Author: Suk-Hun Choi
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Category : Cathode sputtering (Plating process)
Languages : en
Pages : 206

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Author: Clifford Fredrick Knollenberg
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Category :
Languages : en
Pages : 248

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Author: Annabel Susan Nickles
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Category :
Languages : en
Pages : 418

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Author: Aaron Welsh
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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.

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Category :
Languages : en
Pages :

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Traditionally, multifunctional complex oxide thin films, like the common ferroelectric materials lead zirconate titanate (PZT) and barium titanate (BaTiO3) have been limited to substrates with noble metal or conductive oxide bottom electrodes. This constraint originates from the vulnerability of base metals to oxidation when traditional ceramic processing parameters--high temperatures and oxygen rich atmospheres--are used to synthesize ferroelectric films. With current technology, ferroelectric thin films have demonstrated vast applicability as tunable capacitors, sensors, piezoelectric actuators, and non-volatile memories. By integrating ferroelectrics thin films with base metals, the barrier to mass production is lowered through reduced expense and simplified electrode patternability. Moreover, base metals have higher conductivities and offer the possibility for increased functionality by incorporation of ferromagnetic or shape memory alloys. Recent research efforts have adapted 1970s thick film multilayer capacitor technology to process thin films of the (Ba, Sr)TiO3 family directly on nickel and copper substrates. This methodology relies on processing these materials within a window of temperature and oxygen partial pressure (pO2) that affords thermodynamic equilibrium between the oxidized perovskite film and unoxidized base metal substrate. Although the family of (Ba, Sr)TiO3 materials offers excellent dielectric properties, the material PZT could provide a complementary set of functionality to satisfy applications that require an enhanced ferroelectric or piezoelectric response. Unfortunately, fundamental materials differences--particularly PbO volatility and a narrow thermodynamic stability window--make equilibrium processing impractical for PZT/base metal systems. In this thesis, integration of PZT directly on copper surfaces via a chemical solution deposition (CSD) route is investigated. Using this platform a new me.

Author: Travis Peters
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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.

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Languages : en
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The purpose of this research has been to demonstrate the possibility of integrating piezoelectric, dielectric and ferroelectric- lead and barium based oxide thin films and PVDF polymer on flexible metal substrates for microelectronic applications. Investigations on the key processing parameters and properties relationship for lead zirconate titanate (PZT, 52D 8) and barium zirconate titanate (BZT, 35D 5) based thin films on Cu foils were performed and studied. The impact of the oxygen partial pressure on the electrical properties of PZT and BZT thin films during processing has been explored, and demonstrated that high quality films and interfaces can be achieved through control of the pO2 within a window predicted by thermodynamic stability considerations. It should be noted that the high temperature processing of barium based ferroelectric oxides can be processed on Cu foils in a wider window of pO2 compared to that of processing lead based ferroelectric oxides. Also, the high volatile nature of lead makes the processing of lead based ferroelectric oxides difficult. Considering these issues, this work shows the processing technique undertaken to achieve high quality barium and lead based oxide thin films on Cu foils. The demonstration has broad implications, opening up the possibility of the use of low cost, high conductivity copper electrodes for a range of Pb-based and Ba-based perovskite materials, including PZT films in embedded printed circuit board applications for capacitors, varactors, and sensors; multilayer PZT piezoelectric stacks; and multilayer lead magnesium niobate-lead titanate-based dielectric and electrostrictive devices. In the case of ferroelectric PZT films on Cu foil, the capacitors do not fatigue upon repeated switching like those with Pt noble metal electrodes. Instead they appear to be fatigue-resistant like ferroelectric capacitors with oxide electrodes. This may have implications for ferroelectric nonvolatile memories. The eff.

Author: Maryam Abazari Torghabeh
Publisher:
ISBN:
Category : Ferroelectric devices
Languages : en
Pages : 193

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As a high performance piezoelectric material widely used in sensors, actuators and other electronic devices, lead zirconate titanate (PZT) ceramics have been the center of attention for many years. However, the toxicity of these materials and their exposure to the environment during processing steps, such as calcination, sintering, machining as well as problems in recycling and disposal have been major concerns regarding their usage all around the globe for the past couple of decades. Consequently, utilizing lead-based materials for many commercial applications have been recently restricted in Europe and Asia and measures are being taken in United States as well. Therefore, there is an urgent need for lead-free piezoelectrics whose properties are comparable to those of well-known PZT materials. Recently, the discovery of ultra-high piezoelectric activity in the ternary lead-free KNaNbO3-LiTaO3-LiSbO3 (KNN-LT-LS) and (Bi, Na)TiO3-(Bi, K)TiO3-BaTiO3 (BNT-BKT-BT) systems have given hope for alternatives to PZT. Furthermore, the demand for new generation of environment-friendly functional devices, utilizing piezoelectric materials, inspired a new surge in lead-free piezoelectric thin film research. In this study, an attempt has been made to explore the development of lead-free piezoelectric thin films by Pulsed Laser Deposition (PLD) on SrTiO3 substrate. While the growth and development process of KNN-LT-LS thin films was the primary goal of this thesis, a preliminary effort was also made to fabricate and characterize BNT-BKT-BT thin films. In a comprehensive and systematic process optimization study in conjunction with X-ray diffractometry, the phase evolution, stoichiometry, and growth orientation of the films are monitored as a function of deposition conditions including temperature and ambient oxygen partial pressure. Processing parameters such as substrate temperature and pressure are shown to be highly dominant in determining the phase and composition of the films. Oxygen partial pressure has shown to control the chemical composition of the films through solid-gaseous phase equilibrium and substrate temperature has mostly influenced the growth mode and microstructure. Findings of this study has shown that 300-500 nm single-phase epitaxial KNN-LT-LS and BNT-BKT-BT thin films could indeed be obtained at a temperature of 700-750 oC and 300-400 mTorr of oxygen partial pressure. Following a series of studies on effect of doping, it was revealed that addition of 1 mol% Mn to KNN-LT-LS composition resulted in a significant suppression of leakage current and enhancement of polarization saturation. A remanent polarization of 16 æC/cm2 and coercive field of 20 kV/cm were measured for such thin film, which are comparable to those of hard PZT counterparts. Also, a high remanent polarization and coercive field of 30 æC/cm2 and 95 kV/cm were achieved in 350 nm BNT-BKT-BT thin films. Longitudinal (d33) and transverse (e31, f) piezoelectric coefficients of KNN-LT-LS thin films were found to be 55 pm/V and -4.5 C/m2 respectively, prepared at the optimized conditions, whereas 350 nm BNT-BKT-BT thin films exhibited an e31, f of -2.25 C/m2. The results of this study present the great potential of KNN-LT-LS and BNT-BKT-BT thin films for piezoelectric MEMS devices and provide a baseline for future investigations on lead-free piezoelectric thin films.

Author:
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Category : Aeronautics
Languages : en
Pages : 538

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Author: James A. et al Voigt
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Category : Phase transformations
Languages : en
Pages : 8

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Film processing temperature and time was varied to characterize the pyrochlore-to-perovskite crystallization of solution-derived PZT 20/80 thin films. 3000 [Angstrom] thick films were prepared by spin deposition using 100 single crystal MgO as substrate. By controlled rapid thermal processing, films at different stages in the perovskite crystallization process were prepared with the tetragonal PZT 20/80 phase being 100/001 oriented relative to the MgO surface. An activation energy for the conversion process of 326 kJ/mole was determined by use of an Arrhenius expression using rate constants found by application of the method of Avrami. Activation energy for formation of the PZT 20/80 perovskite phase of the solution-derived films compared favorably with that calculated from data by Kwok and Desu for sputter-deposited 3500 [Angstrom] thick PZT 55/45 films. Similarity in activation energies indicates that the energetics of the conversion process are not strongly dependent on the method used for film deposition.