The reliability properties of sputtered and sol-gel derived lanthanum doped lead-zirconatetitanate (Pb1-xLax(Zr,Ti)O3) have been studied for DRAM applications. A strong polarity dependence for times-to-breakdown (tbd) and significant space charge effects are observed under constant voltage stressing, and are understood to be related to the movement of oxygen vacancies in the d.c. field. The equilibrium current density attained during d.c. stressing appears to be Schottky emission limited. The endurance of lanthanum doped films to high voltage d.c. stressing improves with increasing lanthanum content and a linear extrapolation of log(tbd) with reciprocal electric field indicates a lifetime of ∼10 years. The low-voltage polarizability of fresh sputtered films depends strongly on the polarity; a.c. stressing leads to hysteresis relaxation. The asymmetry in the response to a.c. stressing is possibly due to the structural asymmetry of the device. Neither tbd nor the fatigue-rate seem to depend on the capacitor area for the areas studied.

Thin film process for Pb-based perovskite ferroelectrics has been investigated. Synthesis of epitaxial PLZT, PLT and PZT thin films by rfmagnetron sputtering in our laboratory was reviewed. Basic thin film process and applications were discussed. For further investigation, film preparation process was developed by co-deposition and assisted deposition techniques. The substrate temperature required for in-situ preparation of perovskite could be reduced to room temperature by an ion- and photoassisted co-evaporation technique.

The optical emission spectra resulting from if magnetron sputtering a BaTiO3 target were observed to survey substrate position implications. A collimated optical fiber bundle parallel to the plane of the sputter target was translated vertically and horizontally to spectroscopically profile the sputter process. The resulting Ar, O, Ba, and Ti emission intensity contours and the O/Ba and Ba/Ti intensity ratio contours suggest substrate positions that should provide uniform undistorted films. Films deposited on sapphire substrates were found to differ in orientation, lattice parameter, and index of refraction. The optimum offaxis deposition position shifted as the chamber pressure was varied.

Lead zirconate titanate thin films have been grown by rf magnetron sputtering an oxide target of nominal composition [Pb(Zr0.55,Ti0.45)O3 or PZT] in argon. The kinetics of the sputtering process and the effect of sputtering parameters on film composition have been studied and related to the continuously monitored optical emission of the plasma. The relative and absolute 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 conditions for the deposition at room temperature of stoichiometric PZT films were established.

Anomalous layers 20-40nm thick were found at the interfaces of lead zirconate-titanate films and Pt electrode films. Detailed study has shown evidence that absorption of PbO by Pt during sputtering resulted in a Pb deficiency in the PZT films and the formation of PbTi3O7 phase. The anomaly was also partly due to island formation at the initial PZT film deposition which allowed PbO to react with Pt films. The Pb controlled PZT films 50nm thick exhibited excellent ferroelectric properties comparable to thicker ones.

Thin films, 0.2 μm to 2 μm thick, of ferroelectric PbTiO3 have been deposit ed on Pt coated Si wafers using a novel dual target ion beam sputtering technique. The sputtering targets of PbO and Ti are shuttled back and forth into a Xe ion beam, depositing very thin (10 - 15 Å) alternating layers of PbO and TiO2. The substrate is heated in situ, allowing interdiffusion of the thin layers into a homogeneous PbTiO3 film. Film composition can be controlled accurately and repeatably by controlling the ratio of the sputtering times from each target. Structural characteristics were analyzed by x-ray diffraction, Rutherford backscattering as a function of the sputtering time ratio and the deposition temperature on Pt and Si3N4 coated Si substrates. The stoichiometric PbTiO3 films have a tetragonal perovskite structure with a slight c-axis preference. Capacitor structures show ferroelectric hysterisis loops, dielectric constants of 100-250, loss tangents between 0.002 and 0.04 and a pyroelectric coefficient greater than 5 x 10−8 C/cm2 °C.

PZT films < 700Å have been synthesized by in-situ ion beam sputter deposition on Pt/Ti/MgO and RuO2/SiO2/Si substrates using deposition temperatures ≤ 500°C. Films on Pt/Ti/MgO had a highly preferred (001) orientation, whereas, the films on RuO2/SiO2/Si were randomly oriented. The formation of perovskite vs. pyrochlore phases has been studied. In the case of heavily Sn doped samples, it appeared that the doping promoted the nucleation of pyrochlore. We believe this effect was caused by a substantial reduction in the A:B cation ratio which was the result of Sn contaminated Pb targets. Electrical characterization was performed using parallel-plate electrodes. Hysteresis measurements showed high polarization values and coercive fields for the highly oriented films, whereas, the randomly oriented films showed much lower values of polarization. Fatigue measurements on the highly oriented films showed a sharp drop in polarization at 105 or 106 cycles. A decrease in Pr with time has been observed and is discussed.

PbTiO3 thin films on Si (100) plane were prepared by the DC reactive multitarget cosputtering technique. The film composition and structure were examined as a function of deposition parameters. The crystal structure and microstructure of PbTiO3 thin film deposited on Si at low substrate temperature of 200°C were examined as a fuction of post-annealing temperature by X-ray diffraction and transmission electron microscopy.The ferroelectric domain configurations were analyzed by plane-view TEM. The preferred orientation of PbTiO3 thin films deposited on MgO (100) and sapphire (1102) at high substrate temperature of 520°C were also examined.

For the successful integration of ferroelectric thin films in IC technology, there is a need for a deposition technique capable of growing homogeneous layers at high growth rates over large-area structured substrates. Organometallic chemical vapor deposition (OMCVD) is a promising technique for meeting these demands.

Ferroelectric layers of PbZrxTi1-xO3 (PZT) were grown by OMCVD on Pt-coated 10 cm diameter Si-substrates using the precursors tetra-ethyl-lead, tetra-iso-propoxy-titanium and tetra-tertiary-butoxy-zirconium at 700 °C without any post anneal. At this temperature the layers are single phase and highly (h00) and/or (00l) oriented. The layers show good ferroelectric switching properties with high remanent polarizations, but also with high coercive field strengths. Fatigue measurements are presented for these OMCVD grown PZT layers. The layers have a switching lifetime exceeding 1011 cycles at a switching amplitude of 5 V.

The ferroelectric thin films of bismuth titanate (Bi4Ti3O12) have been prepared by metalorganic chemical vapor deposition ( MOCVD) technique at atmosphere. The triphenyl bismuth (Bi(CaH5 ) 3)and tetrabutyl titanate (C16H36O4Ti) were used as precursors. Dense Bi4Ti3 O12 films with smooth shinning surface have been grown on Si( 100) substrates at 550°C whithout postannealing. The as- grown films were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersion analysis ( EDAX). The films showed well-ordered crystallinity with an (001)preffered orientation. The influence of growth parameters on deposition rate, composition and morphology of as-grown films was also discussed.

BaTiO3 thin films have been prepared by low pressure organometallic chemical vapor deposition on (100) MgO and (100) LaAlO3 substrates using the volatile precursors, titanium(IV) tetraisopropoxide and barium (hexafluoroacetylacetonate)2 (tetraglyme). The phase composition and structure of the films depends on the reactant partial pressure, growth temperature, and substrate. High quality, epitaxial BaTiO3 films can be prepared in-situ on LaAlO3 as confirmed by x-ray diffraction measurements. These BaTiO3 films exhibit smooth surface morphologies as evidenced by scanning electron microscopy. Electrical resistivity measurements indicate that the films are semi-insulating.

Bulk BaTiO3 has a large linear electro-optic coefficient and a very high dielectric constant. We report results obtained for two different MOCVD processes designed to deposit BaTiO3 films with properties suitable for nonlinear electro-optic or high charge storage applications. Epitaxial BaTiO3 films have been grown on NdGaO3 [100] substrates using a high temperature thermal process; the substrate temperature was 1000°C and the total pressure was 4 torr. Selected area electron diffraction (SAED) measurements indicate highly textured, single phase films on the NdGaO3 substrate which are predominantly [100] oriented. Fine grained polycrystalline films have been grown on Pt at 600°C by plasma-enhanced metalorganic chemical vapor deposition (PEMOCVD). Specular IR reflectance was used to determine the concentration of BaCO3 in the film, which was significantly reduced by the plasma. The polycrystalline films had dielectric constants as large as 300 and resistivities exceeding 5 x 108 Ω-cm at room temperature.

Thin films of lead-titanate were deposited by chemical vapor deposition (CVD) using tetraethyl lead and titanium isopropoxide. Good high frequency hysteresis curves were obtained with platinum contacts. Low resistance of the material (estimated at 108 ohm-cm) affected low frequency measurements.

Optimized experimental parameters (pressure, temperature, gas flows, oxidizer) were derived from a designed experimental matrix using response surface methodology. This approach significantly reduced the number of deposition trials required.

We are developing strategies to form single-component precursors to perovskite phase mixed metal oxides where the stoichiometry of the precursor is fixed at the molecular level to be that of the final desired phase. These strategies ean be applied to the formation of perovskite phase thin films. Two such methods are described herein, relying on ester elimination and alcohol elimination reactions. We have found the reaction between lead(II) acetate and titanium(IV) isopropoxide in ethanol results in ligand redistribution at room temperature. Reactions between (β-diketonate)2M(OR)2 where M = Ti, Zr and Sn and lead(II) acetate do not result in any detectable ester elimination under the reaction conditions employed, and this approach was not successful. Alcohol elimination experiments have been explored as an alternative strategy using a bifunctional glycolate ligand. Lead carbonate reacted with glycolic acid to form the corresponding lead glycolate complex Pb(O2CCH2OH)2. This compound reacted with (β-diketonate)2M(OR)2, M = Ti and Sn, to eliminate two equivalents of alcohol and form the corresponding single component (β-diketonate)2M(OCH2CO2)2Pb complexes. These complexes start to thermally decompose at 150°C and loss of weight is complete by 450°C to yield a product whose weight loss corresponds to the formation of PbTiO3 for M = Ti. Bulk thermolysis of a sample of (dpm)2Ti(OCH2CO2)2Pb at 400°C resulted in formation of crystalline perovskite phase lead titanate together with PbO, massicot and α-PbO phases.

Ferroelectric PZT 53:47 thin films were prepared by two different solution deposition methodologies. Both routes utilized carboxylate and alkoxide precursors and acetic acid, which served as both a solvent and a chemical modifier. We have studied the effects of solution preparation conditions on film microstructure and ferroelectric properties, and have used NMR spectroscopy to characterize chemical differences between the two precursor solutions. Films prepared by a sequential precursor addition (SPA) process were characterized by slightly lossy hysteresis loops, with a Pr of 18.7 μC/cm2 and an Ec of 55.2 kV/cm. Films prepared by an inverted mixing order (IMO) process were characterized by well saturated hysteresis loops, a Pr of 26.2 μC/cm2 and an Ec of 43.3 kV/cm. While NMR investigations indicated that the chemical environments of both the proton and carbon species were similar for the two processes, differences in the amounts of by-products (esters, and therefore, water) formed were noted. These differences apparently impacted ceramic microstructure. Although both films were characterized by a columnar growth morphology, the SPA derived film displayed a residual pyrochlore layer at the film surface, which did not transform into the stable perovskite phase. The presence of this layer resulted in poor dielectric properties and lossy ferroelectric behavior.

Sol-gel derived PZT films were successfully prepared from precursor solutions based on lead acetate and Zr/Ti alkoxides. A pyrochlore phase was observed in films fired at low temperatures, while single-phase perovskite films were obtained at temperatures above 725C. The dielectric constant increased to above 1000 when there was a higher proportion of perovskite than pyrochlore. The films were essentially fatigue-free up to 108 cycles and exhibited a low aging rate of 5.7% / decade-sec.

Lead zirconate titanate thin films containing 0-4 wt.% of 2CdO·B2O3 glass phase additive have been fabricated by sol-gel processing. Smooth dense perovskite films of approximately 3500Å thickness were formed on Si wafers by a multiple layer spin coating process followed by rapid thermal annealing. Remanent polarizations of up to 23μC/cm2 were measured. Hysteresis properties were found to be very sensitive to annealing time at 700°C, with remanence being maximized at 100-200 seconds.

Both La and Nd–doped PZT, i.e., PLZT and PNZT, ferroelectric thin films were prepared by the metalorganic deposition (MOD) process. The precursor solutions used were derived from lead acetate, lanthanum acetylacetonate, neodymium acetate, zirconium n–propoxide, and titanium iso–propoxide. The dopant concentration of the films analyzed by electron microprobe indicated a one–to–one correspondence between film composition and the composition of the precursor from which the film was made. In this study, the effects of Nd and La dopants in PZT films on Curie temperature was determined by in–situ hot–stage TEM and compared with those of bulk materials. Lattice parameter and phase transformation were determined by both X–ray and electron diffraction. Our observations were: (1) Curie temperature decreases with increasing dopant concentration for both thin foils and bulk ceramics, (2) for a given dopant concentration, Curie temperature and crystal tetragonality of PNZT thin foils is lower than those of PLZT samples, (3) Curie temperature of thin foils was found to be less than those of the corresponding bulk materials, and (4) ferroelectric domains is easily observed in both PLZT and PNZT TEM specimens prepared by the spin–coating method.

Crack free transparent ferroelectric PLZT (9/65/35) thin films were deposited on silicon substrates using the sol-gel deposition technique. An intermediate layer of PLT was used to improve the PLZT's optical quality and to reduce the amount of film cracking. Wet chemical, plasma and reactive ion etching are investigated as means of realizing the necessary waveguide structures. Waveguiding is observed in 2-4mm long PLZT (9/65/35) fabricated by reactive ion beam etching.

High dielectric constant thin film capacitors for integrated circuits were fabricated with an LSI process. The capacitors comprized AI/TiN top electrode, Si3N4 interlayer insulator, SrTiO3 dielectric and Pt/barrier-metal/Si bottom electrode. Two types of capacitor structure were discussed on the basis of dielectric property and fabrication process. The TiN layer played an important role in suppressing degradation of insulating properties at elevated temperature, which was caused by a reaction between Al and SrTiO3. Breakdown strength larger than 6.6 MV/cm was obtained for 0.001 mm2 area capacitors. However, the strength decreased with increasing capacitor area. The area dependence may be due to surface defects which were introduced during the processes subsequent to SrTiO3 film deposition. The capacitance density of about 9 fF/μm2 was obtained for 150nm thick film. Recent activities of ferroelectric thin film research in Japan was given as well.