Room Temperature Phase Transition of W‐Doped VO₂ by Atomic Layer Deposition on 200 mm Si Wafers and Flexible Substrates

Abstract

The unique structural transition of VO2 between dielectric and metallic phases has significant potential in optical and electrical applications ranging from volatile switches and neuromorphic computing to smart devices for thermochromic control and radiative cooling. Critical condition for their widespread implementation is scalable deposition method and reduction of the phase transition to near room temperature. Here, a W:VO2 process based on atomic layer deposition (ALD) is presented that enables precise control of W‐doping at the few percent level, resulting in a viable controllable process with sufficient W incorporation into VO2 to reduce the phase transition to room temperature. It is demonstrated that the incorporation of 1.63 at.% W through ALD growth leads to a state‐of‐the‐art phase transition at 32 °C with emissivity contrast between the low‐temperature and high‐temperature phase exceeding 40% in a metasurface‐based radiative cooling device configuration. The process is shown to be viable on 200 mm silicon substrates as well as flexible polyimide films. The full and self‐consistent temperature‐dependent characterization of the W‐doped VO2 using spectroscopic ellipsometry, electrical conductivity, mid‐wave infrared camera, and Fourier transform infrared emissivity, allows for a fully validated material model for the theoretical design of various smart and switchable device applications.

Infrared radiative switching with thermally and electrically tunable transition metal oxides-based plasmonic grating

“…Here, we also demonstrate the effect of doping tungsten to VO 2 which shifts the transition temperature to room temperature. The filling ratio f and q for VO 2 , W-doped VO 2 (1.63at.%) and cWO 3 is taken and derived from the literatures (See Table S1 ) 22 , 50 , 51 . Figure 6 represents the result of the radiative power which is the integrated spectral emissive power P λ = α λ E BB , T , where E BB , T is the blackbody radiation at temperature T , in respect with temperature or voltage.…”

“…As a consequence, VO 2 experience rapid increase in radiative power because of shorter transition window of about 5 K 50 . However, with tungsten doping, it results in slower increase in power because of wider transition window of about 50 K 22 . Because of larger concentration tungsten, higher absorption is expected even at insulating phase at 293 K. Therefore, overall emissive power from insulating to metallic phase is high compared to pure VO 2 .…”

“…Because of larger concentration tungsten, higher absorption is expected even at insulating phase at 293 K. Therefore, overall emissive power from insulating to metallic phase is high compared to pure VO 2 . It has been examined that with lower W concentration, the extinction coefficient can be reduced at insulating phase but with increase in transition temperature 22 . In contrast, cWO 3 have its ability to switch on and off the radiative power by applying voltage while changing its color.…”

“…Although, some of which are designed specifically for radiative cooling do not effectively perform as a passive radiative cooler because of higher transition temperature which is higher than room temperature. To resolve the issue, one can dope tungsten to VO 2 to lower its transition temperature but with smaller infrared switching window 22 . Alternatively, electronically tunable metal oxides, known as electrochromic materials such as tungsten trioxide (WO 3 ) and molybdenum trioxide (MoO 3 ) can replace VO 2 due to its tunability with smaller voltage supply 23 , 24 .…”

Frequency Modulation Based Long‐Wave Infrared Detection and Imaging at Room Temperature

“…Although, we employed VO 2 as the phase change material in our work, this detection scheme can be extended to other PCM exhibiting NDR, and different spectral regions of light can be covered depending on the absorption properties of the material. Furthermore, PCMs such as W‐doped VO 2 with lower phase transition temperature [ 44 ] can be operated with smaller drive current, which is beneficial for a dense focal plane array formation. The operational wavelength may also be tuned by changing the cavity thickness.…”