Multi-scale compliant structures for use as a chip-scale dry adhesive

Many insects and lizards display the amazing ability to climb and stick to just about any surface. Recent research has honed in on these systems to better understand how they work (Autumn et al., 2000, Autumn et al., 2002, Persson, 2003, Spolenak et al., 2005), particularly on how fine sub-micron hairs enhance van der Waals, or other interactions. Provided enough intimate surface contact these "weak" forces can add up to produce significant amounts of adhesion. Additionally the attractive interaction, adhesion, must be much larger than repulsive forces, due to elastic deformation, for the adhesive to be effective. To achieve this, nature has created a hierarchal structure to conform over a range of size scales (Hildebrand, 1988). In this work, microfabrication techniques are used to create a synthetic dry adhesive modeled after the fine hair adhesive motif found in nature. The artificial structure consists of a silicon dioxide platform, covered with polymeric nanorods, and supported by a single single-crystal silicon pillar. The multiscale integrated compliant structures (MICS) offer three levels of surface compliance: (1) the nanorods on the surface (also necessary for enhancing surface adhesion), (2) the fingers of the platforms, and (3) the flexibility of slendor silicon pillar supporting the platform. For the first time large arrays, 1cm × 1cm, have been batch fabricated across an entire 10 cm wafer. A new testing technique was developed using a nanoindenter to measure adhesion between the structures and a 5 mm aluminum flat punch. Results indicate improved adhesion with the integration of the nano- and micro-structures. The multi-scale structures also demonstrated improved wear characteristics over isolated nanorods.