Mid‐Infrared Reflectance Modulator Based on a Graphene CMOS‐Compatible Metasurface

Abstract Optical modulators based on tunable graphene‐metal hybrid metasurfaces have emerged as promising optoelectronic devices due to their high speed and efficient modulation that is controllable through electrostatic gating. In particular, optical modulation in the mid‐infrared region has attracted considerable interest for applications in biosensing, imaging, communication, and computing. However, the scalability of metasurfaces poses a challenge as typical fabrication pathways are not compatible with complementary metal‐oxide‐semiconductor (CMOS) technology. In this work, a tunable graphene‐metasurface absorber is presented that integrates a metal‐dielectric‐metal optical cavity with a graphene layer. Stable performance in ambient conditions is achieved by the incorporation of an ultrathin Al₂O₃ capping layer. This barrier layer prevents direct contact between the metallic antennas and the graphene layer, which results in a large on/off ratio. For a gold metasurface, the creation of an optical cavity strongly enhances the modulation depth of the reflectance between 7 µm to 8 µm from 11% to 47%. By replacing gold with aluminum, a cost‐effective material employed in foundry processes, a comparable maximum modulation depth of 49% is obtained. These results open a new pathway for the integration of tunable graphene–metal hybrid metasurfaces with CMOS‐compatible technologies, facilitating a scalable production of mid‐infrared modulators.