High emissive contrast of patterned tungsten-doped VO2 thin film composites

Thermal regulation is essential for numerous applications across multiple industries such as the efficient temperature control of indoor facilities and the reliable operation of many electronic systems. Vanadium dioxide (VO2) is a phase change material that is well-suited for thermal regulation as a result of its ultrafast, reversible, solid-state transition at 68 degrees C that produces a significant contrast in its infrared (IR) emissive properties. To meet application demands, VO2's transition temperature can be tuned via doping with a reduction in temperature of similar to 22 degrees C per atomic percent tungsten (at. % W6+). However, historically this decrease in the transition temperature has coincided with a reduction in IR optical contrast between the two phases. In this investigation, we demonstrate that by patterning VO2 thin film composites with preoptimized thicknesses, a thermal regulation system with a tunable transition temperature and no significant degradation of contrast between the states is produced. Through carefully selected user-defined patterning of the undoped VO2 layer within the multilayer film, a 64% operating optical contrast was achieved across the 8 - 13 mu m spectral region as compared to 42% in the as-deposited film Additionally, at a doping level of 1.7%, the transition temperature in a VO2 thin film composite with micron-scaled patterning was reduced to 25 degrees C while maintaining 58% emissive contrast in the 8 - 13 mu m spectral region.