We have studied the effects of La concentration on the dielectric and ferroelectric properties of lead lanthanum titanate (PLT) thin films by using sol-gel method. Both the dielectric and ferroelectric properties were greatly affected by the La concentration. The dielectric constants of the films varied from 340 to 870 with varying La concentration in the range from 15 to 33 mol%. Hysteresis loop became slimmer with the increase of La concentration from 15 to 28 mol% and a little fatter again with the increase of La concentration from 28 to 33 mol%. Among the films investigated in this research, PLT(28) thin film showed the best dielectric properties for the application to the dielectrics of ULSI DRAM's. At the frequency of 100 Hz, the dielectric constant and the loss tangent of PLT(28) thin film were 940 and 0.08, respectively. Its leakage current density at 1.5×10 V/cm was 1×10−6 A/cm2. The comparison between the simulated and the experimental curves for the switching transient characteristics showed that PLT(28) thin film behaved like normal dielectrics.

SrTiO3 thin films have been prepared by MOCVD. A novel Sr source of Sr(DPM)2-tetraen2 was used to stabilize source delivery and to reduce the vaporization temperature of Sr source. Films were deposited on Pt/Ta/Si substrates at deposition temperatures from 450 °C to 600 °C. The relative dielectric constant was about 220 at the deposition temperatures from 550 °C to 600 °C for as-deposited 90-nm-thick films. The leakage current density was in the range of 10−7 A/cm2, typically.

The advantages of MOCVD for the growth of Pb(Zr,Ti)O3 (PZT) and (Pb,La)(Zr,Ti)O3(PLZT) thin films were discussed, with emphasis on the controllability of film composition, crystalline structure and electrical properties. The possibilities of lowering the processing temperature and scaling up the process to commercial-based production were investigated. The preparation of PZT films and electrodes with a specific focus on improving the I-V and fatigue characteristics was also investigated.

Epitaxial SrRuO3 thin films were deposited by RF sputtering on SrTiO3 or MgO substrates for use as underlying electrodes. On these conductive substrates, epitaxial Pb(Zr0.35Ti0.65)O3 (PZT) and PbTiO3 (PT) thin films were deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD), RBS channeling (RBS), transmission electron microscopy (TEM) and optical waveguiding were used to characterize the phase, microstructure, defect structure, refractive index, and film thickness of the deposited films. The PZT and PT films were epitaxial and c-axis oriented. 90° domains, interfacial misfit dislocations and threading dislocations were the primary structural defects, and the films showed a 70% RBS channelling reduction. Hysteresis and dielectric measurements of epitaxial PZT ferroelectric capacitor structures formed using evaporated Ag or ITO glass top electrode showed: a remanent polarization of 46.2 μC/cm2 a coercive field of 54.9 kV/cm, a dielectric constant of 410, a bipolar resistivity of ∼5.8×109 ω-cm at a field of 275 kV/cm, and a breakdown strength of >400 kV/cm.

Ferroelectric superlattice structures composed of three-dimensionally epitaxial PbTiO3 and PLT thin films have been successfully grown on SrTiO3 substrates by metalorganic chemical vapor deposition. The modulation structures were confirmed by θ-2θ XRD, and the excellent in-plane orientational relationship between the superlattice film and the substrate by (100), (110), and (111)-pole figures. The φ-scans through the (110) and (111) reflections were used as additional evidence for three-dimensional epitaxy. The substrate dependence of the epitaxial orientation of PLT and PbTiO3 single-layered thin films was investigated. PbTiO3 thin films with very high crystalline perfection can be successfully grown on KTaO3 substrates.

High quality lanthanum doped PZT films were deposited on platinum coated silicon wafers by direct liquid injection MOCVD using lead bis-tetramethylheptadione, lanthanum tri-tetramethylheptadione, zirconium tetramethylheptadione, and titanium ethoxide as precursors. The films were deposited at 650°C and a reduced pressure of 5 Torr. The deposition rates were higher than 10 nm/min. The liquid delivery system led to highly reproducible deposition rate, composition, and ferroelectric properties in the PLZT films. The remanent polarization of the films decreased from about 25 μC/cm2 for PLZT(0/55/45) to about 12 μC/cm2 for PLZT(8/55/45). The coercive field of the films seemed to be independent on the La doping concentration up to 8% La doping.

SrTiO3 thin films with various compositions have been prepared on Pt coated sapphire substrates by electron cyclotron resonance plasma chemical vapor deposition at 450 °C and 600 °C. The stoichiometric (Sr/(Sr+Ti)=0.50) films have maximum dielectric constants (εr) of 190 for the 600 °C deposition and 170 for the 450 °C deposition. The dielectric constant decreases abruptly with increasing or decreasing the Sr/(Sr+Ti) value from the stoichiometry, especially for the 450 °C deposition. The Ti-rich films include titanium suboxide (TiOx). In the Sr-rich films, excess SrO is thought to be inserted into the SrO plane and TiO2 plane in SrTiO3. In addition, SrCO3 is included in Sr-rich films. The concentration of these impurities is greater for the 450 °C deposition than for the 600 °C deposition. The leakage current density increases with increasing the Sr/(Sr+Ti) value, and the leakage current density for the 450 °C deposition is larger than for the 600 °C deposition in the Sr-rich composition region. These impurity phases may be related to the higher leakage current density. These results suggest that precise composition control in stoichiometry is necessary to deposit SrTiO3 films with superior electrical properties.

Recently, we reported results of an investigation of the preparation of highly textured (Pb1−xLax)TiO3 (PLT) thin films grown on Si(100) by metalorganic chemical deposition (MOCVD) [1]. In this paper, we discuss an extension of this work to the growth of PLT thin films on fused quartz substrates by the MOCVD technique. A series of PLT films with x between 0 and 0.32 were prepared. Characterization by x-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and Raman scattering has been performed on these ferroelectric thin films. XRD indicated the polycrystalline nature of the PLT films and the variation of their tetragonality. The film thickness and La composition were determined by RBS. Raman spectra, measured at 300 and 80 K, showed features of the PLT film and quartz substrate. By using a “difference Raman” technique, more PLT modes were shown. The variations of the PLT Raman modes with the La composition and the measurement temperature were studied. Related physical phenomena and problems are discussed.

Ferroelectric PbTiO3 and Pb(Zr,Ti)O3 thin films with a perovskite structure were grown on MgO and Pt/Ti/SiO2/Si by MOCV.D. The microstructure and composition of the films were characterized by x-ray diffraction, SEM, and AES. Preferred orientation of either (111) or (100)/(001) was obtained on the Pt/Ti/SiO2/Si substrates at temperatures from 600 °C to 650 °C The preferred (111) orientation was attributed to the formation of the Pt3Ti phase in the Pt layer of the substrates, whereas the (100)/(001) orientations were inferred as the growth rate effect. AES depth profiling indicated a uniform composition through the thickness of the PZT films. However, SEM showed different topography and microstructure of the PZT films deposited in different oxygen partial pressure. Electrical properties of the PZT films appear varied as a function of the oxygen partial pressure in the reactor.

Lead titanate thin films were deposited on Pt(111)/Ti/SiO2/Si(100) and RuO2/SiO2/Si(100) substrates using metalorganic chemical vapor deposition (MOCVD). Atomic force microscopy revealed that films on ruthenium oxide were rougher than films on platinum. Also the grain size of the film on ruthenium oxide was larger than that on platinum. X-ray analysis revealed that the preferred orientations for films on platinum and ruthenium oxide were different. Hysteresis and fatigue tests were performed to evaluate capacitor structures on these substrates. Films on RuO2 had lower coercive fields than films on platinum. Comparison of polycrystalline and oriented films on platinum indicated that the oriented films were easier to switch and fatigued at a slower rate than the polycrystalline films. But long term property (fatigue, imprint) testing on lead titanate resulted in resistance degradation of these contacts, unlike PZT films.

Pb(THD)2 is one of the most popular CVD precursors for lead. It was found in this study that the volatility of Pb(THD)2 can be considerably improved by using ammonia as a carrier gas. An adduct between Pb(THD)2 and NH3 is generated in-situ, when the NH3 carrier gas is passed through the bubbler containing Pb(THD)2. The ammoniated precursor was isolated and its molecular structure was characterized by elemental analysis, infrared and NM.R. PbO thin films could be prepared with this precursor system while maintaining the bubbler temperature at 110° C, which is considerably lower than the temperature used with the Pb(THD)2 precursor in the commonly used carrier gas.

Metalorganic chemical vapor deposition (MOCVD) was used to deposit epitaxial BaTiO3 thin films on (100) MgO substrates at 600°C. The metalorganic precursors employed in the deposition experiments were hydrated Ba(thd)2 (thd = C11H19O2) and titanium isopropoxide. The films were analyzed by means of transmittance spectroscopy, wavelength dispersive x-ray spectrometry, secondary ion mass spectrometry depth profiling, x-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction, nanoscale energy dispersive x-ray spectrometry and second harmonic generation measurements. There was no evidence for interdiffusion between the film and substrate. The x-ray and electron diffraction studies showed that the films were oriented with the a-axis normal to the substrate surface, whereas second harmonic generation measurements showed that the films had some c-axis character.

We have investigated influences of Ti sources on properties of (Ba,Sr)TiO3 [BST] films prepared on Pt/SiO2/Si substrates by liquid source chemical vapor deposition (liquid source CVD): TiO(DPM)2 [titanyl bis (dipivaloylmethanato), TiO(C11 H19O2)2], Ti(O-i-Pr)2 (DPM)2 [bis (isopropoxy) bis (dipivaloylmethanato) titanium, Ti(o-i-C3H7)2(C11H19O2)2], and TTIP [titanium tetraisopropoxide, Ti(O-i-C3H7)4]. Improved electrical properties and step coverage were obtained using TiO(DPM)2 at a substrate temperature TS=420'C and a reactor pressure P=1.5Torr as follows: a dielectric constant ε=210, equivalent SiO2 thickness teq=0.51nm, leakage current density JL=6.6×10∼−8A/cm2 at +1.1V, dielectric loss tan δ=0.007, and coverage of 0.8. However, hillocks appeared on the BST film surface under these conditions, while the film surfaces were relatively smooth using TTIP. The density of these hillocks appeared to be related to the BST(110) peak intensity of the X-ray diffraction pattern.

The theoretical basis of an autostoichiometric vapor deposition method is discussed. We try to define and analyze through the stagnant film model for vapor deposition, the mechanism through which the stoichiometry of a multicomponent oxide film can be precisely controlled. It is found that the utilization of a thermally stable, heterometallic molecular precursor, and a chemical reaction scheme which partially protects the integrity of the precursor molecule during deposition are essential for autostoichiometric vapor deposition. An ideal deposition reaction is the vapor phase hydrolysis, substrate surface polycondensation of volatile double alkoxides. A simple low pressure apparatus can be used to realize autostoichiometric vapor deposition.

Sol-gel processing methods are frequently used for the fabrication of lead zirconate titanate (PZT) thin films for many electronic applications. Our standard approach for film fabrication utilizes lead acetate and acetic acid modified metal alkoxides of zirconium and titanium in the preparation of our precursor solutions. This report highlights some of our recent results on the effects of the addition of a second chelating ligand, acetylacetone, to this process. We discuss the changes in film drying behavior, densification and ceramic microstructure which accompany acetylacetone additions to the precursor solution and relate the observed variations in processing behavior to differences in chemical precursor structure induced by the acetylacetone ligand. Improvements in thin film microstructure, ferroelectric and optical properties are observed when acetylacetone is added to the precursor solution.

Rapid thermal processing (RTP) has been used to examine the crystallization kinetics of lead zirconate titanate (PZT) fabricated using a sol gel process. Depth profiling of PZT films was performed with glancing angle x-ray diffraction and transmission electron microscopy. The films were annealed using RTP ramp rates from 10°C/s to 200°C/s and hold temperatures from 525°C to 650°C. The effect of ramp rate on the phase transformation is presented, and the growth of oriented columnar structures is demonstrated. Films subjected to RTP at 650°C for 1s using a ramp of 10°C/s began to transform to perovskite and were ferroelectric while a ramp of 100°C/s (same hold) produced a linear material which was pyrochlore. Longer hold conditions such as 650°C for 30s produced ferroelectric films with Pr in excess of 20μC/cm2 and relative permittivities ε > 600.

We have characterized the pyrochlore-to-perovskite crystallization process in solution-derived Pb(Zr0.20Ti0.80)O3 thin films on (100) MgO single crystal substrates. It has been determined that the perovskite phase nucleated preferentially at the film/MgO interface out of a nanocrystalline (≈100Å grains) pyrochlore matrix. During the early stages of the pyrochlore-to-perovskite conversion process, perovskite growth proceeded nearly isotropically from the substrate to form hemispherically shaped grains. Deviations from isotropie growth were shown to result from a growth dependence based on the crystallographic orientation of a growing perovskite grain relative to the orientations of pyrochlore grains being transformed. The volume change that occurs during the pyrochlore-to-pervoskite transformation along with two-dimensional grain growth has been used to develop a mechanism for formation of porosity that commonly is concentrated in grain boundary regions.

Thin films of Pb(Mg,Zn)1/3Nb2/3O3 were fabricated by spin casting the Pb-Mg-Zn-Nb-0 complex alkoxide sols on (111)Pt-coated MgO (100) planes. It was observed that the rheological characteristics of sol greatly influenced the orientation of perovskite grains after thin-film formation. A strong preferential orientation of (100)-type planes of the perovskite grains was obtained in the thin films derived from the sols exhibiting pseudoplastic behavior. Small angle X-ray scattering experiment in the Porod region was performed to correlate the observed preferential orientation with the network structure of precursors at various stages of aging. It was shown that weakly branched precursor chains led to highly oriented grains after thin-film formation.

The effects of the microstructure of PZT sol-gel thin films, processed using different solutions, on their material and electrical properties have been studied. The films have different degrees of preferred orientation of the perovskite crystals as well as different grain size. The material characteristics are evaluated using SEM micrographs and XRD. Correlation of these material properties with the electrical properties for both NVRAM and DRAM applications is made.

Epitaxial and highly oriented lead titanate based thin films were prepared by a sol-gel process using non-hydrolyzed methoxyethoxide precursors and RTA process. PbTiO3 crystallized with preferred (001) or (100) orientation on SrTiO3 (100) and MgO (100). Solid phase (001) oriented epitaxial growth of PZT on SrTio3 was observed at 425°C, directly from the amorphous phase. That of PZT on MgO was observed at temperatures above 550°C, after the formation of pyrochlore phase. The PZT on SrTiO3 had a single (001) orientation and rocking curve full width at half maximum less than 0.08°. PZT showed a weak preferred (111) orientation on sapphire (0001) substrates, while highly (111) oriented PLT thin films were obtained on them. The guided wave modes were excited by a prism coupling for PZT thin films crystallized on SrTiO3 and MgO. Electrical properties of epitaxial PZT and PLT thin films on Nb-SrTiO3 substrates were characterized.