Development of materials and manufacturing processes for sustainable printed electronics
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Date
2023
Publication Type
Doctoral Thesis
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yes
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Abstract
The development of internet-of-things for wearables, point-of-care testing or packaging, as an example, has given rise to a new generation of electronics that is characterized by a short service-life and a large quantity of devices produced. Today, a significant mismatch between the possible maximum lifespan and most common service-life of such connected devices exists. The service-life is typically measured in days, as opposed to years or even decades for the lifespan. This discrepancy is generating an exponentially increasing amount of electronic waste (e-waste). Unfortunately, the recovering and recycling of this e-waste is a tedious and expensive process with most of i ending up buried or discarded in landfills, po-tentially causing health and environmental risks. To mitigate e-waste generation and its as-sociated environmental threats, new materials strategies are needed regarding electronics constituents, as well as a shift of paradigm regarding the key production metrics such as cost, industrialization and production throughput. Some of these metrics, for instance cost and throughput, have been widely investigated through the development of printed electron-ics. However, the use of sustainable or even biodegradable materials is still largely unex-plored in the field of printed electronics, and their impact on devices' performance is rarely studied.
Through the development of biodegradable materials and associated processes for printed electronics, we aim to propose an alternative to toxic materials, towards the safe disposal of e-waste. The results presented in this thesis include cellulose-based substrates and electrical-ly conductive ink developments, as well as three different devices incorporating these ele-ments. As detailed for each chapter hereunder, the focus is primarily given to cellulose ma-terials, as they are combining biodegradability, abundance and multifunctional properties.
The first chapter sheds light on the topic of cellulose and biodegradable materials for printed electronics. It gives an overview of the existing printing and processing techniques and discusses limitations and current challenges to manufacture electronics from biode-gradable materials. The second chapter clarifies the objectives and research questions of this thesis. The third chapter investigates the use of cellulose and nanocellulose for substrates in electronics. By combining nanocellulose with cellulose pulp, the electrical conductivity of printed electrodes is improved due to a lower porosity compared to specialty paper for elec-tronics. The second concept combines cellulose with polymers, resulting is a lower hygroex-pansion and, thus a limited effect on the electrical conductivity of the printed electrodes, once again compared to specialty paper for electronics. The fourth chapter describes re-search on an electrically conductive ink composed of carbon particles dispersed in an alco-hol solution of shellac. Shellac is proposed as a binder due to its hydrophobicity, as opposed to cellulose. This metal-free formulation combines carbon black and graphite flakes to max-imize electrical properties. The formulation is patented and compatible with industry-relevant patterning methods such as screen-printing and robocasting, with a maximum elec-trical conductivity of 103 S m-1. The fifth chapter presents works on electrically conductive inks based on zinc particles. Successive electrochemical and photonic flash sintering steps are used to remove the native zinc oxide layer at the particle surface and to sinter the parti-cles. With this combination of processes, printed zinc patterns can reach conductivities up to 106 S m-1 on cellulose-based substrates. The sixth chapter investigates printed capacitive humidity sensors and temperature resistive detectors composed exclusively of biodegradable materials. The performance of the sensors is compared on glass, cellulose and shellac-based substrates, reaching a sensitivity of 0.02 %RH -1. The seventh chapter presents a fully printed and disposable supercapacitor. The device is exclusively manufactured by robocasting and printed using non-toxic and renewable materials. Nanocellulose is used as a rheology modi-fier, dispersing, gelling and network forming agent; carbon is used to achieve high surface area electrodes as well as to provide electrical conductivity to the current collector; glycerol is used as plasticizer in the nanocellulose substrate and as the electrolyte solvent to achieve a temperature stable and non-toxic electrolytic gel. The eighth chapter studies zinc-air bat-teries, using zinc as a metal anode; graphite, manganese dioxide or pyrolyzed nanocellulose as cathode and paper as a biodegradable substrate. The battery is manufactured with printing techniques, which allow to create batteries of arbitrary shape and size, to reach around 3 mW and 0.8 mWh with the design proposed. In addition, the battery is water-triggered and re-mains inactive until water is provided, thereby being absorbed by the paper substrate and closing the electrochemical cell. The ninth chapter explores the use of cellulose nanofibrils to control and to tune the rheological properties of water-based inks. Two systems are pre-sented: the first one uses hydroxypropyl cellulose, carbon nanotubes and cellulose nano-fibrils to create a multi stimuli responsive color-changing material, applied in a color dis-play. The second one combines gelatin, glycerol and cellulose nanofibrils to create a soft and mechanically stable composite applied in a pneumatic actuator. Finally, the tenth chapter discusses the overall results implications and the eleventh chapter highlights remaining open questions that may give directions for future studies.
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Examiner : Niederberger, Markus J.
Examiner : Nyström, Gustav
Examiner : Spolenak, Ralph
Examiner : Kaltenbrunner, Martin
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ETH Zurich
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Subject
Sustainable electronics
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03763 - Niederberger, Markus / Niederberger, Markus