Stretchable conductors: thin gold films on silicone elastomer
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U6.9.1
Stretchable conductors: thin gold films on silicone elastomer Stéphanie P. Lacour1, Sigurd Wagner1, Z. Suo2 1
Department of Electrical Engineering
Princeton University, Princeton NJ 08544, USA. 2
Division of Engineering and Applied Sciences
Harvard University, Cambridge MA 02138, USA. ABSTRACT Thin stripes of gold deposited onto elastomeric substrates can be stretched reversibly by more than 20 % while remaining electrically conducting. We are developing such stripes to serve as electrical interconnects on stretchable electronic skins. The gold layers are 25-nm to 500-nm thick. We observe two different film morphologies: the stripe is either buckled and continuous, or flat and contains micrometer-long cracks. Stretchability is correlated with the thickness and initial topography of the gold layer. Stripes thicker than 100-nm fail electrically at tensile strain of ~ 1 %, while thinner stripes remain conducting up to much larger strain. Upon stretching the buckled stripes flatten and break into islands of 1 to 100 micrometers on a side, while the initially microcracked stripes retain their micrometer scale structure. The electrical resistance of the buckled stripes is the lowest but the micro-textured stripes can be stretched more. INTRODUCTION Sensitive skin for robots and medical prostheses will be multifunctional structures where sensors and actuators are closely integrated with microelectronic circuits [1-3]. Such structures will sense physical parameters such as temperature, pressure, or flow. They will be electrically controlled, and mechanically constrained as the robot/human body moves. The skin may be stretched over elbow-like joints. There it will be stretched and relaxed many times, which imposes large cyclic mechanical deformation on the skin. Integrated circuits and MEMS technology use rigid and stiff substrates that are not adapted to flexible structures. Free-standing thin films break under tensile strain of the order of a percent. To achieve flexible and stretchable skin, cells composed of a transducer and an electronic circuit will be made as mechanically separated islands, which are fabricated on a deformable substrate that takes up most of the total strain [3]. The cells will be electrically connected with stretchable metal conductors. We recently discovered that thin gold films on an elastomeric substrate can be stretched far more than free-standing gold films, yet remain electrically conducting [2,4-6]. The metal film can be deposited either directly on the elastomeric substrate or on a stretched elastomeric substrate. In the first case, the gold stripe is either flat or it buckles spontaneously [2,4-5]. In the second case, upon release of the pre-stretched substrate, a sinusoidal surface wave forms [6].
U6.9.2
In this paper we concentrate on stretchable gold conductors prepared directly on elastomeric silicone membranes. When a thin metal film is bonded to on a compliant substrate, its mechanical fracture hence its electrical failure is suppressed or delayed [7]. We review the fabr
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