Metallization Process for Polydimethylsiloxane (PDMS) Rubber
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1009-U06-04
Metallization process for polydimethylsiloxane (PDMS) rubber Stéphane Béfahy1,2, Sami Yunus1, Véronique Burguet1, Jean-Sébastien Heine1, Etienne Dague3, Michel Trooters2, and Patrick Bertrand1 1 PCPM, Université catholique de Louvain, Place Croix du Sud, 1A1, Louvain-la-Neuve, 1348, Belgium 2 Neurotech, Chemin du Cyclotron, 6, Louvain-la-Neuve, 1348, Belgium 3 CIFA, Université catholique de Louvain, Place Croix du Sud, 1A0, Louvain-la-Neuve, 1348, Belgium ABSTRACT A process to fabricate stretchable and adherent gold tracks on flat silicone rubber substrates is studied by X-ray photoelectron spectroscopy (XPS), static water contact angle measurement, atomic force microscopy (AFM) and scanning electron microscopy (SEM). The process involves several steps: curing flat silicone substrate; removing uncured oligomers by hexane Soxhlet extraction; pre-stretching the substrate; activating the strained silicone surface by an oxygen plasma treatment; coating the strained substrate with 5nm titanium and 80nm gold layers by e-beam evaporation; and finally releasing the sample. The plasma treatment creates a thin brittle silica-like layer that temporarily increases the substrate’s surface energy. Indeed the plasma treatment is followed by a hydrophobic recovery. As a consequence, the delay between plasma treatment and metal deposition has to be reduced as much as possible. The silica-like layer can be nicely observed after release. Its thickness is estimated to be around 20nm to 50nm. The entire process allows us to obtain stretchable metallized samples that remain conductive even after an excessive deformation leading to electrical failure. INTRODUCTION Nowadays, implantable electrodes for neurostimulation are mostly fabricated with PDMS as a substrate and platinum as conductive circuitry. Presently, the fabrication of such devices is still complex and usually consists in a mechanical assembly of preformed platinum elements on the PDMS substrate. Our work aims at developing a reliable metallization process that allows the deposition of noble metals, like platinum or gold, to be performed and that avoids mechanical assembly of preformed parts. This process should guarantee a strong adhesion between metal and PDMS and a good electrical behavior during mechanical solicitations. However, before reaching this goal, three key challenges have to be tackled. Firstly, after its preparation, PDMS rubber always contains unreacted oligomers that easily diffuse [1] and dominate the surface properties, preventing an efficient coating process [2]. Secondly, apart from the oligomer diffusion, PDMS rubber has a very low surface energy and, consequently, the PDMS surface has to be activated in order to increase the adhesion of metallic coating [3]. Thirdly, a strategy allowing the metal coating to be compliant and stretchable has to be used [4, 5, 6]. In this paper we report on our fabrication process and analytical measurements of stretchable gold conductors. With the aim to understand and optimize the physico-chemical properties r
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