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A wearable body temperature sensor would allow for early detection of fever or infection, as well as frequent and accurate hassle-free recording. This thesis explores the design of a body-temperature-sensing device inkjet-printed on a flexible substrate. All structures were first modeled by first-principles, theoretical calculations, and then simulated in HFSS. A variety of planar square inductor geometries were studied before selecting an optimal design. The designs were fabricated using multiple techniques and compared to the simulation results. It was determined that inductance must be carefully measured and documented to ensure good functionality. The same is true for parallel-plate and interdigitated capacitors. While inductance remains relatively constant with temperature, the capacitance of the device with a temperature-sensitive dielectric layer will result in a shift in the resonant frequency as environmental or ambient temperature changes. This resonant frequency can be wirelessly detected, with no battery required for the sensing device, from which the temperature can be deduced. From this work, the optimized version of the design comprises of conductive silver in with a temperature-sensitive graphene oxide layer, intended for inkjet-printing on flexible polyimide substrates. Graphene oxide demonstrates a high dielectric permittivity with good sensing capabilities and high accuracy. This work pushes the state-of-the-art in applying these novel materials and techniques to enable flexible body temperature sensors for future biomedical applications.

Transparente Elektroden finden breite Verwendung in unterschiedlichen kommerziellen Produkten. Dünnschichtsolarzellen basieren ebenso auf diesen Funktionsschichten wie Displays oder organische Leuchtdioden. Im Falle von Dünnschichtsolarzellen kann durch gezielte Einstellung der Oberflächentextur der transparenten Elektrode ein entscheidender Einfluss auf die erreichbare Effizienz genommen werden. Dabei wird eine Verlängerung der Weglänge des Lichtes im Absorbermaterial durch Mehrfachreflexionen angestrebt. Häufig werden dafür Schichten transparenter leitfähiger Oxide (TCO) gezielt texturiert. Eine weitere Möglichkeit zur Erzeugung transparenter Elektroden stellt die Verwendung feiner Metallgitter dar. Diese ermöglichen hohe Leitfähigkeiten im Bereich der Gitterstege und hohe Transparenz im Bereich zwischen den Stegen. In dieser Arbeit sollte ein auf nasschemischen Prozessen basierendes Verfahren entwickelt werden, mit dem es möglich ist, sowohl strukturierte TCO-Elektroden als auch Metallgitter unterschiedlicher Geometrien gezielt herzustellen. Die Leistungsfähigkeit der Elektroden sollte anhand der Integration in entsprechende Bauteile bewertet werden. Namentlich sollte dieser Prozess für Cd2SnO4 (engl. Cadmium Tin Oxide, CTO) als ein TCO-Material hoher Transparenz und Leitfähigkeit sowie für Silber und Kupfer als metallische Systeme anwendbar sein. Als zielführende Methode kam die Nanoprägelithographie (von engl. Nanoimprint Lithography, NIL) zum Einsatz. Dieses Verfahren erlaubt die schnelle, einfache und kostengünstige Herstellung strukturierter Oberflächen. Grundsätzlich wird dazu ein strukturierter Elastomerstempel in eine Schicht eines zu vernetzenden Materials gepresst. Während des Pressens findet die Vernetzung statt. Nach anschließender Separation von Stempel und Schicht resultiert eine strukturierte Oberfläche. Gängige Präkursorensysteme für anorganische Verbindungen, bei denen Vernetzungsprozesse ablaufen, stellen Sol-Gel-Methoden und sogenannte polymere Präkursoren dar. Für letztere werden Metallzitrate mit Ethylenglykol verestert, um ein vernetztes Polymer zu generieren. Nach thermischem Entfernen der Organik bleibt das Metalloxid zurück. Im Rahmen dieser Arbeit ist ein Präkursorensystem entwickelt worden, das Metallionen komplexiert, auf Glassubstrate beschichtet werden kann und eine thermische Polymerisation erlaubt. Aus dem erhaltenen polymeren Präkursor konnten die Zielverbindungen durch thermisches Zersetzen einerseits in Pulverform und andererseits über vorhergehende Schleuderbeschichtung in Form dünner Schichten erhalten werden. Im Falle des kubischen Cd2SnO4 wurde im Rahmen dieser Arbeit erstmals eine Nanopulver-Synthese mit phasenreinem Produkt aus flüssigem Präkursor beschrieben. Dafür stellten sich der Anteil der verwendeten organischen Bestandteile sowie die Zersetzungsgeschwindigkeit als entscheidende Einflussparameter heraus. Zudem wurden CTO Dünnschichten mit dem beschriebene Präkursor hergestellt. Eine optimale Brenntemperatur zur Erzeugung phasenreiner CTO-Schichten von 700 ‰ wurde ermittelt. Die Zersetzungsgeschwindigkeit (bzw. Aufheizrate) beeinflusste die Oberflächenmorphologie der erhaltenen Schichten maßgeblich. Eine schrittweise Zersetzung (100 ‰°C, 200 °C‰, Zieltemperatur) führte dabei in effizienter Weise zu kompakten Schichten. Diese zeigten sehr gute optische und elektronische Eigenschaften. So konnten etwa 300 nm dicke CTO-Schichten mit spezifischen Widerständen von ca. 1 • 10^(−5) Ohm m bei einer Transmission von etwa 80 % (inklusive Glassubstrat) erhalten werden. Derartige CTO-Schichten konnten erfolgreich als transparente Frontelektroden für a-Si Dünnschichtsolarzellen verwendet werden. Ein positiver Einfluss periodischer Linienstrukturen auf die Lichteinfangeigenschaften und den resultierenden Photostrom im Vergleich zu flachen CTO-Schichten wurde bestätigt. Auch für die Herstellung von CdTe-Dünnschichtsolarzellen konnten die CTO-Schichten erfolgreich eingesetzt werden. Die erreichten Effizienzen lagen jedoch lediglich im Bereich von 3 bis 3,6 %. Ein signifikanter Unterschied zwischen flachen und strukturierten Proben konnte nicht ausgemacht werden. Durch die reduzierenden Eigenschaften von Zitronensäure und Ethylenglykol gegenüber Ag+ und Cu2+ Ionen war es möglich, die Metalle in elementarer Form durch einfache thermische Behandlung des Präkursors zu erhalten. Während dieser Prozess für silberhaltige Systeme relativ einfach zu realisieren war, musste bei kupferhaltigen Proben die Bildung oxidischer Nebenphasen festgestellt werden. So war für Letzteres eine reduktive Nachbehandlung vollständig oxidierter Proben im Wasserstoffplasma zielführend und lieferte leitfähige Dünnschichten mit hohem Cu(0)-Anteil. Im Falle von Silber führte eine geeignete thermische Behandlung der Präkursorschicht zu dünnen, leitfähigen Silberschichten mit spezifischen Widerständen von ca. 6 • 10^(−8) Ohm m (Festkörper: ca.1 • 10^(−8) Ohm m). Die Übertragung des NIL-Prozesses gelang sowohl für silber- als auch kupferhaltige Systeme. Mit NIL-strukturierten Silberdünnschichten gelang so die Herstellung semitransparenter Elektroden mit spezifischen Widerständen von 2,2 • 10^(−7) Ohm m, welche in Elektrolumineszenzbauteilen verwendet wurden. Aufgrund der relativ niedrigen Temperaturen, die für die Zersetzung des Silberpräkursors nötig waren (ca. 250 ‰ ), war die Fertigung entsprechender Elektroden und Bauteile auch auf Polyimidfolien möglich. Insgesamt bleibt die Erkenntnis, dass NIL-strukturierte dünne Schichten erfolgreich in optoelektronische Bauteile integriert werden konnten. Variable Präkursorsysteme erlauben die Herstellung verschiedener Schichten und somit Anwendungen in unterschiedlichen Bauteilen. Polymere Präkursoren haben sich als geeignet für dieses Vorgehen erwiesen und können relativ einfach auf diverse oxidische Stoffsysteme übertragen werden. Gleichzeitig eignen sie sich zur Herstellung metallischer transparenter Elektroden durch NIL-Strukturierung, was insbesondere im Hinblick auf flexible Bauteile von Vorteil ist.

[pt] Nas últimas décadas a tecnologia de displays e células solares evoluiu consideravelmente. Há menos de cinco décadas atrás a tecnologia de volume (bulk) era a mais amplamente utilizada no mundo. Com o surgimento das tecnologias de dispositivos planos ocorreu uma grande revolução e, nos dias atuais, é a tecnologia dominante na área de displays e de células solares. Já a tecnologia do futuro surgiu com a descoberta dos materiais orgânicos semicondutores tornando possível a substituição dos convencionais substratos de vidro por substratos flexíveis, como os substratos poliméricos ou metálicos. Nesta tese foram desenvolvidos diferentes tipos de substratos compósitos poliméricos baseados no termoplástico comercial de alto desempenho, poli(éter imida) (PEI), e na celulose bacteriana (CB), um polímero natural e biocompatível comumente utilizado como pele artificial. Os nanocompósitos foram idealizados para aplicação como substratos flexíveis em dispositivos orgânicos. Três tipos de substratos foram estudados: nanocompósito PEI/nanotubos de carbono (CNTs); nanocompósito CB/PEI; e CB modificada por camada de dióxido de titânio dopado com alumínio (AlTiO2). Os dois primeiros substratos foram utilizados na produção de dispositivos orgânicos emissores de luz (OLEDs), enquanto o último na produção de um dispositivo fotodetector em meio aquoso – implante de retina. Os novos materiais foram caracterizados, principalmente, por suas propriedades ópticas e morfológicas, e os resultados foram utilizados para determinar suas possíveis aplicações. O nanocompósito PEI/CNT apresentou propriedades similares ao polímero puro quando produzido com baixas concentrações de CNTs. Para maiores concentrações os resultados obtidos mostraram-se inferiores aos do polímero puro. Já o nanocompósito CB/PEI apresentou propriedades comparáveis ou melhores que dos polímeros puros. Podemos destacar a grande melhoria em sua transparência óptica na região do visível, além de ter sido possível a obtenção de uma rugosidade superficial comparável à encontrada para substratos de vidro e com maior homogeneidade em relação aos substratos de PEI. Ambos substratos foram funcionalizados pela deposição de uma camada de óxido de índio-estanho (ITO), que foi utilizado como eletrodo transparente na produção dos OLEDs. A análise da funcionalização da superfície mostrou que os filmes de ITO sobre os compósitos apresentou propriedades elétricas também comparáveis aos obtidos para substratos de vidro e PEI. No caso do substrato de CB/PEI foi verificada melhor estabilidade do filme de ITO nos testes de flexão, não sendo observado variações no valor de sua resistividade mesmo após sofrer flexão de 5mm de diâmetro. Os dispositivos produzidos no substrato compósito PEI/CNT também apresentaram propriedades semelhantes às obtidas pela utilização do polímero puro. A maior eficiência atingida por ambos dispositivos flexíveis chegou a 1,45 cd/m2, ainda abaixo dos valores obtidos para os substratos de vidro – 2,15 cd/m2 no caso do substrato com ITO comercial e 2,00 cd/m2 no caso do substrato com ITO depositado. Já os dispositivos produzidos no nanocompósito CB/PEI apresentou excelente eficiência (2,50 cd/m2), sendo maior que o obtido para subtratos revestidos com ITO comercial. O substrato de CB/AlTiO2 foi idealizado para melhorar a aderência do ITO no filme de CB quando em contato com a água. O resultado obtido foi bastante satisfatório, pois, além de manter a camada de ITO aderido ao substrato, melhorou em 46 porcento sua rugosidade superficial. Essa modificação na morfologia da superfície acarretou em uma melhora significativa da resistividade elétrica do filme de ITO sobre o substrato flexível, uma redução de aproximadamente 63 porcento. Os substratos modificados foram utilizados para a produção de um dispositivo fotodetector. Os resultados obtidos apontam substratos promissores para a produção de implantes de retinas flexíveis e biocompatíveis. / [en] Over the past decades displays and solar cells technology had substantially evolved. For less than five decades ago the bulk technology was the most widely used worldwide. With the emergence of flat device technology a great revolution has occurred and, nowadays, this is the dominant technology in the field of displays and solar cells. The future technology has begun with the discovery of the organic semiconductor material which makes possible to replace conventional glass substrates for flexible substrates such as polymeric or metallic ones. In this thesis different types of polymeric composite substrates based on commercial high performance thermoplastic polyetherimide (PEI), and a natural and biocompatible polymer commonly used as artificial skin, bacterial cellulose (BC) has been developed. The above mentioned nanocomposites were developed for application as flexible substrates in organic devices. Three types of substrates were studied: PEI/carbon nanotubes (CNTs) nanocomposite; BC/PEI nanocomposite; and BC modified with an aluminum doped titanium dioxide (AlTiO2) layer. The first two substrates were used for the production of organic emitting devices (OLEDs), while the latter one was used for the production of a photodetector device in aqueous medium – retinal prosthesis. The new materials were mainly characterized by its optical and morphological properties and the results were used to determine its possible applications. PEI/CNT nanocomposite presented similar properties to the pure polymer when produced with low CNTs contents. For higher concentrations the results were inferior to those of the pure polymer. BC/PEI nanocomposite has showed comparable or better properties when compared with pure polymers. A highlight was the great improvement in their optical transparency in the visible region of electromagnetic spectrum, and the smooth surface achieved by the nanocomposite – comparable to that found for glass substrates and with better uniformity in relation to PEI substrates. Both substrates were functionalized by depositing a layer of tin doped indium oxide (ITO), which was used as a transparent electrode in the production of OLEDs. The analysis of surface functionalization showed that electrical properties of ITO films onto composites were also comparable to those obtained for glass and PEI substrates. However, BC/PEI substrate presented better ITO film stability in bending tests, showing no changes in its resistivity value even after undergoing 5 mm diameter of bending. The devices produced in the PEI/CNT composite substrate has also similar properties to those obtained by using pure polymer. The higher efficiency achieved by both flexible devices reached 1.45 cd/m2 which is still below the values obtained for the glass substrates – 2.15 cd/m2 in the case of commercial ITO substrate and 2.00 cd/m2 in the case the substrate with deposited ITO. The devices produced onto CB/PEI composite substrates showed excellent efficiency (2.50 cd/m2), a higher value than that obtained for substrates coated with commercial ITO. The CB/AlTiO2 substrate was designed to improve the adhesion of the ITO film onto BC substrate when in contact with water. The result was quite satisfactory, because in addition to maintaining the ITO layer adhered to the substrate it has a 46 percent improvement in surface roughness. This change in surface morphology resulted in a significant improvement of ITO electrical resistivity, a reduction of approximately 63 percent was observed. The modified substrates were used for production of a photodetector device and the results showed a promising substrate for production of biocompatible and flexible retinal prosthesis.

Organic electronic devices such as organic field effect transistors (OFETs), light- emitting diodes (OLEDs), resistive memory elements or organic solar cells have attracted an increasing attention in recent years due to the vision of a low-cost and large-scale production of printable electronics. Many papers published during the last decade focused on the intrinsic properties of organic conductors, semiconductors and dielectric materials. Since most of the devices consist of multilayer structures the mutual influence of the processes that take place in the particular layers are important for the functionality of the whole device. This work is aimed to contribute to the characterization and understanding of the mutual interactions of individual layers in the multilayer structures of organic devices. The main achievements of this work can be listed as: (i) Optimization of the thermal stability and dielectric properties of cyanoethylated polyvinylalcohol (CEPVA) high-k dielectric by the crosslinking reaction with the low molecular weight materials or mixing with a high Tg polymer. (ii) Finding possible phenomena in the CEPVA polymer dielectric that influence the charge carrier transport in the OFET active channel made of bis(triisopropylsilylethynyl) pentacene organic semiconductor, using a...

This paper describes the evaluation of screen printed materials fabricated with an additive manufacturing process for flexible biomedical applications. Five different conductive polymeric thick film pastes, printed on a polyimide substrate have been investigated. For the intended biocompatible applications, the cytotoxicity of the used materials was tested through adherent cell test. Furthermore, the electrical resistance, the printed structure thickness, the surface energy and roughness have been examined. Additionally, the mechanical resilience of the printed materials was tested through a bending test. During the bending the electrical resistance of printed meander structures could be monitored indicating failures. Two out of five materials were qualified as non-toxic, all of the materials are useable for flexible electronics, as they provide good electrical and mechanical properties.

<p>The recent advances in flexible piezoelectric technologies have sparked a great interest in developing multifunctional next-generation transducers and actuators that are increasingly becoming high demand for a range of challenging applications, including self-powered structural and personal health monitoring systems to flexible loudspeaker devices. </p><p>In this research, novel <i>quasi </i>1–3 piezoelectric nanocomposites are introduced with record-high piezoelectric voltage coefficients (g₃₃), reaching up to 0.709 Vm N⁻¹ (approximately 20 percent greater than the recently reported highest g₃₃ value in the literature). These materials are produced via dielectrophoretic process where both piezoelectric lead zirconate titanate (PZT) nanoparticles and graphene nanoplatelets (GNPs) are simultaneously aligned in a silicone-based polymer matrix (polydimethylsiloxane—PDMS) at a range of concentrations up to 13 vol%, leading to densely structured cone-shaped "nanocolumn forests" in the thickness direction. It is shown that the electric field induced alignment of particles not only improves the overall piezoelectric properties of the composite at relatively low filler concentrations, but also increases the transparency of the system by enabling the light to travel with little scattering or absorption in the “Z” direction through the particle depleted zones created between micro- and nano-sized columns. The details of these unique column morphologies are investigated by various off-line and on-line characterization techniques such as microcomputed tomography—microCT and real-time light transmission measurements to better understand the effect of both material (i.e., concentration) and process-based parameters (e.g., electric field, frequency) on pearl-chain formation. </p><p>To show its versatility and high-performance, the applications comprising both direct (e.g., force sensing, energy harvesting, structural and personal health monitoring) and inverse (e.g., loudspeaker) piezoelectric effect are also demonstrated and extensively characterized. </p><p>Additionally, to demonstrate the scalability of the process, large-area samples are also produced via the continuous dielectrophoretic process (utilizing a novel 44 ft long custom designed multifunctional roll-to-roll (R2R) manufacturing line), resulting in the largest single piece piezoelectric films ever reported in the literature. </p>

<p>Neuromorphic computing endeavors to develop computational systems capable of emulating the brain’s capacity to execute intricate tasks concurrently and with remarkable energy efficiency. By utilizing new bioinspired computing architectures, these systems have the potential to revolutionize high-performance computing and enable local, low-energy computing for sensors and robots. Organic and soft materials are particularly attractive for neuromorphic computing as they offer biocompatibility, low-energy switching, and excellent tunability at a relatively low cost. Additionally, organic materials provide physical flexibility, large-area fabrication, and printability.</p><p>This doctoral dissertation showcases the research conducted in fabricating a comprehensive spiking organic neuron, which serves as the fundamental constituent of a circuit system for neuromorphic computing. The major contribution of this dissertation is the development of the organic, flexible neuron composed of spiking synapses and somas utilizing ultra-low voltage organic field-effect transistors (OFETs) for information processing. The synaptic and somatic circuits are implemented using physically flexible and biocompatible organic electronics necessary to realize the Polymer Neuromorphic Circuitry. An Axon-Hillock (AH) somatic circuit was fabricated and analyzed, followed by the adaptation of a log-domain integrator (LDI) synaptic circuit and the fabrication and analysis of a differential-pair integrator (DPI). Finally, a spiking organic neuron was formed by combining two LDI synaptic circuits and one AH synaptic circuit, and its characteristics were thoroughly examined. This is the first demonstration of the fabrication of an entire neuron using solid-state organic materials over a flexible substrate with integrated complementary OFETs and capacitors.</p>

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