Authors: KuanChang Pan
Source: OhioLink ETD Center (Ohio Library and Information Network) (article, 2018-01-01)
Field: Materials Science — Polymers and Plastics

Vanadium Dioxide Based Radio Frequency Tunable Devices Phase change materials (PCMs) have always been an interesting topic for scientists.The materials with tunable electrical properties can be used in various microwave devices such as antennas, phase shifters and varistors.Vanadium dioxide (VO2) is a unique phase change material (PCM) that shows a transition from insulator to metal above a transition temperature of 68.By doping different ratios of tungsten with vanadium dioxide, the transition temperature of tungsten-doped vanadium dioxide (W-doped VO2) can be lower than 68 which gives the researchers more flexibilities for designing tunable radio frequency (RF) devices.Therefore, the purpose of this dissertation is to design tunable microwave devices such as RF switches and antennas using the phase change material (PCM) VO2 and W-doped VO2.This dissertation reports different topics of VO2 thin films.First, the fabrication process of undoped and W-doped VO2 thin films.The pulsed laser deposition (PLD) was used to fabricate the undoped, 0.34 at.% W-doped, 0.54 at.% W-doped and 1.1 at.% Wdoped VO2 thin films on sapphire substrates.Second, the measurements and analysis of undoped and W-doped VO2 thin films.Scanning electron microscope (SEM), X-ray v diffraction (XRD) analysis and electrical resistivity of different W-doped VO2 thin films have been provided.Third, undoped and W-doped VO2 thin films based RF switches and reconfigurable antennas are reported.The single pole single throw (SPST) switches and reconfigurable antenna have been designed, fabricated and characterized for undoped and W-doped VO2 thin films integrated into those devices.The SPST switches are designed using coplanar waveguide (CPW) transmission lines, and the switches can be turned on or off by adjusting the temperature.At room temperature (20C), the switch is in off state, and when the temperature is above 68C, the switch is in the on state.The return loss (S11) of the switch is less than 1 dB at 20 C, and it is better than 20 dB at 80C.The isolation of the switch (S21) is better than 30 dB at 20 C in the off state, and the insertion loss in the on state is less than 4 dB at 80 C.The radio frequency (7 GHz) and W-band (93 GHz) CPW reconfigurable antennas have been demonstrated, and the wafers with undoped and tungsten-doped (0.1% to 1% tungsten) VO2 integrated with these antennas have been fabricated and tested.For the 0.54 at.% W-doped VO2 thin film based CPW bowtie antenna, the frequency tuning range is from 6.753 GHz with S11 -25.25 dB (10) to 6.346 GHz with S11 -30.26 dB (30), and the antenna is inactive when the temperature is above 40 .For the 93 GHz antenna, when the W-doped VO2 is in low conductivity, the simulation shows that the resonant frequency of the antenna is at 92.9 GHz with S11 -51.4dB.When the W-doped VO2 is in high conductivity, the resonant frequency shifts to 91.4 GHz with S11 -43.03dB.The analyses of the undoped and W-doped VO2 thin films have been provided in this dissertation.The simulations and measurements successful demonstrated the tunability and the applications of the undoped and W-doped VO2 thin films.vi Dedicated to my daughter, my wife, and my parents. Vanadium dioxide ; Environmental science ; Telecommunications ; Remote sensing ; Computer science ; Materials science ; Geology ; Nanotechnology Transition Metal Oxide Nanomaterials ; Gas Sensing Nanomaterials and Sensors