Mass Manufacturing of Metasurfaces

This metasurface display can be fabricated in less than half an hour, paving the way to mass production. (Source: A*Star / OSA)

Metasurfaces are synthetic, two-dimensional materials covered in tiny indi­vidual shapes with sizes and spacings smaller than the wavelengths of visible light. These sub-wavelength structures enable scientists to precisely control the propa­gating shape, or wavefront, of light beams. As such, metasurfaces show promise for many appli­cations from high-resolution imaging and color printing to controlling light polari­zation. Mass production of meta­surfaces, however, has proven challenging, limited by the complexity of realizing such precise patterns.

Now, Ting Hu and his colleagues at A*STAR’s Institute of Micro­electronics (IME) have developed a method of building silicon-based meta­surfaces by introducing existing techniques from semi­conductor fabrication. Their new meta­surface design can produce high-resolution red-green-blue (RGB) color displays. Until now, meta­surfaces have mainly been fabricated via electron beam litho­graphy (EBL), which is not applicable to mass production, as Hu explains: “With EBL, the focused electron beam moves slowly, step by step, across the meta­surface substrate. Metasurfaces with millions – possibly billions – of elements require a very long time to be patterned via EBL. We desired a faster and more efficient way of patternation.”

Hu and the team based their technique on immersion litho­graphy, which has long been used to etch patterns on to electronic components. With multiple exposures, complex patterns can be built up. The researchers used ultra­violet-based (UV) lithography for initial patternation on to silicon substrates, followed by plasma etching to form the designs in small pixel blocks that were assembled into a 12-inch display surface. “Our UV litho­graphy tool is a scanner, which can pattern a whole 12 inch wafer with designed devices within half an hour,” says Hu. “We designed the physical dimensions of the nano-pillar arrays of the meta­surface to accurately display colors, with fantastic results, for example displaying the letters I, M and E in red, green and blue respec­tively.”

Hu and the team hope to optimize their design and improve the etching process to minimize losses induced by light scattering and defects in the nano­structure arrays. They are also making efforts to realize flat, light­weight meta-lenses and dot projectors with potential uses in facial recognition tech­nologies. (Source: AStar)

Reference: T. Hu et al.: Demonstration of color display metasurfaces via immersion lithography on a 12-inch silicon wafer, Opt. Exp. 26, 19548 (2019); DOI: 10.1364/OE.26.019548

Link: Institute of Microelectronics, Agency for Science, Technology and Research (A*STAR), Singapore

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