Inkjet printing has emerged from a digital graphic arts printing technology to become a versatile tool for the patterned deposition of functional materials. This thesis contributes to the research in the area of functional inkjet printing by focusing on two different topics: (i) inkjet printing of colloidal suspensions to study the principles of deposit formation and to develop deposits with photonic properties based on self-assembly, and (ii) the development of a reliable manufacturing process for all-inkjet-printed thin-film transistors, highlighting the importance of selection of materials and inks, print pattern generation, and the interplay between ink, substrate and printing conditions. (i) Colloidal suspensions containing nanospheres were applied as ink formulation in order to study the fundamental processes of layer formation and to develop structures with periodically arranged nanospheres allowing the modulation of electromagnetic waves. Evaporation-driven self-assembly was found to be the main driver for the formation of the final deposit morphology. Fine-tuning of inkjet process parameters allows the deposition of highly ordered structures of nanospheres to be arranged as monolayer, multilayer or even three-dimensional assemblies with a microscopic spherical shape. (ii) This thesis demonstrates the development of a manufacturing process for thin-film transistors based on inkjet printing. The knowledge obtained from the study with the colloidal nanospheres is used to generate homogeneous and continuous thin films that are stacked well-aligned to each other to form transistors. Industrial printheads were applied in the manufacturing process, allowing for the up-scaling of the manufacturing by printing of several thousands of devices, and thus the possibility to study the process yield as a function of printing parameters. The discrete droplet-by-droplet nature of the inkjet printing process imposes challenges on the control of printed patterns. Inkjet printing of electronic devices requires a detailed understanding about the process and all of the parameters that influence morphological or functional characteristics of the deposits, such as the selection of appropriate inks and materials, the orientation of the print pattern layout to the deposition process and the reliability of the inkjet process.

Inkjet printing has emerged from a digital graphic arts printing technology to become a versatile tool for the patterned deposition of functional materials. This thesis contributes to the research in the area of functional inkjet printing by focusing on two different topics: (i) inkjet printing of colloidal suspensions to study the principles of deposit formation and to develop deposits with photonic properties based on self-assembly, and (ii) the development of a reliable manufacturing process for all-inkjet-printed thin-film transistors, highlighting the importance of selection of materials and inks, print pattern generation, and the interplay between ink, substrate and printing conditions. (i) Colloidal suspensions containing nanospheres were applied as ink formulation in order to study the fundamental processes of layer formation and to develop structures with periodically arranged nanospheres allowing the modulation of electromagnetic waves. Evaporation-driven self-assembly was found to be the main driver for the formation of the final deposit morphology. Fine-tuning of inkjet process parameters allows the deposition of highly ordered structures of nanospheres to be arranged as monolayer, multilayer or even three-dimensional assemblies with a microscopic spherical shape. (ii) This thesis demonstrates the development of a manufacturing process for thin-film transistors based on inkjet printing. The knowledge obtained from the study with the colloidal nanospheres is used to generate homogeneous and continuous thin films that are stacked well-aligned to each other to form transistors. Industrial printheads were applied in the manufacturing process, allowing for the up-scaling of the manufacturing by printing of several thousands of devices, and thus the possibility to study the process yield as a function of printing parameters. The discrete droplet-by-droplet nature of the inkjet printing process imposes challenges on the control of printed patterns. Inkjet printing of electronic devices requires a detailed understanding about the process and all of the parameters that influence morphological or functional characteristics of the deposits, such as the selection of appropriate inks and materials, the orientation of the print pattern layout to the deposition process and the reliability of the inkjet process.:Bibliography II Abstract III Preface and acknowledgements IV On the major results and novelty of the thesis VII Table of contents VIII List of abbreviations and symbols X List of figures XII List of tables XX 1 Introduction 1 2 Fundamentals 6 2.1 Inkjet printing – an overview 6 2.2 Piezoelectric inkjet technology and a historical overview of inkjet printing 10 2.3 Pattern and film formation in inkjet printing under the scheme of self-assembly 20 2.4 Inkjet printing of colloidal nanospheres 27 2.5 Spherical colloidal assemblies 29 2.6 All-inkjet-printed thin film transistors 31 3 Experimental section 35 3.1 Inkjet printing systems and accessories 35 3.2 Inks and substrates 38 3.3 Print patterns 43 3.4 Post-processing 46 3.5 Optical, morphological and functional characterization 47 4 Inkjet printing of colloidal nanospheres: Evaporation-driven self-assembly based on ink-substrate interaction 49 4.1 Single droplet deposit morphology: Interaction of substrate and ink 49 4.2 Optical properties of inkjet-printed single droplet monolayers and multilayers 54 5 Inkjet printing of colloidal nanospheres: Evaporation-driven self-assembly of SCAs independent on substrate properties 58 5.1 Inkjet printing of spherical colloidal assemblies and their identification 58 5.2 Fine-tuning of the waveform applied to the printhead 60 5.3 Interaction of substrate and ink 66 5.4 Structures, morphologies and materials of SCAs 68 5.5 Optical properties of SCAs 76 6 Inkjet printing of TFTs: Process development and process reliability 80 6.1 Influence of print layout design 80 6.2 Selection of materials and inks 91 6.3 Manufacturing workflow and electrical TFT parameters 108 6.4 Manufacturing yields and failure origins 113 7 Summary and conclusion 124 References 127 Documentation of authorship and contribution of third persons 149 List of publications 151 APPENDIX A Formation of colloidal hemispheres on hydrophobic PTFE substrates 161 APPENDIX B Inkjet-printed higher-order cluster with N < 100 using BL280 162 APPENDIX C Inkjet-printed SCAs based on BS305 with similar sizes and inkjet-printed SCA based on PSC221 163 APPENDIX D Microreflectance spectra of SCAs and the processing of the spectra using the Savitzky-Golay filter with a second-order polynomial and a moving window of 100 data points 164 APPENDIX E Waveform, drop ejection and photographs of the printed patterns of Sun Chemical EMD5603 and UTDots UTDAgIJ1 165 APPENDIX F Smoothening of profiles obtained by profilometry of EMD5603 and UTDAgIJ1 and dependency of print resolution of layer height 166 APPENDIX G Percentage of area increase based on a 4 mm x 4 mm digital print pattern using the ink Harima NPS-JL and influence of print resolution and post-treatment temperature on sheets resistance 168 APPENDIX H Cross-sectional view of a TFT stack printed with the dielectric Sun Chemical EMD6415 that shows high layer thickness due to ink contraction after the deposition as presented in Figure 46 169 APPENDIX I Influence of printing parameters on the dielectric layer applied in the TFT 170 APPENDIX J Reduction of channel length by decreasing the S-D electrode channel length in the print pattern layout 171

Les assemblages colloïdaux représentent une nouvelle piste très prometteuse dans le domaine de l'ingénierie tissulaire. Idéalement, ce type d'assemblage permet l'obtention de matériaux injectables et gélifiants sur le site lésionnel, favorisant par la suite le développement de néo-tissus viables. Ce travail porte sur la formation de tels assemblages à base de chitosane et de poly(acide lactique) (PLA). Deux types d'assemblages ont été conçus et étudiés dans ce travail. Dans une première approche, le mélange de particules anioniques de poly (acide lactique) (PLA) avec du chitosane en solution faiblement acide conduit à la formation de « gels composites », résultant des interactions colloïde-polymère. Des analyses rhéologiques et de diffusion des rayons X aux petits angles ont permit de mettre en évidence le mode de formation et l'influence de plusieurs paramètres sur les propriétés finales de ces gels. Notamment, ils présentent des propriétés rhéofluidifiantes et un caractère réversible, c'est-à-dire que le gel peut se reformer après déstructuration mécanique. Le second type d'assemblage résulte du mélange de particules anioniques de PLA et de nanogels cationiques de chitosane, conduisant à la formation de « gels colloïdaux », par interactions colloïde-colloïde. L'influence de plusieurs facteurs sur la formation et les propriétés de ces gels a également été étudiée par mesures rhéologiques. Notre étude s'est notamment orientée sur la caractérisation et la stabilité des hydrogels physiques de chitosane sous forme colloïdale, ainsi que sur l'optimisation de leur cohésion / Colloidal assemblies may be a promising pathway to obtain injectable scaffolds favoring the development of neo-tissue in regenerative medicine. This work investigates the formation of such assemblies composed of chitosan, soluble or in suspension (nano-hydrogel), and poly(lactic acid) (PLA) nanoparticles. Two types of assemblies are studied. As a first approach, mixing negatively charged PLA particles and chitosan solution leads to the formation of “composite gels”, based on colloidpolymer interactions. Rheological and Small Angle X-Ray Scattering measurements highlighted the formation process and the influence of various parameters on final properties of these gels, which features shear-thinning and reversibility behavior, that is, the capacity to gel again after yielding. PLA nanoparticles could also be mixed with cationic chitosan nanoparticles, which are crosslinker free nano-hydrogels, leading to the formation of “colloidal gels”, based on colloid-colloid interactions. Influence of various parameters on gel synthesis and properties are investigated through rheological measurements. The study also focuses on the characterization and control of the morphological and cohesion properties of chitosan nanogel