Die Discrete Mode Matching Methode für konforme mehrlagige Strukturen mit anisotropen Substraten

The discrete mode matching method has been proven to be an efficient numerical method to analyze multilayered structures with thin dielectric layers for microwave and optical technologies. The main contribution of this thesis is to extend the method to structures which consist of anisotropic or isotropic, homogeneous or inhomogeneous dielectric layers, or metamaterials. The mathematical formulation is well suited for the analysis of conformal structures (e.g., arbitrarily shaped waveguides and antennas).Discrete Mode Matching ist eine bewährte Methode zur Analyse von mehrlagigen Strukturen mit dünnen dielektrischen Lagen, wie sie in der Mikrowellentechnik und Optik eingesetzt werden. Der Hauptbeitrag dieser Dissertation ist die Erweiterung dieser Methode auf Strukturen, die aus anisotropen oder isotropen, homogenen oder inhomogenen dielektrischen Lagen sowie Metamaterialien bestehen. Die mathematische Formulierung ist für die Analyse von Strukturen mit beliebiger Form (z. B. Antennen) geeignet

Beam lead technology

Beam lead technology for microcircuit interconnections with applications to metallization, passivation, and bondin

Contribution to the characterization of stratified structures : electromagnetic analysis of a coaxial cell and a microstrip line

The objective of this dissertation is the development of electromagnetic modelling software specific to the cells of microwave material characterization. This development is based on numerical methods that are alternative to finite element method which is widely used in commercial software. For the need to extract the properties of materials by inverse modelling methods, research into the numerical efficiency of direct analysis is the focus in this thesis. The characterization targeted cells in this work concern a coaxial cell and a planar line. The presence of an unknown material is modelled by a stratified heterogeneous transmission structure. The application of the transverse operator method (TOM) on the multi-layered coaxial cell allowed the determination of the propagation constant of fundamental mode and its corresponding field distribution of the electromagnetic fields, and the characteristics of higher-order modes for the need of the characterization of discontinuities between empty line and loaded line. In the case of the microstrip line, the use of the modified transverse resonance method (MTRM) allowed the determination of characteristics of the fundamental and higher order modes. Since each cell consists of several different sections, the matrix S of the set will be determined by the use of the several modal methods, such as modal connection method (''mode matching'') and multimodal variational method (MVM). The direct analysis codes are coupled with several optimization programs to constitute the software for extracting the material parameters. These are applied to material samples in cylinder form holed by the coaxial cell, or thin rectangular wafer by the microstrip line. Broadband extraction results were obtained, values are comparable with those published. Both high-loss dielectrics and nanostructured materials have been studied by our method

Carbon Nanotube Interconnects for End-of-Roadmap Semiconductor Technology Nodes

Advances in semiconductor technology due to aggressive downward scaling of on-chip feature sizes have led to rapid rises in resistivity and current density of interconnect conductors. As a result, current interconnect materials, Cu and W, are subject to performance and reliability constraints approaching or exceeding their physical limits. Therefore, alternative materials such as nanocarbons, metal silicides, and Ag nanowires are actively considered as potential replacements to meet such constraints. Among nanocarbons, carbon nanotube (CNT) is among the leading replacement candidate for on-chip interconnect vias due to its high aspect-ratio nanostructure and superior currentcarrying capacity to those of Cu, W, and other potential candidates. However, contact resistance of CNT with metal is a major bottleneck in device functionalization. To meet the challenge posed by contact resistance, several techniques are designed and implemented. First, the via fabrication and CNT growth processes are developed to increase the CNT packing density inside via and to ensure no CNT growth on via sidewalls. CNT vias with cross-sections down to 40 nm 40 nm are fabricated, which have linewidths similar to those used for on-chip interconnects in current integrated circuit manufacturing technology nodes. Then the via top contact is metallized to increase the total CNT area interfacing with the contact metal and to improve the contact quality and reproducibility. Current-voltage characteristics of individual fabricated CNT vias are measured using a nanoprober and contact resistance is extracted with a first-reported contact resistance extraction scheme for 40 nm linewidth. Based on results for 40 nm and 60 nm top-contact metallized CNT vias, we demonstrate that not only are their current-carrying capacities two orders of magnitude higher than their Cu and W counterparts, they are enhanced by reduced via resistance due to contact engineering. While the current-carrying capacities well exceed those projected for end-of-roadmap technology nodes, the via resistances remain a challenge to replace Cu and W, though our results suggest that further innovations in contact engineering could begin to overcome such challenge

LIGA cavity resonators and filters for microwave and millimetre-wave applications

High performance microwave cavities for various circuits in the front-end of transceivers such as filters, diplexers, and oscillators have conventionally been built with rectangular or cylindrical metallic waveguides, which typically have low loss, high quality (Q) factor, and higher power handling capability. However such waveguide cavity based circuits made by traditional metal machining techniques tend to be costly, particularly for complex multiple cavity based circuits, and not well suited to high volume commercial applications and integration with planar microwave integrated circuits. As commercial transceiver applications progress toward higher microwave and millimetre-wave frequencies, the use of waveguide based circuits for compact, highly integrated transceivers is becoming feasible, along with an increasing need for cost effective batch fabrication processes for realizing complex metallic cavity circuits without sacrificing structural quality and performance. It is expected that significant advancements in both microwave performance and integration will be achieved through the development of novel technologies for realizing vertically oriented three-dimensional (3-D) structures.Although improvement has been made on increasing the resonator Q factor by exploiting silicon micromachining and low-temperature cofired ceramics (LTCC) techniques, there are some drawbacks inherent to silicon cavity micromachining and LTCC technology, including non-vertical sidewalls, depth limitations, and surface roughness for the silicon resonator, and dielectric and radiation loss for LTCC resonator.Polymer-based fabrication is a promising alternative to silicon etching and LTCC technologies for the batch fabrication of ultra-deep microwave cavity structures. In particular, deep X-ray lithography (XRL), as part of the LIGA process, is a microfabrication technology for precisely structuring polymers, and is increasingly being applied to RF/microwave microstructures. In addition to precise patterning capabilities, deep XRL is able to structure ultra-deep cavities due to the penetration ability of hard X-rays. Cavities of several millimetres are possible in a single lithographic exposure, and with excellent sidewall quality, including verticality near 90 degrees and surface roughness on the order of tens of nanometres. These structured polymers are subsequently used as electroforming templates for fabricating metal structures with correspondingly good sidewall quality.This thesis investigates the possibility of realizing high-Q cavity resonators and filters at microwave frequencies using the LIGA microfabrication process. Finite element method (FEM) electromagnetic simulation results based on the cavity models representing different fabrication conditions show that smooth LIGA cavity structures result in promising Q improvement over silicon and LTCC structures. And the potential advantages of LIGA resonators are more dramatic with cavity height and increasing operating frequency. Deep polymer cavity structures (1.8 mm) fabricated using deep XRL demonstrate excellent sidewall verticality in the PMMA structure, with only slight shrinkage at the top surface of 8.5 2.5 mm in either lateral dimensions. This corresponds to sidewalls with verticality between 89.82o and 89.9o. The structure polymers are subsequently used as templates for metal electroforming to produce cavity resonators. The performance of the resonator is measured in a planar environment. A RT/duroid6010 soft substrate patterned with coupling structures forms the sixth side, and thus completes the cavity. Despite the rather crude test assembly for the sixth side made by clamping, the measured resonator has a high unloaded Q of 2122.2 85 at the resonant frequency of 24 GHz, indicating that LIGA cavities are especially promising for high performance applications. The relatively simple, single-step lithographic exposure also facilitates extension to more structurally complicated waveguide and multiple cavity-based circuits. This research work also proposes a high performance ``split-post' 3-pole cylindrical post coupled Chebyshev bandpass filter suitable for LIGA fabrication. In addition to potentially batch fabricating such a filter lithographically by exposing the entire waveguide depth in a single exposure, the filter structures composed of three cavities with metallic multi-post coupling would be extremely difficult to fabricate using traditional machining techniques, due to the extremely fine post structure and high vertical aspect ratio required. However, these types of structures could be ideal for LIGA fabrication, which offers sub-micron features, aspect ratios of 100:1 or higher, resist thicknesses of up to 3 mm, and almost vertical and optically smooth sidewalls. Also, representative LIGA sidewall roughness is used to predict very low loss and high performance, suggesting that complicated structures with multiple resonator circuits and high internal components with high aspect ratios are possible

Sonic and Photonic Crystals

Sonic/phononic crystals termed acoustic/sonic band gap media are elastic analogues of photonic crystals and have also recently received renewed attention in many acoustic applications. Photonic crystals have a periodic dielectric modulation with a spatial scale on the order of the optical wavelength. The design and optimization of photonic crystals can be utilized in many applications by combining factors related to the combinations of intermixing materials, lattice symmetry, lattice constant, filling factor, shape of the scattering object, and thickness of a structural layer. Through the publications and discussions of the research on sonic/phononic crystals, researchers can obtain effective and valuable results and improve their future development in related fields. Devices based on these crystals can be utilized in mechanical and physical applications and can also be designed for novel applications as based on the investigations in this Special Issue

Etude de circuits intégrés micro-ondes planaires et non planaires

Rapide survol de la technologie des circuits intégrés micro-ondes (MIC) -- Lignes de transmissions planaires et techniques de modélisation -- Méthode spectrale améliorée (Enhanced spectral domain approach) -- Caractéristiques de lignes à fentes coulées avec différent type de montage -- Analyse d'une structure guide d'onde uniplanaire auto-blindée -- Design de coupleur uniplanaire en anneau avec inverseur de phase -- Approche avec partition de domaines -- Analyse spectrale d'un résonnateur diélectrique cylindrique rayonnant

Electronic dura mater soft, multimodal neural interfaces:technology, integration and implementation to surface implants

Neuroprosthetic devices are engineered to study, support or replace impaired functions of the nervous system. The neural interface is an essential element of neuroprosthetic systems as it allows for transduction of signals and stimuli of desired functions (recording, stimulation, neuromodulation). A persistent challenge for translating neuroprosthetics from the laboratory to the clinic is the lack of long-term biointegration of neural interfaces. This thesis aims at improving biointegration of neural interfaces by reducing the mechanical mismatch between implant and neural tissue. In this thesis, the design, fabrication and characterization of soft surface neural interfaces is described. These soft neural interfaces, termed electronic dura mater or e-dura, were designed to mimic the mechanical properties of dura mater. In contrast with conventional neural technologies, e-dura neural interfaces were made of soft and compliant materials. They conform to the circumvolutions of the brain and spinal cord and follow their dynamic deformation without damaging the surrounding neural tissues. These soft multimodal neural interfaces were fabricated on silicone substrates using techniques imported from the microfabrication industry and incorporate compliant electrodes, stretchable electrical interconnects and a micro-catheter for drug delivery. Evaluation of the e-dura biointegration with spinal tissues demonstrated reduced foreign body reaction, compared to stiff polyimide based implants. Additionally, mechanical tests on an in-vitro spinal surrogate provided insights on the complex biomechanical coupling between implants and neural tissue. E-dura interfaces, implanted in rodents, maintained their functionality over extended periods and provided high-resolution neuronal recordings and concurrent delivery of electrical and chemical neuromodulation. Eventually, the use of gallium thin films was explored to create highly conductive and stretchable interconnects for integration of active electronic components in e-dura neural interfaces

Synthesis of multi-layer frequency selective surfaces of quasi-optical systems

This thesis investigate design techniques for multilayer Frequency Selective Surfaces (FSS) and its applications in quasi-optical (QO) systems. Design challenges that involve higher order filter and practical implementation of multilayer FSS at higher frequencies are reviewed. Multilayer FSS structures are commonly realized by cascading two or more FSS panel to achieve higher order responses, which usually rely on dielectric substrates to support the FSS arrays. It is noted that existing design approaches involved elaborate manufacturing processes as well as the requirement of custom dielectric thickness for the implementation of multilayer FSS. These design issues poses practical problems in the realization of multilayer FSS of higher order and its demonstration at higher frequencies. Furthermore, realization of higher order multilayer FSS with custom dielectric thicknesses are not feasible with low cost Printed Circuit Board (PCB) technology. As a result of this investigation, a novel design and synthesis technique is developed to address the aforementioned design issues. Equivalent circuit modelling and full wave electromagnetic simulation are employed for this purpose. The developed design technique enable practical realization of QO filter to have all transmission lines of predefined fix length. As a result, the proposed technique is able to resolve the limited availability of custom dielectric thicknesses, thus enable demonstration of multilayer FSS of higher order at higher frequencies. Particularly, the proposed design methodology allow rectification by design to adapt to any small variations in the dielectric thicknesses. Subsequently, based on this technique, a novel QO reflector design is developed to demonstrate proof of concept for time delay multiplexing that are employed in a radar system. The implementation of time delay between two polarization multiplexed beams initially requires true time delay structures that are difficult to integrate due to their electrically large structure. In order to address this problem, the designed QO reflector is able to perform same functionalities, i.e. a significant group delay difference for the two orthogonal linear polarization. Specifically, the designed QO reflector has the capability to de-multiplex an incoming wave into two linear polarized waves, whereby one of the reflected wave is time delayed while the other wave is unaffected. A synthesis method for QO reflector design with time delay multiplexing has been presented. Based on the design procedures reported in this thesis, prototypes for both QO filter and QO reflector of fourth order has been developed to operate at 15 GHz with 5% and 3.5% bandwidth respectively. The performances of the developed prototypes are verified with free-space measurement setup. The measured insertion loss of the QO filter is observed to be in the range of 0.5 dB – 2.83 dB, while the measured return loss of the QO reflector is the range of 1.5 dB – 2.3 dB. In order to demonstrate the effect of the group delay from the QO reflector, frequency domain analysis is performed by post-processing the measured data to obtain the required time domain signals. Overall the experimental measurement results corroborate well with both full-wave and circuit simulation

Advanced Carbon Fiber Composite Materials for Shielding and Antenna Applications

Due to the low weight, ease of fabrication, low cost, high stiffness, high thermal and electrical conductivity, advanced carbon fiber composite (CFC) material is one of the most desirable materials which have been considered recently in the aerospace, electronic, and infrastructure industry. This thesis examines the use of CFC materials for electromagnetic field shielding and antenna applications. Using a suitable electromagnetic model of composite materials, we evaluate the shielding effectiveness (SE) and other EM properties of composites paying attention to antenna design. Analytical and simulation results are compared with experimental data. Two kinds of composite materials are investigated, namely reinforced continuous carbon-fiber (RCCF) composites and carbon nanotube (CNT) composites. For analytical SE analysis of multilayer RCCF composites, the material shows anisotropic behavior along the direction of the fibers, and we employ the transmission matrix method in conjunction with the anisotropic properties of each layer. The shielding performance of composites is also experimentally investigated. In order to enhance the conductivity of an RCCF composite, a small volume fraction of multi-walled carbon nanotubes (MWCNTs) is added to the RCCF material. We investigate the SE of the proposed MWCNT “nanocomposite” over a wide frequency band up to 26.5 GHz. The effect of aspect ratio on shielding performance is addressed as well. The effective conductivity of the nanocomposites was determined over the frequency range of interest. The use of RCCF and single-walled carbon nanotube (SWCNT) composite is investigated for building antennas, by replacing the metal with CFC. We use an RCCF composite to build resonant and wideband antennas. The effect of the conductivity tensor of RCCF composite on the antenna performance is addressed. We also study the performance of a microstrip patch antenna with the ground plane made of RCCF composite. As one of the most highly-conductive composite materials, single wall carbon nanotube (SWCNT) buckypapers are used to build composite antennas. A new fabrication method is proposed to print arbitrarily-shaped full-composite SWCNT antenna on any type of substrate. Various types of SWCNT antennas are fabricated for different antenna applications, namely UHF-RFID, WLAN, UWB, and mm-wave applications. Good agreement is observed between simulation and experimental results for all the aforementioned composite antennas. Using the spectral domain method, the Green’s function is obtained for an infinitesimal HED on a dielectric slab over a CFC ground plane. Due to the high conductivity, CFCs are modeled using a surface impedance. The expressions for the electric field components are derived. The numerical integration details particularly dealing with low-converged tail of the integrand for fields at the air-dielectric interface are addressed. Numerical results based on this method compare well with results based on a time-domain finite integration technique. The effect of conductivity and anisotropy of the composite ground plane on electric field is investigated