| Summary: | Dynamic structural color based on tunable optical resonance plays a key role in applications including encryption visualization, camouflage and colorimetric sensing. However, the current design requires either complex growth processes of the high-quality tunable materials or complicated circuit designs. This work makes a humidity-swelling hydrogel layer for metal–insulator–metal (MIM) structure in the dynamic multi-color display. Here, polyvinyl alcohol (PVA) hydrogel structure is patterned through grayscale e-beam lithography and the controlled PVA thickness leads the programmable reflective resonance covering the entire visible range. By varying the ambient humidity between 9.8 and 90.1% RH, the reflective resonance of the structure is tailored across a wavelength range over 100 nm. Our materials platform of humidity-sensitive hydrogel resist presents a novel approach of the stepwise and reversible optical tunability for photonic devices.
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