We have designed, fabricated, and tested large sheets of photonic bandgap (PBG) material that have a "cubic array of cubes" structure. Structures with bandgaps in two wavebands have been fabricated: the thermal IR (8-12μm) and the visible/near IR (0.6-2.5μm). A thermal-IR PBG can modify the emission properties of structures for temperature control. Visible/near-IR PBGs can be used in photonic circuits and can improve illumination efficiency.
The LIGA microfabrication technique offers a unique method for fabricating 3-dimensional photonic lattices based on the Iowa State "logpile" structure. These structures represent the  orientation of the  logpile structures previously demonstrated by Sandia National Laboratories. The novelty to this approach is the single step process that does not require any alignment. The mask and substrate are fixed to one another and exposed twice from different angles using a synchrotron light source. The first exposure patterns the resist at an angle of 45 degrees normal to the substrate with a rotation of 8 degrees. The second exposure requires a 180 degree rotation about the normal of the mask and substrate. The resulting pattern is a vertically oriented logpile pattern that is rotated slightly off axis. The exposed PMMA is developed in a single step to produce an inverse lattice structure. This mold is filled with electroplated gold and stripped away to create a usable gold photonic crystal. Tilted logpiles demonstrate band characteristics very similar to those observed from  logpiles. Reflectivity tests show a band edge around 5 μm and compare well with numerical simulations.
This paper describes improvements that enable engineers to create three-dimensional MEMS in a variety of materials. It also provides a means for selectively adding three-dimensional, high aspect ratio features to pre-existing PMMA micro molds for subsequent LIGA processing. This complimentary method involves in situ construction of three-dimensional micro molds in a stand-alone configuration or directly adjacent to features formed by x-ray lithography. Three-dimensional micro molds are created by micro stereolithography (MSL), an additive rapid prototyping technology. Alternatively, three-dimensional features may be added by direct femtosecond laser micro machining. Parameters for optimal femtosecond laser micro machining of PMMA at 800 nanometers are presented. The technical discussion also includes strategies for enhancements in the context of material selection and post-process surface finish. This approach may lead to practical, cost-effective 3-D MEMS with the surface finish and throughput advantages of x-ray lithography. Accurate three-dimensional metal microstructures are demonstrated. Challenges remain in process planning for micro stereolithography and development of buried features following femtosecond laser micro machining.