The composition dependent variation of ferroelectric domain structure in lead zirconate titanate (Pb(Zr0.52Ti0.48)O3) ceramics have been investigated within the morphotropic phase boundary (MPB). Tetragonal phase in sintered samples were identified via X-ray diffractometry (XRD). Representative microstructures of ferroelectric domains were examined using scanning electron microscopy (SEM). £\-boundaries, £_- boundaries, and £k-boundaries were analyzed from the contrast of extreme fringe patterns by transmission electron microscopy (TEM). Twin planes for 90o domains lie in {011) and for 180o domains lie in {100) and {220) were determined by selected area diffraction patterns (SADP). Traditional contrast analysis was adopted for determining displacement vectors (R). 90o domains with R = £`[011] and 180o domains with R = n[001]. Convergent beam electron diffraction (CBED) was performed to identify crystalline phases of different domain configurations. By examined the symmetry along the Z = [100], [110], and [111] zone axis, both £_-boundaries and £k-boundaries are tetragonal phase.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. "x̳", "1̳-x", and "3̳" are subscripts. Abstract. Includes bibliographical references (leaves 120-128). Also available via the Internet.

Ferroelectric random access memories (FRAM) are considered as future memories due to high speed, low cost, low power, excellent radiation hardness, nonvolatility, and good compatibility with the existing integrated circuit (IC) technology. The non-volatile FRAM devices are divided into two categories, based on reading technique: destructive readout (DRO) FRAM and non-destructive readout (NDRO) FRAM. Lead zirconate titanate (PZT) is recently considered as one of the most promising materials for DRO FRAM devices due to its excellent ferroelectric properties. There are remarkable advances in the applications of PZT thin films, but the direct integration into high density CMOS devices is restricted by high processing temperatures. Hence, it is desirable to lower processing temperature and develop novel high temperature electrode-barrier layers for achieving high density DRO FRAM devices. The NDRO FRAM devices have been developed mainly using metal-ferroelectric-semiconductor (MFS) and metal-ferroelectric-metal-insulator-semiconductor (MFMIS) structure. This devices use the remanent polarization of ferroelectric films to control the surface conductivity of a silicon substrate. The problem of the NDRO FRAM is that the actual electric field applied to ferroelectric films is very small compared to the external electric field, because of the large depolarization field in the MFS structure and the high capacitance ratio of ferroelectric capacitor and SiO2 capacitor in series in the MFMIS structure. Since the typical ferroelectric films show very high dielectric constant over 400, it is desired to develop ferroelectric films with low dielectric constant and low coercive electric field. This research is primarily focused on developing low temperature processing and high temperature electrode-barrier layers for DRO FRAM application, and exploiting novel ferroelectric materials for NDRO FRAM application. The low temperature processing was achieved by a novel sol-gel processing, which takes advantage of in-situ electrode template layer, rapid heating-treatment without pyrolysis step, and molecularly modified precursors. The PZT films with various composition were also investigated as a function of Ti content. In order to study the integration issues for these PZT films, a substrate was constructed as Pt/TiN/TiSi₂/poly-Si, which represents a scheme of capacitor in high density DRO FRAM devices. The ferroelectric films were incorporated into the substrate, and their ferroelectric properties were investigated as a function of annealing temperature. Excellent ferroelectric properties were observed for the thin films processed at a low temperature of 500 °C as contacting between top Pt and bottom polysilicon. The other approach we have taken to overcome the integration problems in high density DRO FRAM devices is to develop high temperature electrode barrier layers. In this research, Pt/IrO2/Ir hybrid layers were prepared on poly-Si substrate as high temperature electrode-barriers. The PZT films fabricated on the Pt/IrO₂/Ir/poly-Si substrates exhibited good ferroelectric properties and outstanding fatigue properties after high temperature processing. It was observed from Auger electron spectroscopy (AES) profiles that the hybrid oxide electrode minimized fatigue problem by reducing the oxygen vacancies entrapment at the electrode/ferroelectric interfaces. This results indicated that Pt/IrO₂/Ir high temperature electrode-barrier layers promise to solve major problems of PZT integration into high density DRO memory devices. For the NDRO FRAM devices, Sr₂Nb₂O₇ and La₂Ti₂O₇ thin films were prepared on Pt-coated silicon, Si(100), and Pt/IrO₂/SiO₂/Si substrates by metalorganic deposition (MOD) technique. The Sr₂Nb₂O₇ and La₂Ti₂O₇ thin films showed the dielectric constant values of 48 and 46, respectively. However, no ferroelectricity was observed at room temperature, which might be attributed to extremely small grains. Extensive studies on preparation and properties of Sr₂(Ta_1-xNb_x)O₇ (STN) both in bulk and thin film form were carried out as a function of composition. The STN films exhibited small dielectric constant of around 46, irrespective of the composition. / Ph. D.

No description available.

An investigation into the processes taking place at the surface interface of ferroelectric Pb(Zr1-x,Tix)O3 immersed in metal salt solution under ultraviolet illumination is presented. The semiconducting and switchable dipolar nature of this material allows the spatial separation and control of photo-induced reduction and oxidation across its surface interface. These properties can be of application in novel techniques such as the controlled growth of metallic nanoparticles across specific polar domains. 70nm thick Pb(Zr0.3,Ti0.7)O3 samples, PZT(30/70), are manufactured using the sol gel methodology, two crystallographic orientations being produced. The orientation being controlled by the substrate used; Si was used for [111] orientation and MgO for [100]. The initial work with wideband ultraviolet light shows that the reduction and growth of silver on the PZT surface is greatly influenced by the structure of the film. The crystallographic orientation of the film affects metal deposition such that on [111] films the metal deposits only on positive domains, where as the [100] films experience deposition on both positive and negative domains. This is shown to be due to the difference in width of the space charge region, Δw = 4.4nm, between the [111] and [100] samples so that the negative domain on [100] samples have 10 19 times higher chance of electron tunnelling compared to the [111]. It is also shown that grain boundaries have the greatest effect on the growth of metal, with a metal cluster growth rate 51 times faster than elsewhere on the surface. This increased rate of growth is due to the effect a grain boundary has on the surrounding area, the energy band bending at the boundary attracting charge carriers from the grains around it. The interface types ranked from greatest to lowest influence are grain boundaries, positive domains, domain boundaries and finally interphase boundaries.ii It is shown that the stern layer, strongly adsorbed charged ions of opposite sign to the surface charge, at the PZT/solution interface act as an insulating layer to metal reduction. The accumulation of photoexcited charge carriers at points along grain boundaries causes the surface potential gradient to alter and allows metal reduction and thus clusters to nucleate. The energy required to cause this variation is investigated by use of narrow band, 5nm bandwidth, ultraviolet. For energy from 4.4eV to 5 eV, it is found there is an increase in the average silver cluster cross sectional area by a ratio of ca 1.6 to 1 for both the [111] and [100] orientations of PZT. Finally it is shown that the type of metal salt used in the photochemical process affects the type of reaction that takes place at the sample surface. For a cation to reduce on positive domains its reduction potential needs to be below the bottom edge of the conduction band of PZT. Chloride salts, that sit above the conduction band, cause decomposition of the negative domains. Use is made of these effects to find the position of the bottom of the conduction band for PZT. It is found that across similar [111] PZT samples FeCl2 can both reduce on positive domains and decompose negative domains, this puts the bottom of the conduction band for PZT(30/70) between 4.06 and 4.36 eV from vacuum. It is also discovered that the type of anion affects the decomposition of the negative domains. Nitrate salts with cations above the conduction band cause no decomposition whereas chlorides do. The decomposition is shown to be the loss of Pb from the negative surface.

Undoped and doped Pb(Zr_xTi_1-x)O₃, i. e. PZT, ferroelectric thin films were prepared by chemical solution deposition and spin-coating method. The precursors for making the undoped PZT films were derived from lead acetate, zirconium n-propoxide, and titanium iso-propoxide. In addition, lanthanum acetylacetonate, neodymium acetate, and niobium ethoxide were introduced into the precursor solution to accomplish doping of the corresponding elements. Both doped and undoped PZT films were coated onto Pt/Ti/SiO₂/Si, RuO_x and single-crystal sapphire substrates of various thickness and annealed at a range of temperatures and times. The effects of dopants were studied in terms of the Curie temperature, crystal distortion, transformation temperature, microstructure, optical properties, and electrical properties. In addition to the dopant effect, the effects of substrates were also investigated with regard to crystallization and preferred orientation. The Curie temperature of the doped and undoped PZT films was determined by in-situ hot-stage transmission electron microscope (TEM) and compared with those of bulk ceramics. Lattice distortion and phase transformation were determined by x-ray diffraction (XRD). Microstructure of the films was characterized by using optical microscopy, scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM). Optical properties were characterized by a UV-VIS-NIR scanning spectrophotometer and electrical properties and fatigue testing were measured on a standardized RT66A using a Virtual-Ground circuit. It was observed that the addition of Nd and La dopants tends to enhance perovskite phase formation and improve electrical properties of PZT films. Higher refractive indices in La and Nd-doped PZT films imply that packing densities of PZT films are improved by adding dopants. Furthermore, the lower leakage currents and improved fatigue properties in PZT films were also observed by the addition of Nb dopants. / Master of Science

Rapid determination of drugs effective against bacterial strains is critically important to stopping further spread of an infection and reducing antibiotic resistance. Antimicrobial susceptibility testing (AST) is done to determine what type of antibiotic and what concentration will be effective in treating an infection. Current, growth-dependent, AST methods are reliant on the growth rate of the bacteria and can take several days to several weeks to get results. A piezoelectric plate sensor can be used to measure an instant change in the minute physiological stresses of the bacteria cells when they are exposed to an effective concentration of antibiotic. This work aims to investigate the feasibility of piezoelectric plate sensors used for instantaneous AST (iAST) results and develop a technological framework for scaling this technology to a clinical lab setting. Four Clinical and Laboratory Standards Institute (CLSI) quality control strains of bacteria were tested with a wide range of antibiotics from various drug classes using the piezoelectric sensor. Results were obtained within 30 minutes and compared to standard of care AST methods used in clinical labs, and CLSI prescribed ranges for each strain of bacteria. This thesis will also discuss a framework for developing more scalable sensors, and challenges associated with the different sensor designs.

Ferroelectric materials have received lots of attention thanks to their intriguing properties such as the piezoelectric and pyroelectric effects, as well as the large dielectric constants and the spontaneous polarization which can potentially be used for information storage. In particular, perovskite crystal has a very simple unit cell structure yet a very rich phase transition diagram, which makes it one of the most intensively studied ferroelectric materials. In this dissertation, we use effective Hamiltonian, a first-principles-based computational technique to study the finite-temperature properties of ferroelectric perovskites. We studied temperature-graded (BaxSr1-x )TiO3 (BST) bulk alloys as well as the dynamics of nanodomain walls (nanowalls) in Pb(ZrxTi1-x )O3 (PZT) ultra-thin films under the driving force of an AC field. Our computations suggest that, for the temperature-graded BST, the polarization responds to the temperature gradient (TG), with the "up" and "down" offset observed in polarization components along the direction of TG, in agreement with the findings from experiments. For the nanowalls in PZT, the dynamics can be described by the damped-harmonic-oscillator model, and we observed a size-driven transition from resonance to relaxational dynamics at a critical thickness of 7.2 nm. The transition originates from the change in the effective mass of a nanowall as a film thickness increases. Some of the findings may find potential applications in various devices, such as thermal sensors, energy converters, or novel memory units.

No description available.

abstract: There is a strong medical need and important therapeutic applications for improved wireless bioelectric interfaces to the nervous system. Multichannel devices are desired for neural control of robotic prosthetics that interface to remaining nerves in limb stumps of amputees and as alternatives to traditional wired arrays used in for some types of brain stimulation. This present work investigates a new approach to ultrasound-powering of implantable microelectronic devices within the tissue that may better support such applications. These devices are of ultra-miniature size that is enabled by a wireless technique. This study investigates two types of ultrasound-powered neural interfaces for multichannel sensory feedback in neurostimulation. The piezoceramics lead zirconate titanate (PZT) ceramic and polyvinylidene fluoride (PVDF) polymer were the primary materials used to build the devices. They convert ultrasound to electricity that when rectified by a diode produce a current output that is neuro stimulatory to peripheral nerve or the neurons in the brain. Multichannel devices employ a form of spatial multiplexing that directs focused ultrasound towards localized and segmented regions of PVDF or PZT that allows independent channels of nerve actuation. Different frequencies of ultrasound were evaluated for best results. Firstly, a 2.25 MHz frequency signal that is reasonably penetrating through body tissue to an implant several centimeters deep and also a 5 MHz frequency more suited to application for actuation of devices within a less than a centimeter of nerve. Results show multichannel device performance to have a complex inter-relationship with frequency, size and thickness, angular incidence, channel separations, and number of folds (layers connected in series and parallel). The output electrical port impedances of PVDF devices were examined in relationship to that of stimulating electrodes and tissue interfaces. Miniature multichannel devices were constructed using an unreported method of employing state of the art laser cutting systems. The results show that PVDF based devices have advantages over PZT, because of better acoustic coupling with tissue, known better biocompatibility, and better separation between multiple channels. However, the PZT devices proved to be better overall in terms of compactness and higher outputs for a given ultrasound power level. / Dissertation/Thesis / Masters Thesis Bioengineering 2015