Study Of THz Wave Modulator Based On VO₂Nano-film

THz wave has potential applications in many areas, such as imaging,communication and biomedicine, because of its unmatched characteristics comparedwith waves in other bands. Modulation devices play a key role in the THz technology.Nowadays, with the development of THz wave emission and detection techniques, thestudy of THz modulators has been drawing increasing attention. In this thesis, a studyof THz wave filtering by the modulation of THz wave amplitude based onphase-change VO2nano-films is carried out.First, the relevant parameters of THz modulators are extracted. For this purpose,the general relationship between the material parameters and the THz transmissionspectrum is derived, and the parameters of bulk crystals and thin film materials arecalculated, depending on the material thickness. Furthermore, the refractive index,conductivity and dielectric constant of sapphire substrate and VO2films involved insubsequent studies are obtained based on the above methods.Second, VO2thin films were prepared through magnetron sputtering with a rapidthermal annealing process, and the photo-induced phase transitions properties of VO2thin films treated at different annealing temperatures and by different periods of timewere investigated by THz time-domain spectroscopy. By analyzing the depth andwidth of the phase transition point and the phase change threshold, we found that theproperties of VO2thin films were best at and annealing temperature of560°and foran annealing time of60s, with a THz wave modulation depth of80%. In addition, theheat-induced phase transition of VO2films was also studied, and was consistent withthose of photo-induced phase transitions.Finally, phase-transition VO2thin films were combined with surface plasmonpolaritons (SPPs) to achieve flexible modulation of THz wave in structures withdifferent metal holes arrays and dielectric layers. The connection between SPPresonance characteristics and the cross shapes in the structures and the substrate VO2film conductivity were simulated. A metallic copper SPP structure with a line width of10μm and VO2thin film as the substrate were fabricated by photolithography. Theexperimental results were consistent with the calculation, and a relative shift of thecentral resonance frequency by31.5%was obtained.