Impact of electrode preparation on the bending of asymmetric planar electro-active polymer microstructures Florian M. Weiss *a,b , Tino Töpper a , Bekim Osmani a , Carla Winterhalter a and Bert Müller a a Biomaterials Science Center, University of Basel, c/o University Hospital, 4031 Basel, Switzerland; b Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland. ABSTRACT Compliant electrodes of microstructures have been a research topic for many years because of the increasing interest in consumer electronics, robotics, and medical applications. This interest includes electrically activated polymers (EAP), mainly applied in robotics, lens systems, haptics and foreseen in a variety of medical devices. Here, the electrodes consist of metals such as gold, graphite, conductive polymers or certain composites. The common metal electrodes have been magnetron sputtered, thermally evaporated or prepared using ion implantation. In order to compare the functionality of planar metal electrodes in EAP microstructures, we have investigated the mechanical properties of magnetron sputtered and thermally evaporated electrodes taking advantage of cantilever bending of the asymmetric, rectangular microstructures. We demonstrate that the deflection of the sputtered electrodes is up to 39 % larger than that of thermally evaporated nanometer-thin film on a single silicone film. This difference has even more impact on nanometer-thin, multi-stack, low-voltage EAP actuators. The stiffening effect of many metallic electrode layers is expected to be one of the greatest drawbacks in the multi-stack approaches, which will be even more pronounced if the elastomer layer thickness will be in the sub-micrometer range. Additionally, an improvement in voltage and strain resolution is presented, which is as low as 2 V or 5 × 10 -5 above 10 V applied. Keywords: Compliant electrodes, asymmetric planar electro active polymers, Young’s modulus, thermal evaporation, magnetron sputtering, cantilever bending, polyetheretherketone, polydimethylsiloxane. 1. INTRODUCTION Metal coatings of low weight, low cost and compliant materials gain increasing interests in areas as packaging industry and microelectronics [1-4]. Thus, metal deposition onto polymer materials has been a subject of research. Investigations concerning the bi-layer systems of relatively soft polymer bulk material and rather rigid thin-layered coatings have been published. Here, the diffusion of metals into the bulk [5-7] and barrier materials [7], the wettability [8], as well as the conductivity have been considered [1-4, 9-13]. Further, investigations on the surface reactivity, activation and modification were conducted suggesting the formation of a third interfacial metal/polymer composite layer, when subject to cold ion plasma sputtering [2, 4, 9, 10, 12, 13]. For dielectric elastomer actuators (DEA) the choice of the electrode material including the preparation is of key importance. Especially for multi-stack DEA’s compliant electrodes, which do not dominate the stiffness of the entire structure, have to be identified. The use of nanometer-thin metallic films as electrodes is a widespread approach. It is well known that the compliance of metals is usually not given and only allows for strains between 1 and 2 % [14]. There are examples of ultra-thin noble metal films on polymers including polydimethylsiloxane (PDMS), which give rise to strains well above 10 % [14]. Nevertheless, the impact of the Young’s modulus from the metal onto the effective modulus of the entire EAP structure cannot be neglected, although the electrodes are much thinner than the polymer layer. The stiffening effect is pronounced in multi-stack actuators [14, 15]. For the optimization of ultra-thin metal layer electrodes in DEA’s we hypothesize that the film preparation, for example by thermal evaporation and by magnetron sputtering, has a significant impact on the actuation of DEA-microstructures. Our instrument to evaluate this impact is based on a matured technique used in a broad range of applications [16-22] and has been introduced as a method to evaluate EAP microstructures with high resolution at low voltages [23, 24]. *florian.weiss@unibas.ch; phone 41 61 265 9618; fax 41 61 265 9699; www.bmc.unibas.ch Electroactive Polymer Actuators and Devices (EAPAD) 2014, edited by Yoseph Bar-Cohen, Proc. of SPIE Vol. 9056, 905607 · © 2014 SPIE · CCC code: 0277-786X/14/$18 · doi: 10.1117/12.2045152 Proc. of SPIE Vol. 9056 905607-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/26/2014 Terms of Use: http://spiedl.org/terms