, the (100) films were of exce lent quality, being single crystalline with smooth surfaces.

Transparent lithium niobate (LiNbO3) with thickness from 0.1 - 1.2 μm were made on silicon, fused silica, and sapphire substrates by the sol-gel processing. Alkoxide solutions were used as starting materials. X-ray diffraction has been used to confirm the crystallization of the films. Refractive index, dielectric and ferroelectric properties of LiNbO3 films were studied. Absorption spectra of films of LiNbO3 and LiNbO3 with doping of different amount of Fe (0.1 - 2.5mol%) were measured. Short-circuit photocurrent measurements revealed both transient and steady state components attributed to a pyroelectric effect and a bulk photovoltaic effect respectively. Epitaxial growth of LiNbO3 thin film on sapphire(012) substrate by sol-gel method was also obtained.