Synthesis and Drop-on-Demand Deposition of Graphene Derivative Inks for Flexible Thin Film Electronics

This dissertation presents methods for deposition and post-processing of Graphene-Carboxymethyl Cellulose (G-CMC) and Graphene Oxide (GO) aqueous functional inks using a custom drop-on-demand (DOD) printer to fabricate mechanically flexible, non-transparent and transparent thin film electronic devices. Thin films on flexible substrates find use in lightweight, low profile, and conformable electronic devices. Such devices can include chemical sensors, flexible RFID tags, bioelectronics circuits, lightweight electronics for space systems, and transparent electrodes for optoelectronic systems. The goal of this research project is to provide simple methods for fabrication of these devices using environmentally friendly and easy to synthesize functional inks. Therefore, two graphene based inks are utilized; GO and a novel Carboxymethyl Cellulose (CMC) functionalized aqueous dispersion of Graphene, G-CMC. Proposed functional inks are deposited on treated substrates by DOD printing. Deposited thin films were post-processed by use of a muffle furnace or a pulsed laser system. Furthermore, gold doped G-CMC films and G-Silver Nanoprism (G-AgNP) composite inks were developed to enhance film electrical properties. Inkjet printed films on glass substrates were characterized in terms of their electrical, optical, and mechanical properties. Correlations between film thickness, optical transmittance, and conductivity were investigated. It was possible to deposit homogeneous thin films at 100 nm to 2000 nm thickness. G-CMC films exhibited good scaling of conductance where thicker films had ~ 660 Ω/sq sheet resistance. Gold doped and G-AgNP composite semi-transparent films exhibited enhanced conductance with sheet resistances of ~ 700 Ω/sq at 35% transparency and ~ 374 Ω/sq at 50% transparency, respectively. Laser assisted treatment of samples was conducted to investigate two opportunities; pulsed laser thermal treatment and pulsed laser micromachining on rigid and flexible substrates. Effect of laser parameters was investigated to establish guidelines for thin film thermal treatment and micromachining Finally, novel flexible sensors and circuits were fabricated to demonstrate task driven performance of proposed materials and methods. Based on the presented work, proposed methods and functional inks show promise for fabricating simple electronic devices on flexible and rigid substrates. It is believed that presented advances may benefit industrial fields that require scalable and simple thin film fabrication methods

Design and fabrication by inkjet printing of electrodes for electromyography

Tese de mestrado integrado em Engenharia Biomédica e Biofísica, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2013A utilização de impressoras de jacto de tinta (inkjet printers) tem dado um enorme contributo na indústria eletrónica reduzindo as dimensões dos componentes e introduzindo processos de fabricação mais rápidos e menos dispendiosos. Uma das grandes vantagens deste método de fabricação é a facilidade de design dos circuitos, a deposição de materiais directamente no substrato sem haver contacto, a sobreposição de desenhos impressos e a versatilidade de materiais utilizados, tirando o maior partido das suas características. Duas formas de tirar partido das funcionalidades de uma impressora inkjet, em engenharia biomédica, é, por um lado, desenvolver circuitos elétricos desenhados especialmente para aquisição de sinais fisiológicos. Esses circuitos, aliados às capacidades da impressão por jacto de tinta, poderão resultar em eletrónica flexível com materiais com elevada biocompatibilidade, promovendo desta forma uma próxima interacção com o corpo humano. Por outro lado, as aplicações da impressora inkjet podem levar ao desenvolvimento de eletródios impressos enquadrando-os no conceito de pele eletrónica, isto é, integrar dispositivos eletrónicos utilizando características da pele humana (flexibilidade, extensibilidade e compatibilidade). Assim, o principal objectivo deste trabalho é fabricar, utilizando esta técnica, elétrodos com a capacidade de medir sinais electromiográficos dos músculos responsáveis pelo movimento da mão e dedos. A fim de utilizar as potencialidades da tecnologia inkjet, os eléctrodos devem obter medições congruentes do ponto de visto fisiológico e devem se mostrar vantajosos face aos, já convencionais, eléctrodos descartáveis. A finalidade da construção destes eléctrodos deverá preencher a carência que os eléctrodos convencionais possuem, de não serem flexíveis e de não serem utilizados durante largos períodos de tempo. As vantagens extraídas de eléctrodos impressos poderão ainda ser mais vastas não só a nível económico, pela construção de eléctrodos low-cost, mas também a nível de desempenho, biocompatibilidade e design, com o desenvolvimento de eléctrodos finos, paper-like e passiveis de acoplarem circuitos eletrónicos também impressos. O desenvolvimento do trabalho apresentou uma variedade de tarefas, com inicio na aprendizagem dos conceitos e métodos de funcionamento da impressora FujiFilm Dimatrix 2831 Materials Printer. Esta impressora, utilizada para obtenção de todos os eléctrodos e circuitos aqui referidos, possui uma tecnologia drop-on-deman coordenada por material piezoeléctrico, conseguindo uma resolução até -5 um. As voltagens induzidas a este material tem um enorme impacto na formação das gotas de tinta, e por isso a uma boa qualidade de impressão. No entanto, outros factores como a viscosidade da tinta e a tensão de superfície também desempenham importantes papeis para aumento da qualidade de impressão. As tarefas seguintes incluíram a otimização dos procedimentos para tratamento dos substratos de forma a que a deposição da tinta de prata fosse óptima. Os substratos utilizados neste trabalho foram: papel fotográfico, biocelulose e polidimetilsiloxano (PDMS). Também os métodos de impressão tiveram que ser optimizados controlando a velocidade e a direcção da deposição das gotas de tinta. Uma vez que foi apenas utilizado um tipo de tinta prata, uma dispersão de nanopartículas de prata, foi utilizada a mesma velocidade de deposição das gotas, 10 m/s com temperatura do tinteiro constante, de 30ºC. Por fim, houve necessidade de melhorar o processo de sinterização que visa a remoção do solvente e outras substâncias presentes na tinta de prata, e que tem enorme impacto na resistividade final do padrão impresso. Um bom processo de sinterização faz com que as nanopartículas de prata tenham um forte contacto entre elas, aumentando consideravelmente a conductividade do material. Para este fim, foi testada a sinterização térmica padrão e introduzida um novo método, a sinterização elétrica cuja aplicação de uma diferença de potencial permite a passagem de corrente elétrica gerando calor localmente. Para impressão de eléctrodos, os seus designs foram adaptados às características dos materiais, sendo que, por exemplo, para materiais mais flexíveis foram implementadas conexões serpenteadas entre pequenos eléctrodos. Para outros substratos, como o papel fotográfico, foi optado um design semelhante ao dos eléctrodos convencionais para obter melhor termo de comparação. Já para aplicação de sinterização elétrica, optou-se por um design que consiste num único filamento para que seja possível a aplicação de uma diferença de potencial em ambas as extremidades. Durante o aperfeiçoamento dos eléctrodos, foi elaborado uma série de estudos acerca das características dos mesmos (resistividade e impedância) e as suas medições foram comparadas com os resultados obtidos, em condições semelhantes, aos eléctrodos tipicamente utilizados em ambiente clínico. Como resultados de medições de sinais electrocardiográficos, os eléctrodos impressos em papel fotográfico mostraram-me vantajosos quanto à morfologia do traçado, pois o termo de comparação foi similar aos obtidos por eléctrodos convencionais. No estudo de sinais electromiográficos, os eléctrodos impressos em biocelulose e papel fotográfico tiveram taxas de sinal-ruído abaixo das obtidas pelos tradicionais eléctrodos de uso clínico. Ainda assim, os dados dos eléctrodos impressos podem ser utilizados para captação de sinais fisiológicos pois foi possível demonstrar a extração de informações acerca do movimento dos músculos esqueléticos e cardíaco. Contudo, não foi possível a obtenção de sinais fisiológicos utilizando eléctrodos impressos em PDMS. Devido a uma fraca adesão da tinta de prata à superfície do substrato, a tinta era removida do eléctrodo quando havia contacto entre o eléctrodo e a pele. Tarefas intermédias incluíram a impressão de pequenos circuitos eletrónicos, nomeadamente um circuito impresso cuja principal função é a leitura e tratamento (amplificação e filtragem) de sinais electrocardiográficos. Dois outros circuitos, mais simples, foram impressos: um díodo emissor de luz e um sensor de luz. Todas as pistas de condução de ambas as camadas foram impressas com prata em papel fotográfico e os componentes eletrónicos foram colados com cola de prata. A otimização deste processo poderá trazer enormes vantagens pela possibilidade de construção de circuitos eletrónicos flexíveis e finos com eléctrodos incorporados. Por fim, a última tarefa inclui processamento de sinal a qual inclui a implementação de algoritmos em ambiente MatLab para extracção de movimentos dos músculos do antebraço. Com a informação extraída por três movimentos distintos da mão foi provado que os eléctrodos impressos podem ser usados para posterior reconhecimento de padrões. A distinção dos três movimentos foi feita com sucesso, sobretudo para os eléctrodos impressos em biocelulose e para os eléctrodos de baixa resistividade em papel fotográfico. Este trabalho também abriu portas para investigações futuras em que mais substratos e tintas podem ser testadas e mais componentes podem ser integrados aos já aqui desenvolvidos. Desta forma, a tecnologia inkjet pode contribuir com a sua versatilidade para a inovação nos campos electrofisiologia e das interacções homem-máquina.Inkjet technology has advantages as a fabrication method when compared to other conventional procedures. Inkjet technology allows the deposition of several materials directly with non contact with it, mask-less and the possibility of printing over a previous printed pattern. Due its versatility of inks (conductive, polymers and organic) and substrates, direct deposition of materials with high precision (-5 um) using simple methods, this technique shows a high potential as a fabrication method. Despite the wide range of applications of inkjet printing in electronics, a lack of intend for printing devices for collecting biosignals. The subject of the work presented was the first step towards the development of a inkjet device for a close contact with skin for collecting biosignals. One way to apply the functionalities of an inkjet printer, in biomedical engineering, is developing printed electrodes introducing electronic skin concept, i.e., implement electronic devices using features of electronic skin (exibility, extensibility and compatibility). Thus, the major goal of this work was develop, using this technique, electrodes capable of measuring electromyographic signals from the forearm's muscles responsible to move hand and fingers. In order to use the potentials of inkjet technology, these electrodes must obtain congruent measurements and should prove advantageous when compared to the standard electrodes. The versatility of inkjet printing allowed to print electrodes, using a inkjet printer DMP-2831, onto substrates that included photographic paper, biocellulose and PDMS and test the performance of different designs: standard at discs, spiked, filamentary and serpentine array of small electrodes. This thesis presents the development of tasks that includes the design and choice of materials, optimization of printing and sintering procedures, printing electronic circuits and ends with signal processing. During the optimization of the electrodes measurements of resistivity and impedance were performed to understand the behavior and characteristics of them. Finally, a linear discriminant analysis was used to successfully distinguish between three hand movements

Design et développement d'un capteur acoustique imprimé.

The objective of this work was to design and fabricate a low cost resonant capacitive acoustic sensor using printing techniques. It falls within the frame of a collaborative research project named “Spinnaker”, set up by TAGSYS RFID, a French company, which has planned to integrate this sensor to improve the geolocalization of their RFID tags. This work started with the design and optimization of the sensor using finite element modeling (COMSOL) and design of experiments (DOE). This first step has enabled the identification of the optimum set of parameters and demonstrated that the output responses were in accordance with the specifications. Then, we have developed the different technological building blocks required for the fabrication of the prototypes using jointly the 2D inkjet printing technique and 3D printing method. The functionality of the sensors has been characterized using both capacitive and acoustic measurements using laser Doppler vibrometer. Experimental results showed that sensitivity and selectivity were within the specifications and in good agreement with the modeling results. Finally, we investigated the piezoelectric approach which could be an interesting option to the capacitive one. Since no inkjet printable piezoelectric ink is commercially available, stable inkjet printable polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) ink has been developed. PVDF-TrFE layers were then successfully printed and characterized. The results were quite promising, however further improvements of the ink and printing process are required before stepping towards piezoelectric based device fabrication.L’objectif de ce travail était de concevoir et réaliser par impression un capteur acoustique capacitif résonant bas coût. Il s’inscrit dans le cadre d’un projet collaboratif de recherche intitulé « Spinnaker », défini par la société Tagsys RFID qui souhaite intégrer ce capteur afin d’améliorer la géolocalisation des étiquettes RFID. Ce travail a débuté par la conception et l’optimisation du design en utilisant la simulation par éléments finis (COMSOL) ainsi que des plans d’expériences (DOE : Design of Experiment). Cette première étape a permis de déterminer les paramètres optimaux et démontrer que les performances obtenues étaient conformes aux spécifications. Nous avons ensuite développé les différentes briques technologiques nécessaires à la réalisation des prototypes en utilisant conjointement l’impression 2D par inkjet et l’impression 3D. Nous avons vérifié la fonctionnalité de ces capteurs à l’aide de mesures électriques capacitives et acoustiques par vibrométrie laser. Nous avons démontré la sélectivité en fréquence des capteurs réalisés et comparé les résultats expérimentaux à ceux obtenus par simulation. Enfin, nous avons enfin exploré la « voie piezoélectrique » qui nous semble être une alternative intéressante au principe capacitif. En l’absence d’encre piézoélectrique commerciale imprimable par jet de matière, nous avons formulé une encre imprimable à base du co-polymère PVDF-TrFE et démontré le caractère piézoélectrique des couches imprimées. Les résultats sont prometteurs mais des améliorations doivent encore être apportées à cette encre et au procédé d’impression avant de pouvoir fabriquer des premiers prototypes

Compact microscopy systems with non-conventional optical techniques

This work has been motivated by global efforts to decentralize high performance imaging systems through frugal engineering and expansion of 3D fabrication technologies. Typically, high resolution imaging systems are confined in clinical or laboratory environment due to the limited means of producing optical lenses on the demand. The use of lenses is an essential mean to achieve high resolution imaging, but conventional optical lenses are made using either polished glass or molded plastics. Both are suited for highly skilled craftsmen or factory level production. In the first part of this work, alternative low-cost lens-making process for generating high quality optical lenses with minimal operator training have been discussed. We evoked the use of liquid droplets to make lenses. This unconventional method relies on interfacial forces to generate curved droplets that if solidified can become convex-shaped lenses. To achieve this, we studied the droplet behaviour (Rayleigh-Plateau phenomenon) before creating a set of 3D printed tools to generate droplets. We measured and characterized the fabrication techniques to ensure reliability in lens fabrication on- demand at high throughput. Compact imaging requires a compact optical system and computing unit. So, in the next part of this work, we engineered a deconstructed microscope system for field-portable imaging. Still a core limitation of all optical lenses is the physical size of lens aperture – which limits their resolution performance, and optical aberrations – that limit their imaging quality performance. In the next part of this work, we investigated use of computational optics-based optimization approaches to conduct in situ characterization of aberrations that can be digitally removed. The computational approach we have used in this work is known as Fourier Ptychography (FP). It is an emerging computational microscopic technique that combines the use of synthetic aperture and iterative optimization algorithms, offering increased resolution, at full field-of-view (FOV) and aberration-removal. In using FP techniques, we have shown measurements of optical distortions from different lenses made from droplets only. We also, investigated the limitations of FP in aberration recovery on moldless lenses. In conclusion, this work presents new opportunities to engineer high resolution imaging system using modern 3D printing approaches. Our successful demonstration of FP techniques on moldless lenses will usher new additional applications in digital pathology or low-cost mobile health

Printable organic and inorganic materials for flexible electrochemical devices

Portuguese Science Foundation - project Electra PTDC/CTM/099124/2008 and the PhD grant SFRH/BD/45224. financial support: Professor E. Fortunato’s ERC 2008 Advanced Grant (INVISIBLE contract number 228144), “APPLE” FP7-NMP-2010-SME/262782-2 and “SMARTEC” FP7-ICT-2009.3.9/25820

Inkjet-printed sensors and via-enabled structures for low-cost autonomous wireless platforms

Fundamental research to implement the printed autonomous wireless sensor platform is studied in three aspects: fabrication method, material selection, and novel applications for autonomous sensing/communication. Additive fabrication processes, such as inkjet printing technology and electroless electroplating, are discussed and the additively created metal layers are characterized. Fundamentals for material characterization utilizing resonators are presented and electrical properties of flexible low-cost substrates like synthetic Teslin paper and Poly(methyl methacrylate) (PMMA) are characterized. Widely used flexible substrates for printing, such as Liquid Crystal Polymer (LCP) and Kapton (polyimide), are summarized and tabulated as well. Novel antenna-based applications for efficient and autonomous operation of wireless sensor system, such as an antenna on Artificial Magnetic Conductor (AMC) for wearable applications, an active beacon oscillator for Wireless Power Transfer (WPT), and a multiband RF energy harvester, are designed and their performances are experimentally verified. The printed RFID-enabled sensor topologies with/without RFID chip are discussed as a new sensor platform for autonomous wireless operation. Fully inkjet-printed via topology for system miniaturization and integration is proposed for the first time. Challenges, circuit modeling and experimental data are presented. Future and remaining work to implement the novel low-cost autonomous wireless sensor platform are also discussed.Ph.D

Innovative micro-NMR/MRI functionality utilizing flexible electronics and control systems

Das zentrale Thema dieser Arbeit ist die Entwicklung und Integration von flexibler Elektronik für Mikro-Magnetresonanz (MR)-Anwendungen. Zwei wichtige Anwendungen wurden in der Dissertation behandelt; eine Anwendung auf dem Gebiet der Magnetresonanztomographie (MRI) und die andere auf dem Gebiet der Kernspinresonanz (NMR). Die MRI-Anwendung konzentriert sich auf die Lösung der Sicherheits- und Zuverlässigkeitsaspekte von MR-Kathetern. Die NMR-Anwendung stellt einen neuartigen Ansatz zur Steigerung des Durchsatzes bei der NMR-Spektroskopie vor. Der erste Teil der Dissertation behandelt die verschiedenen Technologien die zur Herstellung flexibler Elektronik auf der Mikroskala entwickelt wurden. Die behandelten MR-Anwendungen erfordern die Herstellung von Induktoren, Kondensatoren und Dioden auf flexiblen Substraten. Die erste Technologie, die im Rahmen der Mikrofabrikation behandelt wird, ist das Aufbringen einer leitfähigen Startschicht auf flexiblen Substraten. Es wurden verschiedene Techniken getestet und verglichen. Die entwickelte Technologie ermöglicht die Herstellung einer mehrschichtigen leitfähigen Struktur auf einem flexiblen Substrat (50 $\mu$m Dicke), die sich zum Umwickeln eines schlanken Rohres (>0,5 mm Durchmesser) eignet. Die zweite Methode ist der Tintenstrahldruck von Kondensatoren mit hoher Dichte und niedrigem Verlustkoeffizienten. Zwei dielektrische Tinten auf Polymerbasis wurden synthetisiert, durch die Dispersion von TiO$_2$ und BaTiO$_3$ in Benzocyclobuten (BCB) Polymer. Die im Tintenstrahldruckverfahren hergestellten Kondensatoren zeigen eine relativ hohe Kapazität pro Flächeneinheit von bis zu 69 pFmm$^{-2}$ und erreichen dabei einen Qualitätsfaktor (Q) von etwa 100. Außerdem wurde eine Technik für eine tintenstrahlgedruckte gleichrichtende Schottky-Diode entwickelt. Die letzte behandelte Technologie ist die Galvanisierung der leitenden Startschichten. Die Galvanik ist eine gut erforschte Technologie und ein sehr wichtiger Prozess auf dem Gebiet der Mikrofabrikation. Sie ist jedoch in hohem Maße von der Erfahrung des Bedieners abhängig. Darüber hinaus ist eine präzise Steuerung der Galvanikleistung erforderlich, insbesondere bei der Herstellung kleiner Strukturen, wobei sich die Pulsgalvanik als ein Verfahren erwiesen hat, das ein hohes Maß an Kontrolle über die abgeschiedene Struktur bietet. In diesem Zusammenhang wurde eine hochflexible Stromquelle auf Basis einer Mikrocontroller-Einheit entwickelt, um Genauigkeit in die Erstellung optimaler Galvanikrezepte zu bringen. Die Stromquelle wurde auf Basis einer modifizierten Howland-Stromquelle (MHCS) unter Verwendung eines Hochleistungs-Operationsverstärkers (OPAMP) aufgebaut. Die Stromquelle wurde validiert und verifiziert, und ihre hohe Leistungsfähigkeit wurde durch die Durchführung einiger schwieriger Anwendungen demonstriert, von denen die wichtigste die Verbesserung der Haftung der im Tintenstrahldruckverfahren gedruckten Startschicht auf flexiblen Substraten ist. Der zweite Teil der Dissertation befasst sich mit interventioneller MRT mittels MR-Katheter. MR-Katheter haben potenziell einen erheblichen Einfluss auf den Bereich der minimalinvasiven medizinischen Eingriffe. Implantierte längliche Übertragungsleiter und Detektorspulen wirken wie eine Antenne und koppeln sich an das MR-Hochfrequenz (HF)-Sendefeld an und machen so den Katheter während des Einsatzes in einem MRT-Scanner sichtbar. Durch diese Kopplung können sich die Leiter jedoch erhitzen, was zu einer gefährlichen Erwärmung des Gewebes führt und eine breite Anwendung dieser Technologie bisher verhindert hat. Ein alternativer Ansatz besteht darin, einen Resonator an der Katheterspitze induktive mit einer Oberflächenspule außerhalb des Körpers zu koppeln. Allerdings könnte sich auch dieser Mikroresonator an der Katheterspitze während der Anregungsphase erwärmen. Außerdem ändert sich die Sichtbarkeit der Katheterspitze, wenn sich die axiale Ausrichtung des Katheters während der Bewegung ändert, und kann verloren gehen, wenn die Magnetfelder des drahtlosen Resonators und der externen Spule orthogonal sind. In diesem Beitrag wird die Abstimmkapazität des Mikrodetektors des Katheters drahtlos über eine Impulsfolgensteuerung gesteuert, die an einen HF-Abstimmkreis gesendet wird, der in eine Detektorspule integriert ist. Der integrierte Schaltkreis erzeugt Gleichstrom aus dem übertragenen HF Signal zur Steuerung der Kapazität aus der Ferne, wodurch ein intelligenter eingebetteter abstimmbarer Detektor an der Katheterspitze entsteht. Während der HF-Übertragung erfolgt die Entkopplung durch eine Feinabstimmung der Detektorbetriebsfrequenz weg von der Larmor-Frequenz. Zusätzlich wird ein neuartiges Detektordesign eingeführt, das auf zwei senkrecht ausgerichteten Mikro-Saddle-Spulen basiert, die eine konstante Sichtbarkeit des Katheters für den gesamten Bereich der axialen Ausrichtungen ohne toten Winkel gewährleisten. Das System wurde experimentell in einem 1T MRT-Scanner verifiziert. Der dritte Teil der Dissertation befasst sich mit dem Durchsatz von NMR-Spektroskopie. Flussbasierte NMR ist eine vielversprechende Technik zur Verbesserung des NMR-Durchsatzes. Eine häufige Herausforderung ist jedoch das relativ große Totvolumen im Schlauch, der den NMR-Detektor speist. In diesem Beitrag wird ein neuartiger Ansatz für vollautomatische NMR-Spektroskopie mit hohem Durchsatz und verbesserter Massensensitivität vorgestellt. Der entwickelte Ansatz wird durch die Nutzung von Mikrofluidik-Technologien in Kombination mit Dünnfilm-Mikro-NMR-Detektoren verwirklicht. Es wurde ein passender NMR-Sensor mit einem mikrofluidischen System entwickelt, das Folgendes umfasst: i) einen Mikro-Sattel-Detektor für die NMR-Spektroskopie und ii) ein Paar Durchflusssensoren, die den NMR-Detektor flankieren und an eine Mikrocontrollereinheit angeschlossen sind. Ein mikrofluidischer Schlauch wird verwendet, um eine Probenserie durch den Sondenkopf zu transportieren, die einzelnen Probenbereiche sind durch eine nicht mischbare Flüssigkeit getrennt, das System erlaubt im Prinzip eine unbegrenzte Anzahl an Proben. Das entwickelte System verfolgt die Position und Geschwindigkeit der Proben in diesem zweiphasigen Fluss und synchronisiert die NMR-Akquisition. Der entwickelte kundenspezifische Sondenkopf ist Plug-and-Play-fähig mit marktüblichen NMR-Systemen. Das System wurde erfolgreich zur Automatisierung von flussbasierten NMR-Messungen in einem 500 MHz NMR-System eingesetzt. Der entwickelte Mikro-NMR-Detektor ermöglicht hochauflösende Spektroskopie mit einer NMR-Empfindlichkeit von 2,18 nmol s$^{1/2}$ bei Betrieb der Durchflusssensoren. Die Durchflusssensoren wiesen eine hohe Empfindlichkeit bis zu einem absoluten Unterschied von 0,2 in der relativen Permittivität auf, was eine Differenzierung zwischen den meisten gängigen Lösungsmitteln ermöglichte. Es wurde gezeigt, dass eine vollautomatische NMR-Spektroskopie von neun verschiedenen 120 $\mu$L Proben innerhalb von 3,6 min oder effektiv 15,3 s pro Probe erreicht werden konnte

Inkjet printing: technique and applications for organic electronic devices

Since the discovery of the polyacetylene conductivity in 1977 by Shirakawa,MacDiarmid and Heeger, Organic Electronics has been growing and establishing for a new generation of electronic devices. On one hand, the unique properties of polymeric semiconductors and conductors, such as flexibility and transparency, allow the fabrication of low-cost devices over large area: the most common are the Organic Light Emitting Diodes (OLEDs) and the organic photovoltaic cells. On the other hand, much effort has been made to investigate new technologies and processes for the realization of high-performance organic transistors and sensors. Among them, Inkjet Printing is a promising technique which exploits all the advantages of organic materials, such as low-cost and solution processability, and allows the large-scale automated fabrication of large area devices. This thesis describes the work carried outwith a piezoelectric drop-on-demand inkjet printer, theDimatixMaterials Printer 2831. The first chapter gives an overview on Organic and Printed Electronics state-of-art, also describing the physical principles of conductivity in organic molecules. The second chapter is totally focused on the inkjet printing technique: after a brief description of the printer employed, a detailed description of the printing process, from the ink formulation to the drop deposition and drying phenomena, is presented. Moreover the materials employed are described together with the printing parameters set for achieving the best deposition condition. Chapter 3 is devoted to tactile sensing, which is the main application of the Organic Field-Effect Transistors (OFETs) in this work within the ROBOSKIN project. After an overview of inorganic tactile sensors and of the fundamentals of strain sensing in OFETs, the fabrication steps are described followed by the detailed electromechanical characterization of the various strain sensors realized. Finally, the fourth chapter describes other applications of inkjet printing developed in this work: organic diodes and photodiodes within the HYMEC project, patterned electrodes for the detection of cells electrical activity, both in vivo and in vitro, and a RFID tag antenna