Goals and outline of the project

The aim of this project is to fabricate micro-scale dielectric electroactive polymer actuators (DEAP actuators).

In contrast to actuators based on rigid materials such as silicon, actuators based on elastomers can have very large percentage displacements, often exceeding 100% elongation. The key to achieve large displacements is to have compliant electrodes. Large devices (artificial muscles) have electrodes made of powder or conducting grease. This is not applicable to micro-scale devices which need to have patterned electrodes. We make the electrodes by implantation of metal ions into the polymers at high doses and low energies. This has allowed us to reach the same efficiency with our mm-scale, batch fabricated devices, as with macroscopic EAPs. A list of publications can be found at the bottom of the page.

Ion Implantation to create highly compliant electrodes

The major challenge to miniaturizing artifical muscles is making electrodes that can be patterned on the micron scale, yet can sustain strains of 100% and do not significantly stiffen the very soft elastomer.

We use a 30 micron thick PDMS (polydimethylsiloxane) membrane as the active part of the device.

We have shown that Filtered Cathodic Vacuum Arc (FCVA) can be used to implant and deposit a metal film in/on the elastomer, yielding conductive electrodes that can be strained to over 50% for thousands of cycles, adding only 1 MPa to the Young's modulus of the membrane.

Young's modulus and Resistivity vs. ion dose

The plot on the right shows the Young's modulus of the implanted membrane (red x) and the surface resistivity (turquoise +) as a function of ion dose.

As the dose increases, the film becomes conductive and also more rigid. The fascinating aspect is that thanks to the nanostructure obtained by this deposition technique, the stiffness of the membrane is about 5 times less than if an equivalent layer of gold had been evaporated, and the film ca sustain up to 100% strain while remaining conductive, but only 3% strain is possible with evaporated or sputtered films.

The conductive electrodes thus made are ideal for micro-polymer actuators, because they allow the actuator to have large displacements (up to 100%), they can be patterned on the micron scale, they are stable in time, and can sustain many 10's of thousands of repeated cycles.

TEM cross-section of FCVA implanted PDMS

Preparing TEM lamella of soft elastomers is very challenging. Two ultra-cryomicrotomy techniques were successfully developed in our lab.

On the right, a TEM cross-section of an implanted PDMS membrane, showing the nanoparticles of gold resulting from a ion implantation, with dose 1.5 x10^16 ions/cm2, initial accelerating potential 2.5 keV per pulse.

The TEM cross-sections allow the microstructure to be analyzed, with the goal of linking the measured macroscopic properties (resistivity, Young's modulus) with the nanostructure.

TEM cross-sections were made for different doses and energies, and clearly show an increase in nanoparticles size with increasing dose.

Actuator performance

We have developed two types of actuators. The one shown on the right is a buckling-type actuator. Recent progress in the lab has enabled us to reach vertical displacements of nearly 25% the device diameter, as seen on he figure on the right for three different diameter membranes.

These actuators operate at faster than 1 kHz, and can generate roughly 5x larger forces than similar size electrostatic silicon actuators with air or vacuum gaps because of larger dielectric constant of the polymer and increase in area with actuation.

We have developed comprehensive performance models, allowing the actuators to be dimensioned for different applications, for instance micropumps, or steerable antennae.

Buckling mode actuator

Image of a 3 mm diameter EAP membrane with ion implanted electrodes on both sides, at 0 V and at 1000 V, with a small (120 Pa) back-pressure to promote upwards buckling.

Publications from this lab on EAPs

• Philippe Dubois et al. , "Microactuators based on ion implanted dielectric electroactive polymer membranes (EAP)," presented at Transducers 05, Seoul, Korea , June 5-9, 2005, pp.2048.
• Philippe Dubois et al., "Microactuators based on ion implanted dielectric electroactive polymer (EAP) membranes," Sensors and Actuators A 130-131, pp. 147-154, 2006.
• S. Rosset et al., "Mechanical properties of electroactive polymer microactuators with ion implanted electrodes", SPIE EAPAD conference proceedings, 2007.
• S. Rosset et al., "Ion-implanted Compliant and Patternable Electrodes for Miniaturized Dielectric Elastomer Actuators", SPIE EAPAD conference proceedings, 2008.
• S. Rosset et al, "Mechanical characterization of a dielectric elastomer microactuator with ion-implanted electrodes", Sensors and Actuators A, 144, pp 185-193, 200 .
• S. Rosset et al., "Performance characterization of miniaturized dielectric elastomer actuators fabricated using metal ion implantation," IEEE 21st conference on MEMS, 2008 .
• Ph. Dubois et al., "Voltage control of the resonance frequency of dielectric electroactive polymer (DEAP) membranes", JMEMS, vol 17 p 1072, 2008.
• M. Niklaus et al., "Microstructure of 5 keV gold-implanted polydimethysiloxane", Scripta Materialia 59, pp 893-896, 2008.
• Ph. Dubois et al., "Metal Ion Implanted Compliant Electrodes in Dielectric Electroactive Polymer (EAP) Membranes", Advances in Science and Technology, vol. 61, 2008, p.18-25 .
• S. Rosset et al., "Metal Ion Implantation for the Fabrication of Stretchable Electrodes on Elastomers", Advanced Functional Materials, vol 19, pp 470-478, 2009
• S. Rosset et al., "Large-Stroke Dielectric Elastomer Actuatros with Ion-Implanted Electrodes", JMEMS , vol 18,, num. 6, pp. 1300-1308, 2009

PhD thesis of S. Rosset

Links

The LMTS is a member of the ESNAM network (European Scientific Network for Artificial Muscles).