Interconnects for Elastically Stretchable and Deformable Electronic Surfaces
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Interconnects for Elastically Stretchable and Deformable Electronic Surfaces Joyelle Jones, S.P. Lacour, and Sigurd Wagner Department of Electrical Engineering, Princeton University Princeton, NJ 08544, U.S.A. Abstract Deformable, large-area electronic surfaces are desirable for many human-machine interfaces. The goal of our research is to fabricate elastically deformable electronics by integrating electronic devices and stretchable interconnects onto a flexible substrate. The focus of this paper is the fabrication and electrical performance of the stretchable interconnects. Au was deposited onto a silicone elastomer (PDMS) and patterned to achieve a resolution of 2 µm. Two patterning techniques are presented: patterning by shadow mask and patterning by photolithography. Photolithographic patterning on PDMS is not straightforward. First, we discuss the challenges in patterning and then the morphology of lines patterned by both techniques. The electrical resistance of the Au lines under tensile strain is presented. Interconnects patterned by shadow mask remain electrically conductive up to 100 % strain. Those patterned by photolithography maintain electrical conductivity when strained up to 60 %. Introduction Elastically deformable, large area electronics are a next generation of integrated electronics. Examples include electronic muscles1, sensor skins2, and conformal displays3. Fabricating deformable electronics is challenging because semiconductor integrated circuits use rigid, stiff substrates in addition to thin active device materials which fracture at tensile strains near 1 %4. Hsu, et. al.3 presented a structure that enables the fabrication of electronic devices on a deformable substrate. Strong, brittle materials are first patterned into islands on the flexible substrate. Electronic devices can then be built on top of these rigid islands. When the substrate is strained, most of the strain occurs in the regions between the islands, thus enabling the islands – and the electronics on top of the islands – to remain intact. Because most of the strain is developed in the inter-island regions, stretchable metal interconnects are needed. The most challenging applications, such as robotic skins, are estimated to uni-axially strain the interconnects by approximately 15 %. Therefore, we aim to fabricate thin film interconnects that remain electrically conductive up to 15 % strain. Au was used as the conducting layer for the interconnects because this metal is highly conductive, and electrical contacts are easily made. Polydimethyl siloxane (PDMS) was chosen as the substrate because this elastomer is flexible and stretchable up to twice its initial length. Previous experiments have proven that interconnects patterned using shadow masks are stretchable up to 100 % strain5. However, patterns made using shadow masks are too coarse for integrated circuit electronics. Therefore, photolithographic patterning is necessary for adequate pattern resolution. Unfortunately, photolithographic patterning on PDMS is not strai
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