Process to print flexible e-stickers
A process developed by KAUST prints silicon-based networked sensors on to soft, sticker-like surfaces that can be attached anywhere. Pressure-sensitive ‘e-stickers’ contain all the functionality of traditional silicon circuits, but can be fabricated into complex, flexible shapes such as butterflies.
Flexible printed circuits require conventional silicon components to handle applications such as digitising analogue signals. According to the research team, such rigid modules can create hot spots on the body and increase device weight.
“We are trying to integrate all device components-sensors, data management electronics, battery, antenna-into a completely compliant system,” explained scientist Muhammad Hussain. “However, packaging these discrete modules on to soft substrates is difficult.”
Searching for potential electronic skin applications, the researchers developed a sensor containing narrow strips of aluminium foil that changes conductivity at different bending states.
The device, which could monitor a patient’s breathing patterns or activity levels, features high mobility zinc oxide nanotransistors on silicon wafers thinned down lithographically to microscale dimensions for maximum flexibility. Using 3D printing techniques, the team encapsulated the silicon chips and foils into a polymer film backed by an adhesive layer.
The researchers found a way to make the e-sticker sensors work in multiple applications. They used inkjet printing to write conductive wiring patterns on to different surfaces, such as paper or clothing. Custom-printed decals were then attached or re-adhered to each location.
“You can place a pressure-sensing decal on a tire to monitor it while driving and then peel it off and place it on your mattress to learn your sleeping patterns,” said PhD graduate Galo Torres Sevilla.
The team claim the robust performance and manufacturing potential of decal electronics could launch a number of innovative sensor deployments.
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