Design And Research Of THz Functional Devices Based On Ferroelectric Thin Film Metamaterials

Terahertz wave,with both electronics and photonics characteristics,occupies an important position in the electromagnetic spectrum.In terahertz band,it is difficult for materials in nature to exhibit electromagnetic response,therefore the realization of metamaterials provides a strong support for the development of functional devices.Moreover,electromagnetic properties of metamaterials can be optimized by changing unit size or and structure arrangement in order to obtain the unique properties which do not exist in nature materials.The main contents of this thesis:1.The development process and basic characteristics of ferroelectric materials are introduced,their classification is also summarized.In terahertz band,a research of optical modulation characteristics for potassium tantalate,a classical ferroelectric materials,by using terahertz time-domain spectroscopy system is demonstrated.The dielectric constant of potassium tantalate at 0.1-0.8 THz is modulated by 532nm continuous-wave laser at room temperature.The dielectric constant decreases with the increasing laser power,especially the real part,which decreases 3.5%when the laser power is 600mW.We carried out the theoretical analysis and fit the change of dielectric constant by using four parametric oscillator model,which agrees well with the experimental results.We also found that the refractive index change linearly with the increase of laser power,which is interpreted as the linear electro-optic effect induced by internal space charge field of the crystal.2.A new Ba_0.6Sr_0.4TiO₃-silicon ferroelectric metamaterial device is fabricated and studied.Many ferroelectric materials such as barium strontium titanate,exhibiting strong response to external electric field,hold great promise in both microwave and terahertz tunable devices.The interdigital electrode control the change of the applied electric field in this modulator.In the process of experimental studies,we considered the square split ring resonators,barium strontium titanate thin film and silicon substrate as an uniform effective dielectric media.The active barium strontium titanate thin film hybrid metamaterial,with nanoscale thickness,delivers a transmission contrast up to 79%due to electrically enabled carrier transport between the ferroelectric thin film and silicon substrate.This work has significantly increased the low modulation rate of ferroelectric based devices in terahertz range.3.We designed and simulated some terahertz modulator and absorber structures based on metamaterials by using CST MWS software,then analyzed the simulation results.In the modulator part,we firstly analyzed the characteristics of split ring resonators,then simulated the modulation of both transmission amplitudes and resonance frequencies by changing the conductivity of silicon substrate and embedding material?gallium arsenide?.In the absorber part,I proposed two structures corresponding to single and double band absorbers,respectively.In order to get perfect absorption for terahertz wave,both structure size of the resonator and the thickness of the dielectric substrate are optimized.