Leveraging past research activities in orientation control of lead zirconate titanate (PZT) thin films [1,2], this work attempts to optimize those research results using the fabrication equipment at the U.S. Army Research Laboratory so as to achieve a high degree of {001}- texture and improved piezoelectric properties. Initial experiments examined the influence of Ti/Pt and TiO2/Pt thins films used as the base-electrode for chemical solution deposition PZT thin film growth. In all cases, the starting silicon substrates used a 500 nm thermally grown silicon dioxide. The Pt films were sputter deposited onto highly textured titanium dioxide films grown by a thermal oxidation process of a sputtered Ti film [3]. The second objective targeted was to achieve highly {001}-textured PZT using a seed layer of PbTiO3 (PT). A comparative study was performed between Ti/Pt and TiO2/Pt bottom electrodes. The results indicate that the use of a highly oriented TiO2 led to highly {111}-textured Pt, which in turn improved both the PT and PZT orientations. Both PZT (52/48) and (45/55) thin films with and without PT seed layers were deposited and examined via x-ray diffraction methods (XRD) as a function of annealing temperature. As expected, the PT seed layer provides significant improvement in the PZT {001}-texture while suppressing the {111}-texture of the PZT. Improvements in the Lotgering factor (f) were observed upon comparison of the original Ti/Pt/PZT process (f=0.66) with samples using the PT seed layer as a template, Ti/Pt/PT/PZT (f=0.87), and with films deposited onto the improved Pt electrodes, TiO2/Pt/PT/PZT (f=0.96).

The fundamental physical property used for data storage in a ferroelectric non-volatile memory (FRAM) is the remanent polarization of a ferroelectric capacitor. In order to sense the data state of the capacitor, the charge pulse generated by either a switching or non-switching ferroelectric polarization is detected. Since the polarization of the ferroelectric is a vector property, the switchable polarization response of a ferroelectric capacitor is necessarily dependent on the texture of the ferroelectric material used to make the capacitor. A series of Ca, Sr, and La doped PbZr0.4Ti0.6O3 (PZT) capacitor test samples were produced with texture ranging from nearly complete {111} texture to random orientation. The volume fraction of the textured material was quantified by X-ray diffraction. An experimental correlation between texture and the switchable polarization was established using pulse switching measurements. A mathematical model was developed to explain the dependence of the switchable polarization on the crystallographic texture. It was found that the dependence of the saturated switchable polarization on texture required that there was no 90° domain reorientation. The impact of these findings will be related to the performance of FRAM.

The crystallographic texture of PZT thin films has been proven to play a critical role in the electrical performance of PZT used in non-volatile FRAM. During both development and production of FRAM, PZT texture must be monitored to assure ferroelectric performance. A common method for monitoring texture is to use normalized intensities collected from X-ray diffraction 2-theta scans. Although this method can reveal thin film texture, it does not give a quantitative measure of the volume of textured and/or random material. In addition, this method can only be used to compare films with constant thickness since differences in X-ray absorption are not taken into account. A new method for calculating the volume fractions of textured and randomly oriented material in PZT thin films has been developed. This new method for calculating textured volume fractions still utilizes integrated intensities from 2-theta scans, but the calculations include corrections for film thickness and geometrical factors. The calculated volume fractions obtained from this new method of data analysis can be used directly for physical evaluation of PZT thin film ferroelectric performance.

Pt/Ti/SiO2/Si structures have been studied to investigate the structural, chemical, and microstructural changes that occur during annealing. Grain growth of the as-deposited Pt columns was observed after annealing at 650 °C, and extensive changes in the Pt microstructure were apparent following a 750 °C anneal for 20 min. In addition, two types of defects were identified on the surfaces of annealed substrates. Defect formation was retarded when the surface was covered with a ferroelectric film. Concurrent with the annealing-induced Pt microstructure changes, Ti from the adhesion layer between the Pt and the SiO2 migrated into the Pt layer and oxidized. It was shown with spectroscopic ellipsometry and Auger electron spectroscopy that for long annealing times, the titanium oxide layer can reach the Pt surface. Consequently, at the processing temperatures utilized in preparing many ferroelectric thin films, the substrate is not completely inert or immobile. The changes associated with Ti migration could be especially problematic in techniques that require the substrate to be heated prior to film deposition.

Microtubes of ZnO have been produced using sputter coating and a fugitive phase technique. ZnO was sputtered onto polyester fibers by dc magnetron sputtering, and the polyester fiber fugitive phase was subsequently burned out by annealing in air or oxygen. Tubes with an inside diameter of 23 μm and a length of 3 cm were obtained. The 3 to 6 μm thick walls of the tubes exhibited a [002] radial texture.

Thin films in the Pb-La-Ti-O (PLT) system were prepared under two different oxygen partial pressure (Po2) conditions by multi-ion-beam reactive sputtering (MIBERS). The oxidation of the depositing species was determined from the deposition rate dependence on Po2 and the Po2 dependence of the positive secondary ion emission from the sputtering targets. Films deposited at high Po2 (Po2 greater than the critical partial pressure for oxidation of the Pb target surface) were fully oxidized, and they formed the pyrochlore phase during annealing. The low Po2 conditions (Po2 less than or equal to the critical partial pressure for oxidation of the Pb target surface) caused sputtering of incompletely oxidized Pb species, and the resulting oxygen deficient films produced phase-pure perovskite. The formation of the pyrochlore phase at high Po2 and the perovskite phase at low Po2 is independent of Pb content within the film; the phase formation is dependent on the oxidation state of the Pb, which is sensitive to both the Po2 and the sputtering rate of the Pb. A perovskite/pyrochlore phase formation model (PPFM) that incorporates annealing time, temperature, and heating rate, and thin film oxygen deficiency was developed to explain the formation of the perovskite and pyrochlore phase during postdeposition annealing of PLT thin films.

Axially symmetric coatings of ZnO and PZT have been deposited onto fiber substrates by reactive dc magnetron sputtering. Multi-layer Cr/Au/ZnO/Cr/Au coating structures on optical fibers have been used to make integrated phase modulator devices. An analysis of the structural properties and piezoelectric response of the phase modulator devices will be presented. Microtubes of ZnO and Pt/ZnO/Pt multi-layers have been prepared by coating polyester fibers that act as a fugitive phase. After burning away the polyester fiber, up to 3 cm long micro-tubes with a 23 μm inside diameter and 3 to 9 μm wall thickness were obtained.

This paper, the second of three parts, presents a detailed analysis of the crystallographic texture observed in lead lanthanum titanate (PLT) thin films deposited by multi-ion-beam reactive sputtering. Since films were deposited at a substrate temperature of 100 °C, they exhibit an amorphous structure that can be described by the structure zone model. The as-deposited microstructure is transformed via crystallization of the perovskite phase and PbO evaporation during postdeposition annealing. Transmission electron microscopy was used to determine that phase pure PLT films develop textured clusters (as large as 700 nm in diameter) consisting of 〈100〉 aligned 10 nm nanocrystals. As excess PbO is added to the PLT film, the textured cluster size decreases until only isolated PLT nanocrystals exist. Below a critical quantity of excess PbO in the as-deposited film (approximately 15 mole%), the textured cluster structure produces a 〈100〉 texture through the film thickness, which generates x-ray diffraction patterns typical of textured microstructures. At high PbO contents, the excess PbO causes the formation of clusters that are smaller than the film thickness, resulting in a polycrystalline-type x-ray diffraction pattern. A qualitative model describing microstructure development is presented.

This paper, the third and final of a three part series, presents the electrical properties of postdeposition annealed, lead lanthanum titanate (PLT) thin films deposited by multi-ion-beam reactive sputtering (MIBERS). Also, a model is presented that explains the relations among composition, crystallographic structure, microstructure, and electrical properties of the PLT thin films. Thin films of PLT consisting of the perovskite phase exhibit 〈100〉 textured microstructures. Addition of a critical quantity of excess PbO results in the loss of this 〈100〉 texture, and continuity of the perovskite phase is disrupted while both excess PbO and porosity phases become continuous due to a percolation effect. Films with textured microstructures consisting of a continuous perovskite phase exhibit relatively high dc resistivities, high dielectric permittivities, and high remanent polarizations. At the transition between textured and nontextured microstructures, a discontinuous drop in the electrical properties occurs due to the ensuing continuity of the excess PbO and porosity. These composition-induced changes in the electrical properties were quantitatively modeled by applying a simple mixing rule model to the microstructure model developed in Part II of this series.

Material properties are greatly dependent upon the structure of the material. This paper, the first of three parts, discusses how composition influences the crystallographic structure and microstructure of lead lanthanum titanate (PLT) thin films grown by the multi-ion-beam reactive sputtering (MIBERS) technique. A transmission electron microscopy (TEM) study detailing the relationship between crystallographic texturing and microstructure development will be presented in a second paper. The dependence of the ferroelectric properties on observed crystallographic structure and microstructure is presented in the third paper of this series. As-deposited PLT microstructures coincide with the structure zone model (SZM) which has been developed to describe the microstructure of thin films deposited by physical vapor deposition. The as-deposited PLT structures are altered during post-deposition annealing as a result of crystallization and PbO evaporation. Amorphous films with more than 10 mole % excess PbO become polycrystalline with porous microstructures after annealing. When there is less PbO in the as-deposited film, 〈100〉 texture and dense structures are observed. Porosity results from PbO evaporation, and 〈100〉 texture is inhibited by excess PbO.