Stretchability of complex patterns of thin metal conductors on elastomeric skin
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U12.10.1
Stretchability of complex patterns of thin metal conductors on elastomeric skin
Stéphanie P. Lacour and Sigurd Wagner Department of Electrical Engineering Princeton University, Princeton NJ 08544, USA. ABSTRACT We have previously shown that 25nm thick gold stripes on 1mm thick silicone membrane retain electrical conduction when stretched up to 100% along their long dimension. To function as electrical interconnects in conformable integrated circuits, the metallization must be stretchable in arbitrary directions. Therefore we have made and tested the mechanical and electrical properties of complex conductor patterns including X and Y oriented lines and cross junctions. We find that the metal patterns continue to conduct under uniaxial stretching in the X or Y direction and under radial, biaxial stretching. INTRODUCTION The success of thin film electronics in flat panel displays is encouraging the exploration of conformable electronic systems that are distributed over large and deformable surfaces. A variety of potential uses have been demonstrated, including smart textiles [1] and rollable displays [2]. Stretchable electronics need materials that can be deformed, but most device materials, inorganic or organic, tend to break when stretched. We have demonstrated that thin metallic conductors patterned on elastomeric membrane can be stretched by up to 100% without electrical failure [3-5]; recently, similar experiments have been reported by other groups [6,7]. This opens the way to elastic electronic circuits fabricated on elastomeric substrates as matrices of rigid device platforms interconnected with metal conductors that will deform with the substrate [8]. Most of the mechanical deformation is taken up by the elastomer substrate exposed between stiff device platforms. Metallic stretchable interconnects guarantee the mechanical integrity and electrical functionality of the circuit. There are various ways to deform and shape a surface: rolling or bending over developable surfaces, e.g., cylinder or cone, inflating to a dome, and, uni-axial or biaxial stretching. Bending usually produces small and elastic strain, which is a function of the thickness of film and substrate and of radius of curvature. Inflation to a hemisphere requires large, plastic deformation of the substrate. This deformation easily can become larger than the critical fracture strain of the film. Stretching generates large and elastic strains up to tens of percent. We have already shown that metallic conductors made of thin gold films on elastomeric membrane can be bent [9] and uni-axially stretched [3-5,9-11]. Here we describe their 1D, uni-axial (x), stretching with attention to their simultaneous in-plane (y) contraction, and their 2D, biaxial, radial, stretching. 1D and 2D stretching are studied with two different apparatuses. We report electrical conduction and surface morphology.
U12.10.2
1D and 2D STRETCHING The membrane studied in the 1D stretching device is rectangular, with one end fixed while the opposite end is stretched [4].
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