Inkjet printed stretchable electrodes for tunable focus lens

A soft tunable lens with integrated dielectric elastomer actuator (DEA) can act like an eye lens to tune the distance of focal point. It has potentials to replace multiple hard lenses for cameras' autofocus. The tunable range of focus depends on the voltage-induced deformation of DEA, which is a soft capacitor with compliant electrodes of carbon-grease or graphite powder. These grease or particulate electrodes for DEAs are not stable and difficult to be patterned for miniaturized tunable lens. Metal film electrodes, which are more stable and conductive, are not common for DEAs because their high stiffness impedes dielectric deformation. Patterned thin-film metal is expected to make stable and stretchable electrodes for DEA. The patterning techniques, such as lithography using a hard mask or pad printing using a stamp, are good for batch process for an electrode design, but preparation of mask and stamp takes time and slows the design cycle. Inkjet printing technology is a facile and versatile method to print different patterns of metal electrodes. Inkjet printing of metallic electrodes is suitable for electroactive polymeric tunable lenses because this process is low-temperature, non-hazardous, and compatible with wide range of elastomer materials. In this article we demonstrate inkjet printing of Silver Nano-particles thin films on a soft 3M VHB substrate as part of DEA electrode. Circular electrodes are printed to make a DEA for tunable lens. Upon 4.5KV activation, the circular DEA was able to produce up to 10% area actuation. In comparison, a DEA using carbon grease electrodes demonstrated 190% area actuation. This low performance of inkjet-printed silver electrode is attributed to the high stiffness of silver thin film electrode. Line patterns of silver electrode obviously increase in the electrode stretchability. However, the silver line electrode cracks at 6.5% areal strain and thus limit the DEA's further actuation.