Universal Anisotropically Conductive Nano-adhesive of PDMS Oligomers
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Universal Anisotropically Conductive Nano-adhesive of PDMS Oligomers Yuzhe Ding1, Shaun Garland1, Michael Howland2, Alexander Revzin2 and Tingrui Pan1 1 Micro-Nano Innovations (MiNI) Laboratory, Department of Biomedical Engineering, University of California Davis, Davis, CA, 95616, U.S.A. 2 Department of Biomedical Engineering, University of California Davis, Davis, CA, 95616, U.S.A. ABSTRACT A nanopatternable oligomeric PDMS layer has been first verified as a nano-adhesive for its intrinsic transferability and universal adhesiveness. Utilizing the well-established PDMS surface modification and bonding techniques, we have been able to form irreversible bonding between a wide range of substrate pairs, representing ones within and across different material categories, including metals, ceramics, thermoset, and thermoplastic polymers. The anisotropic conductivity of the PDMS oligomer nano-adhesive has been investigated, which allows specific and excellent directional conductivity between bonded electrodes without risk of electrical shorts across different contacts. INTRODUCTION Joining heterogeneous surfaces has been a pressing issue in development of micronanoengineered systems, where multiple processing constraints have to be taken into consideration as a whole, e.g., specific material sensitivities to mechanical, thermal, and/or chemical treatment. [1] Recently, an intriguing mass transfer process has been discovered accompanying the micro-contact printing process, that is, a nanometer-thick PDMS oligomer layer has been deposited on the imprinted substrates with excellent adhesion. [2] In this paper, we utilize the intrinsic transferrable and adhesive natures of the PDMS oligomers as a universal, interfacial nano-adhesive to bond a group of micro-nanofabrication materials within and across different categories (e.g. metals, ceramics, thermoset and thermoplastic polymers). The PDMS oligomer nano-adhesive is featured with several unique advantages, including: (a) materialindependent universal applicability with high bonding strength (up to 400kPa), (b) ultrathin nanopatternable layer of PDMS oligomer without potential structural deformation and blockage, (c) simple and reliable operation process without sophisticated thermal or chemical treatments, (d) excellent anisotropic electrical conductivity in the thickness direction. EXPERIMENT The initial step started with modification of the substrate surfaces for PDMS oligomer transfer. Oxygen plasma treatment was applied to introduce hydroxyl groups on the targeted surfaces, followed by imprinting of oligomers from planar or micro-nanostructured PDMS stamps, during which the oligomer transfer happened only upon physical contact. Subsequently, a second oxygen plasma (at 90 W for 30 s) was applied to both PDMS oligomer-coated
substrates. Finally, two substrates were brought into contact using capillary forces from DI water added in between [3]. The thickness of micro-nanopatterned PDMS oligomer is measured by an iElli2000 imaging ellipsometer (Nanofilm, Germany) and atomic
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