114 research outputs found
ALD, ALE and 2D Materials: atomic scale processing for optoelectronics applications
Get PDFMany applications are seeing a trend towards miniaturization and utilization of nanoscale effects. In this presentation atomic-scale processing techniques offered by Oxford Instruments will be discussed and possible benefits for optoelectronics applications are highlighted
Atomic layer deposition : from reaction mechanisms to 3D-integrated micro-batteries
Get PDFOne major difficulty in maintaining the size reduction in electronic devices is the controlled deposition of high-quality thin films with the right film properties. Besides this trend of miniaturization in information processing technology, i.e., the "More-Moore" trend, there has been another trend for non-digital technology which is designated as "More-than-Moore". "More-than-Moore" is the trend towards diversification within electronic devices, in which multiple functionalities are integrated into a single unit of the device. All-solid-state 3D-integrated micro-batteries are a good example of the More-than-Moore approach as they integrate energy storage, which is a traditionally macroscopic non-semiconductor technology, into a chip-size unit using techniques compatible with semiconductor technology. In all-solid-state 3D-integrated microbatteries, the various battery materials have to be deposited as thin films. Furthermore, to achieve a high capacity per footprint area on the chip surface, the thin films have to be deposited in high-aspect-ratio structures etched in the Si substrate. Controlled deposition of high-quality films with the right film properties is therefore also a challenge in this research field. A thin-film deposition technique which typically exhibits a high material quality, a high uniformity, precise growth control, and an excellent conformality is atomic layer deposition (ALD). ALD has the potential to be an enabling technology for a wide range of applications. To be able to develop new ALD processes and materials, detailed understanding of the reaction mechanisms and the ALD process itself are essential. Besides the conventional thermallydriven ALD processes, the usage of energy-enhanced methods is considered, i.e., plasma-assisted and ozone-based processes. Plasma-assisted ALD can for instance facilitate deposition of conductive films. Furthermore, oxygen plasma and ozone gas are well-suited to grow oxide thin films even at low substrate temperatures. The reactive reactants used can, however, recombine at surfaces which could complicate deposition in 3D structures. In this thesis new energy-enhanced ALD processes are developed and further understanding is obtaned on their reaction mechanisms. Also the ability of energy-enhanced ALD processes to conformally coat 3D structures is investigated. Moreover, the application of ALD in energy technologies is further explored by focussing on solid-state 3D-integrated batteries. The use of ALD in Li-ion battery synthesis is relatively unexplored and therefore the potential of ALD for Li-ion batteries is reviewed in this work. Not only the More-than-Moore application of all-solid-state 3D-integrated microbatteries is considered, but also larger-scale Li-ion battery concepts that can benefit from ALD as well. Nanostructuring is targeted as a solution to achieve the improvements required for implementing batteries in a wide range of applications. The potential of ALD is discussed for three battery concepts that can be distinguished, i.e., particle-based electrodes, 3D-structured electrodes, and 3D solid-state micro-batteries. It is discussed that a large range of materials can be deposited by ALD and recent demonstrations of improvements in battery technology by ALD are used to exemplify its large potential. Conformal deposition of conductive materials is needed in a variety of More-than-Moore applications, e.g., for electrodes and current collectors. TiN and TaN deposited by plasma-assisted ALD were demonstrated to serve as Li barrier and anode current collector for micro-batteries and also as Cu diffusion barrier in advanced interconnect technology for 3D-integration. Furthermore, conformal deposition of TiN films by plasma-assisted ALD was demonstrated. For some electrodes, such as the cathode current collector, a highly-chemically-stable conductive material is needed. A plasma-assisted ALD process was developed for the deposition of Pt films with excellent material properties in terms of density and resistivity. By using an additional H2-gas reduction-step, the deposition of Pt at low temperatures with good material properties was achieved, which can be of interest for deposition of Pt on plastics. Furthermore, using longer plasma exposure times, PtO2 could be deposited which is difficult to obtain by ALD. Using mass spectrometry, the reaction mechanism of plasma-assisted ALD of TaNx was investigated. For this process the reaction products released from the surface during the plasma step were found to interact with the plasma. Furthermore, the material properties of TaNx are influenced to a large extent by this interaction. Interaction of ALD reaction products with the plasma is expected to be of general significance for plasma-assisted ALD processes. The reaction products of the thermal ALD process for Pt were quantified using insitu gas-phase infrared spectroscopy and a reaction mechanism was proposed. The film growth was found to be ruled by the surface coverage of dissociatively chemisorbed oxygen with which the precursor molecules interact. The capability of plasma-assisted ALD to deposit in 3D structures was investigated using Monte Carlo simulations. It was found that deposition in 3D structures can be classified in three regimes: i.e., reaction-limited, diffusionlimited, and recombination-limited. For low values of the recombination probability, or, conformal deposition in high-aspect-ratio structures can still be achieved, as also experimentally observed for several metal oxides. For high values of the recombination probability, r, as appears to be the case for many metals, achieving a reasonable conformality becomes challenging, especially for aspect ratios >10. Sufficient conformal deposition was demonstrated for both the TiN and the Pt plasma-assisted ALD processes. For the medium aspect ratios targeted for the Li-ion micro-batteries, plasma-assisted ALD should be able to conformally deposit all materials. Similarly the loss of O3 in 3D structures was investigated where the loss of O3 on several materials was tested. To determine O3 recombination probabilities over a wide range, a method was developed using high-aspect-ratio capillaries at the inlet to a mass spectrometer. O3 typically has higher loss on materials such as MnOx and Co3O4, which can also be considered as battery materials. Several material systems were investigated and a considerable amount of fundamental understanding in ALD was generated. In particular, understanding of energy-enhanced ALD processes and understanding of their ability to coat 3D structures conformally are essential for many new application fields in which these techniques will be required
Surface loss in ozone-based atomic layer deposition processes
No full textThe recombinative surface loss of O3 was investigated and its effects on the initial growth, film uniformity, and film conformality in atomic layer deposition (ALD) processes were illustrated. To determine O3 recombination probabilities over a wide range, a method was developed using high aspect ratio capillaries at the inlet to a mass spectrometer. Using this method, we measured O3 recombination probabilities ranging from 10-3 depending on the composition and temperature of the capillary surface. We utilized these measurements to understand dramatic variations in O3 loss observed during the initial growth of O3-based ALD Pt on Al2O3 and vice versa. Next, we studied the uniformity of O3-based ALD using ZnO ALD as a model system. Changes in the spatial uniformity of the ALD ZnO films and the O3 concentration in the reactor as a function of the O3 exposure were explained by a transition from reaction- to recombination-limited growth. This explanation was validated using a simple plug-flow model. Finally, we estimated the maximum aspect ratios that can be coated for a given O3 recombination probability in O3-based ALD processes using reasonable cycle times
3D negative electrode stacks for integrated all-solid-state lithium-ion microbatteries
Get PDFThe deposition feasibility and electrochemical evaluation of highly structured negative electrode stacks for 3D-integrated batteries is demonstrated. The stacks comprise a TiN thin film, serving as both current collector and Li-barrier layer, covered by a polycrystalline Si (poly-Si) thin film as electrode material. In comparison with planar films, these poly-Si films present a storage capacity increase of about 5x for the highest pore aspect ratio electrodes. The step coverage of poly-Si can be considerably improved by growing TiN and poly-Si into wide trenches. This results in much smoother poly-Si films and significantly improved step coverage. Further optimization of the trench dimensions should result in poly-Si films with a Li-storage capacity increase of more than one order of magnitude with respect to planar films
MRI-Compatible Endovascular Instruments: Improved Maneuverability during Navigation
No full textEndovascular diagnostics and interventions are performed using long, thin and flexible instruments that are inserted in the blood vessel and manipulated toward a target in the vasculature. This technique has proven to be successful with the millions of patients diagnosed and treated worldwide every year. Though, this technique presents several drawbacks: the tools are limited in shape and flexibility and are difficult to control and, as endovascular interventions are performed under 2D projection X-ray image guidance, any difficulty in navigating the instruments increases exposure of patient and staff to ionizing radiation. In this thesis, we focus on the navigation challenges during procedures performed in the peripheral vasculature. It is imperative to reach the target in the anatomy quickly and safely, while protecting both the patient and staff from ionizing radiation. For this reason, navigation under Magnetic Resonance Imaging (MRI) is considered. In this project, novel endovascular instruments with improved maneuverability at the tip were designed to support navigation during endovascular intervention in the peripheral vascular tree under real-time MRI guidance. The instruments were assembled, and their capabilities evaluated in pre-clinical settings. We believe that the designed instruments are a good first step toward novel easy-to-use endovascular instruments, which will enable interventionalists to perform a broader range of interventions more quickly, safely and with greater accuracy under MRI-guidance (or X-ray). Fully compatible with conventional instruments, they will increase the efficiency of cath-labs without requiring the purchase of additional equipment.BioMechanical EngineeringMechanical, Maritime and Materials Engineerin
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Get PDFThe author presents a survey of the men involved in the Afrikaans translations of the Bible, stretching from the earliest efforts to 7979. In the first section he presents the translators: J.D. du Toil, H.C.M . Fourie, B.B. Keet.J.D . Kestell, E.E. van Rooyen
Electron scattering and doping mechanisms in solid-phase-crystallized ln2O3:H prepared by atomic layer deposition
Get PDFHydrogen-doped indium oxide (In2O3:H) has recently emerged as an enabling transparent conductive oxide for solar cells, in particular for silicon heterojunction solar cells because its high electron mobility (>100 cm2/(V s)) allows for a simultaneously high electrical conductivity and optical transparency. Here, we report on high-quality In2O3:H prepared by a low-temperature atomic layer deposition (ALD) process and present insights into the doping mechanism and the electron scattering processes that limit the carrier mobility in such films. The process consists of ALD of amorphous In2O3:H at 100 °C and subsequent solid-phase crystallization at 150–200 °C to obtain large-grained polycrystalline In2O3:H films. The changes in optoelectronic properties upon crystallization have been monitored both electrically by Hall measurements and optically by analysis of the Drude response. After crystallization, an excellent carrier mobility of 128 ± 4 cm2/(V s) can be obtained at a carrier density of 1.8 × 1020 cm–3, irrespective of the annealing temperature. Temperature-dependent Hall measurements have revealed that electron scattering is dominated by unavoidable phonon and ionized impurity scattering from singly charged H-donors. Extrinsic defect scattering related to material quality such as grain boundary and neutral impurity scattering was found to be negligible in crystallized films indicating that the carrier mobility is maximized. Furthermore, by comparison of the absolute H-concentration and the carrier density in crystallized films, it is deduced tha
Bristol F2B biplane G-AUEB on an airfield outside a hangar, 1923 [picture].
No full textPart of the: Horrie Miller aviation photograph collection, 1906 to 1984.; Bristol fighter aircraft with 340 h.p. Hispano Suiza engine, with the author sold to Qantas in 1923.; Inscription: "Bristol fighter plane sold to Qantas by H.C.M."--In pencil on verso.; Title devised by cataloguer.; Also available in an electronic version via the internet at: http://nla.gov.au/nla.pic-vn4774350
Multi-Selective Catheter with Two Deflectable Segments
No full textEndovascular interventions are a type of minimally invasive surgery used to diagnose and treat vascular conditions. Long, thin and flexible medical devices like catheters are percutaneously inserted into the blood vessels. Time-action analysis has shown that the navigation of the medical devices from the access to the destination site is inefficient, thereby increasing the inherent risks and costs of endovascular interventions. A new steerable catheter with two deflectable segments may benefit the procedure by reducing the number of device exchanges while speeding up the process. The new catheter is designed for navigation to the arteries in the legs. Currently, multiple selective catheters are used consuctively to first cross the aortic bifurcation and then navigate down the leg. The new steerable catheter is designed to three commonly used selective catheters. A handle is also designed to actuate the two deflectable segments. A prototype is built and experimentally evaluated. The catheter has the required axial and rotational stiffness, but lacks the required bending elasticity. The deflectable segments can successfully be actuated into the desired geometries. However, the bending elasticity must be improved before conclusive evidence can be found that the catheter can replace the selected conventional catheters. Experiments within a vascular model show promising initial results.BMDBioMechanical EngineeringMechanical, Maritime and Materials Engineerin
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