Electrically Activated W-Doped VO₂ Films for Reliable, Large-Area, Broadband THz Wave Modulators

THz amplitude modulators and switches are considered to be the main building blocks of future THz communication systems. Despite rapid progress, modulation and switching devices in this electromagnetic spectrum lag far behind other frequency ranges. Currently, THz modulators face major challenges in consistently producing high modulation depths over large frequency bands. Moreover, a convenient integration for practical applications requires that the modulation/switching properties can be electrically controlled. Devices fulfilling all these conditions remain to be demonstrated. In this work, we show that W-doped VO₂ films grown by direct-current magnetron sputtering can be efficiently used for the development of reliable, large-area, broadband THz wave modulators. We demonstrate that W doping permits not only to tune the insulator-to-metal transition (IMT) temperature of VO₂ but also, most importantly, to control the topology of the electrically activated transition. In situ/operando X-ray diffraction and Raman spectroscopy characterizations of the devices, coupled with standard resistivity measurements and time-domain THz spectroscopy, unambiguously demonstrate that the changes in the spatial distribution of the IMT are due to structural distortions induced by W doping. These findings are exploited to validate VO₂-based devices whose IMT can be triggered either thermally or electrically over areas as large as 3.8 × 10 mm², hence permitting the development of efficient THz modulators operating over a large spectral range (0.2-2 THz) with MDs reaching 96%.