Fabrication of Skin-Like Sensors in Thin Polymeric Membranes

• Autor(a) principal: Fernandes, Paulo Edgar Geraldes
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/92225
• topic: Wearable devices; PDMS; Parylene C; Pressure sensors; Metals adhesion; Domínio/Área Científica::Engenharia e Tecnologia::Nanotecnologia

Recently, research in health care improved the creation of devices that accurately monitor various physiological stimuli (wearable devices) which provide better health care and help to predict possible diseases through continuous data collection. However, wearable devices are at an early stage of development and several improvements must be made, both at structural and materials level. Some examples of devices on the market such as smartwatches or fitness bands are still very bulky and the goal is to make them as small and functional as possible. This work focuses on the improvement of fabrication process steps of pressure sensors, based on micro-structured thin polymeric films of Polydimethylsiloxane (PDMS) or Parylene C, namely micro-structuration techniques and electrode deposition. To create domeshaped structures, Polystyrene (PS) microspheres were deposited by Langmuir-Blodgett (LB) process over Parylene C and then subjected to a Reactive Ion Etching (RIE) process to create the mold. Pyramidal structures were made by anisotropic etching of silicon with potassium hydroxide (KOH) to make molds. Both molds were further used to produce micro-structured PDMS films by soft lithography. Through these techniques, PDMS domes with diameters between 2.3 m and 3.0 m and heights between 1.6 m and 1.7 m, and PDMS pyramids with a size of 50 m to 100 m and a height of 34.3 m to 66.4 m were achieved. To work as a piezoresistive pressure sensor, the micro-structures must be covered with a conductive layer that will play the role of electrode. To overcome adhesion issues between PDMS and some metals, the possibility of using a thin film of Parylene C on top of PDMS was studied. The metals explored were aluminium, copper, and titanium with gold, where the latter presented better adhesion and electrical properties. The developed micro-structured films were assembled and tested as piezoresistive or capacitive pressure sensors achieving sensitivities up to -1.1 102 kPa1 and 3.1 102 kPa1 respectively.