Publication

Gallium-Based Thin Films for Wearable Sensors and Electronic Skins

Laurent Mirko Dejace
2020
Thèse EPFL
Résumé

Integrated wearable electronics capable of providing biophysical information on complex and dynamic systems have attracted high interest in diverse fields such as healthcare, gaming and robotics. Wearable sensors can create artificial, electronic skins with human-like sensory capabilities, but also control next-generation robots based on flexible and compliant materials. One of the key challenges in wearable technology is the ability to combine the desired device functionality with a satisfactory degree of integration with the host. Gallium and gallium-based liquid metals have recently gathered attention for their excellent combination of stretchability and electrical conductivity. However, liquid metals feature complex physical and chemical properties that pose challenges to the integration of useful soft and stretchable electronics. In this thesis, different strategies were explored to pattern gallium-based thin films for wearable sensors and electronic skins. Microfabrication techniques were combined to surface engineering to form soft and stretchable liquid metal electronic conductors embedded in silicone substrates. In the first chapter I present intrinsically stretchable, biphasic solid-liquid thin film electronic conductors obtained by thermal evaporation of gallium on flat, gold pre-coated PDMS substrates. Thin (< 20 Όm), highly conductive (Rs = 0.5 Ω / sq.), stretchable (400 % strain) and durable (1 million cycles) electrical conductors were manufactured and implemented into wearable strain sensors for accurate monitoring of the finger movements of a human hand. Despite their excellent stretchability and high electrical conductivity, the thin films displayed a short functional lifetime, poorly reproducible and unstable electromechanical properties over time. Structure-property investigations attributed these limitations to the heterogeneous morphology of the thin films. In the second chapter I describe my approach to tackle the aforementioned challenges by introducing smooth and homogeneous, gallium-based thin films electronic conductors obtained by thermal evaporation of gallium on textured, gold pre-coated PDMS substrates. The surface coating and the topography of silicone substrates were engineered to form homogeneous thin films (1.5 Όm) on large-areas (> 10 cm2) with highly reliable, reproducible and stable electromechanical properties. Demonstrations included stick-on motion sensors that could reliably monitor the movements of a human hand and replicate it with a virtual model and the first integration of a sensory skin made of liquid metals with vacuum-powered soft pneumatic actuators. In the third chapter I introduce a new manufacturing process combining soft lithography, self-assembly and physical vapor deposition techniques to pattern gallium features with micron-scale lateral resolution, high surface density over large areas. The process enables a range of channel designs and geometries that can be used to form miniaturized conductors with unprecedented performance, such as micrometer wide stretchable liquid metal conductors with large form factor (= 10000), highly stretchable (100 %) and transparent (T > 89 %) electronic conductors, and miniaturized arrays with high density of capacitance for proximity sensing. In the future, the developments reported in this thesis may enable liquid-metal based devices that open up new avenues in diverse fields such as human-machine interfaces, soft robotics and healthcare.

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Concepts associés (36)
Couche mince
Une couche mince () est un revêtement dont l’épaisseur peut varier de quelques couches atomiques à une dizaine de micromètres. Ces revêtements modifient les propriétés du substrat sur lesquels ils sont déposés. Ils sont principalement utilisés : dans la fabrication de composants électroniques telles des cellules photovoltaïques en raison de leurs propriétés isolantes ou conductrices ; pour la protection d'objets afin d'améliorer les propriétés mécaniques, de résistance à l’usure, à la corrosion ou en servant de barrière thermique.
Robotique
thumb|upright=1.5|Nao, un robot humanoïde. thumb|upright=1.5|Des robots industriels au travail dans une usine. La robotique est l'ensemble des techniques permettant la conception et la réalisation de machines automatiques ou de robots. L'ATILF donne la définition suivante du robot : « il effectue, grâce à un système de commande automatique à base de microprocesseur, une tâche précise pour laquelle il a été conçu dans le domaine industriel, scientifique, militaire ou domestique ».
Technologie portable
thumb|Montres connectées Une technologie portable ou technologie mettable (de l'anglais wearable technology, appelée également habitronique) est un vêtement ou un accessoire comportant des éléments informatiques et électroniques avancés. Les technologies portables incluent notamment des textiles (chandails, gants, Hexoskin, maillots de bain connectés, pansements connectés), des lunettes (Google Glass), des montres connectées (Pebble Watch, Apple Watch) et des bijoux.
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