Influence of annealing on structure, phase and electrophysical properties of vanadium oxide films

The aim of this work was to study the effect of the parameters of deposition process and subsequent annealing on the properties of vanadium oxide VO_x films deposited by the pulsed reactive magnetron sputtering of a V target in an Ar/O₂ gas  mixture.  The  dependences  of  the  structure,  phase,  temperature  coefficient of resistance (TCR), resistivity p, band gap Egof the films on the oxygen concentration in Ar/O₂ gas mixture during the deposition Г_O2, and the temperature of annealing in an O₂ atmosphere were obtained. The films were found to have an amorphous structure after deposition. Crystallization processes are observed at temperatures above  275 °C.  In  this  case,  depending  on  the  temperature,  polycrystalline  films  with  a  monoclinic,  cubic or mixed crystal lattice are formed and a transition occurs from the intermediate oxide V₄O₉ to the mixed phase VO₂/VO_x/V₂O₅ and then to the higher oxide V₂O₅. The character of changes in p, TCR and Egof films coming from the change in the annealing temperature is complex and largely determined by Г_O2. It was established that with the view of using VO_x films as thermosensitive layers, the following conditions of deposition and annealing would be preferable: films deposited at the oxygen concentration 25 % in Ar/O₂ gas mixture and annealed at a  temperature  of  250–275 °C  in  an  O₂ atmosphere  for  10  min.  Under  these  conditions  VO_x films  with  the following properties were obtained: p= (1.0 – 3.0)^.10^-2 Ohm^.m, TCR = 2.05 %/°C, and E_g= 3.76–3.78 eV.

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