Electronic skin: architecture and components
Wagner, Lacour, Jones, Hsu, Sturm, Li, Suo, Physica E 25 (2004), 326-334
Flexible electronics have a host of potential applications ranging from medicine (e.g. prosthetic skin) to flexible electronic devices. The materials traditionally used for the fabrication of circuits, such as silicon, are stiff. Flexible counterparts may be possible with the combination of an elastomer substrate on which conducting metal connections can be deposited; the system may then sustain considerable stress. The question the authors address is how subjecting a flexible substrate to strain affects the electrical properties of the deposited conductors.
Their initial approach to fabricating these systems was based on the creation of wavy metal films on elastomer substrates which could be stretched reversibly. The waviness of the films was caused by internal stresses within the metal-elastomer system, in a way that they have modelled in a previous publication . Interestingly, such wavy films are not only stretchable, but they maintain their conductivity while stretched. In order to have more control over the orientation and lengthscale of the film features, and thus over the stretchability of the conducting film, the authors have also deposited metal films on stretched PDMS substrates. When the substrates are let to relax, the superimposed films buckle in a way that correlates with the initial conditions of the substrate: peaks and troughs form along the axis of initial expansion. Furthermore, the existence of a substrate on which the metal is bonded makes the films more robust to deformations.
 S.P.Lacour, S.Wagner, Z.Huang, Z.Suo, Mater.Res.Soc.Proc. 736 (2002) D4.8.1