Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

Thin films of Pb(Sc1/2Ta1/2)O3 (PST) were fabricated using an optimized chemical solution deposition procedure involving the de-hydration of scandium acetate and the addition of up to 30% excess lead in solution. The choice of substrate was found to impact the thermal induced stress in the films as confirmed by wafer bending and in-plane grazing angle x-ray diffraction measurements. The presence of either a compressive or a tensile in-plane stress led to a reduction in the temperature of the dielectric maximum, whereas the value of the dielectric maximum remained relatively unchanged; its value reduced by an order of magnitude compared with ceramic samples. It is concluded that mechanical stress alone is not the sole factor in the reduction of PST thin film permittivity. Microstructural features resulting from processing induced defects or an incomplete transformation to the relaxor state may be responsible for this commonly observed phenomenon.

The results of structural and electrical characterizations of SrTiO3 thin films deposited onto LaAlO3 substrates by pulsed laser deposition technique are presented. The appearance of the ferroelectric phase in these films has been experimentally documented, the transition temperature being in the range of 90–120K. The hysteresis loops have been monitored in a wide temperature range by using thin film planar capacitors, the driving field being predominantly in the plane of the film. The switching properties of the films has been studied at low temperatures (∼25K) and well saturated loops have been observed with relatively low coercive field (<6kV/cm for 10μm gap). The presence of the imprint phenomenon has been also found at low temperatures.

The microstructure of the investigated SrTiO3 thin films has been studied by using a high resolution transmission electron microscope (TEM). It has been found that the annealed and as-deposited thin films, being of the same composition, have quite different microstructures. The difference observed in the polarization response of the films is related to that in their microstructure.

Thin film capacitor structures of Pb(Mg1/3Nb2/3)O3 (PMN) - PbTiO3 (PT) were fabricated using pulsed laser deposition (PLD) on MgO{100} substrates using (La1/2,Sr1/2)CoO3 (LSCO) as a lower electrode. Crystallographic and dielectric characterisation confirmed perovskite relaxor-like behaviour. Measurements of the electrostrictive coefficients by in-situ X-ray diffraction, piezo-response atomic force microscopy and three point bending experiments showed both Q11 and Q13 to be comparable to accepted values for single crystals. However, for a given field, the electric field-induced strain in the thin films was much less than that of single crystal. This was clearly intimately linked to poor thin film polarisability. Previous work had shown sol-gel PMN-PT films to have significantly greater permittivities than PLD films, and a TEM investigation was undertaken to see if functional differences could be related to differences in microstructure, and hence if the functional and electromechanical properties of PLD films could be improved by attempting to replicate sol-gel microstructures.

In-situ, reactively sputter deposited 300 nm thick Pb(Zrx,Ti1-x)O3 films on Pt/Si based substrates are investigated as a function of composition and texture. (111) PZT is grown on a (111) oriented Pt bottom electrode covered with a very thin TiO2 film. Highly {100} oriented PZT is grown on Pt (111) by means of a 10 nm thick PbTiO3 seed layer. Pronounced deviations from known bulk PZT behavior are observed for the (111) texture. Maximum of d33 and ε are shifted to 40/60 and 45/55 compositions, respectively. (100) textured films exhibit a higher d33. 1.3 μm (100) thick films attain the predicted d33 value of clamped bulk ceramics. Coercive fields and voltage offsets increase strongly with increasing Ti content. In parallel, the as-grown polarization increases. Polarization switching is not possible for x ≤ 0.1. Post-anneals in O2 and hot poling show that oxygen vacancies play an important role in this phenomenon. Ti-rich (100) oriented films exhibit very high and stable pyroelectric and piezoelectric coefficients whithout poling treatments.

It is suggested that the processes of charge injection and entrapment at the interfacial layer of Pb(Zr,Ti)O3 (PZT) film capacitors are responsible for both polarization fatigue and size effects on ferroelectric switching. The study of the charge injection by analyzing the dependence of coercive field on maximum polarization shows that there is a direct relationship between the charge injection properties and fatigue performance. Based on our results, we conclude that enhancement of charge relaxation at the interfaces of PZT capacitors results in two positive effects: improvement of polarization fatigue performance and suppression of size effects on ferroelectric switching, which are detrimental for low-voltage PZT film capacitors.

This idea has been implemented experimentally by introducing a thin RuO2 layer into the top-electrode interface of the Pt/PZT/Pt capacitor. PZT film capacitors of 100–170 nm thickness prepared in this way exhibited substantially improved fatigue in combination with weak size effects, which allows reduction of the operation voltage down to 0.8 V without degradation of the hysteresis properties. Our results show that the control of charge relaxation at the interface is a key issue for development of the low-voltage ferroelectric capacitors.

Lead magnesium niobate, Pb(Mg1/3Nb2/3)O3, thin films were formed from alkoxide-based solution precursors. To obtain stable and reproducible PMN precursor solution, a special effort has been undertaken to optimize the precursor synthesis. The organic decomposition behavior and crystalline phase development in a dried gel powder are reported. The influence of different seeding layers on the microstructures is shown. Dielectric and electromechanical measurements were carried out. Films show relaxor-like behavior, but with dielectric permittivity which is low (4500 at peak) compared to bulk ceramics and single crystals. Several parameters which might be responsible for this lower permittivity are suggested. Large electric dc bias fields (up to 120 kV/cm) can be applied to the films. This dc field reduces the permittivity, suppresses the frequency dispersion and flattens the permittivity peak. The anomaly associated with the field induced transition into a ferroelectric phase was not observed. Electrostrictive strains versus amplitude of electric field were measured and are discussed.

A systematic investigation of the piezoelectric and dielectric properties of Pb(Zr1-xTix,)O3 (PZT) thin films fabricated by chemical solution deposition was carried out for rhombohedral (x= 0.40), tetragonal (x=0.55) and morphotropic (x=0.47) composition. Each composition was grown with three different crystallographic orientations (textures): “random”, (111) and (100). Nonlinearity (field dependence) of d33 piezoelectric coefficient and dielectric permittivity of the films was studied in detail under subswitching conditions to reveal domain-wall related contributions to the properties. After analyzing for each texture and composition the domain-wall structure, contributions due to domain-wall displacements, and effects of film clamping by the substrate a consistent interpretation of the electro-mechanical properties and nonlinear behavior was proposed. The (100) oriented rhombohedral films show the largest piezoelectric coefficient (intrinsic effect) but limited nonlinearity (domain-wall structure effect) and should therefore be considered as potential candidates for piezoelectric devices.

Electrode stability, interdiffusion, phase purity and deviation from stoichiometry at the PZT-electrode interface are key issues in PZT thin film integration. This article highlights the use of transmission electron imaging combined with energy dispersive spectroscopy (EDS) for the investigation of these phenomena. The accuracy of the EDS analysis is discussed. It will be shown that using a standard PZT sample and controlled conditions, reliable analysis can be performed.

Diffusion mechanisms have been studied for Pt based electrode systems and RuO2-based electrode systems developed for direct integration onto silicon. The materials studied were composed of stacks of silicon-silicon oxide, an adhesion layer (Ti, Ta or TiOx), an electrode (Pt or RuG2) and PZT (45/55). The PZT was deposited by sol gel using the same parameters to allow for comparison of the different electrodes. Four different electrode / adhesion layer materials were compared (Pt/Ti, Pt/TiOx, Pt/Ta and RuO2 / TiO2). In the case of Pt, lead and oxygen diffusion through the electrode is observed. While the initial Ta layer transforms into a homogeneous pyrochlore phase, the Ti adhesion layer is heavily deformed. In the case of TiOx the lead is mainly incorporated at the interfaces with Pt and with SiO2. No lead diffusion to the adhesion layer is observed for the RuO2 electrode. In-situ sputtering and sol-gel deposition of PZT are also compared. The sol-gel films are close to the right stoichiometry for the perovskite while the sputtered films contained an excess of lead. No sign of second phase is found by X-ray diffraction (XRD), by EDS and by high resolution transmission electron microscopy (HRTEM) which suggests that the excess lead is accommodated in the perovskite lattice.

Piezoelectric properties of Pb(Zr,Ti)O3 (PZT) and PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT) films are investigated by interferometric technique combined with conventional dielectric and polarization measurements. It is shown that the piezoelectric d33 coefficient of both materials can be expressed based on their polarization and dielectric constant values using an equation for the electrostriction biased by the polarization. The obtained values of electrostriction coefficients are nearly field-independent and significantly smaller than in bulk materials of the same composition. Polarization offset is observed in PZT films subjected to bipolar fatigue, UV illumination and poling at high temperature, and is explained based on the pinning of ferroelectric domains in preferred orientations. The piezoelectric properties of rhombohedral PZT films are found to depend on their texture. The highest piezoelectric coefficient is observed in (100) oriented films, which have smaller polarization as compared to films having (111) preferred orientation. This difference is explained by the different values of electrostriction coefficients in materials with different textures.

Rhombohedral Pb(Zr0.70Ti0.30)O3 thin films of four different well-defined textures, namely, (100), (111), bimodal (110)/(111), and (100)/(111), were prepared by a sol-gel method. The films were characterized in terms of grain size, presence of second phases, surface roughness, columnarity of grains, and other microstructural features. The dielectric, ferroelectric, and fatigue properties were investigated, with emphasis on the hysteresis switching characteristics. Results are discussed from the reference point of the allowable spontaneous polarization directions available for the different textures. The values of coercive field, remanent and saturation polarization, and slope of the loop at the coercive field, at saturating fields can be qualitatively explained based on the texture, independent of microstructural differences. The occurrence of surface pyrochlore, however, is observed to affect the functionality of the saturation curves, particularly for the samples of bimodal texture. Shearing of the hysteresis curves of the bimodal films is also attributed to surface microstructural features. The occurrence of nonswitching 71° or 109° domains in the (111) and (110)/(111) textured films is hypothesized based on a comparison with the data from the (100) textured film. Corrected saturation polarization values agree with the spontaneous polarization values of rhombohedral PZT single crystals and published calculated values for rhombohedral PZT ceramics. The fatigue characteristics show increases in the switching component of polarization in the range 103−107 bipolar cycles, particularly for the (111) textured sample. Onset of fatigue is observed for all samples between 107 and 108 switching cycles.

Fiber optic modulators were fabricated by coating optical fibers with electrode and piezoelectric ZnO layers. The techniques of piezoelectric fiber optic modulator (PFOM) fabrication are presented, and the microstructure and crystallographic texture of the coatings are analyzed. In order to produce thick (approximately 5 μm) ZnO coatings, it was necessary to study the reactive dc magnetron sputtering process in O2/Ar gas mixtures under conditions close to the transition between an oxidized and nonoxidized Zn target surface. In situ quartz crystal microbalance measurements of the deposition rate revealed thee distinct regions in the deposition rate (R) vs oxygen partial pressure behavior, at constant total pressure, for sputtering under conditions that provided an oxidized Zn target surface. Additionally, a transition between oxygen and argon dominated sputtering as observed by varying the sputtering pressure while maintaining a constant The transition between oxygen and argon dominated sputtering influences R to varying extents within the three R vs regions for an oxidized target surface. Correlations among the cathode current and voltage, deposition rate, and gas flow rate are presented to give a better understanding of the reactive sputtering processes occurring at the oxidized Zn target surface. Sputtering conditions optimized for a high ZnO deposition rate were used to produce 〈001〉 radially oriented ZnO fiber coatings for PFOM devices that can produce optical phase shifts as large as 0.38 rad/V.

The piezoelectric and dielectric properties of ferroelectric thin films and ceramics were investigated in detail as a function of the frequency and amplitude of the driving field. A description, which is based on the theories of domain wall pinning by randomly distributed imperfections in magnetic materials, is used to interpret the electromechanical behaviour of several ferroelectric bulk ceramic and thin film compositions. With this approach, it is possible to make quantitative estimates of the domain wall contributions to the electromechanical properties of ferroelectric sensors and actuators.

A combination of different empirical methods which allow the prediction of the dielectric properties of non-ferroelectric complex perovskites has been proposed and its present limits verified. The long term purpose is to engineer new microwave materials with increased relative permittivity ε0 and low thermal coefficient of the resonant frequency τf.

The estimation of the dielectric properties has been accomplished by means of structural predictions based on the tolerance factor and a microscopic model. Furthermore, the optical permittivity based on the Gladstone-Dale relation and the total polarisability according to the molecular/ion additivity rule were also estimated. Ceramics of new compositions were then fabricated and analysed to verify the dielectric properties predicted by the empirical methods. Results show good agreement with the expected structural features and optical permittivities, and the method is sufficiently reliable to estimate the end values, or at least to estimate trends of the dielectric properties induced by partial substitution of cations on site A. The importance of the electronic polarisability on the end value of τε has been demonstrated.

Piezoelectric ZnO coatings were used in this work to develop a flexural actuator for an optical fiber. The basic device geometry was as follows: inner Cr/Au electrodes were evaporated onto a cleaned optical fiber; a thick ZnO coating was then grown by sputtering; finally a set of 2mm ring top electrodes were deposited through a shadow mask. Flexural actuators were made by photolithographically patterning either the inner or outer Cr/Au drive electrodes so that it was split down the length of the fiber. This enables each half of the fiber to be actuated independently. The result is that the optical fiber is forced to flex.

A processing scheme by which 30 μm gaps could be patterned into the electrodes was developed using standard clean room techniques. Such flexural actuators are attractive for scanning near field optical microscopes and in fiber alignment devices.

Active thin film coatings on optical fibers provide a variety of functions that are being used to develop active all-fiber optical devices. Two types of active coatings that are of interest for device development include resistive and piezoelectric coatings. Resistive coatings can be used to heat an optical fiber, while piezoelectric coatings can be used to strain the fiber. Localized changes in the fiber waveguiding properties can be achieved by electrically activating the fiber coating. These coated fibers show promise for applications such as optical phase shifters and modulators.

Recent developments in the fabrication of diffraction gratings within the core of an optical fiber have provided the means for making a variety of intra-core reflection and band pass filters. By combining these passive intra-core fiber devices with active coatings, wavelength tunable devices have been demonstrated. Wavelength tunable devices are expected to have a variety of applications in telecommunications and sensing networks. A review of recent developments in fiber coating and analysis techniques, device fabrication, and applications of active all-fiber devices are presented along with a discussion of which coating materials are of interest in active devices.

The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350–450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.

The piezoelectric properties of lead zirconate titanate (PZT) thin films deposited on thick silicon substrates and thin silicon membranes were investigated using optical interferometry. The effect of the geometrical constraints and clamping effects on the piezoelectric response is discussed. The study of the dielectric permittivity and the loss as a function of the amplitude of the alternating electric field reveals that extrinsic contributions to the dielectric permittivity become active at large fields. The DC electric field has the effect of freezing out the extrinsic contributions. The influence of the dielectric loss on the piezoelectric properties is discussed.

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.