Mitigating Electrode-Induced Polarization Artifacts in Miniaturized Terahertz Detectors via a Ring-Shaped Electrode Design

Terahertz (THz) polarization detection provides critical insights into material properties but faces a fundamental constraint upon miniaturization: subwavelength metallic electrodes induce strong localization and distortion of the incident field, thereby convoluting the intrinsic device response with electrode-induced artifacts. Here, we overcome this limitation with a ring-shaped electrode architecture that suppresses field perturbations across a broad bandwidth from 2.0 to 5.0 THz. The resonant frequency of the ring electrode can be flexibly detuned from the target operation frequency by adjusting its inner and outer radii, while the smooth, edge-free geometry minimizes the lightning-rod effect. These design features collectively lead to a pronounced suppression of localized THz field enhancement. Numerical simulations reveal an 8.48x reduction in the local field strength compared with conventional rod-shaped electrodes. Consistent with this, experimental measurements on graphene-based detectors exhibit a 6.95x decrease in photocurrent for the ring-shaped electrode relative to the rod-shaped configuration. Moreover, the ring geometry effectively reduces the linear polarization ratio of the photocurrent from >3 to <1.4, confirming its effectiveness in mitigating electrode-induced polarization anisotropy. Our design decouples the detection response from electrode-induced artifacts, enabling compact THz detectors that preserve intrinsic signal fidelity for high-quality polarization-resolved imaging and diagnostics.

💡 Research Summary

The paper addresses a critical limitation in miniaturized terahertz (THz) detectors: sub‑wavelength metallic electrodes act as resonant antennas that strongly localize and distort the incident THz field, thereby imprinting their own polarization response onto the detector and obscuring the intrinsic material response. Conventional electrode geometries—rod, L‑shaped, and Y‑shaped—exhibit pronounced polarization dependence because of sharp edges and asymmetric layouts that generate “lightning‑rod” field enhancements, especially when the electrode dimensions become comparable to the THz wavelength (2–5 THz).

To eliminate these artifacts, the authors propose an annular (ring‑shaped) electrode architecture. The ring possesses C₄ rotational symmetry, which guarantees identical field distributions for any linear polarization angle, and its smooth, edge‑free contour prevents charge accumulation at terminations. Crucially, the inner (R_in) and outer (R_out) radii can be tuned independently, allowing the resonant frequency of the electrode to be detuned away from the operational band (centered at 2.52 THz in this work). Full‑wave finite‑element simulations on a Si/SiO₂ substrate (300 nm SiO₂) with the electrode modeled as a perfect electric conductor show that increasing R_in while keeping R_out fixed progressively red‑shifts the resonance and narrows the scattering peak. By fixing the ring width (R_out − R_in = 6 µm) and scaling both radii proportionally, the resonance can be shifted below 1 THz, effectively suppressing scattering above 2 THz to <500 µm².

The optimized geometry (R_out = 30 µm, R_in = 26 µm) yields an 8.48‑fold reduction in the mean field enhancement factor (MFEF) compared with a conventional rod electrode of 20 µm × 8 µm. This reduction directly translates into a lower localized electric field at the electrode–active‑layer interface, which is the primary source of polarization‑dependent artifacts.

Experimental validation employed monolayer graphene channels, whose intrinsic response is essentially polarization‑insensitive. Devices were fabricated with either the ring or a rod electrode, and photocurrent measurements under broadband THz illumination confirmed the simulations: the ring‑electrode device exhibited a 6.95‑fold lower photocurrent, indicating that the field localization—and thus the coupling into the graphene channel—has been dramatically suppressed. To further test the impact on polarization sensitivity, the authors patterned graphene into plasmon‑polariton atomic cavities (PPACs) that provide strong, polarization‑independent absorption. With rod electrodes, the PPAC detector displayed a linear polarization ratio (LPR) exceeding 3, evidencing strong electrode‑induced anisotropy. In contrast, the ring‑electrode PPAC reduced the LPR to below 1.4, demonstrating near‑isotropic response.

Overall, the study establishes that a ring‑shaped electrode, by virtue of its symmetry and dual‑parameter tunability, decouples the detector’s intrinsic response from electrode‑induced artifacts across a broad THz bandwidth. This design enables truly compact THz detectors capable of accurate polarization‑resolved measurements, which are essential for applications such as high‑resolution THz imaging, non‑destructive testing, biomedical diagnostics, and future 6G communication systems that rely on polarization multiplexing. The approach is compatible with standard microfabrication processes and can be readily adapted to other detector materials and frequency ranges.