| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Wednesday Sessions |
| Session TF+EM-WeA |
| Session: | Emerging Thin Film Materials: Ultra-wide Bandgap and Phase Change Materials |
| Presenter: | Virginia Wheeler, U.S. Naval Research Laboratory |
| Authors: | V.D. Wheeler, U.S. Naval Research Laboratory C.T. Ellis, U.S. Naval Research Laboratory M. Currie, U.S. Naval Research Laboratory J.R. Avila, U.S. Naval Research Laboratory M.A. Meeker, U.S. Naval Research Laboratory A.J. Giles, U.S. Naval Research Laboratory J.D. Caldwell, Vanderbilt University J.G. Tischler, U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
VO2 is a phase change material that undergoes a first order crystalline phase transition at a critical temperature (Tc = 68oC), resulting in significant changes in intrinsic electrical and optical properties, especially in the infrared. Optical changes with this phase transition are of particular interest as passive and active components of optoelectronic devices, specifically for thermal regulation and modulated signaling. Realizing this type of device often requires the integration of thin, conformal VO2 films with complex, non-planar structures (like metamaterials). Thus, atomic layer deposition (ALD) is the ideal deposition method in these cases.
Traditional metal-based plasmonic materials suffer from high optical losses, which has promoted research towards alternative low-loss materials that can support plasmonic-like effects. One such approach employs phonon-mediated collective-charge oscillations (surface phonon polaritons, SPhPs) that are supported by nanostructured polar dielectric materials (SiC, AlN, etc), which inherently are low-loss. Geometric design of the nanostructures enables spectral tuning of resonant features between the longitudinal and tranverse optical phonons of the polar material, typically in the infrared regions. However, the spectral position and amplitude of these resonances remain fixed after fabrication. Integrating phase change materials with these structures provides a way to achieve active modulation of resonances.
In this work, nanopillar arrays were etched into SiC and AlN to create narrowband resonances in the long-wave infrared region. These structures were subsequently coated with ALD VO2 films with different thicknesses (8-75nm). As-deposited VO2 films are highly conformal and amorphous, and cause the resonances to shift and broaden due to the different dielectric environment. However, after annealing the films at 525°C in 6x10-5 Torr, the VO2 films crystallize resulting in sharper resonances and spectral locations close to the initial uncoated structures. Temperature-dependence reflectance and emission measurements show that by heating through the VO2 transition temperature, the amplitude of the resonances can be modulated. Full signal modulation (ie. on/off) requires at least a 16nm VO2 film. This work shows the ability to actively tune surface phonon polariton resonances using ALD phase change materials.