The Research On Silica Based Vanadium Dioxide Thin Films And Its Application Of Terahertz Switch

Vanadium dioxide(VO2) is an exotic material since discovered they underwent a metal-to-insulator transition when exposed to thermal or voltage stimuli. Due to their dramatic changes in their electrical, optical and magnetic properties during the phase transition, the VO2 thin films may have numerous applications in thermal, electrical,and optical devices, etc.We first discusses the phase transition performance of different crystallization.Then, we deposited VO2 film with resistance change of 2 orders magnitude on Si substrate. The large crystal lattice mismatch sets big obstacles for directly depositing VO2 on silicon substrate. To better apply to the electronic and optical devices, it is urgent to improve the quality of VO2 thin film on silicon substrate.A dense and smooth Al2O3 thin film was deposited by PE-ALD technique to tune the phase transitions of VO2 thin film on the silicon substrate. Much larger resistance change, smaller thermal hysteresis and sharper phase transitions were observed for the VO2 thin film grown on the Al2O3 buffer layer in comparison with their counterparts that grown directly on silicon. The electrically-driven MIT(E-MIT) characteristics have also been investigated by applying voltage to VO2 thin film based a two-terminal device. In the I-V curves, a variation amplitude of two orders in electric current are observed with.At room-temperature, the electrically induced phase transition occurs in a voltage width of only 0.1V.We know that the oxygen partial pressure seriously affect the MIT performance.By optimizing oxygen content, quality enhanced VO2 thin films have been successfully deposited. Dramatic change in electrical resistivity(almost 4 orders of magnitude) and a small thermal hysteresis loop(~4 K) are obtained across the metal-insulator phase transition(MIT). Remarkably, by applying perpendicular voltage to VO2/Al2O3 based MOS device, electrically driven MIT switching characteristics have been observed with a tiny tunneling leakage current of ~10μA. A study about vanadium dioxide thin films MOS capacitance is described. Then, the capacitance-voltage curves was measured under different applied voltage. These tests show that electric field alone is sufficient to trigger the MIT of vanadium dioxide, and the realization of VO2 based ultrafast electrical switching devices on silicon substrate is possible.Terahertz(THz Terahertz) technology is one of the "change the future of the world’s top ten technology", which has been applied in the field of wireless communication, medical diagnosis and etc. Since the fabrication of adjusting conventional electronic devices into THz spectrum devices is a difficult job,researching on neotype materials and functional devices is very important. For a long time, people studied more on the thermal-induced phase transition of VO2 thin film and already applied in THz Modulation devices; But we learned less and used less of the electrically induced phase transition properties.A kind of electric control switch which can be used in THz spectrum is carried out by plating multi-electrode array on the VO2 film. We have tested the modulation performance of the device by terahertz time-domain spectroscopy measurement. The results show that the VO2 film has a significant effect on the THz switch, and the extinction ratio reached almost 11 dB from 0.2THz to 1THz. The broadband electric control THz switch will be devoted much attention, being advantages of easy control performance and high efficiency.