Title

Vanadium Dioxide Based Radio Frequency Tunable Devices

Date of Award

1-1-2018

Degree Name

Ph.D. in Engineering

Department

Department of Electrical and Computer Engineering

Advisor/Chair

Advisor: Guru Subramanyam

Abstract

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. % W-doped 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 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 (20░C), the switch is in off state, and when the temperature is above 68░C, 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 80░C. 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░C) to 6.346 GHz with S11 -30.26 dB (30░C), and the antenna is inactive when the temperature is above 40░C. 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.

Keywords

Electrical Engineering, Materials Science, Electromagnetics, Vanadium Dioxide, VO2, Tungsten Doped Vanadium Dioxide, Coplanar Waveguide, CPW, Bowtie, Reconfigurable Antenna, switch

Rights Statement

Copyright 2018, author

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