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Electrical Switching in Semiconductor-Metal Self-Assembled VO 2 Disordered Metamaterial Coatings

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ABSTRACT

As a strongly correlated metal oxide, VO2 inspires several highly technological applications. The challenging reliable wafer-scale synthesis of high quality polycrystalline VO2 coatings is demonstrated on 4” Si taking advantage of the oxidative sintering of chemically vapor deposited VO2 films. This approach results in films with a semiconductor-metal transition (SMT) quality approaching that of the epitaxial counterpart. SMT occurs with an abrupt electrical resistivity change exceeding three orders of magnitude with a narrow hysteresis width. Spatially resolved infrared and Raman analyses evidence the self-assembly of VO2 disordered metamaterial, compresing monoclinic (M1 and M2) and rutile (R) domains, at the transition temperature region. The M2 mediation of the M1-R transition is spatially confined and related to the localized strain-stabilization of the M2 phase. The presence of the M2 phase is supposed to play a role as a minor semiconducting phase far above the SMT temperature. In terms of application, we show that the VO2 disordered self-assembly of M and R phases is highly stable and can be thermally triggered with high precision using short heating or cooling pulses with adjusted strengths. Such a control enables an accurate and tunable thermal control of the electrical switching.

No MeSH data available.


Scanning electron micrographs showing the evolution of film morphology at different stages of film processing from (a) the as-grown amorphous vanadium oxide film, (b) sintered V2O5 film to a (c) sintered VO2 by vacuum reduction. 4 hours annealing of VO2 at 600 °C under vacuum induces a marginal morphological impact (d). The film thickness is 500 nm.
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f2: Scanning electron micrographs showing the evolution of film morphology at different stages of film processing from (a) the as-grown amorphous vanadium oxide film, (b) sintered V2O5 film to a (c) sintered VO2 by vacuum reduction. 4 hours annealing of VO2 at 600 °C under vacuum induces a marginal morphological impact (d). The film thickness is 500 nm.

Mentions: Two approaches were implemented to induce the sintering of VO2 films. Annealing under vacuum in the absence of oxygen was performed at 600 °C directly in the deposition chamber. As this temperature is far below the melting point (1970 °C) of VO2, no significant sintering took place as shown in Fig. 2(a–d). The second approach involves the conversion of VO2 to V2O5, that exhibits a lower melting point (690 °C), prior sintering. This approach proves to be successful as displayed in Fig. 2(a,b). The conversion of VO2 to V2O5 was performed under the O2 partial pressure of 0.01 mbar. The XRD analysis, supplementary information (S1), shows the occurrence of the VO2 – V2O5 conversion already at 400 °C. Fixing the temperature at 600 °C was essentially implemented to induce an efficient sintering over a short period (1 h) and to simplify this multi-step process by keeping the substrate temperature constant.


Electrical Switching in Semiconductor-Metal Self-Assembled VO 2 Disordered Metamaterial Coatings
Scanning electron micrographs showing the evolution of film morphology at different stages of film processing from (a) the as-grown amorphous vanadium oxide film, (b) sintered V2O5 film to a (c) sintered VO2 by vacuum reduction. 4 hours annealing of VO2 at 600 °C under vacuum induces a marginal morphological impact (d). The film thickness is 500 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121613&req=5

f2: Scanning electron micrographs showing the evolution of film morphology at different stages of film processing from (a) the as-grown amorphous vanadium oxide film, (b) sintered V2O5 film to a (c) sintered VO2 by vacuum reduction. 4 hours annealing of VO2 at 600 °C under vacuum induces a marginal morphological impact (d). The film thickness is 500 nm.
Mentions: Two approaches were implemented to induce the sintering of VO2 films. Annealing under vacuum in the absence of oxygen was performed at 600 °C directly in the deposition chamber. As this temperature is far below the melting point (1970 °C) of VO2, no significant sintering took place as shown in Fig. 2(a–d). The second approach involves the conversion of VO2 to V2O5, that exhibits a lower melting point (690 °C), prior sintering. This approach proves to be successful as displayed in Fig. 2(a,b). The conversion of VO2 to V2O5 was performed under the O2 partial pressure of 0.01 mbar. The XRD analysis, supplementary information (S1), shows the occurrence of the VO2 – V2O5 conversion already at 400 °C. Fixing the temperature at 600 °C was essentially implemented to induce an efficient sintering over a short period (1 h) and to simplify this multi-step process by keeping the substrate temperature constant.

View Article: PubMed Central - PubMed

ABSTRACT

As a strongly correlated metal oxide, VO2 inspires several highly technological applications. The challenging reliable wafer-scale synthesis of high quality polycrystalline VO2 coatings is demonstrated on 4” Si taking advantage of the oxidative sintering of chemically vapor deposited VO2 films. This approach results in films with a semiconductor-metal transition (SMT) quality approaching that of the epitaxial counterpart. SMT occurs with an abrupt electrical resistivity change exceeding three orders of magnitude with a narrow hysteresis width. Spatially resolved infrared and Raman analyses evidence the self-assembly of VO2 disordered metamaterial, compresing monoclinic (M1 and M2) and rutile (R) domains, at the transition temperature region. The M2 mediation of the M1-R transition is spatially confined and related to the localized strain-stabilization of the M2 phase. The presence of the M2 phase is supposed to play a role as a minor semiconducting phase far above the SMT temperature. In terms of application, we show that the VO2 disordered self-assembly of M and R phases is highly stable and can be thermally triggered with high precision using short heating or cooling pulses with adjusted strengths. Such a control enables an accurate and tunable thermal control of the electrical switching.

No MeSH data available.