Sol-Gel derived Pb0.85La0.15TiO3 PLT15) thin films were deposited on solution derived RuO2/Si, RuO2/Pt/Si and Pt bottom electrodes. Dielectric, tangent loss, hysteresis, J-E, measurements were also carried out on these films. X-ray results established the single phase perovskite formation with no secondary phases of PLT15 thin film on these electrodes. PLT15 thin films on RuO2 bottom electrode showed relatively inferior ferroelectric and dielectric behavior as compared to Pt electrode. Low leakage currents (10-8 A/cm2 at 10 kV/cm) and the observed J-E characteristics have been attributed to poor film-electrode interface. Observed electrical and dielectric properties have been correlated with the film-electrode interface. The interface characteristics were further augmented by depth profile analysis using Auger Electron Spectroscopy.

Precursor chemistry was found to have a dominant effect on the electrical properties of sol‐gel‐derived Pb0.85La0.15TiO3 (PLT15) thin films prepared using different precursor sources for lanthanum, namely, lanthanum acetate dissolved in acetic acid (LAA) and lanthanum 2‐methoxyethoxide in 2‐methoxyethanol (LMM). The LMM‐derived PLT15 films had lower dielectric constants (KLMM= 394, KLAA= 548, measured at 100 kHz, applying 500 mV oscillation voltage), poorer polarization hysteresis characteristics, and higher leakage current densities (JLMM∼ 1.5 × 10−7 A/cm2, JLAA∼ 2 × 10−9 A/cm2, measured at 10 kV/cm field). Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) measurements in conjunction with Fourier transformed infrared spectroscopy (FTIR) and X‐ray photoelectron spectroscopy (XPS) analyses indicate that better removal of C–O moieties are the key step to yield improved electrical properties in these films. Possibly, C–O moieties reduce the metallic oxides to their corresponding metals and the presence of the metallic constituent(s) (e.g., lead), in turn deteriorate the electrical properties. In line with these postulations it was found that, when the pyrolysis temperature is increased from 450° to 550°C, the organic contents of LMM‐derived films are reduced and their electrical properties are indeed comparable to that of the LAA‐derived films.

Neodymium-substituted Bi4Ti3O12 (i.e., Bi4−xNdxTi3O12) were synthesized by sol–gel process for different compositions. Thin films were deposited on Pt (i.e., Pt/TiO2/SiO2/Si) substrate by spin coating. Materials were characterized by x-ray diffraction and Raman spectroscopy. This study indicates that the material makes a solid solution for the compositions: x=0.00, 0.26, 0.46, 0.75, 0.85, 1.00, and 2.00, where an Nd ion replaces the Bi site. The prominent effect of Nd substitution is observed in low-frequency Raman modes. Sol–gel derived thin films of Bi3.54Nd0.46Ti3O12 on a Pt substrate and postannealed at 700 ° C were tested for ferroelectric response which showed high remnant polarization (Pr=25 μC/cm2).

Room temperature micro-Raman scattering, P-E hysteresis and temperature dependent dielectric measurements were carried out on sol-gel derived ferroelectric Pb1-xLaxTiO3 (PLT x = 0.0 to 0.30) thin films. micro-Raman results indicate that the crystal structure of the PLT films was strongly influenced by the La contents. The dielectric properties of PLT thin films were studied in the temperature range 80 700 K and frequencies (1 kHz - 1 MHz). Results indicate that PLT thin films undergo normal-to-relaxor ferroelectric transformation with 30 at% La content in PLT films. The observed behavior is evaluated in terms of diffuseness and Vogel-Fulcher relationship, which is typical for relaxor ferroelectrics.

In this article we have reviewed our recent research efforts on the synthesis and characterization of a wide spectrum of ferroelectric thin films for a variety of electronic and electro-optic devices including computer memories, tunable microwave devices, infra-red detectors, and electro-optic modulators. The review is separated into three sections; first we have described the process induced modifications of the properties of perovskite films prepared by sol-gel technique. The next section reviews the effect of certain impurity elements (e.g. La, Nd, Ce etc) in modifying the electrical characteristics of perovskite thin films followed by our experimental observations on the synthesis of epitaxially grown perovskite thin films by sol-gel technique. The epitaxial quality of BST thin films has been evaluated by fabricating eight element coupled microstrip phase shifters at NASA Glenn Research Center. Finally, future directions of sol-gel thin film research have been highlighted in view of these experimental observations.

Sol–gel derived Pb0.85La0.15TiO3 thin films were deposited on Pt, Pt/Si, RuO2/Pt/Si and RuO2/Si bottom electrodes. The structural and microstructural characteristics of the films were studied using X-ray diffraction and atomic force microscopy techniques. Dielectric, ferroelectric and leakage current characteristics were evaluated and depth profile Auger electron spectroscopy was used to obtain direct evidence for reactivity and compositional changes at the film/electrode interface and determine their effect on the ferroelectric and dielectric properties of films. Films deposited on Pt electrode showed a relatively higher dielectric constant of approximately 1300, while the films on RuO2 exhibited lower dielectric constant of only 470. J–t characteristics with leakage current of approximately 10−8 A/cm2 under low biasing field (10 kV/cm) was observed for the films under study. The steady state field dependent dc conductivity was examined by the measurement of J–E characteristics. At very low fields (<30 kV/cm) films followed ohmic behavior and was fitted with a space-charge-limited conduction mechanism in the intermediate fields (30–60 kV/cm). The on-set voltage for the non-linearity was considered as VTFL using which, the trap concentration estimated for films on RuO2/Si electrode was 1.23×1017 cm−3. Observed current characteristics have been correlated with large interfacial resistance at the film–electrode boundary. In the case of RuO2 bottom electrodes, the dielectric and ferroelectric properties are correlated with the electrode characteristics and Si diffusion at the film–electrode interface.

Lanthanum-modified lead titanate, Pb(1-x)La(x)Ti(1-x/4)O(3) (PLT), films with different compositions, such as x = 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30 were deposited on platinized silicon substrates using the sol-gel process. Raman scattering technique was utilized to study the dynamics of phase transitions and possible relaxor behavior in these compositions in a wide range of temperatures 100-873K. The outcome indicates change of the structure with the increase of La doping, as well as an increase in diffused phase transition behavior. The residual intensities of phonons above the tetragonal-to-cubic phase transition temperature suggest a diffuse nature of the ferroelectric phase transition, due to the short-range structural disorder in the paraelectric cubic phase. The Lyddane-Sachs-Teller (LST) relations were employed to analyze changes in the Raman mode positions in order to obtain the optical dielectric constants. The results are in good agreement with the previous dielectric studies.

Room-temperature micro-Raman scattering and temperature-dependent dielectric measurements were carried out on sol-gel-derived ferroelectric Pb1−xLaxTi1−x/4O3 (PLT x=0.05–0.30) thin films. Results indicate that the crystal structure and the electrical properties of PLT films were strongly influenced by the La contents. The dielectric properties of PLT thin films were studied in the temperature range of 80–700 K and frequencies in the range of 1 kHz–1 MHz. Results show that PLT thin films undergo normal-to-relaxor ferroelectric transformation with 30 at. % La contents. The observed relaxor behavior is established in terms of diffuse phase transition characteristics and Vögel–Fulcher relationship.

Sol–gel derived Pb La TiO thin films were deposited on Pt, PtySi, RuO yPtySi and RuO ySi bottom electrodes. The 0.85 0.15 3 2 2 structural and microstructural characteristics of the films were studied using X-ray diffraction and atomic force microscopy techniques. Dielectric, ferroelectric and leakage current characteristics were evaluated and depth profile Auger electron spectroscopy was used to obtain direct evidence for reactivity and compositional changes at the filmyelectrode interface and determine their effect on the ferroelectric and dielectric properties of films. Films deposited on Pt electrode showed a relatively higher dielectric constant of approximately 1300, while the films on RuO exhibited lower dielectric constant of only 470. J–t characteristics with 2 leakage current of approximately 10 Aycm under low biasing field (10 kVycm) was observed for the films under study. The y8 2 steady state field dependent dc conductivity was examined by the measurement of J–E characteristics. At very low fields (-30 kVycm) films followed ohmic behavior and was fitted with a space-charge-limited conduction mechanism in the intermediate fields (30–60 kVycm). The on-set voltage for the non-linearity was considered as V using which, the trap concentration TFL estimated for films on RuO ySi electrode was 1.23=10 cm . Observed current characteristics have been correlated with large 17 y3 2 interfacial resistance at the film–electrode boundary. In the case of RuO bottom electrodes, the dielectric and ferroelectric 2 properties are correlated with the electrode characteristics and Si diffusion at the film–electrode interface. 2002 Elsevier Science B.V. All rights reserved.

Temperature dependent dielectric behavior of sol-gel derived ferroelectric Pb 1−x LaxTiO 3 (PLT) (x = 0.05 to 0.30) thin films on Pt/Si substrates has been studied. The characteristics of the diffuse phase transition and possible relaxor behavior of PbTiO 3 thin films doped with different amounts of La are investigated. Room temperature X-ray and micro Raman results indicate that the crystal structure of the PLT films was strongly influenced by the La content. The softening of the E(1TO) mode with increasing La content indicates that the incorporation of La in the PT lattice results in a structural disorder in the material. The dielectric permittivity and loss tangent of the PLT thin films were measured in the temperature range of 80–700 K at frequencies between 1 kHz and 1 MHz. Transition temperatures (T m ) for PLT (x = 0.05, 0.20, and 0.30) are 640, 460, and 254 K respectively, and are higher in comparison to reported values of bulk ceramics. The permittivity maximum broadened, and showed relaxor- type frequency dependent permittivity characteristics for PLT (x = 0.30) films. The broadening parameter was significantly influenced by La doping and our results indicate that PLT thin films undergo a normal-to-relaxor ferroelectric transformation for La concentrations of 25 at% in PLT films.

Ruthenium Oxide (RuO2) thin films were prepared on silicon substrates by solution chemistry technique. X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), micro-Raman, X-ray photoelectron spectroscopy (XPS), and four probe Van-der-paw technique were used for the film characterization. X-ray analysis shows a rutile structure in these films. The films annealed at 700°C showed lowest resistivity of 29 × 10−5 ohm-cm. The presence of Eg, A1g, and B2g modes is consistent with the Raman spectrum of rutile phase. These modes as well as additional unidentified band at about 477 cm−1 were investigated by temperature dependent Raman studies. Based on the result, band at 477 cm−1 that disappears above 370 K is attributed to hydrated RuO2 present in the films. XPS analysis show stoichiometric rutile RuO2 present in the films. Small concentrations of RuCl3, RuO3 and hydrated RuO2 were also detected. Pb0.9La0.15TiO3 (PLT15) thin films were deposited on RuO2/Si substrates and characterized for its ferroelectric properties to demonstrate that solution deposition technique offers an alternative approach for preparing high quality RuO2 bottom electrodes.

Ruthenium oxide (RuO2) was synthesized in thin film and powder forms using the solution chemistry technique. The oxide electrodes on Si substrates were characterized in terms of their structure, composition, stoichiometry, and conductivity. X-ray lattice parameter calculations and micro-Raman analysis revealed the rutile structure in the material. Both films and powders exhibited an unassigned Raman band at about 477 cm−1 in their Raman spectra. Performing peak frequency calculations for B2g and A1g modes of RuO2 using the rigid-ion model, which ruled out the possibility that this band originated from disorder induced symmetry, allowed silent mode. Based on the x-ray photoelectron spectroscopy (XPS) and temperature dependent Raman studies, this band was assigned to hydrated RuO2. XPS characterizations of our samples revealed minute surface contamination of oxygen and chlorine, probably due to the film preparation and high temperature deposition processes. Films with uniform microstructure, low surface roughness, and good electrical properties meet the requirements for serving as the bottom electrode for the ferroelectric capacitor.

Ferroelectric Pb0.90La0.15TiO3 (PLT15) thin films were deposited by sol-gel method on Pt, Pt/Si, ruthenium oxide (RuO2)/Si and RuO2/Pt/Si bottom electrodes. X-ray diffraction, and micro-Raman spectroscopy techniques were used for structural characterization of these films. PLT15 films deposited on RuO2 electrodes show (100) preferred orientation of growth and result in larger crystallites. Films on Pt electrode exhibited higher dielectric constant (1300 at 100 kHz) and high values of P-m, P-r values, 68 and 46 muC/cm(2) respectively. AC field dependence of dielectric permittivity at sub-switching fields was fitted using the Rayleigh law. The reversible polarization components estimated from the CV and quasi-static hysteresis measurements for films on Pt/Si (24%), was larger than that of Pt (11%) bottom electrodes. The observed results were correlated with the domain wall pinning at the disturbed film-electrode interface.

Pb 0.90 La 0.15 TiO 3 (PLT15) thin films were deposited by the sol-gel method on Pt, Pt/Si, and RuO2 on Si and Pt/Si bottom electrodes. X-ray diffraction, micro-Raman spectroscopy, and atomic force microscopy techniques were used for structural characterization of these films. PLT15 films on different electrodes showed good surface morphology with dense and uniform microstructure. PLT15 films on solution derived RuO2 bottom electrodes show (100) preferred orientation of growth and result in larger crystallites. Films deposited on a Pt bottom electrode show sharp and intense Raman features indicating better crystallinity and insignificant film–electrode interactions. PLT15 film on a Pt bottom electrode exhibited higher dielectric constant (1300 at 100 kHz) and high values of Pm and Pr, 68 and 46 μC/cm2, respectively, compared to other electrodes. Films on a RuO2 bottom electrode showed relatively inferior dielectric and ferroelectric properties. The ac field dependence of dielectric permittivity at subswitching fields was fitted using the Rayleigh law. It was found that ∼22% of the total measured permittivity was due to irreversible domain wall displacement for the films on a Pt electrode. The reversible polarization components estimated from the capacitance–voltage (C–V) and quasistatic hysteresis measurements showed that Prev/Psat at Vmax for the case of Pt/Si (24%), was larger than that of Pt (11%) bottom electrodes. The observed results were correlated with the domain wall pinning at the disturbed film–electrode interface.

We have studied the effect of rare earth dopants (Nd, Gd and Cc) on the phase formation behavior and electrical properties of sol-gel derived Pb-1.05(Zr0.53Ti0.47)O-3 thin films. In all these films the perovskite phase is obtained up to 5 at% doping and beyond that pyrochlore phase was found to coexist with the perovskite phase. Ce and Gd doping(1-2 at%) exhibited improved ferroelectric and dielectric properties as compared to the undoped PZT films. Nd doping (2 at%) was found to be effective to increase the retained switchable polarization of undoped PZT from 63% to 84%. The transition temperature of undoped PZT film was found to be reduced with Nd doping. The Nd doped films also exhibited typical relaxer behavior and a diffuse phase transition, characteristic of the relaxer material. Introduction of Nd into the PZT lattice probably introduces disorder in the B site of ABO(3) lattice which causes the observed relaxer behavior.

La-graded heterostructure films were prepared by sol-gel technique on platinum substrates and electrical properties of these films were compared with those of conventional thin films of similar compositions. X-ray diffraction results indicate the pure perovskite polycrystalline structure of these films. Atomic Force Microscopy analysis revealed a finer grain size and relatively lower surface roughness. Relatively higher values of Pm and Pr (69 and 38 μC cm−2, respectively) and excellent dielectric properties with lower loss (K=1900, tanδ=0.035 at 100 kHz) were observed for La-graded heterostructure films. Also lower leakage current density (∼2.5 nA cm−2) and a higher onset field (∼50 kV cm−1) of space charge conduction indicated higher breakdown strength and good leakage current characteristics. The ac electric field dependence of the permittivity at sub-switching fields was analyzed in the framework of the Rayleigh dynamics of domain walls. The estimated irreversible domain wall displacement contribution to the total dielectric permittivity was 17 and 9% for conventional 15 at.% La doped PbTiO3 and La-graded heterostructure films, respectively. The improved dielectric and polarization behavior of La-graded heterostructure films may be attributed to homogenous dopant distribution compared to the conventional 15 at.% La doped PbTiO3 films.

Lead zirconate titanate (PZT) thin films with composition Zr/Ti similar to 0.53/0.47 were deposited by the sol-gel technique. The films were characterized in terms of its polarization relaxation, fatigue and imprint characteristics. We have found that the polarization relaxation is due to the presence of a depolarization field which increases dramatically with the rise in temperature. Improved fatigue performance was observed when the film was fatigued with higher frequency. The direction of imprint depends on the state of polarization. With the increase in net polarization, the trapped charge density at the film-electrode interface increases which leads to imprint characteristics. Also the imprint increases considerably with the rise in temperature. Finally, we have made an attempt to correlate simultaneously fatigue, polarization relaxation, and imprint characteristics with the presence of mobile charge defects (viz. V-o) and defect dipoles (viz. V-Pb - V-o) in the film.