| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF+EM+MI-WeA |
| Session: | Thin Films for Microelectronics |
| Presenter: | Virginia Wheeler, U.S. Naval Research Laboratory |
| Authors: | V.D. Wheeler, U.S. Naval Research Laboratory B.P. Downey, U.S. Naval Research Laboratory J. Roussos, U.S. Naval Research Laboratory M. Currie, U.S. Naval Research Laboratory A. Giles, U.S. Naval Research Laboratory C. Ellis, U.S. Naval Research Laboratory J. Tischler, U.S. Naval Research Laboratory J. Caldwell, U.S. Naval Research Laboratory D.J. Meyer, U.S. Naval Research Laboratory C.R. Eddy, Jr., U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
VO2 films are known to undergo a metal-insulator phase transition (MIT) at a critical temperature (Tc = 68°C) near room temperature which results in significant changes in thermal emittance, optical transmittance and reflectance, and intrinsic electrical properties; thus attracting interest in a variety of new electronic, optoelectronic, and photonic applications. Atomic layer deposition (ALD) provides a way to obtain large area film uniformity, abrupt interfaces and angstrom-scale control of thickness conformally across planar, as well as three-dimensional, high surface area nanostructures, which could be used to integrate VO2 films into complex electronic and optical devices for additional functionality. In this work, VO2 electrical devices and VO2 coated SiC-based nanoresonantors are used to investigate the impact of film thickness on electrical and optical properties.
The influence of VO2 thickness on electrical performance was investigated using a simple two-terminal device structure. Sheet resistance measurements as a function of temperature revealed that the Roff/Ron ratio increased with increasing VO2 thickness, up to Roff/Ron of ~7000 for a 92 nm film. Similarly, the Tc increased slightly with increasing thickness (Tc = 66oC for 35nm, 73oC for 92nm), while all films show relatively low hysteresis (ΔT<8oC). Initial small-signal rf measurements using the 92 nm ALD VO2 film demonstrated a cut-off frequency of greater than 1 THz, indicating the potential for rf-switch applications into millimeter wavelength frequencies using these ultra-thin ALD films, and the potential of these films to be conformally integrated into complex circuits with an ALD process.
For applications in the infrared, surface phonon-polariton-based SiC nanoresonators exhibiting strong, narrowband absorption features within the 10-12.5 μm range were coated with different thickness ALD VO2 films. Since these films are transparent to infrared light below the Tc and reflective above the Tc, conformally coating these SiC nanostructures provides a way to add functionality to these structures by modulating the amplitude of the resonances with temperature. Initial results show that the magnitude of the resonance suppression increases with increasing VO2 thickness and a VO2 film thickness greater than 16nm is required to fully inhibit the signal. It was also determined that the SiC resonances become increasingly shifted and broadened with increasing thickness of the VO2 coating. These results suggest that VO2 can add active tunability and integrated switching to optical structures.