Electromagnetic Interference Shielding Property of p-Doped Graphene with Large Area and High Optical Transparency Characterized through Free-Space Measurement

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Graphene can be utilized in 5G technology millimeter-wave devices as a transparent conductive film (TCF) owing to its excellent optical transparency, robustness, flexibility, and conformability to different shapes and substrates. The sheet resistance ( R sheet ) of graphene (−750 Ω/sq) is high and must be minimized. Carrier doping can decrease the resistance of graphene, yet research on carrier-doped graphene for millimeter-wave devices remains limited. We prepared large-area samples (80 × 80 mm 2 ) of single-layer graphene (SLG) and three-layer stacked graphene (3LG) using chemical vapor deposition followed by coating with bis(trifluoromethanesulfonyl)amide (TFSA). TFSA, known for optical transparency, has a p-type doping effect on graphene. In particular, the TFSA-coated 3LG demonstrated a low sheet resistance of 115 Ω/sq while maintaining 89% optical transmission at 550 nm. Subsequently, we measured the electromagnetic interference (EMI) shielding ability in the 24–94 GHz range using the free-space (FS) method and observed an 80–90% shielding performance, depending on the operating frequency, marking the highest reported EMI shielding properties by a TCF composed solely of graphene. Finally, an equivalent circuit model of the FS measurement system was constructed, and simulation results significantly aligned with the experimental results. This study provides design guidelines for leveraging graphene as a transparent millimeter-wave control material.

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