Metal ion implanted electrodes for dielectric elastomer actuators

This thesis reports on the successful use of low-energy metal ion implantation to fabricate compliant electrodes for miniaturized dielectric elastomer actuators (DEAs, also known as artificial muscles). DEAs are elastomeric actuators capable of large deformations (above 100% depending on conditions) and which require deformable electrodes. On most of the macroscale DEAs, they are made of carbon powder or grease, which can be easily applied on large uniform surfaces (cm2 to m2). This technology is not applicable to small-size DEAs which require reliable electrodes that can be patterned on a mm-to-µm scale. On the other hand, metallic thin-film deposition can be used to make patterned electrodes, but their maximum strain is limited to that of metals, i.e. 2-3%. The Microsystems for Space Technologies Laboratory (LMTS) has introduced implantation of metallic elements into soft polydimethylsiloxane (PDMS) layers by filtered cathodic vacuum arc, as a means of creating compliant electrodes on elastomers. The incoming metallic particles have an energy between 0.05-5 keV, which leads to a spatial distribution of the implanted elements between the surface of the elastomer, and a depth of 50-60 nm. The implanted atoms form nanometer-size clusters which are in contact but can slide relative to each other, hence keeping a conduction path at large strain. Titanium, palladium and gold implantations were conducted in an experimental implanter. Au-implanted electrodes exhibited the best overall performance, combining low sheet resistance (100-200 Ω/square), high maximum strain before loss of conductivity (175%), and a small impact on the Young's modulus of the PDMS on which they are created (50-100% relative increase). Small-size circular diaphragm dielectric elastomer actuators (∅1.5-3 mm) with Au-implanted electrodes were fabricated and characterized. Out of plane displacements up to 25% of the membrane's diameter were observed. This is a factor 4 increase compared to similar devices using patterned Au thin-film as electrode material, thus demonstrating the outstanding properties of metal-ion implanted layers as compliant electrodes for DEAs.