Coplanar Waveguide-Fed Broadband Microwave Devices with (or without) a Thin Dielectric Substrate for Use in Flexible Electronic Systems

Two examples of microwave devices, fed by a coplanar waveguide and realized on a thin substrate (or without such a substrate), are employed to investigate the influence of devices’ curvatures and the proximity of different materials on their parameters. To perform the tests, a broadband antenna and a low-pass filter are chosen. A feeding coplanar waveguide is realized on a dielectric material brick attached to an SMA connector and the main device structure is placed in the air or on a thin substrate. The utilization of a thin substrate or its removal from the structure gives rise to the possibility of placing the devices on curved surfaces. The investigated devices are redesigned and manufactured. The antenna has a total size of 46 mm × 44 mm and covers a frequency range of 2.4–35 GHz which gives a 174% fractional bandwidth. The filter has a total size of 50 mm × 80 mm and its bandwidth has a cutoff frequency of 3.4 GHz. The obtained results are verified by measurements and good agreement is achieved

Electromagnetic Band Gap Structure Integrated Wearable Monopole Antenna For Spacesuit

Research and development of body-worn communication systems and electronics have become very prominent in recent years. Some applications include intelligent garments equipped with wireless communication devices for sports, astronauts’ spacesuits [1], and fire fighters’ uniforms [2]. These systems are unthinkable without different kinds of body worn textile or flexible antennas. In this thesis, we will discuss the design and fabrication of a compact wearable textile antenna within the Industrial, Scientific and Medical (ISM) band operating frequency, proposed for incorporation into a flight jacket of the astronaut inside the habitat. The antenna is integrated with artificial material known as Electromagnetic Band Gap (EBG) structures for performance enhancement. The purpose of the system is to constantly monitor vital signals of the astronauts. In this thesis the design, simulation, prototype fabrication and antenna testing under different environmental condition, in a word the entire design cycle of wearable Co-Planar Waveguide (CPW) fed monopole antenna is discussed. As human body tissues are lossy in nature, the radiation efficiency of the antenna will be affected due to the absorption of the radiated energy. Therefore, alteration in the radiation characteristics of the wearable antenna like resonant frequency, realized gain and impedance bandwidth will take place. For overcoming these obstacles, addition of EBG layers are recommended to isolate the antenna from near body environments. The proposed wearable antenna was tested under real operating conditions such as pressure and stretching conditions

Direct Laser Writing of Metal and Metal Oxide Patterns for Flexible and Memristive Electronic Components

Growing interest in the fields of flexible electronics and AI are leading the development of new manufacturing techniques able to make computer hardware devices that can suite their unique needs. Research into these areas is stalled by the high cost of manufacturing putting rapid and low-cost manufacturing methods in high demand. Direct Laser Writing, as a novel manufacturing technique, has been shown to be able to produce flexible electronic devices rapidly and with the use of inexpensive raw materials. It works by treating a substrate coated in a metal ion precursor with focused laser irradiation. Where the laser interacts with the precursor organic reduction agents within the precursor are able to reduce the metal ions which then form nanoparticles that are then sintered to form interconnected nanoparticle networks. In this work direct laser writing is utilized to develop a manufacturing technique of novel flexible electronics for neuromorphic computing hardware. Direct laser writing of copper and copper patterns is used to study the relationship between applied laser energy and electrical properties of deposited patterns. Other metals are also studied. Anodic metals are not able to be fully reduced and are deposited as metal oxides. Cathodic metals are easily reduced and deposited as metals. Metals with intermediate reduction potentials can selectively be deposited as either metals or metal oxides. Deposition of metal alloys with homogenous composition is also demonstrated through the deposition of copper-nickel alloys. Memristor devices fabricated from Cu/Cu2O/Cu patterns are produced using direct laser writing. Planar patterns are fabricated and shown to have a high sensitivity to changing laser settings used to print the oxide region. Bipolar resistive switching is observed with setting and resetting occurring near +/- 0.7V, and ratios between the high and low resistance states being as high as 102 are achieved. Fabricated devices are shown to flexible and stable over long periods of time. Memristor based logic structures Including Boolean “And” and “Or” gates are fabricated in planar patterns from memristor pairs. Logic gates show signal processing in times as short as 300ns. Moderate signal degradation from the logic gates are noted at 9% and 21% in the “Or” gate and “And” gate respectively. Memristor crossbar arrays are also fabricated from Cu/Cu2O/Cu and Ag/Cu2O/Cu patterns. Their multiple resistance states are programmed and performances are compared. In summary Direct laser writing is demonstrated as a process that has promise as a method for producing flexible novel computer hardware. Further work is recommended to focus on identifying combinations of materials and laser settings that can further improve the consistency and performance of the direct laser writing fabricated memristor devices

Modeling competing fracture for dry transfer of thin films to a flexible substrate

Dry transfer printing is where a thin film is transferred from a host substrate to a target substrate by taking advantage of the difference in adhesion between the thin layer and the substrates. This technique can lead to high throughput industrial-scale manufacturing of flexible devices using thin films and 2D materials. A major roadblock for applying the method is an inadequate understanding of how transfer printing depends on the material properties of the substrates and the thin film and their interfacial interactions, which limits the reliability of dry transfer methods. This dissertation provides this knowledge through computational analysis with cohesive zone models. Two approaches are used: 2D finite element simulations and 1D finite difference beam theory models. Both mode I and mixed-mode fractures are simulated. Scaling equations are developed to quantify load, crack length, end rotation, damage zone length and mode-mix as a function of material and interface properties. Competing fracture during the transfer of a 2D material like graphene is simulated with finite element models in ABAQUS®. Two damage initiation criteria are used with cohesive zone models. Interface strength is observed to be the primary factor affecting crack path selection for both damage criteria. Weaker interfaces break first, independent of the fracture energy. However, convergence issues with ABAQUS® are identified. So, fast, robust beam theory models are developed to understand the parametric dependence of crack growth on material and interface properties and captured in a fracture map. In addition to 2D materials, transfer printing of thin films is also studied. Parameters such as interface defects, thin film thickness and interface properties are varied to understand crack growth in thin film transfer. Interface defects modeled as initial crack lengths are observed to be the most significant factor in determining the success of the transfer process. When interface cracks are of equal lengths, fracture energy determines the crack path selection for stiff thin films and thicker films whereas for soft thin films, interface strength determines which interface breaks. A strong correlation between steady state crack tip mode-mix and crack path selection is observed despite using a mode-independent fracture energy.Chemical Engineerin

New Materials, Methods, and Molecules for Microelectronic and Molecular Electronic Devices

This dissertation reports a variety of new methods and materials for the fabrication of electronic devices. Particular emphasis is placed on low-cost, solution based methods for flexible electronic device fabrication, and new substrates and molecules for molecular electronic tunnel junctions. Chapter 2 reports a low-cost, solution based method for depositing patterned metal circuitry onto a variety of flexible polymer substrates. Microcontact printing an aluminum (III) porphyrin complex activates selected areas of an oxidized polymer substrate to electroless copper metallization. Chapter 3 reports a new transparent conductive electrode for use in optoelectronic devices. A highly conductive, transparent silver nanowire network is embedded at the surface of an optical adhesive, which can be applied to a variety of rigid and flexible polymer substrates. Chapter 4 describes a new approach to the self-assembly of mesoscale components into two-dimensional arrays. Unlike most previously reported self-assembly motifs, this method is completely dry; eliminating solvent makes this method compatible with the assembly of electronic components. Chapter 5 describes a new class of self-assembled monolayer (SAM) on gold formed from dihexadecyldithiophosphinic acid ((C 16 ) 2 DTPA) adsorbate molecules. The binding and structure (C 16 ) 2 DTPA SAMs is dependent upon the roughness and morphology of the underlying gold substrate. Chapter 6 investigates the influence of chain length on the binding and structure of dialkyl-DTPA SAMs on smooth, template-stripped (TS) gold. Binding of the DTPA head group is independent of the length of the alkyl chain, while the structure of the organic layer has a counter-intuitive dependence: As the length of the alkyl chain increases, these SAMs become more disordered and liquid-like. Chapter 7 describes the fabrication of ultra smooth gold substrates using chemical mechanical polishing (CMP). These substrates are smooth, uniform, and prove to be ideal candidates for bottom electrodes within SAM-based molecular electronic tunnel junctions. Chapter 8 investigates the charge transport properties of new diphenyldithiophosphinic acid (Ph 2 DTPA) SAMs on TS gold within metal-SAM//Ga 2 O 3 /EGaIn molecular tunnel junctions. A computational investigation provides insight into the electronic structure of the junction