In situ observations on deformation behavior and stretching-induced failure of fine pitch stretchable interconnect
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Mario Gonzalez IMEC, Kapeldreef 75, 3001, Leuven, Belgium
Frederick Bossuyt, Fabrice Axisa, and Jan Vanfleteren IMEC-Centre for Microsystems Technology, 9052 Gent-Zwijnaarde, Belgium
Ingrid De Wolf IMEC, Kapeldreef 75, 3001, Leuven, Belgium; and Department of Materials Engineering, Katholieke Universiteit Leuven, 3000 Belgium (Received 15 June 2009; accepted 29 July 2009)
Electronic devices capable of performing in extreme mechanical conditions such as stretching, bending, or twisting will improve biomedical and wearable systems. The required capabilities cannot be achieved with conventional building geometries, because of structural rigidity and lack of mechanical stretchability. In this article, a zigzag-patterned structure representing a stretchable interconnect is presented as a promising type of building block. In situ experimental observations on the deformed interconnect are correlated with numerical analysis, providing an understanding of the deformation and failure mechanisms. The experimental results demonstrate that the zigzag-patterned interconnect enables stretchability up to 60% without rupture. This stretchability is accommodated by in-plane rotation of arms and out-of-plane deformation of crests. Numerical analysis shows that the dominating failure cause is interfacial in-plane shear stress. The plastic strain concentration at the arms close to the crests, obtained by numerical simulation, agrees well with the failure location observed in the experiment.
I. INTRODUCTION
Large area deformable macroelectronics have attracted increasing attention in recent years, particularly because they cannot only withstand bending and twisting but also the most challenging deformations, such as stretching. This deformability allows the macroelectronics to be used in applications that are hard to cover by conventional semiconductor microelectronics.1,2 Therefore, various concepts have been developed in recent years to fulfill the demands of extreme deformations. For most of these concepts, thin and lightweight sheets of elastic polymers represent ideal substrates. By depositing conductive polymers or small molecule organics on top of these substrates, it is believed that flexibility and modest stretchability can be achieved. However, the main disadvantage of this concept is that the electrical performances are often limited by the material properties of the polymers or molecules used. For example, the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0447 J. Mater. Res., Vol. 24, No. 12, Dec 2009
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mobility of polymers and molecules is weaker than those composed of inorganic materials. This consideration, combined with the uncertain reliability of the organics, has recently led to interest in using hybrid systems. These hybrid systems are usually composed of inorganic-based rigid or bendable elements and an organic-stretchable substrate such as rubber. To achieve deformability, the rigid or bendable inorganic-based ele
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