The incorporation of metallic species (Bi, Sr and Ta) during the growth of layered perovskite SrBi2Ta2O9 (SBT) on a-axis oriented YBa2Cu3O7−x (YBCO) conducting oxide substrates has been investigated using in situ low energy mass spectroscopy of recoiled ions (MSRI). This technique is capable of providing monolayer-specific surface information relevant to the growth of single and multi-component thin films and layered heterostructures. The data show a temperature dependence of metallic species incorporation during co-deposition of Sr, Bi and Ta on YBCO surfaces. At high temperatures (400 < T ≤ 700°C), negligible incorporation of Bi is observed as compared to Ta and Sr. At low temperatures (≤ 400°C), there is a substantial incorporation of Bi, Sr and Ta on the surface of YBCO, and the MSRI signal intensities for Sr, Bi and Ta are nearly independent of substrate temperature. According to thermodynamic calculations, the presence of Ba and Y on the YBCO surface inhibit the incorporation of Bi due to competition for oxygen required to establish bonding of metallic species to the surface. This may be the explanation for the observed Bi deficiency in films grown on YBCO surfaces at temperatures > 400°C. SBT films grown at temperatures ≤ 400°C and annealed in oxygen or air at 800°C exhibit a polycrystalline structure with partial a-axis orientation.

It is known that the forming gas (N2-H2 mixture) annealing process required for microcircuit fabrication results in an unacceptable electrical degradation of SrBi2Ta2O9 (SBT) ferroelectric capacitors due mainly to the interaction of H2 with the ferroelectric layer of the capacitor. We have found a strong relationship between changes in the surface composition of the ferroelectric layer and the electrical properties of SBT capacitors as a result of hydrogen annealing. Mass spectroscopy of recoiled ions (MSRI) analysis revealed a strong reduction in the Bi signal as a function of exposure to hydrogen at high temperatures (∼500°C). The Bi signal reduction correlates with Bi depletion in the SBT surface region. Subsequent annealing in oxygen at temperatures in the range of 700–800°C resulted in the recovery of the MSRI Bi signal, corresponding to the replenishment of Bi in the previously Bi-depleted surface region. XRD analysis (probing the whole SBT film thickness) showed little difference in the XRD spectra of the SBT films before and after hydrogen and oxygen-recovery annealing. The combined results of the MSRI and XRD analyses can be interpreted as an indication that the degradation of the electrical properties of the SBT capacitors, after hydrogen annealing, is mainly due to the degradation of the near surface region of the SBT layer.

Using a KrF or ArF excimer laser as an irradiation photon source, we have succeeded in crystallizing amorphous SrBi2Ta2O9 films at 200-290°C, quite lower temperatures than the conventional crystallization temperature. The crystallization is enhanced when the substrate temperature, irradiation time, or the laser power density is higher.

Preferentially (105)-oriented Sr0.7Bi2.8Ta2O9(SBTO) thin films on SiO2/n-Si(100) have been prepared by pulsed laser deposition at temperatures as low as 350°C, which is the lowest process temperature for growing SBTO ferroelectric thin films. Dielectric properties of the SBTO films have been improved by increasing the Sr/Bi atomic ratio from 0.7/2.8 to 0.7/2.0. Memory windows of as large as 3.6V and 4.V in the MFIS capacitor have been obtained at Sr/Bi ratios of 0.7/2.0 and 1.0/2.0 respectively and are the largest values reported in the MF(I)S diode structures. Little C-V degradation is observed up to with the 1010 cycles for the process temperature of 400°C, especially for Sr/Bi of 0.7/2.0, with the memory window remaining at more than 3.2V. Memory retention time was about 3×103 sec at which the difference in capacitance between “ON” and “OFF” states reduces to half of its initial value. Optimum hold bias voltage exists in the retention test. Improvement in memory characteristics is strongly related to the insulating properties of the ferroelectric and dielectric thin films rather than the value of dielectric constant.

New approaches for improving fatigue performance of sol-gel PZT based ferroelectric capacitors with RuO2 electrodes are discussed. The use of thin (∼5 nm) high-Ti PZT seed layer was found to be effective for improving fatigue performance. For an optimized seedlayer thickness, FECAPs with excellent fatigue characteristics (less than 10% decrease in Pr after 1011 cycles) were obtained.

A two-step pulsed laser deposition (PLD) process, including PLD at a substrate temperature lower than 150°C and rapid-thermal-annealing (RTA) at around 550°C (30 s), has been successfully applied for growing (Pb0.97La0.03)(Zr0.66Ti0.034)0.9875O3, PLZT, thin films. Interdiffusion between layers is pronouncedly suppressed due to the presence of the SrRuO3 layer, which markedly improves the electrical properties of PLZT films. The PLZT films thus obtained exhibit large remanent polarization P,=19 µC/cm2 (with coercive force Ec=78 kV/cm), low leakage current density J11≤8 × 1O−6 A/cm2 (up to 400 kV/cm) and fatigue free characteristics.

Pb(ZrxTi1−xO3 (lead zirconate titanate or PZT) ferroelectric thin film capacitors are of considerable interest for the realization of memory devices such as nonvolatile random access memories (NVRAMs). The PZT capacitors were prepared on platinized silicon Pt/(100)Si using conducting oxide LaxSrl.xCOO (lanthanum strontium cobalt oxide or LSCO) as electrodes. The PZT and LSCO thin films were deposited by the KrF excimer laser ablation technique. The optimum preparation conditions such as oxygen pressure, laser energy influence and substrate temperature were investigated. The PZT and LSCO films grown on Pt/(100)Si are polycrystalline. The crystallographic properties of the films were determined using X-ray diffractometer (XRD) method. The cross-sectional transmission electron microscope showed very smooth interface among different layers of films. The electrical characterizations of the films including hysteresis loop, fatigue, and retention properties were determined by the RT66A Standardized Ferroelectric Test System.

The grain size of MOCVD-Pb(Zr,Ti)O3 (PZT) thin films was successfully controlled by changing the grain size of Ir bottom electrodes and by changing the growth rate of PZT films. In Ir/PZT/Ir/SiO2/Si capacitors, the grain size of PZT thin films increased from 120 to 240nm as the grain size of bottom Ir electrodes increased from 50 to 200nm. The dielectric constants of PZT thin films increased from 760 to 1440 as the grain size increased from 120 to 240nm. Remanent polarization increased and coercive field decreased as the grain size increased. This dependence of electrical properties on the grain size coincided with that of ceramics.

MOCVD is a useful method for the deposition of thin films of metal oxides containing early transition metals, e.g., lead zirconium titanate, (PZT), because of its good step coverage and control of composition. Results are presented on a number of novel compounds which may be, or are, good MOCVD precursors. The compounds studied are in several general classes and include M(←diket)x, M(OR)x, M(←diket)x (OR)y [where M = Ti, Zr, Hf, Ta; ←-diket = tmhd (2,2,6,6-tetramethylheptane-3,5-dione), acac (acetylacetonate), hfac (1,1,1,5,5,5-hexafluoroacetylacetonate); R = Me, Et, Pr1, Butt]. We have sought to modify the precursors through chemical methods and have synthesized a number of novel, volatile, and intrinsically thermally stable MOCVD precursors. Full chemical characterization of the precursors (NMR, IR, MS, CHN, TGA/DSC, Single Crystal X-ray diffraction) has been undertaken.

The (Pb1−xLax)TiO3, (PLT) thin films possessing good ferroelectric properties were successfully obtained by using metal-organic-decomposition (MOD) process, followed by furnace post-annealing at 600-700°C (60 min) or rapid thermal annealing (RTA) at 600-700°C (60 s). Excess Pb-species incorporated in precursors for compensating for the Pb-loss during MOD process results in pronounced modification on thin film's electrical properties. The leakage current is reduced from JL= 1 × 10−3 A/cm2 to 1 × 10−4 A/cm2 (at 400 kV/cm) and the remanent polarization is increased from Pr= 8.3 µ C/cm2 to 12.6 µC/cm2, when 10 mol% excess-Pb is added. On the other hand, larger La-content in PLT films results in more pronounced Pb-loss and induces larger leakage current, which significantly degrades the ferroelectric properties of the films. The best properties obtained for PLT films prepared by the MOD process are: Pr= 12.6 µC/cm2, Ec = 80 kV/cm and JL= 10−5 A/cm2 (at 400 kV/cm).

Single-phase polycrystalline PbZrO3 (PZ) thin films, 3000-6000 A thick, have been grown by metal-organic chemical vapor deposition (MOCVD) on (111)Pt/Ti/SiO2/Si substrates at ≍525°C. X-ray diffraction analysis indicated that the PZ films grown on (111)Pt/Ti/SiO2/Si (Pt/Tgi/Si) showed preferred pseudocubic (110) orientation. In contrast, PZ films grown on 150 A thick PbTiO3 (PT) template layers exhibited a pseudocubic (100) preferred orientation, and PZ films deposited on TiO2 template layers consisted of randomly oriented grains. The PZ films grown on Pt/Ti/Si with or without templates exhibited dielectric constants of 120-200 and loss tangents of 0.01-0.0. The PZ films with (110) orientation exhibited an electric-field-inducedtransformation from the antiferroelectric phase to the ferroelectric phase with a polarization of ≍34 µC/cm2, and the energy that was stored during switching was 7.1 J/cm3. The field needed to excite the ferroelectric state and that needed to revert to the antiferroelectric state were 50 and 250 kV/cm, respectively. Relationships between the MOCVD processing and the film microstructure and properties are discussed.

A heteroepitaxial (001)Pb(ZrxTi1−x)O3(PZT) film was grown on the (100)Ir/(100)YSZ/Si structure with a cube-on-cube relationship by using reactive sputtering. The X-ray diffraction patterns of this sample showed that the double domain crystal layer of the (110) IrO2 was formed between the Ir and PZT films. According to reflection high energy electron diffraction observation and X-ray photoelectron spectroscopy measurements, it was found that the initial epitaxial growth of the PZT film occurred on the Ir film. The polarization-electric field hysteresis loop of the 285-nm-thick epitaxial PZT film with the top electrode of IrO2 showed a saturated square shape at the ac amplitude of 3V, and the remanent polarization 2Pr and the coercive field 2Ec were 80 µC/cm 2 and 100 kV/cm, respectively. The 2Pr's were not reduced up to the switching cycles of 5 × 1010 with ± 5V bipolar pulse.

The domain structure of the 400 nm thick PbZr0.2Ti0.8O3 (PZT) films with different electrode layer configurations was investigated by x-ray diffraction and transmission electron microscopy. The c-domain fractions of the PZT films with no electrode layer, with a 50 nm electrode layer between the film and the substrate, and with 50 nm electrode layers on top and bottom of the PZT film were found to be equal. This means that depolarizing fields do not affect the polydomain structure of the film. Calculations of the in-plane strains based on the lattice parameters of the La0.5Sr0.5CoO3 (LSCO) layer in the above configurations led to the conclusion that the bottom electrode layer is coherently strained to match the substrate.

The morphology and phase evolution of sol-gel PZT thin films during rapid thermal annealing are investigated by in situ recording of scattered light intensity measured in reflected mode and momentary patterns visualized by optical microscope. In addition the texture and fractions of growing phases and the angular dependence of the scattered light are studied in partly annealed films. The kinetic parameters characterizing the transition from pyrochlore to perovskite phase are extracted by mathematical treatment of experimental data. It is shown that the film's texture and the transformation kinetics strongly depend on pyrolysis temperature. A mechanism of texture formation is proposed.

Modified sol-gel processes have been developed for the preparation of precursor solutions of undoped, La and Ta doped PZT (25/75). These processes use different solvents (methoxyethanol, butoxyethanol) and different lead sources (lead acetate, lead oxide). Due to variations in the structure and in the composition of the solutions, significantly different thermal decomposition behaviors were found. These inevitably affected texture and microstructure of the sol-gel derived thin films, demonstrating the important role of precursor chemistry in the improvement of film properties. In the case of tantalum doped Pt/PZT/Pt ferroelectric capacitors a rectangular hysteresis loop, featuring high Pr, was obtained for one specific precursor chemistry.

Incorporation of ferroelectric thin films into integrated microelectronics requires deposition temperatures compatible with back-end processing. Pb(Zr,Ti)O3 (PZT) thin films have been deposited at low temperatures by a thermal chemical vapor deposition process using flash-vaporized metalorganic precursors. Deposition temperatures, A-site to B-site ratios in the precursor solution, and bottom electrodes have been surveyed. Stoichiometric perovskite films with (Zr/Ti) ratios ranging from 20/80 to 50/50 were obtained. Films deposited at temperatures below 500°C possess very fine grain structures. Capacitor structures were fabricated by depositing top electrodes using electron-beam evaporation, followed in some cases by a post-electrode anneal at 650°C. Remanent polarizations greater than 20 μC/cm2 were observed on films deposited on Pt at temperatures as low as 475°C. Perovskite films were obtained on Ir electrodes at temperatures as low as 450°C, with remanent polarization greater than 10μC/cm2 in the as-deposited condition.

For the possible application of PZT thin films in ferroelectric non-volatile memories, the potential of low-voltage switching is a major requirement. By straightforward thickness scaling down to 75nm, operation voltage can be reduced to 1.5V without degradation of the hysteresis properties. However, interface effects increase the coercive field for thinner films, so that operation voltage does not scale linearly with thickness. In view of the large difference in coercive field between bulk and thin-films, on the other hand, material (and interface) optimization may constitute an interesting alternative route for further voltage scaling. By optimizing the composition and stoichiometry, less than 1.5V switching has indeed been obtained even for 150nm films. It is argued that an important material parameter affecting low-voltage switching behavior is the ferroelectric domain configuration and presence/absence of mobile domain walls in the PZT film.

Lead zirconate titanate (PZT) thin films have been deposited in a reactive argon/oxygen gas mixture from a metallic target of nominal composition Pb1.1(Zr0.4Ti0.6)O3 by rf magnetron sputtering on Si substrates and RuO2/SiO2/Si structures. During plasma deposition, in situ Optical Emission Spectroscopy (OES) measurements clearly show a correlation between the evolution of characteristic atomic emission line intensities and the thin film composition determined by simultaneous Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA). As a result, the cathode surface state can be monitored by OES to ensure a good compositional transferability from the target to the film and reproducibility of thin film properties for given values of deposition parameters. Electrical properties and crystallization have been optimized with a 90 nm PZT thin film grown on RuO2 electrodes. These PZT films, annealed with a very modest thermal budget (550°C) are fatigue-free and show very low leakage currents (J=2.10−8 A/cm2 at 1 V). The use of a metallic target allows us to control the oxygen incorporation in the PZT thin film and also, using 18O as a tracer, to study the oxygen vacancy migration which plays a key role in fatigue, leakage current, and electrical degradation/breakdown in PZT thin films.

The PZT thin films were fabricated to investigate the effect of sol-gel processing parameters on the physical and the electrical properties. The films were made with different amount of excess Pb precursors and drying temperatures, and then annealed in various ambients. The physical properties of the films such as crystallinity and microstructure were evaluated using x-ray diffraction, scanning electron microscopy and atomic force microscopy. The ferroelectric properties and current density characteristics of the films were investigated using a standarized feiroelectric test system and pA meter, respectively. It is found that the drying temperature was playing a key role in the formation of the secondary phase on the PZT thin films. In addition, it turned out that the use of nitrogen as an annealing ambient promoted overall ferroelectric properties, when compared to oxygen ambients.

Effects of the purity of metalorganic Pb,Zr and Ti precursors (Pb(C2H5)4, Zr(O-tC4H9)4 and Ti(O-iC3 H 7)4) on the electrical properties of Pb(ZrTi)O3 (PZT) thin films prepared by MOCVD were investigated. Generally, PZT thin films prepared using the high purity Pb source precursor had a tendency to show better current densities, breakdown electric fields and switching fatigue characteristics than those of PZT films prepared using the low purity precursor. On the other hand, distinct purity effects of Zr and Ti source precursors were not observed. These experimental results suggest that some types of impurities play important roles as donors and acceptors and influence ionic movement and space charge. At this stage, it is not well understood which impurities contained in precursors play important roles and what is the difference in the impurity effects between Pb, and Zr and Ti precursors.