Gradual tuning of the terahertz passband using a square-loop metamaterial based on a W-doped VO₂ thin film

Abstract

An electrically controllable terahertz (THz) square-loop metamaterial based on tungsten (W)-doped vanadium dioxide (VO2) films was designed and evaluated. The structure acts as both the bandpass filter and micro-heater. The various W concentrated VO2 films used to integrate with the metamaterial were successfully grown through the sol-gel method. The transition temperature decreased by ∼14 K/at% and the resistance–temperature hysteresis curves broadened with higher doping concentrations. By utilizing the designed device, the transmitted THz wave can be tuned precisely, and the modulation depth can reach up to 0.72 in the 0.3–0.7 THz passband with a bias voltage below 2 V.

W Doping and Voltage Driven Metal–Insulator Transition in VO2 Nano-Films for Smart Switching Devices

“…47 In addition, the conductivity of the HT R-VO 2 was reported to decrease as W elements were doped in VO 2 . 42,48,49 It seriously deteriorates the modulation performance of doped VO 2 . The performance deterioration of the doped VO 2 remains a technique and theoretical challenge.…”

“…Kim et al evidenced that the MIT was driven by hole carriers excited by femtosecond laser pulses. , In terms of theoretical calculations, some researchers considered that the local lattice distortion caused by W dopants accelerated the phase transition from monoclinic to tetragonal structure. ,, Instead, He et al revealed that as the W-doping concentration increased, the d // orbitals in the HT R phase shifted to the higher energy level and the occupancy of d // orbitals decreased, leading to the reduction in the V–V interaction and eventually to the reduction in T MIT . In addition, the conductivity of the HT R -VO 2 was reported to decrease as W elements were doped in VO 2 . ,, It seriously deteriorates the modulation performance of doped VO 2 . The performance deterioration of the doped VO 2 remains a technique and theoretical challenge.…”

A Review of THz Modulators with Dynamic Tunable Metasurfaces

“…Furthermore, due to the hysteresis characteristic of VO 2 , the hybrid metasurface plays another important role of the THz memory device. More recently, a square-loop metamaterial based on W-doped VO 2 was reported, which realized transmission modulation with a lower transition temperature than that of pure VO 2 , while the modulation depth was lower as well [133]. In addition to the metasurface, a photonic crystal waveguide coated by a VO 2 film [134] and an undulated waveguide integrated with a VO 2 film [135] have also been reported.…”

A Band-Switchable and Tunable THz Metamaterial Based on an Etched Vanadium Dioxide Thin Film

“…It is a viable candidate for the development of THz tunable devices because it provides superior modulation and switching characteristics in the wideband THz region, owing to the rapid generation characteristics of free carriers undergoing a phase transition. Tunable metamaterials based on VO 2 offer a promising approach to manipulating THz waves due to their ease of fabrication and high tunability [21][22][23][24][25]. However, the VO 2 thin film-based variable metamaterial is difficult to implement band-changing characteristics when the device is constructed using the entire VO 2 thin film, and transmission loss is relatively large.…”