No description available.

The use of radio frequency (rf) plasma techniques to produce fine structures of precise geometry is widespread in the microelectronics industry. An important factor influencing the functionality of fabricated devices is the wall angle of these structures. In certain applications vertical walls are required - for example to minimise mask degradation and maximise gate densities; in others a sloping sidewall is preferred - to minimise stress in metal coatings when making electrical contact through 'via' holes, for instance. This fine control cannot be achieved on micron and sub-micron scale devices using conventional 'wet' chemical processing techniques and has led to the adoption of so-called 'dry' processing techniques using plasmas. Both vertical and sloping wall profiles can be produced depending upon the plasma conditions. It is apparent, therefore, that a thorough understanding of the processes affecting the etch profile is important. Reactive ion etching (RIE) has been employed to produce micron, and sub-micron size structures in polyimide using an oxygen plasma. Present models of etch directionality all make the initial assumption that the directional component of the etching process can be attributed solely to O2+ ion bombardment of the exposed horizontal surface of the wafer driven by the electric 'sheath' field developed above the electrode. Whether species such as O+ and even multiply charged reactive species such as O++ and O+++ can legitimately be neglected in formulating such a model has yet to be established. That such multiply ionized species exist, however, is highly probable given that plasmas are well known to emit strongly in the ultraviolet. The etching system developed to investigate these problems was equipped with diagnostic techniques including optical emission spectroscopy, mass spectrometry, and a grid energy analyser. The optical emission spectrometer was novel in being capable of measuring emission from the far-ultraviolet emission spectrum of the plasma and was therefore able to detect the high energy ultraviolet light and the singly and multiply ionised species from which this radiation is emitted. Using this technique the role of multiply-ionised species in controlling etch anisotropy was investigated. Results are also presented, obtained from a retarding grid, particle energy analyser built into the surface of the earth electrode, which indicate increased charged particle flux and energy at low pressure providing further information with regard to the process dynamics. The influence of gas pressure and rf excitation frequency on the resultant etch profile have been investigated. Results are presented showing the presence of doubly-ionised atomic oxygen O++ in the plasma. It is shown in this work that O++ also has a role in etch anisotropy at low pressure. This and other more highly charged species need to be considered, therefore, in formulating models of etch anisotropy, etch rate, and etch chemistry and reaction mechanisms. The role of ultraviolet irradiation which is itself of sufficient energy to induce surface reactions must also be considered.

The introduction of deep reactive ion etching (DRIE) technology has greatly expanded the accessible design space for microscopic systems. Structures that are hundreds of micrometers tall with aspect ratios of 40:1, heretofore impossible, can now be achieved. However, this technology is primarily a forming technology, sculpting structures from a substrate. This work seeks to complement deep reactive ion etching by developing an electrical isolation technology to enable electro-mechanical function in these new deep reactive ion etched structures. The objective of the research is twofold. The first is to develop and characterize an electrical isolation technology for DRIE, single crystal silicon (SCS) micro-electro-mechanical systems (MEMS) using temperature gradient zone melting (TGZM) of aluminum junctions for diodic isolation. The second is to demonstrate the utility of this electrical isolation technology in the design, simulation, fabrication, and testing of a MEMS device, i.e. a micro-gyroscope, in such a way that the benefits from junction isolated, deep reactive ion etched, single crystal silicon devices are preserved.

No description available.

L’objectif de ce travail est la réalisation de nouveaux microactionneurs à base depolymère conducteur électronique pouvant être envisagés pour une application denanodrone à ailes battantes.Deux réseaux interpénétrés de polymères (RIPs) POE/PTHF (poly(oxyded’éthylène)/polytétrahydrofurane) et POE/NBR (poly(oxyde d’éthylène/Nitrile Butadiene Rubber) ont été synthétisés et caractérisés. Par le contrôle de la synthèse de ces RIPs,une co-continuité de phase des deux réseaux partenaires a pu être obtenue. Ce travail a ainsi permis l’obtention de matériaux combinant les propriétés propres de chaque réseau, une bonne conductivité ionique (POE) et de bonnes propriétés mécaniques (PTHF et NBR). Les propriétés mécaniques du matériau ont permis de réaliser des matériaux polymères support d’électrolyte manipulables avec des épaisseurs inférieures à 10 μm.Des RIPs conducteurs ont pu être élaborés à partir de ces matériaux en incorporant le polymère conducteur électronique (poly(3,4-éthylènedioxythiophène) - PEDOT), par une dispersion non homogène à partir de la surface vers l’intérieur du film. Après incorporation d’un liquide ionique (le 1-éthyl-3-méthylimidazolium bis-(trifluorométhylsulfonyl)imide ou EMImTFSI), ces matériaux électroactifs ont été caractérisés et ont montré qu’ils pouvaient actionner à des fréquences élevées (100Hz) par rapport aux autres dispositifs de ce type.La mise en forme micrométrique de ces matériaux a ensuite été réalisée par un procédé propre aux microsystèmes. Les techniques de photolithographie et de gravure ionique réactive ont été adaptées et étudiées pour l’élaboration de ces microactionneurs. Un mécanisme de dégradation chimique du matériau a été proposé afin d’expliquer l’étape de gravure. Enfin, la caractérisation des microactionneurs a ensuite aussi été réalisée.La force développée par ces microactionneurs est de l’ordre du μN et le pourcentage de déformation est de 1,8 %. / The aim of this work is the realization of new microactuators based on electronicconducting polymer (ECP) for a flapping wing nano-aerial vehicle.Two Interpenetrating Polymer Networks (IPNs) PEO/PTHF(polyethyleneoxide/polytetrahydrofurane) and PEO/NBR (polyethyleneoxide/NitrileButadiene Rubber) were synthesized and characterized. By controlling the synthesis of these IPNs, a phase co-continuity of the two networks could be obtained. This work has enabled the production of materials combining the specific properties of each network, good ionic conductivity (PEO) and good mechanical properties (PTHF and NBR). The mechanical properties of the material allowed the synthesis of solid polymer electrolyte materials that can be elaborated and manipulated with thicknesses below 10 microns.The conducting IPNs are synthesized from previous IPNs in which the conductingpolymer (poly(3,4-ethylenedioxythiophene)), PEDOT, is non homogeneously dispersed i.e. the content decreases from the outside towards the center of the film.After incorporation of an ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide or EMImTFSI), these electroactive materials werecharacterized and showed their capacity to operate at frequency high frequency (100 Hz) compared to others systems in literature.The micrometer shaping of these materials was then carried out by processes specific to microsystems. Photolithography techniques and Reactive Ion Etching (RIE) have been adapted and designed for the development of microactuators. A chemical degradation mechanism of the material has been proposed to explain the etching step. Finally, the characterization of microactuators have been carried out. The force developed by these microactuators is in the range of N and the bending strain has reached 1.8%.

The conventional large radii bends used in large cross section silicon-on-insulator waveguides were replaced with novel wet etched corner mirrors, potentially allowing much smaller devices, therefore lower costs. If such corners had been based on reactive ion etch techniques they would have had the disadvantage of rougher surfaces and poor alignment in the vertical direction. Wet etching overcomes these two problems by providing smooth corner facets aligned precisely to the vertical {100} silicon crystallographic planes. The waveguides obtained had angled walls, and so numerical analysis was undertaken to establish the single mode condition for such trapezoidal structures. To show the relationship between fabrication tolerances and optical losses a three dimensional simulation tool was developed, based on expansion of the incident mode into plane waves. Various new fabrication techniques were are proposed, namely: the use of titanium as a mask for deep silicon wet anisotropic etching, a technique for aligning masks to the crystal plane on silicon-oninsulator wafers, a corner compensation method for sloping sidewalls, and the suppression of residues and pyramids with the use of acetic acid for KOH etching. Also, it was shown that isopropyl alcohol may be used in KOH etching of vertical walls if the concentration and temperature are sufficiently high. As the proposed corner mirrors were convex structures the problem of undercutting by high order crystal planes arose. This was uniquely overcome by the addition of some structures to effectively convert the convex structures into concave ones. The corner mirrors had higher optical losses than were originally hoped for, similar to those of mirrors in thin film waveguides made by RIE. The losses were possibly due to poor angular precision of the lithography process. The design also failed to provide adequate mechanisms to allow the etch to be stopped at the optimal time. The waveguides had the advantage over thin film technology of large, fibre-compatible cross sections. However the mirror losses must be reduced for the technology to compete with existing large cross section waveguides using large bends. Potential applications of the technology are also discussed. The geometry of the crystal planes places fundamental limits on the proximity of any two waveguides. This causes some increase in the length of MMI couplers used for channel splitting. The problem could possibly be overcome by integrating one of the mirrors into the end of the MMI coupler to form an L shaped junction.

The research presented in this dissertation explores the possibility of using colloidal indium tin oxide (ITO) nanoparticle solutions to direct write transparent conducting coatings (TCCs), as an alternative route for TCC fabrication. ITO nanoparticles with narrow size distribution of 5-7 nm were synthesized using a non-aqueous synthesis technique, and fabricated into films using spin coating on substrates made from glass and fused quartz. The as-coated films were very transparent (>95% transmittance), but highly resistive, with sheet resistances around 10¹³ Ω/sq . Pre-annealing plasma treatments were investigated in order to improve the electrical properties while avoiding high temperature treatments. Composite RIE treatment recipes consisting of alternating RIE treatments in O₂ plasma and in Ar plasma were able to reduce the sheet resistance of as spin coated ITO films by 4-5 orders of magnitude, from about 10¹³ Ω/sq in as-coated films to about 3 x 10⁸ Ω/sq without any annealing. Plasma treatment, in combination with annealing treatments were able to decrease the sheet resistance by 8-9 orders of magnitude down to almost 10 kΩ/sq , equivalent to bulk resistivity of ~0.67 Ω.cm. Investigation into effectiveness of various RIE parameters in removing residual organics and in reducing the sheet resistance of colloidal ITO films suggested that while reactive ion annealing (RIE) pressure is an important parameter; parameters like plasma power, number of alternating O₂-Ar RIE cycles were also effective in reducing the residual organic content. Impedance spectroscopy analysis of the colloidal ITO films indicated the dominance of the various interfaces, such as grain boundaries, insulating secondary phases, charge traps, and others in determining the observed electrical properties.

abstract: Semiconductor nanowires are important candidates for highly scaled three dimensional electronic devices. It is very advantageous to combine their scaling capability with the high yield of planar CMOS technology by integrating nanowire devices into planar circuits. The purpose of this research is to identify the challenges associated with the fabrication of vertically oriented Si and Ge nanowire diodes and modeling their electrical behavior so that they can be utilized to create unique three dimensional architectures that can boost the scaling of electronic devices into the next generation. In this study, vertical Ge and Si nanowire Schottky diodes have been fabricated using bottom-up vapor-liquid-solid (VLS) and top-down reactive ion etching (RIE) approaches respectively. VLS growth yields nanowires with atomically smooth sidewalls at sub-50 nm diameters but suffers from the problem that the doping increases radially outwards from the core of the devices. RIE is much faster than VLS and does not suffer from the problem of non-uniform doping. However, it yields nanowires with rougher sidewalls and gets exceedingly inefficient in yielding vertical nanowires for diameters below 50 nm. The I-V characteristics of both Ge and Si nanowire diodes cannot be adequately fit by the thermionic emission model. Annealing in forming gas which passivates dangling bonds on the nanowire surface is shown to have a considerable impact on the current through the Si nanowire diodes indicating that fixed charges and traps on the surface of the devices play a major role in determining their electrical behavior. Also, due to the vertical geometry of the nanowire diodes, electric field lines originating from the metal and terminating on their sidewalls can directly modulate their conductivity. Both these effects have to be included in the model aimed at predicting the current through vertical nanowire diodes. This study shows that the current through vertical nanowire diodes cannot be predicted accurately using the thermionic emission model which is suitable for planar devices and identifies the factors needed to build a comprehensive analytical model for predicting the current through vertically oriented nanowire diodes. / Dissertation/Thesis / Ph.D. Electrical Engineering 2014

This thesis is devoted to the development of nano-focusing refractive optics for high energy X-rays using planar microelectronic technology. The availability of such optics is the key for the exploitation of high brilliance third and fourth generation X-ray sources. Advancements in the quality of optics available are commensurate with advancements in the fabrication technology. The fabrication process directly influences the quality and performance, so must be understood and controlled. In the first part of this thesis, the development of high aspect ratio Si kinoform lenses is examined. It is shown that control of the re-entrance angle is critical for successful fabrication; in fact, a large re-entrance angle can destroy the lens during the fabrication process. Through an etch study, it was found that as aspect ratio increases, control of the re-entrance angle becomes harder. To control the re-entrance angle for very high aspect ratios, a novel approach based on sacrificial structures was proposed and initial results presented. The second part is dedicated to an experimental study of refractive lenses made from diamond. Due to its low atomic number, relatively high density and very high thermal conductivity, diamond is one of the most desirable lens materials for refractive X-ray optics. However, due to its extreme hardness, it is very difficult to structure into a form suitable for X-ray lenses. To overcome this difficulty a Si moulding technique was used and focusing down to a 400 nm wide spot was achieved. Several obstacles were encountered and successfully overcome. The hardest obstacle was to obtain selective void-free filling in the Si moulds. Several methods were investigated. A method based on a sacrificial oxide layer and an Electrostatic Self-Assembly process was found to be the most useful. The approach discovered in this thesis is not limited to X-ray lenses, but can be applied to a wide variety of high aspect ratio MEMS requiring void-free diamond filling and smooth sidewalls.

This thesis focuses on the use of a design of experiment approach to examine the significance of process factors and interactions on the fabrication of micro- textured surfaces. The micro-textured surfaces examined contain pillar and hole features ranging from 80 – 2 micrometers in diameter. The processes examined are the deep reactive ion etching of silicon wafers for the production of silicon mould inserts and the micro-injection moulding of polypropylene, high density polyethylene and 316LS stainless steel replicate samples of the silicon mould insert. During the deep reactive ion etching of the silicon wafers the design of experiment approach was used to determine the significant of platen power, C4F8 gas flow and switching times to the presence of pillar undercut of 10 x 10, 5 x 5 and 2 x 2 micrometer pillars. Undercuts occur when the pillar base has a smaller cross-section than the apex of the pillar. Switching times was found to be the only statistically significant parameter for both 10 x 10 and 5 x 5 micrometer pillars. The design of experiment approach is used in the micro-injection moulding of polypropylene, high density polyethylene and 316LS stainless steel replicates to examine the significance of mould temperature, cooling time, holding pressure and injection speed on the part and buffer mass of the produce samples, the height and width of pillar on the replicate surfaces and the variation of the replicated pillars height and width from the original silicon mould insert. Examination of the high density polyethylene replicates found that mould temperature was the most significant factor regarding pillar dimensions (and variation from the silicon mould insert) across the range of pillar sizes. Upon examination of the polypropylene replicates it was found that the factor of most significance on pillar dimensions varied across the different pillar sizes. Holding pressure was identified as the most significant factor with regards to the 53 x 29 and 19 x 80 micrometer pillars. Injection speed was found to be most significant for the 25 x 25 and 19 x 29 micrometer pillars. Cooling time was found to be most significant with regards to the 30 x 10, 25 x 10, 20 x 10 and 15 x 10 micrometer pillars. While ii mould temperature was found to be most significant for the 20 x 20, 15 x 15 and 10 x 30 micrometer pillars. The interaction between mould temperature and injection speed was also found to be the most significant factor with regards to the 43 x 29 and 25 x 30 micrometer pillars. Examination of the 316LS replicates found that mould temperature was the most significant factor regarding pillar dimensions for 80 x 80 and 19 x 80 micrometer pillars. While holding pressure was found to be most significant to the 29 x 29 micrometer pillars and injection speed was identified as most significant to the 53 x 80 micrometer pillars. The samples produced during the design of experiment investigations were then used to examine the effect of surface texturing on droplet behaviour. Droplet contact angles were examined on polypropylene, high density polyethylene and silicon samples structured with 10 – 2 micrometer pillar. Initial droplet contact angles were found to be higher on the polypropylene samples than the high density polyethylene or silicon samples. With the lowest initial contact angles being found for the silicon inserts. Droplet ‘channelling’ and evaporation were examined on silicon, polypropylene, high density polyethylene and 316LS samples structured with micro-channel surface pillars and holes ranging from 80 – 2 micrometer in diameter. Contact pinning of the droplet to the surface via the three- phase contact-line was noted during observations of droplet ‘channelling’. This pinning effect was observed at all sample tilt angles (30 - 90 o ). With regards to droplet evaporation, the droplets were noted to evaporate evenly (with no or limited contact pinning) on all unstructured surfaces and the surfaces structured with hole features. On the surfaces structured with pillar features, the droplets appeared too evaporated along the surface gradient from the smallest pillars to the largest.