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.