Modeling and fabrication of self-assembling micron-scale rollup structures

Abstract

Self-assembling micron-scale structures based on standard photolithographic and thin film deposition techniques are investigated. Differences in residual stress between successive thin film layers causes the structures to roll up when an underlying sacrificial layer is removed. The primary structure of interest was a swiss-roll structure comprised of alternating layers of metal and insulator so that the self-assembled system forms an RCL electrical circuit with a well-defined resonant frequency. So-called nanoscroll structures, comprised of two swiss-rolls attached at a common end, were the most commonly observed fabrication result and are expected to have electrical properties very similar to swiss rolls. It has been predicted that such electrical properties lead to, a negative effective magnetic permeability for a narrow frequency band, potentially in the far infrared region. These structures thus can contribute a vital component ([mu]eff < 0) necessary for developing a LHM (left-handed material). Many successful materials combinations have been demonstrated. The layers in the recommended system are (from the bottom up) silicon dioxide, chrome, gold, and chrome. The smallest rollup diameter was achieved for a system of nickel on silicon dioxide and was measured to be 2 [mu]m. Processing conditions such as film thickness and releasing etchant were also optimized. The mechanical behavior of the films was modeled using standard beam theory modified for application to thin films and predicted stresses that are comparable to those found in literature. Other applications for these rollup structures were considered, including a high-speed switching polarizer. Fold-up structures that self-assemble into origami-like shapes due

(cont.) to the same basic principles were also fabricated, though an application for them was not identified.