Journal of Manufacturing Processes 22 (2016) 21–25 Contents lists available at ScienceDirect Journal of Manufacturing Processes j ourna l h o me page: www.elsevier.com/locate/manpro Technical note Photoresist-less patterning of silicone substrates for thick ﬁlm deposition Silvana Mergen a,b,c , Benjamin Johnston d , Robert Cowan a,b , Carrie Newbold a,b,c,∗ a HEARing CRC, 550 Swanston St, University of Melbourne, 3010, Australia b Department of Audiology and Speech Pathology, 550 Swanston St, University of Melbourne, 3010, Australia c Department of Otolaryngology, University of Melbourne, 32 Gisborne St, East Melbourne 3002, Australia d MQ Photonics Research Centre, Department of Physics and Astronomy, Macquarie University, 2109, Australia a r t i c l e i n f o Article history: Received 21 July 2015 Received in revised form 11 January 2016 Accepted 18 January 2016 Keywords: Thick ﬁlm Sputter deposition Platinum electrodes Microelectrode arrays Photoresist-less manufacturing Shadow masks a b s t r a c t Traditionally, fabrication processes to produce microelectrode arrays for neural stimulating electrodes have employed photolithography and a photoresist layer to produce a pattern on a substrate which subsequently has a metal layer deposited. The deposited metal layer is then used to create stimulating electrodes that will ultimately be in close contact with neural tissue. While the process enables accurate fabrication at a reasonable cost, the use of photoresist in the process presents a number of issues. Pho- toresist is a contamination risk with the potential for chemicals to be absorbed into the silicone, which will then subsequently be in close proximity to neural structures, introducing a risk of toxicity. In addi- tion, due to the use of ﬂexible substrates such as silicone elastomer, patterning of ﬁlms greater than 1 m thick can be difﬁcult. Whilst an obvious solution would be to avoid using photoresist in the fabrication process, few alternatives have been systematically investigated. We investigated use of shadow masks fabricated from glass, brass and silicone elastomer, and exploitation of the natural tackiness of the silicone sub- strate for mask adhesion. All three mask materials attached well to silicone, but each presented differing degrees of difﬁculty during alignment and mask removal. Subsequently, thin gold ﬁlms (∼20 nm) and thick platinum ﬁlms (∼8 m) were deposited on the silicone substrates using the shadow masks. We discuss the mask fabrication, pattern deﬁnition, the difﬁculties which arose, and the beneﬁts of using shadow masks for the fabrication of medical devices. © 2016 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. 1. Introduction Patterning techniques that utilise photoresist and photolitho- graphy are common practices used in microelectromechanical systems (MEMS) processing. Using this process, micron-size fea- tures can be produced on silicon wafers and, as such, the technology is frequently used to fabricate neural recording and stimulating electrodes. Photolithography patterning involves high costs due to a num- ber of factors: preparation of the masks; availability of the photolithography equipment; multiple processing steps includ- ing application of the photoresist application, a bake, UV or X-ray exposure and development and removal [1]. In addition, major Abbreviations: MAE, microelectrode array; MEMS, microelectromechanical sys- tems. ∗ Corresponding author. Tel.: +61 399298428. E-mail address: cnewbold@hearingcrc.org (C. Newbold). difﬁculties can arise when thicker ﬁlms than traditional thin ﬁlms are required for patterned deposition of polymer substrates. For example, a 6–7 m photoresist layer is required to pattern a 100 nm thick platinum ﬁlm with good resolution. In the case of a sputtered ﬁlm of several microns being required, the associated thickness increase of the photoresist layer can create difﬁculties in coating and patterning. Although there are photoresist formulations avail- able for producing greater thicknesses, these photoresists cannot easily be removed [16]. In addition, the chemicals and radiation involved with the lithography process can result in swelling or in extreme cases, dissolution of the polymer substrate [2]. Silicone elastomer is a biocompatible material commonly used in neural prostheses such as cochlear implants. It is chemically resistant and has been used previously in combination with pho- toresist to fabricate electrodes for use in neural implants [3–6]. In applications such as cochlear implants and other neural devices, these electrodes are in close proximity to neural tissues, and may remain in contact for extended periods up to 70 years. Photore- sist is toxic to neural tissue, and long-term leaching of even small http://dx.doi.org/10.1016/j.jmapro.2016.01.005 1526-6125/© 2016 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.