Abstract Recently, a-Si:H TFT based liquid-crystal display has encroached on the territory of the cathode ray tubes. There is a tendency to fabricate the active matrix LCD on the plastic or flexible substrates. Instead of glass, flexible substrates will make the application of TFT-LCD extensive due to the several advantages: i.e. ultra-slim, light-weight and unbreakable, etc. Nevertheless, the limitation of process temperature for the low-melting substrates is an important issue. In this thesis, the feasibility of a-Si TFT devices fabricated on flexible substrates by using two different technologies have been evaluated. First, a-Si TFT devices were fabricated on glass at 150¢Jsuccessfully and the characteristics of films deposited at lowtemperature have been studied sequentially. For improving the adhesion between organic and inorganic layers and protecting substrate against water or gas during processes, several hot coating layers were investigated. With hot coating layer be introduced, glass was substituted by plastic substrates. We chose PES as the flexible substrate from several candidates due to better optical transmittance and good thermal stability below 200¢J. After direct fabrication on flexible substrate, the stability of electronic characteristics were been investigated with bending examination. In addition, TFT devices were successfully separated from glass and transferred to flexible substrates such as PES or metal foil. Using this technology, temperature limitation has been circumvented and TFT devices still exhibit good electronic characteristic. Furthermore, the bending measurements have been also applied to devices.

A successful cancer treatment is a combination of early diagnosis and efficient use of anticancer drugs. There is a chance of approximately 70 - 90% of cancer patients surviving if the diagnosis is conducted early. That means if a diagnosis system is in place which can detect multiple types of cancer at an early stage, a potential cancer therapy is most likely to succeed. However, at present, the available biomedical sensors are unable to detect and differentiate between cancerous cells or tumours. They are also not able to provide continuous real-time monitoring of a patient. Additionally, oral anticancer drugs given during chemotherapy, at the moment, suffer from low bioavailability. Also, a variety of these drugs is not targeted in nature. That means the drug will potentially affect areas of the body which do not need it. The low bioavailability of the drug will not only increase the chemotherapy sessions but also makes the entire process more aggravating for the cancer patient. Therefore, there is an absolute need to have innovative and efficient anticancer drug delivery mechanisms. Finally, current biomedical sensors are primarily made up of silicon (Si) or hard substrates based materials. Even if the biomedical sensor is of a flexible material, the material is either a fragile film or flexible but not stretchable polymers such as polyimide (PI). By having a biomedical sensor which is moderately flexible or not flexible at all, a continuous on-body biomedical sensing is not possible in an efficient manner. That is because hard substrates based biomedical sensors would be difficult to be placed on a body at all times. Furthermore, the flexible biomedical sensors currently suffer from problems such as the electrode on top cracking and damaging after few uses rendering them unusable. Hence, a new fabrication process needs to be devised to solve the issues mentioned above. In this work, an attempt is made to utilise zinc oxide (ZnO) nanostructures for biomedical sensing, drug delivery and biomimetics. ZnO nanostructures are synthesised by using a low-cost wet chemistry process known as hydrothermal growth. Due to the inherent biocompatibility and unique electrical/ piezoelectric properties of ZnO, they acted as prime candidates for the applications outlined above. A high-throughput process is used to synthesise ZnO nanowires (NWs) on Si, polyimide-onsilicon (PI/Si) and directly on PI and polydimethylsiloxane (PDMS) substrates. The work utilises a variety of characterization tools. ZnO nanostructures' morphology is characterised by using a Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and Atomic Force Microscope (AFM). X-ray diffraction (XRD) was used to calculate the crystallite size and the crystalline orientation of the nanostructures. A novel fabrication process is developed to allow direct synthesis and direct patterning of metal electrodes on fully flexible, stretchable and bendable PDMS substrates by using standard photolithography. This novel fabrication process makes the PDMS substrates not expand when exposed to temperatures up to 110 °C. Also; the new fabrication process does not cause the PDMS to swell when exposed to various chemicals such as isopropyl alcohol (IPA) or acetone. The fabrication process has created a new paradigm shift in the field of patterning and producing devices directly on flexible and stretchable substrates. The PDMS substrate is further utilised as a sensitive bovine serum albumin (BSA) protein sensor which is capable of detecting up to femtomolar concentrations in just under 5 min of incubation time. Protein biosensing tests were carried out by measuring the change in resistance at 1V bias voltage. The PDMS based biosensor is tested as a protein sensor because proteins are important biomarkers in cancer diagnosis. Also, protein sensors are immensely useful in the detection of bacteria and viruses thereby allowing further expansion to the technology developed herewith. For the first time, ZnO NWs are used to deliver hydrophobic organic dye, Nile red, in a human body like environment. The Nile red simulates an anticancer drug as they share similar surface chemistry. There is an approximately 80% release of Nile red which shows that ZnO NWs can be used as an efficient anticancer drug delivery system with high bioavailability. For the drug delivery experiments, the dynamic dialysis based release of Nile red (Nr) from the ZnO nanowires is carried out by using UV-Visible (UV-Vis) spectroscopy. Fourier Transform Infrared (FTIR) was used to determine the coordination of Nr across the ZnO nanowires. Finally, a novel synthesis process is used to produce individual ZnO NWs on a single ZnO nanoplate (NP) which are named as ZNWNP nanostructures. ZNWNP nanostructures have high hydrophobicity without the need of any functionalization. The hydrophobicity of the hybrid ZnO nanowires on ZnO nanoplate nanostructures (ZNWNP) is characterised by using contact angle goniometry (CAG). Various contact angle theories have been used to calculate the surface free energy (SFE) of the ZNWNP nanostructures. The high hydrophobicity allows these nanostructures to be used for biomimetic applications such self-cleaning, bioinspired sensors and multimodal biosensing. Additionally, ZNWNP nanostructures can be used in biomedical sensors to create multimodal analysis. The multimodal analysis is immensely useful in cancer detection as at least three or more cancer biomarkers can be used to triangulate the diagnosis. The work presented in the thesis aims to utilise ZnO nanostructures for a variety of biomedical applications. The new fabrication process mentioned above has applications not only in biomedicine but also in the flexible electronics industry. The biomimetic nanostructures combined with the biomedical sensor gives rise to a robust multimodal analysis system which can change the course of the cancer diagnosis. That coupled with the usage of ZnO NWs as an effective anticancer drug delivery system gives an immense promise in advancing cancer therapy as a whole and making the entire treatment process less aggravating and less painful for cancer patients.

In this thesis, a number of commercially available paper substrates of various types are characterized and their characteristics related to the performance of inkjet-printed conductors using silver nanoparticle ink. The evaluated performance variables are electrical conductivity as well as the minimum achievable conductor width and the edge raggedness. It is shown that quick absorption of the ink carrier is beneficial for achieving well defined conductor geometry and high conductivity. Surface roughness with topography variations of sufficiently large amplitude and frequency is detrimental to print definition and conductivity. Porosity is another important factor, where the characteristic pore size is much more important than the total pore volume. A nearly ideal porous coating has large total pore volume but small characteristic pore size, preferably smaller than individual nanoparticles in the ink. Apparent surface energy is important for non-absorbing substrates but of limited importance for coatings with a high absorption rate.Additionally, a concept for improving the geometric definition of inkjet-printed conductors on nonporous films has been demonstrated. By coating the films with polymer–based coatings to provide a means of ink solvent removal, minimum conductor width were reduced a factor 2 or more.Intimately connected to the end performance of printed conductors is a well adapted sintering methodology. A comparative evaluation of a number of selective sintering methods has been performed on paper substrates with different heat tolerance. Pulsed high-power white light was found to be a good compromise between conductivity performance, reliability and production adaptability.The purpose of the work conducted in this thesis is to increase the knowledge base in how surface characteristics of papers and flexible films affect performance of printed nanoparticle structures. This would improve selection, adaption of, or manufacturing of such substrates to suit printed high conductivity patterns such as printed antennas for packaging. / I denna avhandling har ett antal kommersiellt tillgängliga papper av olika typ karaktäriserats och deras egenskaper relaterats till prestandan på inkjet-tryckta elektriska ledare tryckta med silvernanopartikelbläck. De undersökta prestandavariablerna är elektrisk ledningsförmåga samt ledarnas minimala linjebredd och kantjämnhet. Det visas att en snabb absorption av bläckets lösningsmedel är gynnsam för både väldefinierad ledningsgeometri och elektrisk ledningsförmåga. Ytråhet med topografiska variationer med tillräckligt stor amplitud och spatiell frekvens korrelerar negativt med tryckdefinition och ledningsförmåga. Porositet är ytterligare en viktig faktor, där karaktäristisk porstorlek är avsevärt viktigare än total porvolym. Nära ideala egenskaper hos en porös bestrykning synes vara en mycket hög total porvolym men med små individuella porer, med fördel mindre än de minsta metallpartiklarna i bläcket. Ytenergi är mycket betydelsefull för icke-absorberande substrat men tappar nästan all sin betydelse för bestrykningar med snabb absorption.Ett koncept för att förbättra den geometriska definitionen på inkjet-tryckta ledare på icke-porösa flexibla filmer har visats. Genom att bestryka filmerna med vissa polymerbaserade material och därmed införa en mekanism för separering av lösningsmedel och partiklar så reducerades ledarnas minimibredd med en faktor 2 eller mer.Intimt förknippad med den slutliga elektriska prestandan på tryckta ledare är också en väl anpassad sintringsmetodik. En jämförande utvärdering av ett flertal selektiva sintringmetoder har genomförts på papper med olika värmetålighet. Pulsat vitt ljus med hög effekt bedömdes som en bra kompromiss mellan elektriska prestanda, tillförlitlighet och anpassningsbarhet för produktionsmiljö.Nyttan med arbetet som presenteras i denna avhandling är att öka kunskapsbasen för hur pappers och flexibla filmers ytegenskaper påverkar prestandan på inkjet-tryckta nanopartikelstrukturer. Detta möjliggör bättre urval, anpassning av, eller tillverkning av sådana substrat för att passa tryckta mönster med hög konduktivitet; som till exempel tryckta antenner på förpackningar.

With the industry striving for smaller devices, new technologies are developed to further miniaturize electronics devices. To this end, realization of 3D/non-planar interconnects, which aim at miniaturizing the interconnects formed between components on the same device, has attracted many researchers. This thesis focuses on a feasibility analysis for developing non-planar interconnects on various flexible substrates using laser assisted maskless microdeposition (LAMM), which is a pressure-less process. There are two types of flexible substrates that are used: double-sided copper substrates separated by a layer of polyethylene terephthalate (PET) as well as a polyethylene terephthalate flexible substrate with surface-mounted resistors. For both substrates, multiple types of experiments were conducted to discover procedures which result in the highest rate of success for forming conductive interconnects. Optimal process parameters and deposition techniques were determined after multiple experiments. After experiments were completed, the resultant substrates were subject to various characterization methodologies including optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and profilometery. The results of these methodologies are documented in this thesis. After many types of experiments involving substrate manipulation of the double-sided copper substrates, it was shown that the silver nano-particles were more likely to form a conductive interconnect when a polished slant was fabricated on the substrate. Many deposition patterns were used for the flexible substrates with surface-mounted resistors. Of these patterns, the two patterns, the ‘zigzag’ and ‘dot solder’ patterns, proved to have a much higher success rate for creating conductive interconnects compared to the other patterns. During this study, the results of the experiments using the LAMM process show that this technology has great potential for creating non-planar interconnects on flexible substrates. The experiments however suggest that the process is very sensitive to the material composition and process parameters. As such, with a small change in parameters, the 3D interconnects can fail to be produced. It was also observed that the possibility of silver interconnect fractures is higher where dissimilar materials with different thermal expansion rates are used for the underlying substrates.

With the industry striving for smaller devices, new technologies are developed to further miniaturize electronics devices. To this end, realization of 3D/non-planar interconnects, which aim at miniaturizing the interconnects formed between components on the same device, has attracted many researchers. This thesis focuses on a feasibility analysis for developing non-planar interconnects on various flexible substrates using laser assisted maskless microdeposition (LAMM), which is a pressure-less process. There are two types of flexible substrates that are used: double-sided copper substrates separated by a layer of polyethylene terephthalate (PET) as well as a polyethylene terephthalate flexible substrate with surface-mounted resistors. For both substrates, multiple types of experiments were conducted to discover procedures which result in the highest rate of success for forming conductive interconnects. Optimal process parameters and deposition techniques were determined after multiple experiments. After experiments were completed, the resultant substrates were subject to various characterization methodologies including optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and profilometery. The results of these methodologies are documented in this thesis. After many types of experiments involving substrate manipulation of the double-sided copper substrates, it was shown that the silver nano-particles were more likely to form a conductive interconnect when a polished slant was fabricated on the substrate. Many deposition patterns were used for the flexible substrates with surface-mounted resistors. Of these patterns, the two patterns, the ‘zigzag’ and ‘dot solder’ patterns, proved to have a much higher success rate for creating conductive interconnects compared to the other patterns. During this study, the results of the experiments using the LAMM process show that this technology has great potential for creating non-planar interconnects on flexible substrates. The experiments however suggest that the process is very sensitive to the material composition and process parameters. As such, with a small change in parameters, the 3D interconnects can fail to be produced. It was also observed that the possibility of silver interconnect fractures is higher where dissimilar materials with different thermal expansion rates are used for the underlying substrates.

This work describes the techniques of assembling colloidal gold on flexible polymeric substrates from solution. The process takes advantage of the strong affinity of gold to thiol and amino groups. Polymeric substrates were modified with silanes having these functional groups prior to Au attachment or in the case of poly(urethane urea) (PUU), no surface functionalization was required. This polymer has terminal amine and N-H groups on the polymer chain, which can act as coordination points for gold. Immersion in the colloidal gold solution led to the formation of a monolayer. Increased coverage was obtained by two methods. The first was a reduction or "seeding" process, where Au was reduced onto the attached particles on the surface. The second was using different linker molecules and creating a multilayered film by a layer-by-layer assembly. Three linker molecules of different lengths were used. Films fabricated using the smallest molecule had the least resistance whereas films fabricated with the longest molecule were not conductive. The resistance of these films may be varied easily by heating. Heating the films at temperatures as low as 120 °C caused a dramatic decrease in the resistance of over six orders in magnitude. Successful attachment of gold to PUU with very good adhesion properties was also demonstrated. The attachment of gold was stable in different solvents. Upon stretching the PUU-Au films, it was observed that there is a reversible resistance increase with strain and at a certain strain, the film becomes non-conductive. This sharp transition from conductive to insulating has potential applications in flexible switches and sensors. A hysteresis in the strain-resistance curves, analogous to the hysteresis in the stress-strain curves of the polymer was also observed. Using PUU as an adhesive agent, gold electrodes were successfully assembled on Nafion-based polymer transducers. These materials showed comparable actuation behavior to the electrodes made by the Pt-reduction method, with the added advantage of the ability to form patterned electrodes for distributed transducers. Patterning techniques were developed to form colloid-polymer multilayers for use in photonic crystal materials using selective deposition on patterned silane monolayers. Patterns of gold electrodes were also made on flexible polymers using a photoresist-based method. / Ph. D.

Approved for public release, distribution is unlimited / Display technologies in the current market range from the simple and cheap incandescent bulb behind a graphic overlay to the upwardly expensive flat panel high definition plasma display. To provide a foundation of understanding for Light Emitting Polymers (LEP), samples were imaged in a scanning electron microscope. This was preformed to identify a potential method for answering questions on polymer charge mobility and diffusion mechanisms, which are currently unknown. Light Emitting Polymer (LEP) displays offer a viable alternative to the active matrix style, when an application calls for information to be sent in a simple visible format. By using the flexibility of the fabrication process, LEP displays can be applied to offer a low cost, lightweight, and durable means of communicating information during shipboard damage control and firefighting. A unique screen printing method was used in collaboration with Add-Vision, to produce a prototype that was designed, fabricated and tested for use in Naval shipboard firefighting evolutions. The application of the LEP technology to shipboard damage control was motivated by the experience gained from being both the Officer in Charge of a Naval Firefighting School and from time in the Fleet as a Damage Control Officer. / Lieutenant, United States Naval Reserve

With the emergence of the Internet of Things (IoT), wireless body area networks (WBANs) are becoming increasingly pervasive in everyday life. Most WBANs are currently working at the IEEE 802.15.4 Zigbee standard. However there are growing interests to investigate the performance of BANs operating at higher frequencies (e.g. millimetre-wave band), due to the advantages offered compared to those operating at lower microwave frequencies. This thesis aims to realise printed conductive traces on flexible substrates, targeted for high frequency wearable electronics applications. Specifically, investigations were performed in the areas pertaining to the surface modification of substrates and the electrical performance of printed interconnects. Firstly, a novel methodology was proposed to characterise the dielectric properties of a non-woven fabric (Tyvek) up to 20 GHz. This approach utilised electromagnetic (EM) simulation to improve the analytical equations based on transmission line structures, in order to improve the accuracy of the conductor loss values in the gigahertz range. To reduce the substrate roughness, an UV-curable insulator was used to form a planarisation layer on a non-porous substrate via inkjet printing. The results obtained demonstrated the importance of matching the surface energy of the substrate to the ink to minimise the ink de-wetting phenomenon, which was possible within the parameters of heating the platen. Furthermore, the substrate surface roughness was observed to affect the printed line width significantly, and a surface roughness factor was introduced in the equation of Smith et al. to predict the printed line width on a substrate with non-negligible surface roughness (Ra ≤ 1 μm). Silver ink de-wetting was observed when overprinting silver onto the UV-cured insulator, and studies were performed to investigate the conditions for achieving electrically conductive traces using commercial ink formulations, where the curing equipment may be non-optimal. In particular, different techniques were used to characterise the samples at different stages in order to evaluate the surface properties and printability, and to ascertain if measurable resistances could be predicted. Following the results obtained, it was demonstrated that measurable resistance could be obtained for samples cured under an ambient atmosphere, which was verified on Tyvek samples. Lastly, a methodology was proposed to model for the non-ideal characteristics of printed transmission lines to predict the high frequency electrical performance of those structures. The methodology was validated on transmission line structures of different lengths up to 30 GHz, where a good correlation was obtained between simulation and measurement results. Furthermore, the results obtained demonstrate the significance of the paste levelling effect on the extracted DC conductivity values, and the need for accurate DC conductivity values in the modelling of printed interconnects.

Current trends in technology are moving to increased use of wireless communication with rapidly increasing data transmission rates and higher frequencies. Miniaturization is essential to allow electronics of increasing complexity to fit into smaller devices. Adaptive technologies allow a single system to operate across multiple wireless protocols, adjusting to changing conditions to minimize interference and enhance performance. Flexibility is essential as the use of wireless technology increases and spreads to new industries. The objective of this research is twofold: to develop novel reconfigurable electromagnetic structures and a novel process to fabricate microelectromechanical systems (MEMS) devices on flexible substrates. The novel electromagnetic structures are passive frequency-switchable parasitic antennas, conformal MEMS-tunable frequency selective surfaces (FSS) and MEMS-tunable electromagnetic bandgap (EBG) structures. Fabricating the reconfigurable conformal FSS and EBG structures requires the development of a new fabrication process to produce MEMS devices monolithically integrated onto a flexible substrate. Novel frequency-switchable parasitic antenna arrays are developed, fabricated and measured. The structure radiates efficiently when placed over metal and absorbing material, improving the range of conventional RFID systems, as well as minimizing blind spots to provide continuous coverage in a hemisphere. A novel analysis method is developed to characterize frequency-switchable parasitic patch arrays. The purpose of the analysis is to provide an approximation of the input impedance and variation of the radiation pattern with frequency. The analysis combines models based on electromagnetic theory and circuit theory to provide a fast and yet reasonable approximation of the parasitic array characteristics. The analysis also provides a good deal of physical insight into the operation of multi-mode parasitic patch arrays. The end result is an initial array design which provides a good starting point for full EM simulation and optimization. The new analysis method is validated alongside measured and simulated results, with good correlation for both impedance characteristics and far-field radiation patterns. A MEMS-based switched parasitic antenna array is designed, fabricated and measured with good correlation between simulated and measured results. The structure is a direct-coupled parasitic patch array which is capable of frequency steering and has additional MEMS-enabled beam-steering capabilities at each frequency. An EBG-based multi-mode radiating structure design is presented, which is capable of frequency-switchable beam steering. The antenna area is significantly reduced compared to the parasitic patch array structure, but at a considerable cost in terms of gain and efficiency. A novel MEMS process is developed to fabricate large numbers of high-performance MEMS devices monolithically integrated onto a rigid-flex organic substrate using low-temperature processes. The rigid-flex substrate is all dielectric, which is amenable to low-loss electromagnetic structures. The substrate provides mechanical support to the MEMS devices while maintaining overall flexibility. The adaptation of each fabrication process step to handle flexible substrates is analyzed and documented in detail. The newly-developed MEMS process is used to fabricate a MEMS reconfigurable frequency-selective surface. A practical bias network is incorporated into the structure design to ensure that all devices are actuated simultaneously. FSS structures operating in the Ku and Ka bands are fabricated and tested, with good correlation between simulated and measured results for individual devices as well as the entire FSS structures. The newly-developed MEMS process is also used to fabricate a MEMS reconfigurable electromagnetic bandgap structure. An EBG structure operating in the Ka band is fabricated and tested to verify the validity of the proposed concept.

Current trends in technology are moving to increased use of wireless communication with rapidly increasing data transmission rates and higher frequencies. Miniaturization is essential to allow electronics of increasing complexity to fit into smaller devices. Adaptive technologies allow a single system to operate across multiple wireless protocols, adjusting to changing conditions to minimize interference and enhance performance. Flexibility is essential as the use of wireless technology increases and spreads to new industries. The objective of this research is twofold: to develop novel reconfigurable electromagnetic structures and a novel process to fabricate microelectromechanical systems (MEMS) devices on flexible substrates. The novel electromagnetic structures are passive frequency-switchable parasitic antennas, conformal MEMS-tunable frequency selective surfaces (FSS) and MEMS-tunable electromagnetic bandgap (EBG) structures. Fabricating the reconfigurable conformal FSS and EBG structures requires the development of a new fabrication process to produce MEMS devices monolithically integrated onto a flexible substrate. Novel frequency-switchable parasitic antenna arrays are developed, fabricated and measured. The structure radiates efficiently when placed over metal and absorbing material, improving the range of conventional RFID systems, as well as minimizing blind spots to provide continuous coverage in a hemisphere. A novel analysis method is developed to characterize frequency-switchable parasitic patch arrays. The purpose of the analysis is to provide an approximation of the input impedance and variation of the radiation pattern with frequency. The analysis combines models based on electromagnetic theory and circuit theory to provide a fast and yet reasonable approximation of the parasitic array characteristics. The analysis also provides a good deal of physical insight into the operation of multi-mode parasitic patch arrays. The end result is an initial array design which provides a good starting point for full EM simulation and optimization. The new analysis method is validated alongside measured and simulated results, with good correlation for both impedance characteristics and far-field radiation patterns. A MEMS-based switched parasitic antenna array is designed, fabricated and measured with good correlation between simulated and measured results. The structure is a direct-coupled parasitic patch array which is capable of frequency steering and has additional MEMS-enabled beam-steering capabilities at each frequency. An EBG-based multi-mode radiating structure design is presented, which is capable of frequency-switchable beam steering. The antenna area is significantly reduced compared to the parasitic patch array structure, but at a considerable cost in terms of gain and efficiency. A novel MEMS process is developed to fabricate large numbers of high-performance MEMS devices monolithically integrated onto a rigid-flex organic substrate using low-temperature processes. The rigid-flex substrate is all dielectric, which is amenable to low-loss electromagnetic structures. The substrate provides mechanical support to the MEMS devices while maintaining overall flexibility. The adaptation of each fabrication process step to handle flexible substrates is analyzed and documented in detail. The newly-developed MEMS process is used to fabricate a MEMS reconfigurable frequency-selective surface. A practical bias network is incorporated into the structure design to ensure that all devices are actuated simultaneously. FSS structures operating in the Ku and Ka bands are fabricated and tested, with good correlation between simulated and measured results for individual devices as well as the entire FSS structures. The newly-developed MEMS process is also used to fabricate a MEMS reconfigurable electromagnetic bandgap structure. An EBG structure operating in the Ka band is fabricated and tested to verify the validity of the proposed concept.