A Rational Fabrication Method for Low Switching-Temperature VO2

Abstract

Due to its remarkable switching effect in electrical and optical properties, VO2 is a promising material for several applications. However, the stoichiometry control of multivalent vanadium oxides, especially with a rational deposition technique, is still challenging. Here, we propose and optimize a simple fabrication method for VO2 rich layers by the oxidation of metallic vanadium in atmospheric air. It was shown that a sufficiently broad annealing time window of 3.0–3.5 h can be obtained at an optimal oxidation temperature of 400 °C. The presence of VO2 was detected by selected area diffraction in a transmission electron microscope. According to the temperature dependent electrical measurements, the resistance contrast (R30 °C/R100 °C) varied between 44 and 68, whereas the optical switching was confirmed using in situ spectroscopic ellipsometric measurement by monitoring the complex refractive indices. The obtained phase transition temperature, both for the electrical resistance and for the ellipsometric angles, was found to be 49 ± 7 °C, i.e., significantly lower than that of the bulk VO2 of 68 ± 6 °C.

Interplay of Thermal and Electronic Effects in the Mott Transition of Nanosized VO2 Phase Change Memory Devices

“…The VO 2 layer (dark gray) was produced by the thermal oxidation of a pure, 100 nm thick V layer. 25 The cross-section of the prepared oxide film was analyzed by transmission electron microscopy (TEM), showing two clearly distinguishable layers, a grainy and thicker dark gray layer at the bottom, which is covered by a thinner, light gray layer (see Figure 1c inset). The thickness of the film was found to expand to around 220 nm during the oxidation, which is consistent with the density and molar mass changes.…”

“…The thickness of the film was found to expand to around 220 nm during the oxidation, which is consistent with the density and molar mass changes. 25 Electron energy loss spectroscopy (EELS) 26−28 was also applied on these layers, indicating different oxidation states. The EELS spectrum of the bottom layer (blue line in Figure 1d and blue dot in the inset) is consistent with the V 2 O 5 phase, whereas the top layer rather shows the presence of VO 2 (red line and dot in Figure 1d).…”

Review of the VO2 smart material applications with emphasis on its use for spacecraft thermal control

“…Reduction of V 2 O 5 films to VO 2 : Reduction of V 2 O 5 in H 2 gas (Manousou et al, 2021) (Pósa et al, 2021;Kumi-Barimah et al, 2020). Preparing VO 2 by magnetron sputtering using V 2 O 5 target with in situ annealing (Ho et al, 2019) or Thermal Evaporation of the V 2 O 5 (Manousou et al, 2021) had been proposed.…”

Real-Time Ellipsometry at High and Low Temperatures

“…The capability of SE to determine not only thicknesses but also both the real and imaginary parts of the dielectric function simultaneously has been utilized in many phase-transition studies in charge transfer solids ( T = 150 → 400 K), 68 crystallization of amorphous Si 29 , 59 also in the presence of Al, 69 annealing of Si, 70 NiSi ( T = 623 → 1023 K), 71 the switchable molecular solid RbMn[FeCN 6 ] ( T = 150 → 400 K), 72 Ge 2 Sb 2 Te 5 phase changing material ( T = 293 → 623 K), 73 relaxation in a-InGaZnO, 74 and phase change in vanadium oxides. 75 − 77 S. Bin Anooz et al 78 determined the phase transition in epitaxial NaNbO 3 films grown under tensile lattice strain on the (110) DyScO 3 substrate up to T = 823 K. The n is measured at an energy of 3.2 eV, i.e., near the band gap of 3.9 eV, to best observe variations with phase transitions and structural changes. At RT, monoclinic a1a2 ferroelectric phase with exclusive in-plane electrical polarization and at T = 523 → 573 K depicts a ferroelectric-to-ferroelectric phase transition.…”