Scalable fabrication of tunable phase-change metasurfaces via soft-nanoimprint lithography [Invited]

Nano-photonic devices based on phase change materials are at the forefront of light management thanks to the electrically or optically tunable response. Their widespread adoption, however, is hampered by the lack of precise, reliable, and scalable fabrication techniques, restricting most demonstrations to proof-of-concept devices. Here we report on scalable approaches for the fabrication of tunable phase-change metasurfaces based on soft-nanoimprint lithography (soft-NIL). Two complementary strategies are showcased: dielectric structures are fabricated by etch-free soft-NIL and used (i) as a template for GeTe deposition or (ii) as etching masks to directly pattern the underlying phase-change material. Both methods enable the realization of centimeter-scale metasurfaces with significantly reduced fabrication complexity compared to conventional lithographic techniques. Reversible switching between melt-quenched and crystalline states is demonstrated using laser-induced phase transitions. The resulting structures exhibit pronounced optical modulation between the amorphous and crystalline states, with modulation depth values reaching up to 7 in both reflection (visible range) and transmission (near-infrared). These performances are comparable to state-of-the-art PCM metasurfaces despite the absence of precise design optimization. The proposed approach is compatible with large-area processing, flexible substrates, and solution-based materials, providing a promising route toward practical, low-cost reconfigurable photonic devices.