Direct‐Write Assembly of Three‐Dimensional Photonic Crystals: Conversion of Polymer Scaffolds to Silicon Hollow‐Woodpile Structures

Abstract

Abstract : Impressive developments in silicon microfabrication are enabling new applications in photonics, microelectromechanical systems (MEMS), and biotechnology. Yet conventional Si microfabrication techniques require expensive masks and time-consuming procedures, including multiple planarization or bonding steps, to generate three-dimensional (3D) structures. In contrast, direct-write approaches, such as laser scanning and ink deposition, provide rapid, flexible routes for fabricating 3D micro-periodic structures. However, these approaches are currently limited to polymeric structures that lack the high refractive index contrast and mechanical integrity required for many applications. To take full advantage of these rapid, flexible assembly techniques, one must develop a replication (or templating) scheme that enables their structural conversion within the temperature constraints imposed by both the organic and inorganic components of the system. Here, we present a novel route for creating 3D Si hollow-woodpile structures that couples direct-write assembly of concentrated polyelectrolyte inks with a sequential silica/Si chemical vapor deposition (CVD) process. The optical properties of the 3D microperiodic woodpiles are characterized after each fabrication step. These interconnected, hollow structures may find potential application as photonic materials, low-cost MEMS, microfluidic networks for heat dissipation, and biological devices.