Microfabrication of complex and reconfigurable structures

Laser origami process generates self-folding 3D microstructures on plastic membranes through the controlled out-of-plane folding of 2D patterns of arbitrary design

Software & Information Technology

Examples of the process using 25 μm thick polyimide foil from which the 2D patterns were laser cut and onto which, silver nano ink pads were laser printed to serve as actuation elements. Actuation takes place only for those elements that have a nano ink pad. By adjusting the amount and distribution of the deposited silver nano ink, it is possible to precisely and reproducibly control the folding angle of the out-of-plane actuation as shown.

The ability to manufacture and assemble tiny yet complex 3D systems is attracting commercial interest as electronic device form factors shrink and the push for more features and functionality increases. However, most of the work to date still utilizes the traditional photolithography patterning and etching processes designed for the semiconductor industry where a 2D structure is first fabricated, followed by some alternative technique for bringing these structures out-of-plane. The use of photolithography to build these 3D devices constrains them to wafer-like form factors which exclude flexible large area sheets or membranes. Further, the deposition and etching processing steps limit the choice of materials to only those that can withstand the required temperatures and etching conditions. These and other challenges are leading to a move away from photolithographic techniques.

One new technique developed by Navy scientists for the fabrication of 3D microstructures and micro-assemblies uses low-temperature substrates such as polymer films. This process relies on the use of laser micromachining of 2D patterns, followed by laser transfer, at a specific region on the patterns, of a layer of actuating material, and then laser activation of the actuating material, causing it to shrink, resulting in the folding out-of-plane of the pattern and generation of 3D micro-assemblies.

This non-lithographic and non-silicon-based process is capable of micro-fabricating 3D structures of arbitrary shape and geometric complexity on low-temperature substrates. The concept allows for the realization of arrays of 3D microstructures, where in principle, each microstructure is pre-programmed with the information required to build itself, and ready to be activated – fold out-of-plane – individually or in batch form. Application of these folded micro-assemblies offers a unique and novel way to develop highly complex yet reconfigurable arrays of 3D microstructures with novel electrical, optical, and mechanical properties.

Perhaps the most important potential application of the process is in the area of artificial electromagnetic materials. These would include meta-materials, frequency selective surfaces, negative index materials, and radar absorbing materials, to name just a few. The process is capable of fabricating 3D structures with dimensions that are sub-wavelength for a large portion of the EM spectrum. For example, sub-wavelength structures arranged in periodic arrays result in unique electromagnetic behavior, and manipulating these sub-wavelength structures gives rise to surfaces with very specific electromagnetic properties.

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