Formation of Microstructure and Ferroelectric Domains in Lead Zirconate Titanate (PZT) Thin Films PDF Download
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Author: Matthew James Lefevre
Publisher:
ISBN:
Category :
Languages : en
Pages : 392
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Author: Matthew James Lefevre
Publisher:
ISBN:
Category :
Languages : en
Pages : 392
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 11
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Factors that control phase evolution, microstructural development and ferroelectric domain assemblage are evaluated for chemically prepared lead zirconate titanate (PZT) thin films. Zirconium to titanium stoichiometry is shown to strongly influence microstructure. As Ti content increases, there is an apparent enhancement of the perovskite phase nucleation rate, grain size becomes smaller, and the amount of pyrochlore phase, if present, decreases. While the pyrochlore matrix microstructure for near morphotropic phase boundary composition thin films consists of two interpenetrating nanophases (pyrochlore and an amorphous phase), the pyrochlore microstructure for PZT 20/80 films deposited on MgO substrates is single phase and consists of 10nm grains. Zirconium to titanium stoichiometry also has a substantial influence on process integration. Near morphotropic phase boundary films exhibit extensive reaction with underlying TiO2 diffusion barriers; conversely, there is no chemical reaction for identically processed PZT 20/80 thin films. The authors have attempted to directly correlate the optical quality of PZT thin films to the following microstructural features: (1) presence of a second phase, (2) domain orientation, and (3) nanometer surface morphology.
Author: Travis Peters
Publisher:
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Category :
Languages : en
Pages : 0
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This thesis probes how extrinsic contributions affect the dielectric, piezoelectric, and ferroelectric properties of morphotropic phase boundary lead zirconate titanate (PZT) films. Secondly, the influence of grain and grain boundary microstructure on domain behavior under an electric field was investigated. Domain wall mobility via the Rayleigh Law was locally probed to investigate avalanche characteristics and the width of influence of individual grain boundaries on the nonlinear piezoelectric response. This was coupled with macroscopic characterization showing the dependence of the domain structure on the thermal stress induced from substrate clamping effects. The results guided an attempt to fabricate a self-powered, wireless PZT thin film insole sensor for applications involving balance detection to assist the elderly population. A novel lead-free flexoelectric array was also prototyped for eventual use in a self-powered force sensing device, that can harvest energy from a heel-strike via the direct flexoelectric effect. In undoped lead zirconate-titanate (PZT) films 1-2 [mu]m thick, domain walls move in clusters with a correlation length of ~ 0.5--2 [mu]m. Mapping of the piezoelectric nonlinearity via band excitation piezoresponse force microscopy (BE-PFM) showed that doping with niobium (Nb) increases the average concentration or mobility of domain walls without changing the cluster area of correlated domain wall motion. In contrast, manganese (Mn) doping reduces the contribution of mobile domain walls to the dielectric and piezoelectric responses without changing the cluster area for correlated motion. In both Nb and Mn doped films, cluster area increases as film thicknesses rise from 250 to 1250 nm while cluster density drops; this can be seen in spatial maps generated from the analysis of irreversible to reversible ratios of the Rayleigh coefficients. Next, the effect of microstructural features such as grain boundaries and triple points on the pinning of domain wall motion in perovskite PZT films was investigated. Spatial variability in the collective domain wall dynamics was assessed using non-linearity mapping via BE-PFM. Collocating the non-linearity maps with triple point locations (visualized by electron back scatter diffraction) allowed for exploration of the effect that local microstructure (e.g., grain boundary) has on domain wall motion. It was found that the extrinsic behavior varied with both the misorientation angle and the proximity to the grain boundary. The width of influence of individual grain boundaries on the motion of domain walls was a function of the character of the grain boundary; random grain boundaries exhibit deeper minima in [alpha]d/d33,initial and larger widths of influence (up to 905 nm) compared to coincident site lattice (CSL) boundaries (up to 572 nm). Additionally, triple points containing larger numbers of random boundaries exhibited non-Rayleigh behavior to greater distances, suggesting that the triple point provides either a deep potential minimum or a region where domain wall motion is unfavorable. Piezoelectric thin films were dip coated onto flexible metal substrates to investigate the dependence of macroscopic dielectric and ferroelectric properties on the coefficient of thermal expansion mismatch and substrate thickness. The bending stiffness was controlled by the thickness of the substrate. Grazing incidence x-ray diffraction displayed distinct peak splitting for Nb-doped PZT on flexible Pt, Ni, Ag, and stiff Ni substrates, where the out-of-plane d-spacing and integrated peak area for c-domains was highest with the largest film compressive stress. As expected, PZT films on stiff Si were under tensile stress and contained more in-plane domains. The dielectric permittivity was highest in PZT on stiff Si and lowest for PZT on thick Ni, while remanent polarization displayed the opposite trend, commensurate with the residual stress state as well as the resistance to bending in thick substrates as a strain-relief mechanism. The irreversible Rayleigh coefficient decreased dramatically upon poling for PZT on flexible substrates compared to PZT on stiff substrates; the [alpha][epsilon]/[epsilon]initial ratio was 56% higher in PZT on a flexible Ni substrate relative to a stiff Ni substrate at 100 Hz prior to electrical poling. This investigation distinguishes the impact of substrate flexibility from thermal expansion on ferroelectric domain mobility and provides dip coating conditions for high quality piezoelectric films on any substrate. The resulting PZT films on metal foils were employed in the fabrication of a low power insole embedded force sensor array attempting to monitor a patient's balance and weight distribution while standing, walking, or running. Flexible piezoelectric films as force sensors eliminate the need for standby energy, providing high sensitivity and flexibility in sensor array design. Lead zirconate-titanate piezoelectric films 1 [mu]m thick were dip coated onto a 25 [mu]m thick stainless steel flexible metal foil. The film displayed a 47% Lotgering factor for the 100 crystallographic direction and exhibited a high-density granular perovskite structure with little pyrochlore near the middle and bottom of the dip cast film. The films showed high remanent polarization values of +28.2 [mu]C/cm2 and -24.3 [mu]C/cm2 and typical coercive fields of 59.4 kV/cm and -56.7 kV/cm. This piezoelectric sensing array with 24 photolithographically-defined electrodes enabled the simulation of a single toe response, the ball of the foot rolling during a step response, and a heel-strike emulation response. Voltage measurements extracted from cyclic applied forces from 0 to 30 N showed a linear response with a sensitivity of -9.76 mV/N between 0 to 12 N and a nonlinear response between 12 to 30 N. The roll test provided ~100 mV responses when expected during a perpendicular and diagonal roll on four individual sensors, each with fast response times and some mixture of bending and compressive stresses. The heel-strike emulation above a single electrode exhibited a response of ~300 mV with 60 N compressive force, ~100 mV from a nearby electrode, and minimal response from electrodes further from the applied force. A discrete circuit was designed and tested on a printed circuit board for multi-channel sensing, digitization, amplification, and wireless transmission of the activation signal. Finally, a lead-free flexoelectric device was fabricated in an attempt to provide a power-source for the electronics associated with the PZT film insole sensor. Flexoelectric polarization output scales with dielectric permittivity and strain gradient; thus, it is proposed that a barrier layer capacitor with doped silicon as the conducting medium will enhance the flexoelectric coefficient via space charge polarizability. A cantilever beam was fabricated as proof of concept, which displayed a flexoelectric coefficient of 4.9 ± 0.4 [mu]C/m. Furthermore, a centrosymmetric 100 silicon wafer was processed with an anisotropic wet etchant into truncated pyramid arrays varying in size from 100s of microns to tens of microns. A dielectric passivation layer acted as the insulating region within the asymmetric barrier layer capacitor, and interfacial space charge polarizability generated effective permittivities that exceed those possible with paraelectrics. The novel centrosymmetric flexoelectric fabrication procedure exhibited here generated the capability to decrease the structure size by orders of magnitude as well, thereby increasing the flexoelectric polarization response in proportion. A scanning probe-based methodology was developed to directly measure the local converse flexoelectric response of a single pyramid with a height of 70 [mu]m. The feasibility of ferroelectric material-free flexoelectricity was analyzed via both direct and converse flexoelectric measurements at the macro-scale and nano-scale.
Author: Jun Ouyang
Publisher: Elsevier
ISBN: 0128138572
Category : Technology & Engineering
Languages : en
Pages : 388
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Nanostructures in Ferroelectric Films for Energy Applications: Grains, Domains, Interfaces and Engineering Methods presents methods of engineering nanostructures in ferroelectric films to improve their performance in energy harvesting and conversion and storage. Ferroelectric films, which have broad applications, including the emerging energy technology, usually consist of nanoscale inhomogeneities. For polycrystalline films, the size and distribution of nano-grains determines the macroscopic properties, especially the field-induced polarization response. For epitaxial films, the energy of internal long-range electric and elastic fields during their growth are minimized by formation of self-assembled nano-domains. This book is an accessible reference for both instructors in academia and R&D professionals. - Provides the necessary components for the systematic study of the structure-property relationship in ferroelectric thin film materials using case studies in energy applications - Written by leading experts in the research areas of piezoelectrics, electrocalorics, ferroelectric dielectrics (especially in capacitive energy storage), ferroelectric domains, and ferroelectric-Si technology - Includes a well balanced mix of theoretical design and simulation, materials processing and integration, and dedicated characterization methods of the involved nanostructures
Author: M. Lawrence Arokia Dass
Publisher:
ISBN:
Category :
Languages : en
Pages : 340
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Author: Yimin Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 171
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Author: Mohammad Abdullah-Al-Mamun
Publisher:
ISBN:
Category :
Languages : en
Pages : 92
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Lead Zirconate Titanate PbZr1−xTxO3, commonly known as PZT, is a piezoelectric material, widely used in memory applications, sensors and actuators. A challenge for PZT thin films is the accurate determination of its structural properties, which are ultimately responsible for improved functionality. Previous studies have concentrated on PZT with x=0.6, for which there is some ambiguity due to the structural phase transition near room temperature. For composition below x=0.5 or so, no such complications occur. For my thesis, I studied PZT films with x=0.2 and Nb-doped PZT PbNby(Zr1−xTix)1−yO3 films with x=0.2 and y=0.04, called PNZT. Doping with Nb increases the carrier concentration and leads to the formation of charged domain walls, i.e. the properties of PZT films can be engineered by controlled doping. I used X-ray diffraction to determine the structural properties (lattice parameters, strain and dislocation density), atomic force microscopy to determine the surface roughness, ferroelectric testing to measure the electric field response of the polarizations for both films and piezo-response force microscopy for the PNZT film. PNZT thin films were found to show improved ferroelectric hysteresis behavior of the polarization compared to PZT. Tentatively, I attributed these differences to the role of Nb defects in PZT and its effects on the ferroelectric domains and domain walls. The piezoelectric response of the PNZT film was found to reflect its polarization behavior.
Author: Ching-Chang Chung
Publisher:
ISBN:
Category :
Languages : en
Pages : 446
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Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 652
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Author: Aaron Welsh
Publisher:
ISBN:
Category :
Languages : en
Pages :
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This thesis describes the utilization and optimization of the soft lithographic technique, microcontact printing, to additively pattern ferroelectric lead zirconate titanate (PZT) thin films for application in microelectromechanical systems (MEMS). For this purpose, the solution wetting, pattern transfer, printing dynamics, stamp/substrate configurations, and processing damages were optimized for incorporation of PZT thin films into a bio-mass sensor application. This patterning technique transfers liquid ceramic precursors onto a device stack in a desired configuration either through pattern definition in the stamp, substrate or both surfaces. It was determined that for ideal transfer of the pattern from the stamp to the substrate surface, wetting between the solution and the printing surface is paramount. To this end, polyurethane-based stamp surfaces were shown to be wet uniformly by polar solutions. Patterned stamp surfaces revealed that printing from raised features onto flat substrates could be accomplished with a minimum feature size of 5 [mu]m. Films patterned by printing as a function of thickness (0.1 to 1 [mu]m) showed analogous functional properties to continuous films that were not patterned. Specifically, 1 [mu]m thick PZT printed features had a relative permittivity of 1050 ± 10 and a loss tangent of 2.0 ± 0.4 % at 10 kHz; remanent polarization was 30 ± 0.4 [mu]C/cm2 and the coercive field was 45 ± 1 kV/cm; and a piezoelectric coefficient e31,f of -7 ± 0.4 C/m2. No pinching in the minor hysteresis loops or splitting of the first order reversal curve (FORC) distributions was observed. Non-uniform distribution of the solution over the printed area becomes more problematic as feature size is decreased. This resulted in solutions printed from 5 [mu]m wide raised features exhibiting a parabolic shape with sidewall angles of ~ 1 degree. As an alternative, printing solutions from recesses in the stamp surface resulted in more uniform solution thickness transfer across the entire feature widths, with increased sidewall angles of ~ 35 degrees. This was at the cost of degrading line edge definition from ~ 200 nm to ~ 500 nm. The loss of line edge definition was mitigated through the combined use of printing from stamp recesses onto raised substrate features. This allowed for printing of PZT features down to 1 [mu]m wide. Solutions could also be transferred onto both fixed and free standing cantilever structures patterned into a substrate surface. Optimization of the stamp removal from the substrate was crucial in increasing sidewall angles of printed PZT films. It was determined that solutions gel once deposited onto the stamp before printing. As a result, printed films could not redistribute easily after transfer had occurred. Through a combination of varying peeling directions and peeling rates, it was possible to deposit thin film PZT on a pre patterned feature ~ 1 [mu]m wide with sidewall angles > 80 degrees. These printing techniques were utilized in printing a 250 nm thick 30/70 PZT onto pre-patterned cantilever structures for use in a bio-functionalized, mass sensing resonating structure in collaboration with a bio-nanoelectromechincal sensing research group from the University of Toulouse, France. The features ranged in lateral size from 30 down to 1 [mu]m. The printed devices exhibited a relative permittivity of 500 ± 10 and a loss tangent of 0.9 ± 0.1 %. The hysteresis loops were well formed, without pinching of the loops, and exhibited remanent polarizations of 24 ± 0.5 [mu]C/cm2, and coercive fields of 110 ± 1 kV/cm. Dry etched features of the same size and thickness displayed a relative permittivity of 445 ± 8 and a loss tangent of 0.9 ± 0.1 %. The hysteresis loops exhibited pinched loops with remanent polarizations of 24 ± 0.7 [mu]C/cm2, and coercive fields of 112 ± 2 kV/cm. Upon cycling, the dry etched films developed a 20 kV/cm imprint with reduced remanent polarizations to 20.5 ± 0.5 [mu]C/cm2. An understanding of the influence of patterning on the material properties is essential to predicting and controlling the behavior of polycrystalline films for MEMS applications. The influence of pinning centers on domain wall motion, particularly near feature sidewalls, in patterned features was explored in reactive ion etched (RIE) and microcontact printed films with the same thickness (i.e. 1 [mu]m) and lateral feature size (i.e. 5 and 10 [mu]m). This was accomplished by measuring global dielectric nonlinearity through Rayleigh and minor hysteresis measurements. For comparative purposes, local quantitative mapping of the piezoelectric nonlinearity was undertaken through the use of band excitation piezo-response force microscopy (BE-PFM). The printed and etched films exhibited differing microstructures which precluded quantitative direct comparisons. However, qualitative trends were identified. The dielectric aging rate of all Rayleigh parameters for the etched films increased with increases in perimeter length. In particular, the aging of the dielectric irreversible/reversible Rayleigh ratio ([alpha]/[epsilon]init) increased from -7 ± 0.6 %/decade to -11.6 ± 0.7 %/decade (600 to 5 [mu]m in width, respectively). In contrast, the printed films showed very slight aging rates. BE-PFM measurements revealed that defects from the etching process introduced large concentrations of pinning centers near the patterned sidewalls, resulting in reductions in the piezoelectric irreversible/reversible Rayleigh ratio ([alpha]/d33,init) as far as 750 nm from the sidewall. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) showed that variations in stoichiometry of crystal quality were not the predominant factor controlling the decreased domain wall mobility near sidewalls. In contrast to the etched films, printed films showed an increase in [alpha]/d33,init as the sidewall was approached due to mechanical declamping from the substrate.
