Grayscale‐patterned metal‐hydrogel‐metal microscavity for dynamic multi‐color display

Abstract

Abstract 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.