We have fabricated epitaxial ferroelectric heterostructures of isotropic metallic oxide (SrRuO3) and ferroelectric thin films [SrRuO3/Pb(Zr0.52Ti0.48)O3 /SrRuO3] on (100) SrTiO3 and YSZ buffer layered Si substrates by 90° off-axis sputtering. These heterostructures have high crystalline quality and coherent interfaces as revealed by X-ray diffraction, Rutherford backscattering spectroscopy and cross-sectional transmission electron microscopy. The ferroelectric layers exhibit superior fatigue characteristics over 1010 cycles with large remnant polarization.

Integration of a ferroelectric capacitor module in a standard CMOS process subjects the ferroelectric to various ambients during backend processing, some of which can render the ferroelectric essentially non-operational for NVRAM applications. Post-crystallization processing of sol-gel deposited integrated ferroelectric PZT capacitors in the presence of hydrogen-containing, reducing ambients is observed to degrade the nonvolatile polarization. Low-pressure hydrogen anneals at temperatures as low as 200°C substantially degrade the nonvolatile polarization while the DRAM polarization remains roughly constant. Leakage current drops by one order of magnitude and fatigue is accelerated. A ferroelectric capacitor module can be integrated with minimal degradation with careful modifications in the backend processing.

An ion assisted deposition technique, called Reactive Partially Ionized Beam (RPIB) deposition, was used to prepare amorphous BaxTi2-xOy thin films at a low substrate temperature (<60°C). The stoichiometry of the films varied from ×=l.0 for BaTiO3 to ×=0.2 for Ti-rich films. The optical, thermal, and broadband electrical properties of this class of thin film dielectrics were systematically studied. A lμm BaxTi2-xOy film is optically transparent with a band gap of 4.6eV. Both transmittance and bandgap decrease when the films are increasingly enriched with Ti. The Ti rich films remain amorphous at 600°C while the stoichiometric BaTiO3 crystallizes into the perovskite structure. Annealed Ti rich films are thermally stable (>700°C) with low leakage (<0.lμ/cm2 at 0.5MV/cm) and moderately high dielectric constant (εr = 15-35). Polycrystalline BaTiO 3 deposited at 600°C on a Pt/Ta/SiO2/Si substrate has an εr = 400. Capacitor structures with various metallizations were used to evaluate the dielectric properties, such as breakdown strength, leakage, εr and tanδ from DC to 600MHz. A generic test vehicle was designed and fabricated to extend the frequency domain characterization of the dielectrics up to 40GHz. No dispersion of εr was observed in this frequency range for amorphous BaxTi2-xOy.

Many attempts have been made to reduce degradation properties of Lead Zirconate Titanate (PZT) thin film capacitors. Although each degradation property has been studied extensively for the sake of material improvement, it is desired that they be understood in a unified manner in order to reduce degradation properties simultaneously. This can be achieved if a common source(s) of degradations is identified and controlled. In the past it was noticed that oxygen vacancies play a key role in fatigue, leakage current, and electrical degradation/breakdown of PZT films. It is now known that space charges (oxygen vacancies, mainly) affect ageing, too. Therefore, a quantitative ageing mechanism is proposed based on oxygen vacancy migration under internal field generated by either remanent polarization or spontaneous polarization. Fatigue, leakage current, electrical degradation, and polarization reversal mechanisms are correlated with the ageing mechanism in order to establish guidelines for simultaneous degradation control of PZT thin film capacitors. In addition, the current pitfalls in the ferroelectric test circuit is discussed, which may cause false retention, imprint, and ageing.

Twin related domain formation is examined as a strain relaxation mechanism for a heteroepitaxial tetragonal film on a cubic substrate. Elastic relaxations are calculated for a single twin band in which the c-axis of the tetragonal domains is either related by a 90* rotation about an axis in the plane of the film or by a 90* rotation about the surface normal. In all cases, the strain energy change is evaluated for both the film and the substrate. A domain pattern map is developed that predicts single domain and multiple domain fields depending on the relative misfit strains and domain wall energy. The concept of a critical thickness, hc, for domain formation is developed. For cases in which the c-axis is rotated 90* about an axis in the plane of the film, the critical thickness depends only on the relative coherency strain between the substrate and film and the ratio of the domain wall energy to the stored elastic energy. For the case of a pattern consisting of energetically equivalent domains with the c-axis in plane, the equilibrium distance of multiple domains is derived. For such multiple domains, a minimum wall separation distance exists which depends non-linearly on the film thickness.

Several conductive structures, which appeared to be usable as base electrodes for integrated devices based on high dielectric materials, have been annealed for 30 minutes in oxygen at 650 °C. Similar structures coated with lead-based ferroelectrics deposited by the sol-gel method have been annealed for 1 min in oxygen at higher temperatures. The materials have been characterized by Rutherford backscattering (RBS) and scanning electron microscopy (SEM) and the crystallographic structure of the ferroelectrics films has been determined by X-ray diffractometry (XRD).

Only RuO2/Ru has been found to be suitable as an electrode, at temperatures not exceeding 650 °C. It has also been found that the electrode materials can strongly affect the crystallization behavior of the sol-gel ferroelectric films and the formation of single-phase perovskite layers.

We report results of pulsed electrical testing of ferroelectric Pb0.9La0.1Zr0.2Ti0.8O3 thin film capacitors with symmetrical La-Sr-Co-O top and bottom electrodes at room temperature and at 100°C. They have been grown on [001] Si with a Yttria stabilized zirconia (YSZ) buffer layer. A layered perovskite “template” layer (200-300Å thick), grown between the YSZ buffer layer and the bottom La-Sr-Co-O electrode, is critical for obtaining the required orientation of the subsequent layers. When compared to the capacitors grown with Y-Ba-Cu-O (YBCO) top and bottom electrodes, these structures possess two advantages : (1) the growth temperatures are lower by 60-150°C; (ii) the capacitors show a large remnant polarization, δP, ( δP = switched polarization -non-switched polarization), 25-30 μC/cm2, for an applied voltage of only 2V (applied field of 70kV/cm). The fatigue, retention and aging characteristics of these new structures are excellent at both room temperature and at 100°C.

The most common electrode structure for lead zirconium titanate (PZT) integrated on Si is platinum with a Ti adhesion layer. However, platinum hillocks that can lead to sample shorting may form during annealing. Careful selection of the Pt/Ti electrode architecture and deposition conditions can give nearly hillock-free electrodes. The phase development and ferroelectric properties of PZT prepared by metallo-organic decomposition (MOD) were studied as a function of Pt electrode structure and PZT composition. In addition to evaporated or sputtered Pt/Ti electrodes, Pt electrode layers were also prepared by MOD. MOD Pt layers showed no hillock formation but generally resulted in greater pyrochlore content in PZT capacitors.

PZT ferroelectric capacitors are commonly fabricated using Pt electrodes. Crystallization in an oxygen ambient of sol-gel deposited PZT films is influenced by the nature of the adhesion layer used for the Pt electrode. Here we report results of the TEM investigation of the microstructures of PZT crystallized on Pt/Ti and Pt/TiO2 substrates. PZT films on either substrate show a two-phase microstructure consisting of larger perovskite grains and finegrained (<3nm) pyrochlore matrix. The perovskite grains are dense, free of any porosity and HRTEM shows the observed domains to be 90° <101> twins. EDS spectra detect a lower Pb/Ti ratio for the pyrochlore matrix compared to the perovskite grains. Differences between the two substrates consist of the perovskite to pyrochlore ratio and more importantly the perovskite grain size.

Characteristics of textured Pb(Zr0.54Ti0.46)O3 (PZT) thin films on (001)Si with YBa2Cu3O7-δ (YBCO) and yttria-stabilized zirconia (YSZ) buffer layers have been studied using X-ray diffraction and high resolution electron microscopy techniques. Excimer KrF laser has been used for deposition of PZT, YBCO and YSZ thin films. The YBCO layer was utilized to provide a seed for PZT growth, while YSZ layer acted as a seed and a buffer layer for the growth of YBCO on (001)Si. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction were used to determine the texture and the nature of defects, interfaces and grain boundaries. Predominant orientation relationships were found to be [001]PZT//[001]YBCO; [001]YBCO//[001]YSZ; and [001]YSZ//[001]Si.

In this paper the growth of PbZrxTi1-xO3 on 10 cm platinized silicon wafers using the precursors cursors tetra-ethyl-lead, titanium-tetra-isopropoxide, or titanium-tetra-tertiarybutoxide and zirconium-tetra-tertiarybutoxide will be discussed in some detail. The composition of the films as a function of growth parameters will be treated and the accompanying change in the ferroelectric properties will be discussed. For device manufacturing, the PbZrxTi1-xO3 films are subjected to a number of processing steps. Some results for partially processed wafers will be presented. Also, preliminary results of depositions on 15 cm wafers will be given.

PbTiO3 thin films grown on (001)MgO and (110)MgO by MOCVD have been characterized by x-ray diffraction and transmission electron microscopy. The PbTiO3 films deposited on (001)MgO under the optimum conditions always show a bi-layer structure. The top layer of the films near the free surface is c-axis oriented with the orientation relationship (001)[100]PbTiO3∥(001)[100]MgO. The bottom layer of the films near the substrate is a-axis oriented with (100)[001]PbTiO3∥(001)[100]MgO. 90° domains were observed, but only in the caxis oriented layers. The thickness of the a-axis oriented layers near the substrate decreases with decreasing the cooling rate. PbTiO3 films deposited on (110) MgO, however, are single-layer, epitaxial films with (101)[001]PbTiO3∥(110)[001]MgO.

Using hot-walled metallorganic chemical vapor deposition (MOCVD), thin fihns of lead zirconate titanate (PZT), lead titanate (PbTiO3 or PT) and bismuth titanate (Bi4Ti3O12 or BiT) were successfully prepared. For each material, titanium ethoxide (Ti(C2H5O)4) was used as the precursor for the titanium source, while lead bis-tetramethylheptadione (Pb(thd)2), zirconium tetrakistetramethylheptadione (Zr(thd)4) and triphenyl bismuth (Bi(C6H5)3) were used as sources for lead, zirconium and bismuth, respectively. Dense, specular and highly transparent films were obtained for all three materials. Deposition conditions are given for each of the materials as well as the properties of the resulting films as determined by XRD, SEM and UV-VIS-NIR spectrophotometry. Ferroelectric properties are also given for the PZT and BiT films; for PZT (%Zr = 41; %Ti = 9) annealed at 600 °C, the spontaneous polarization, Ps, was 23 μC/cm2 and the coercive field, Ec, was 65 kV/cm; for BiT annealed at 550 °C, the spontaneous polarization, Ps, was 27 μC/cm2 and the coercive field, Ec, was 240 kV/cm.

Thin film heterostructures of BaTiO3/YBa2Cu3O7-x (YBCO) and BaTiO3/LaxSrl-xCoO3 (LSCO) have been prepared by a novel single liquid source plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) process. Both YBCO and LSCO are conductive oxides with perovskite structure and lattice parameters closely matched to BaTiO3. YBCO films were found to deteriorate after the deposition of BaTiO3 under the PE-MOCVD conditions as revealed by X-ray diffraction and electrical characterization. LSCO thin films prepared by PE-MOCVD have a mirror-like surface, exhibit low electrical resistivity (p = 200 μΩ-cm at room temperature) and are robust to BaTiO3 deposition. These characteristics make LSCO a promising electrode material for ferroelectric capacitors.

Ferroelectric Pb(Zr,Ti)O3(PZT) films with a perovskite phase were successfully grown by MOCVD using a 6 inch wafer CVD system. A two step growth process was proposed to obtain perovskite PZT films at high gas supplying ratios of [Zr]/([Zr]+[Ti]). The electrical properties of the PZT films obtained were measured. Large area growths of PZT films were carried out and the uniform films could be grown on the entire area of a 6 inch Si wafer. It was also found that the step coverage characteristic of the films grown by MOCVD was good.

A wet chemical deposition process for smooth and crackfree films in the system Pb(Zr 1-x Tix)O3 (PZT) has been developed. Final film thicknesses, reached with one coating step, were in the region of 1 μm. Starting from lead acetate trihydrate, zirconium- and titanium-n-propoxide, high molarity (> 2M) coating sols have been prepared that could be handled in air and were stable for more than 170 days.

Films with compositions near the morphotropic phase boundary (x=47) and various lead contents were deposited on Pt-coated Si-wafers and Al2O3-substrates by a spin-on method. Wet films could be pyrolyzed and densified with a fast heat treatment without cracking. The crystallization of films into the desired perovskite structure started at comparatively low temperatures (ca. 530 °C) and proceeded rapidly at temperatures above 650 °C. A slight molar excess of lead and a proper heating rate were found to produce films with the best electrical properties. The films on platinized A12O3 substrates showed device-worthy dielectric and ferroelectric properties with typical values for Pn, EC, and ε, of 24 μC/cm2, 4.5 KV/mm and 650, respectively.

PLZT thin layers were deposited onto various substrates by sol-gel methods, and crystallized under different conditions and substrate treatments. Relationships are given for the chemical characteristics of the substrate's surface and the preferred orientations which develop on heat treatment. A preferred (111) orientation always developed for perovskite crystallized on Pt layers which contained Ti on the surface. This was attributed to the formation of Pt3Ti and the role of heteroepitaxial nucleation and growth sites. In addition, a preferred (100) orientation was also obtained on unannealed Pt/Ti/SiO2/Si substrates which were free of Ti on the surface. This was attributed to self-textured growth with flat faces striving for minimum surface energy conditions. The results are discussed in terms of the importance of interfacial chemistry on the control of texture for crystallization of PLZT thin layers on coated substrates.

We have optimized the ferroelectric properties and microstructural characteristics of sol-gel PZT thin films used in a CMOS-integrated, 256 bit ferroelectric non-volatile memory. The sol-gel process utilized in our work involved the reaction of Zr n-butoxide, Ti isopropoxide, and Pb (IV) acetate in a methanol/acetic acid solvent system. A 10-factor screening experiment identified solution concentration, acetic acid addition, and water volume as the solution chemistry factors having the most significant effects on the remanent polarization, coercive field, ferroelectric loop quality, and microstruntural quality. The optimal values for these factors were determined by runnig a 3-factor uniform shell design, modelling the responses, and testing the models at the predicted optimal conditions. The optimized solution chemistry generated 3-layer, 300-400 nm thick films on RuO2 coated silicon substrates with coercive fields of less than 25 kV/cm (a 40-50 % improvement over the original solution chemistry), a remanent polarization of 25-30 μC/cm, and a reduction in the pyrochlore phase content below observable levels.

The microstructural evolution of lead titanate prepared by a sol-gel method was examined using transmission electron microscopy (TEM) following treatments in air at progressively higher temperatures. TEM specimens were prepared by spin coating a film or dispersing particles onto specimen grids coated with SiO2 or SiO2 with a barrier layer. The effects of different barrier materials, thermal treatment conditions, and the addition of platinum particles were examined. Lead titanate formed crystalline perovskite at ∼550-600°C on all support materials examined. On SiO2 supports, the pyrochlore phase formed at lower temperatures and converted partially to perovskite at higher temperatures. Barrier layers of TiO2, A12O3 and polyimide prevented pyrochlore formation.

Lithium niobate films were deposited on amorphous carbon, silicate glass, (0001) sapphire, and (100) silicon by spin or dip coating double metal ethoxide sols. The crystallinity and microstructure of the deposited films were examined by XRD and TEM. Crystallization behavior and resulting microstructure were strongly influenced by the type of substrate. The formation of crystalline LiNbO3 on amorphous carbon was detected at room temperature. Randomly oriented polycrystalline films were obtained on glass at 400°C. Choice of one mole of water per mole of ethoxide generated heteroepitaxial growth of LiNbO3 thin films on (0001) sapphire. Oriented but polycrystalline films were obtained on silicon. The electrical behavior of film on silicon was evaluated in metal-ferroelectric-semiconductor configuration. A dielectric constant of 35 and a dissipation factor of 0.004 was measured at 100 KHz.