Facile Fabrication of High-Performance Thermochromic VO₂-Based Films on Si for Application in Phase-Change Devices

Abstract

This work reports on an alternative and advantageous procedure to attain VO 2based thermochromic coatings on silicon substrates. It involves the sputtering of vanadium thin films at glancing angles and their subsequent fast annealing in an air atmosphere. By adjusting thickness and porosity of films as well as the thermal treatment parameters, high VO 2 (M) yields were achieved for 100, 200, and 300 nm thick layers treated at 475 and 550 °C for reaction times below 120 s. Comprehensive structural and compositional characterization by Raman spectroscopy, X-ray diffraction, and scanning-transmission electron microscopies combined with analytical techniques such as electron energy-loss spectroscopy bring to the fore the successful synthesis of VO 2 (M) + V 2 O 3 /V 6 O 13 /V 2 O 5 mixtures. Likewise, a 200 nm thick coating consisting exclusively of VO 2 (M) is also achieved. Conversely, the functional characterization of these samples is addressed by variable temperature spectral reflectance and resistivity measurements. The best results are obtained for the VO 2 /Si sample with changes in reflectance of 30−65% in the near-infrared at temperatures between 25 and 110 °C. Similarly, it is also proven that the achieved mixtures of vanadium oxides can be advantageous for certain optical applications in specific infrared windows. Finally, the features of the different structural, optical, and electrical hysteresis loops associated with the metal−insulator transition of the VO 2 /Si sample are disclosed and compared. These remarkable thermochromic performances hereby accomplished highlight the suitability of these VO 2 -based coatings for applications in a wide range of optical, optoelectronic, and/or electronic smart devices.

Ultrafast Laser Crystallization Dynamics of Thermochromic VO2 Thin Films by Simple Moisture-Assisted Sol–Gel

“…Considering VO 2 thin films, chemical solution deposition (CSD) methods offer notable advantages in terms of simplicity, versatility, low costs, compatibility with large area substrates, and industrial scalability, besides not requiring vacuum-based equipment. However, traditional CSD methods pose a challenge for the crystallization of VO 2 films as they require temperatures above 400 °C and strict control of the atmosphere to avoid unwanted oxides. , With furnace annealing, the formation of a mixed composition of vanadium oxides or the crystallization into a lower or higher oxidation state is a common side effect as the control of temperature, pressure, and atmosphere is not easily fulfilled. − The high temperatures prevent the crystallization of VO 2 on temperature-sensitive substrates, such as polymers or low melting temperature metals, which would unfold multiple solutions for the global energy demand. Unconventional photonic annealing offers a notable and multifaceted alternative to conventional annealing, enabling a rapid processing of the materials at lower temperatures .…”