Tuning Characteristics Of Mid-infrared Plasmonic Antennas Based On Vanadium Dioxide

Vanadium dioxide is a kind of metal oxide with phase transition characteristics.It can reversibly change between the high-temperature metallic phase and the low-temperature semiconducting phase at a phase transition temperature of 68°C,which is usually accompanied with drastic changes of electrical and optical properties.Based on its excellent phase transition characteristics,vanadium dioxide shows great potential applications in microelectronics,optoelectronics,and sensors.In recent years,mid-infrared?3?m-30?m electromagnetic wave?light has received increasing attention from scientific community due to its potential applications in the military and civilian areas.The dynamic modulation of mid-infrared light enabled by the electrical control of vanadium phase transition is of great significance for advancing the mid-infrared technology.In this paper,by using vanadium dioxide as a phase change functional material,a mid-infrared tunable plasma antenna device is designed,fabricated and characterized.The device is a multilayer film structure with a silicon wafer as the substrate.Firstly,a 300 nm thick copper film is deposited on a silicon substrate by electron beam evaporation?EBE?as a reflective layer,Then,a 100 nm thick silicon dioxide film is deposited on the copper film by plasma enhanced chemical vapor deposition?PECVD?as a transition layer,and then a vanadium dioxide thin film with a thickness of 250 nm is deposited on the silicon dioxide film by reactive magnetron sputtering method.Finally,growth of a gold interdigitated antenna with a thickness of 200 nm on a vanadium dioxide film using wet lithography and electron beam evaporation.The gold interdigitated antenna with a thickness of 200 nm has a specific structure with a metal strip width of 2.5?m,a metal strip length of 3.8 mm,an adjacent metal strip spacing of4.5?m,and an overall array size of 4.0 mm×4.0 mm.The interdigitated metal strip array palys the role of both electrode and antenna.In the experimental test,under the voltage excitation mode,we measured a modulation depth of 30%at the antenna resonance at 25.5 THz.The tuning range of the response frequency is 3.5%.Similar results were also obtained during the phase transition test of thermally excited vanadium dioxide films.In order to explore the mechanism of the phase transition of vanadium dioxide,we measured the temperatures of the device for both electrical tuning and thermal tuning,and compared the results with simulated temperatures in COMSOL software.We found that the temperature of the device under voltage excitation is basically the same as that under thermal excitation.Therefore,we conclude that the voltage-induced phase change of vanadium dioxide is primarily caused by Joule heating.The VO₂ tunable antenna demonstrated in this thesis is simple to manufacture,low in cost,and exhibits mid-infrared modulation at a very low operating voltage,which hold great promise for applications such as reconfigurable infrared sensing.