The production of surface relief gratings plays a crucial role in nano-structuring today. For augmented reality (AR) glasses and mixed reality (MR) glasses, surface relief gratings are the in-couplers and out-couplers of the light into the near eye displays. To get a good coupling effect, a high brightness and a high efficiency, these gratings need to be tilted, so the structure is slanted. For advanced grating designs, you also need a variation in the tilt-angle and maybe even in the etch depth.
In his presentation, Matthias Nestler will introduce techniques to create surface relief gratings with constant or with varying slant angle. A common way to produce these structures is ion beam etching. In this process, the ion beam source extracts an ion beam in which the substrate can be tilted to etch slant angles as flat as 60 degrees. On top of the substrate material is a chromium mask, which defines the structures of the grating. These gratings can either be etched directly into the glass or into a master (stamp) that is used to produce the display, e. g. by nanoimprint lithography.
To produce a grating with constant slant angle and etching depth over the whole optical substrate, we recommend Reactive Ion Beam Etching (RIBE). For varying slant angles and different etching depths across the substrate, you need the newly developed technology of Reactive Ion Beam Trimming (RIBT). Thereby, a focused broad ion beam etches over the material, while substrate tilt and etching dwell time is adjustable during the process. So, the slant angle and depth can be controlled within the grating.
Find out more information about RIBE, RIBT and surface relief gratings in the video of Matthias Nestler’s presentation at the 48th International Conference on Micro and Nano Engineering - Eurosensors
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