A piezoelectric microspeaker device that could be used in a variety of acoustic applications was designed and fabricated using a thin film ZnO layer that was reactively DC sputtered onto a single crystalline n-type silicon substrate. When tested the microspeaker did not produce sound due to complications in the etching process, the thickness of the diaphragms, and clamping effects. Instead, a characterization approach was taken and the structural, optical, electrical, and piezoelectric properties of the ZnO were investigated. Scanning electron microscopy, x-ray diffraction, and atomic force microscopy were utilized to discover the ZnO’s structural properties. Using the XRD and SEM, the as-sputtered ZnO films were found to have highly c-axis oriented columnar crystals. Optical properties were determined from the reflectance spectrums obtained from a Filmetrics F20 reflectometer and were used to determine the film thickness, the optical constants, and the optical band gap of the ZnO thin films. Using a four-point probe, the as-sputtered ZnO films were found to be highly resistive and insulative, mainly due to voided growth boundaries between the crystals. To improve electrical conductivity and piezoelectric response, ZnO samples were annealed at varying temperatures in a nitrogen environment. The annealing process successfully increased the electrical conductivity and piezoelectric properties of the films. The local piezoelectric properties of the ZnO were discovered with an Asylum MFP-3D and a piezoresponse force microscopy (PFM) technique called DART-PFM. The ZnO films that were sputtered with 70 watts and an argon to oxygen gas ratio of 2:1 were found to have the highest d33 piezoelectric coefficients. The ZnO sample that was annealed at 600°C for 30 minutes had the highest overall d33 value of 4.0 pm/V, which means that the 600°C annealed ZnO films would have the best chance of making a functional microspeaker.

The bottom-up processing techniques used for making Microelectromechanical systems (MEMS) devices can produce material properties different from bulk processing. The material properties must be evaluated with the process parameters used and for changes in the process parameters. The mechanical properties are needed to design MEMS devices. A material of interest for MEMS devices is nickel titanium (NiTi) shape memory alloy (SMA) because of the high work output (~107 J/m3). This thesis will focus on the fabrication of thin film NiTi by DC magnetron sputtering deposition and testing mechanical properties of the fabricated films by nanoindentation. Thin film NiTi SMA was successfully created by DC magnetron sputtering deposition and high vacuum annealing in the Microfabrication Laboratory at California Polytechnic State University – San Luis Obispo. Characterization of the thin film by nanoindentation produced an elastic modulus of the thin film NiTi SMA with the developed processing parameters was 67.9 GPa with a hardness of 2.1 GPa. The measured thin film NiTi elastic modulus was greater than bulk NiTi of 40 GPa because of the residual stress from the deposition process. The shape memory effect was evaluated at the nanometer scale by measuring the nanoindents before and after thermally inducing a phase transformation. A maximum indentation depth recovery of 58% was measured upon the heat induced martensitic phase transformation. The low recovery was attributed to the high strain of 8% induced by the Berkovich tip. The effects of deposition power on the NiTi as-sputtered film stress, elastic modulus, hardness, and electrical conductivity were evaluated. At the highest sputtering deposition power of 450 Watts, an elastic modulus of 186 GPa with a hardness of 8.3 GPa was measured by nanoindentation. An increase in deposition power increased the residual film compressive stress, elastic modulus, and hardness while the electrical resistivity increased. The mechanisms for the measured properties are discussed in this thesis.

Des films minces de W et de W-Cu ont été déposés par co-pulvérisation GLAD à partir de deux cibles opposées de W et Cu. Chaque cible a été focalisée sur le centre du substrat avec un angle d'inclinaison α = 80°. Plusieurs séries d’échantillons ont été réalisées en faisant varier différents paramètres expérimentaux : la pression de travail, l’épaisseur des films ainsi que les intensités du courant des cibles. La nature des films préparés et leurs propriétés ont été étudiées pour comprendre les corrélations entre les caractéristiques structurales et les comportements électriques des films. Les paramètres expérimentaux jouent un rôle fondamental sur la forme des colonnes, leur angle de croissance, et sur la composition élémentaire des films colonnaires de W-Cu. Une variation systématique de ces paramètres a permis de relier certaines caractéristiques morphologiques et structurales aux propriétés de transport électronique dans ces films colonnaires. Le cuivre a été dissout chimiquement afin d’obtenir une structure plus poreuse, ceci dans l’objectif d’améliorer l’anisotropie électrique. Parallèlement à cette approche expérimentale, un modèle théorique a été développé pour comprendre les propriétés de conduction dans les films en tenant compte de la géométrie anisotrope des colonnes. Ce modèle a été appliqué aux films de W et W-Cu bruts et gravés. / W and W-Cu thin films were deposited by the GLAD co-sputtering technique from two opposite targets: W and Cu. Each target was focused on the center of the substrate with a tilt angle of α = 80 °. Several series were prepared changing some experimental parameters: the sputtering pressure, the film’s thickness as well as the target currents. The nature of as-deposited films and their morphological properties were studied in order to understand the correlations between some structural characteristics and electrical behaviors of these structured films. The experimental parameters play a key-role on the shape of the columns, their angle of inclination, and the elemental composition of these W-Cu films. The influence of these parameters on the films morphology was demonstrated and related to the electronic transport properties in these columnar films. The copper was chemically etched in order to obtain a more porous structure, with the aim of improving the electrical anisotropy. A theoretical model was also developed in order to understand the electrical conductivity mechanism in these columnar films taking into account the anisotropic structure of the columns. This model was applied to W, as-deposited W-Cu and etched W-Cu films.

Les TCOs (Transparent Conductive Oxide) trouvent des applications dans de nombreux domaines s'étendant del'électrochromie au photovoltaique en passant par l'opto-électronique. Parmi les matériaux historiques, les TCOs detype n font l'objet d'une littérature abondante tandis que les TCO de type p sont quant à eux étudiés de façon plusconfidentielle mais commencent à susciter un engouement, notamment dans l'objectif de jonctions p-ntransparentes.Sur la base de la théorie de la méthode de modulation chimique de bande de valence, le composé CuCrO2 destructure délafossite est considéré comme un candidat intéressant de TCO de type p. L'objectif de ces travaux estd'élaborer des films minces à base de CuCrO2 avec une transmittance optique acceptable et une conductivitéélectrique de type p élevée afin de envisager la possibilité de fabrication des jonctions p-n transparents pourdiverses applications.Dans ce travail, les films CuCrO2 ont été déposés par co pulvérisation cathodique magnétron en condition réactiveà partir de cibles métalliques. Une substitution partielle de Cr par Mg a ensuite été effectuée et l'influence del'épaisseur du film CuCrO2 :Mg sur ses propriétés optoélectroniques a été étudiée. Enfin, des revêtementsd'architecture sandwich CuCrO2 :Mg/Ag/CuCrO2 :Mg ont été élaborés en faisant varier le temps de dépôt de lacouche intermédiaire d'argent afin d'améliorer les performances optoélectroniques des films. / Transparent conductive oxides (TCOs) can be widely used in various domains from electrochromics to photovoltaicsowing to their unique optoelectronic properties. During the history of the development of TCOs, most attention hasbeen focused on n-type TCOs, while p-type TCOs have made slow progress. Recently, the studies on p-type TCOsraised many interest especially due to their potential application in the fabrication of transparent p-n junctions.Based on the theory of chemical method of valance band, CuCrO2 compound with delafossite structure isconsidered as an interesting candidate for p-type TCOs. The objective of this work is to synthesize CuCrO2-basedthin films with acceptable optical transmittance and high p-type electrical conductivity in order to explore thepossibility of fabrication of transparent p-n junctions for various applications.In this work, CuCrO2 films were deposited by reactive sputtering from metallic targets. Then, partial Cr substitutionby Mg was performed into CuCrO2 films and the influence of the films thickness on its optoelectronic properties wasstudied. Finally, sandwich architectural coatings of CuCrO2 :Mg/Ag/CuCrO2 :Mg were designed in order to improvethe films optoelectronic performances.

Les zirconates titanates de plomb (PZT) suscitent un intérêt considérable pour plusieurs applications industrielles, au regard de leurs excellentes propriétés piézoélectriques et électromécaniques. Le contexte actuel de l’innovation technologique est la miniaturisation et l’allègement des produits ; c’est pour cette raison que de nombreuses études sont menées depuis une vingtaine d’années sur les techniques et les procédés de synthèse de ces matériaux piézoélectriques sous forme de couches minces tout en garantissant une fiabilité accrue. Dans ce contexte, l’étude menée dans le cadre de cette thèse, a visé l’optimisation du procédé d’élaboration de films minces piézoélectriques de PZT par pulvérisation cathodique magnétron en mode DC et en mode Rf, en vue d’obtenir des capteurs d’efforts piézoélectriques. La synthèse in situ et la cristallisation ex-situ des films élaborés, par recuit classique (CFA) ou recuit rapide (RTA) confirme une structure pérovskite du PZT, complétées par une série de caractérisations morphologiques et structurales. Les domaines ferroélectriques à l’origine des propriétés piézoélectriques sont correctement visualisés par PFM et le calcul du coefficient piézoélectrique d33 des couches synthétisées sur des substrats métalliques, est réalisé par interféromètre laser. En parallèle, une approche expérimentale est menée sur l’évolution des performances piézoélectriques des films de PZT d’une part en fonction du mode d’élaboration et d’autre part en fonction de la texturation des couches, assurée par des traitements thermiques de cristallisation. / Recently, PZTs thin films have been spotlighted for various applications owing to their excellent piezoelectric and electromechanical properties. Most of the existing coating methods have been explored for the deposition of PZT. In this work, amorphous Pb(ZrxTi1-x)O3 (PZT) thin films were prepared by pulsed DC and RF magnetron sputtering in order to device a piezoelectric force sensors. The structure of a perovskite phase of PZT thin films was successfully characterized and morphological characterizations were investigated. Ferroelectrics properties of PZT thin films were determined using Piezoresponse Force Atomic technique (PFM) while the functional response of the films was characterized by measurements of piezoelectric d33 coefficients. Additionally, the coating processes and the crystallization behavior at different temperatures, of amorphous PZT thin films during either conventional furnace annealing (CFA) or rapid thermal annealing (RTA) were studied to understand the evolution of piezoelectric properties of films.

Abstract not available

For thesis abstract select View Thesis Title, Contents and Abstract

Innovation in photovoltaic technology may offer cost competitive options to other energy sources and become a viable solution for the energy and environmental challenges of the 21st century. One proposed innovative technology is based on all-silicon tandem cells, which are constructed using superlattices consisting of environmental friendly Si and its compounds. The well and barrier materials in superlattices are restricted to silicon and silicon oxide during the present study. Single crystalline Si/SiO2 quantum wells (QWs) have been fabricated by thermal oxidation of silicon-on-insulator (SOI) wafers. It is found that oxide properties in QWs are important for SOI wafers prepared by the SIMOX (Separation by Implantation of Oxygen) technique. However, QWs fabricated from SOI wafers prepared by the ELTRAN (Epitaxial Layer TRANsfer) approach show the effect of quantum confinement without evidence of strong oxide interfacial transitions. In these wafers, evidence for an apparently ordered silicon oxide was found with 1.92?atomic fringe spacing along the (110) direction of the Si structure and with the thickness about 17?along the (100) direction of the Si structure. Luminescence wavelength ranges are from 700nm to 918nm depending on the Si thickness. The luminescence measurements on other positions of the sample show peak and shoulder spectra, which are explained by monolayer fluctuations in QW thicknesses, previously observed in III-V QWs and II-VI QWs. Si/SiO2 superlattices are fabricated by RF magnetron sputtering. Si density is the key issue in crystallizing the superlattice. High-density Si layers crystallize either under high temperature furnace annealing or rapid thermal process annealing. However, low density Si would not crystallize even at high temperature. Crystallized nanocrystals in the Si layers are observed by high resolution transmission electron microscopy (HRTEM) when the Si layer is thicker than 3nm. When Si layers are thinner than 3nm, the Si layers are discontinuous and finally deteriorate into small nanocrystals. The suitability of such superlattices for surface passivation and antireflection coatings is reviewed. Initial attempts to fabricate heterojunctions between Si wafers and Si/SiO2 superlattices resulted in open circuit voltage of 252mV. However, it is expected that better results would be obtained if Si/SiO2 superlattices were fully crystallized.

Solid Oxide Fuel Cells (SOFCs) are devices that directly convert chemical energy into electrical energy, without proceeding through a Carnot combustion cycle. These devices are based on the usage of solid oxide electrolytes operating at relatively elevated temperatures. Two major hurdles must be overcome in order to decrease the operating temperatures of practical SOFCs. The first relates to reducing ohmic losses within solid electrolytes. The second relates to the need for developing high performance electrodes since electrolyte reaction rates at both anode and cathode are affected detrimentally as operating temperatures fall. This PhD project has focussed on addressing the first hurdle in two innovative ways: 1. the implementation of solid electrolytes with higher ionic conductivity than zirconia, 2. the development of very thin film electrolytes as thick as 5ƒÝm. Several thin films with novel electrode-electrolyte structures were fabricated and evaluated in order to demonstrate the viability of low temperature SOFC operations. Development of such thin films was innovative and challenging to achieve. The approach taken in this work involved fabricating a dense and thin gadolinia doped ceria (10GDC - Gd 10wt%, Ce 90wt%) oxide electrolyte. 10GDC is an electrolyte exhibiting higher conductivities than conventional materials during low temperature operations. A research contribution of this PhD was the demonstration of the deposition of 10GDC thin films using RF magnetron sputtering for the first time. 10GDC thin film electrolytes with thickness in a range between 0.1 to 5ƒÝm were fabricated on 10 yttrium stabilised zirconium (10YSZ) substrates by using a RF magnetron sputterer. The primary parameters controlling 10GDC thin film deposition using this method were explored in order to identify optimal conditions. The fabricated films were subsequently analysed for their morphology, composition and stoichiometry using a variety of methods, including Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectrometry (EDS), optical microscopy, X-ray Photoelectron Spectroscopy (XPS), and X-ray Diffraction (XRD). A preliminary test was conducted in order to examine the function of 10GDC thin film electrolytes together with the cathode and anode substrates at intermediate temperatures (700oC). A complete planar single cell was designed and assembled for this purpose. However, when fully assembled and tested, the cell failed to generate any voltage or current. Consequently, the remainder of the PhD work was focused on systematically exploring the factors contributing to the assembled fuel cell failure. As fabrication failure analysis is seldom reported in the scientific literature, this analysis represents a significant scientific contribution. This analysis proceeded in a series of steps that involved several different methods, including SEM, red dye analysis, surface morphology and cross section analysis of the cell. It was found that pinholes and cracks were present during the fuel cell operating test. Cathode delamination was also found to have occurred during the test operation. This was determined to be due to thermal expansion mismatch between the cathode substrate and the 10GDC electrolyte thin film. A series of suggestions for future research are presented in the conclusion of this work.

<p>High power impulse magnetron sputtering (HiPIMS) is a novel pulsed power technique. In HiPIMS, high power pulses are applied to the target for short duration with a low duty factor. It provides a high degree of ionization of the sputtered material (in some cases up to 90%) and a high plasma density (10¹⁹ m^-3) which results in densification of the grown films. Recently a large side-transport of the sputtered material has been discovered, meaning that the sputtered material is transported radially outwards, parallel to the cathode surface. In this research, we use this effect and study the side-ways deposition of thin films. We designed a new magnetron sputtering system, consisting of two opposing magnetrons with similar polarity. Ti films were grown on Si using the side-ways transport of the sputtered material. Scanning electron microscope was employed to investigate the microstructure of the grown films. Optical emission spectroscopy (OES) measurements were made for investigating the ionized fraction of the sputtered material while Langmuir probe measurements were made for evaluating the plasma parameters such as electron density. The conclusion is that the system works well for side-ways deposition and it can be useful for coating the interior of cylindrically shaped objects. It is a promising technique that should be used in industry.</p>