Switching Applications Based on Reversible Insulator-Metal Transition of Vanadium Dioxide Thin Films Synthesized by Pulsed Laser Deposition

Vanadium dioxide (VO2) is a phase transition metal oxide that has attracted the attention of researches because of its reversible and abrupt insulator to metal transition. Upon heating through a critical temperature of Tc ≈ 68 °C, VO2 undergoes a structural transformation of the crystalline lattice, from a monoclinic (M1) phase for the low temperature insulating state to a tetragonal/rutile (R) phase for the high-temperature metallic state. There are several ways to trigger this transition other than increase the temperature, including photonic excitation and electric excitation. The purpose of this dissertation is to synthesize high quality VO2 thin films by pulsed laser deposition, utilize its insulator to metal transition to design and fabricate different electronic and optical devices. The devices include thermochromic devices, optical modulators, radio frequency switches, and reconfigurable dipole antennas.;Thermochromic devices were fabricated by depositing a metal layer on top of VO2 thin films. We observed that the magnitude of the reflectivity increases for metal coated VO2 films, but decreases for uncoated VO2 thin films in the near infrared. The measured reflectance results matched well with our calculation results obtained from a double layer model using the optical transfer matrix method. We demonstrate that the magnitude of the reflected color change in that visible portion of the spectrum as VO 2 under goes the insulating to metallic phase transition can be controlled by changing the type of metal, the thickness of the metal and by patterning the metal at the nano scale. The changing dielectreic properties of VO 2 also suggest interactions with plasmons in the nano patterned metal films and plasmonic crystals can lead to new devices.;Optical modulators based on joule heating mechanisms were fabricated with VO2 thin films. The device switches from semiconductor phase to metal phase by applying a constant voltage across two metal contacts. The transition is caused by joule heating from the current flowing through the VO2 thin films. We have improved the performance of the devices by fabricating them on SiNx membranes. Compared to the devices fabricated on the normal substrates, such as sapphire, silicon or glasses, the switching speed of the devices on the membrane is an order of magnitude faster. Decreasing the area and thickness of VO2 on top of thinner membranes allows kHz bandwidths to be achieved.;Applying VO2 to radio frequency (RF) applications were investigated by designing and fabricating RF switches and reconfigurable dipole antennas. The propagation of the RF signal was controlled by the insulating to metal transition of VO2. Simulated results were obtained using the RF simulation software SONNET before fabrication. The measured results show a high contrast between the insertion loss of the on state and isolation of the off state for both of series and shunt configuration switches. The measured return loss of the reconfigurable dipole antennas confirmed the change of the resonance frequency because of the phase transition of VO2.