Electronics are of ever-increasing importance in our daily lives. However, the number of devices like gadgets cannot increase endlessly because user comfort will suffer. Therefore, strategies for embedding intelligence in surroundings have been sought after in recent years. Printed electronics allow the fabrication of electrical devices on 3D shaped, soft, flexible, and even stretchable morphing surfaces, which is impossible for traditional processes. Moreover, this new electronics class can be made thin, lightweight, and cheap compared to conventional devices. Thus, they have marked a new era for applications like human machine interfaces (HMI) and IoT solutions, which interest many industries like healthcare, automotive industry, and consumer electronics.
“However, because this electronics class relies on a direct coating of the target surfaces with functional materials like conductors in liquid ink form, fabrication can become tedious on substrates that repel the coating liquids. Thus, materials with attractive electrical and mechanical properties can be overlooked because of either process-related challenges or susceptible reliability”, says Mikkonen.
Innovative prototypes by inkjet printing
In her thesis, Mikkonen studied the options for applying electrical coatings on surfaces with a water-repelling tendency. Because most device configurations need several functional layers, another aim was to investigate approaches for multilayer fabrication simply by printing. Mikkonen developed an inkjet-printable silicone ink to make soft multi-layered electronics. This ink was applied to sandwich electrical circuits isolated by a dielectric layer, and it was also used in capacitive pressure sensors that detect touch.
“Digital fabrication methods like inkjet printing are useful, especially in the early prototyping phases, because new configurations can be created simply by editing the source image of the printer. Moreover, the on-demand deposition principle reduces waste material compared to methods based on stencil or masks. Moreover, relatively inexpensive tabletop printers are readily available, which means that these methods are within reach for anyone, not just scientists or companies”, Mikkonen explains.
The process outcome will always compromise the end application requirements, chosen materials, and fabrication method. However, the findings suggest that by combining careful process optimization with a hint of creative engineering, plenty of new, conformable applications can be created even on these challenging surfaces. For example, the developed thin pressure sensors could be used in soft robots.
Mikkonen comes from Valkeakoski and is currently works at Forciot as an R&D engineer. The company develops IoT sensor solutions based on printed and stretchable electronics.
The doctoral dissertation of MSc (Tech) Riikka Mikkonen in the field of electronics titled Studies of Low Surface Energy Materials for Printed Electronics Applications will be publicly examined in the Faculty of Information Technology and Communications Sciences of Tampere University at 12 o’clock on Friday 17 June 2022 in auditorium TB109 of Tietotalo building, Korkeakoulunkatu 1, Tampere. The Opponent will be Associate Professor Wim Deferme from Hasselt University, Belgium. The Custos will be Professor Matti Mäntysalo from the Faculty of Information Technology and Communication Sciences of Tampere University.
The dissertation is available online at the http://urn.fi/URN:ISBN:978-952-03-2462-9.
Photo: Tiina Mikkonen