Encapsulation of printed and flexible electronics – A step towards real life applications

• Autor(a) principal: Peixoto, Mariana Coelho
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/162029
• topic: Encapsulation; lifetime optimization; printed and flexible electronics; sustainability; Domínio/Área Científica::Engenharia e Tecnologia::Nanotecnologia

Flexible and printed electronics have had an extensive impact on research in recent years, since there is a high demand for the pursuit of low-energy consumption production methods without vacuum or high temperature steps. Despite that, one of the obstacles yet to overcome to bring these devices to market and make them commercialized is their encapsulation. This is a key aspect as the encapsulation step aims to help devices undergo real situations, such as humidity, temperature, or mechanical stress to prevent inadequate performance and degradation. Furthermore, environmentally friendly encapsulant materials are essential when developing sustainable flexible electronic devices. The main goal of this work is to investigate encapsulant materials for flexible and printed devices, focusing on thermoelectric, thermochromic and piezoresistive sensors. Commercial plastic, polyvinyl alcohol, and ethyl cellulose were used as encapsulant materials on piezoelectric and thermoelectric devices, while fixomull transparent, microporous tape and transpore adhesives were used for thermochromic devices. The encapsulated sensors were compared to non-encapsulated ones to evaluate the encapsulation influence on the devices’ properties and lifetime optimization. For piezoresistive and thermoelectric sensors, a 4 µm wet thickness layer of ethyl cellulose showed promising properties consisting of flexibility, and water resistance. Both devices encapsulated with this green material maintained their electric characteristics after bending cycles, with only a 5% difference in response among both devices. These developments in the use of ethyl cellulose as an encapsulant are particularly encouraging and desirable for the future of printed electronics' compatibility with large-area manufacturing. As for thermochromic sensors, fixomull transparent adhesive was found to be the better encapsulant material for its transparency of 92% and adequate water molecules permeability providing a faster response when heated.