Fabrication of V_1-x Ti _x O₂ thin films by metal-organic decomposition using carbon thermal reduction

Abstract

V1-xTixO2 thin films were fabricated on Si3N4/SiO2/Si substrates by metal-organic decomposition. The VO2 phase in the range of x = 0–0.25 was obtained by preparing the precursor film calcined at 300 °C for 15 min in a N2 atmosphere and firing these films at 580 °C–600 °C for 15 min in a N2 atmosphere. V1-xTixO2 thin films were successfully obtained by carbon thermal reduction. In the resistance–temperature characteristics, the reduction of hysteresis and the broadening of metal–insulator transition (MIT) occurred with increasing x, and hysteresis and a significant resistance change due to the MIT disappeared at x = 0.25. The temperature coefficients of resistance (TCRs) at x = 0–0.25 were as high as −4.1∼−5.5%/K at 27 °C. At x = 0.25, TCRs were −4.3∼−7.0%/K from 45 °C to 65 °C and a flat temperature dependence of TCR were realized at the temperature range from 10 °C to 80 °C.

Investigation of fabrication conditions for VO2 thin films by MOD using carbon thermal reduction

“…Next, in order to use carbon thermal reduction, calcining was performed under atmospheric pressure in nitrogen for a fixed time period t p of 15 min with temperature T p varied from 300 • C to 380 • C; thus, a precursor film with intentionally left carbon was fabricated. 20 In so doing, flow rate was kept at 70 ccm using a mass flow controller; the temperature increase and decrease rate was 20 • C/min. After that, MOD solution was spin-coated again, and all the preceding operations were repeated three times to complete fabrication of precursor film.…”

“…This procedure was performed twice. Next, in order to use carbon thermal reduction, calcining was performed under atmospheric pressure in nitrogen for a fixed time period t p of 15 min with temperature T p varied from 300°C to 380°C; thus, a precursor film with intentionally left carbon was fabricated 20 . In so doing, flow rate was kept at 70 ccm using a mass flow controller; the temperature increase and decrease rate was 20°C/min.…”

“…This problem has been recently resolved, and VO 2 films were directly fabricated; for this purpose, carbon was intentionally left in precursor films, and these precursor films were not thermally reduced at a reduced pressure, but calcined under atmospheric pressure in nitrogen, using the remaining carbon. 20 However, though VO 2 has been obtained by carbon thermal reduction, characteristics of thin films fabricated at varied temperature, time, and other calcination parameters have not been yet explored. When using VO 2 thin films in thermal sensors and other devices, repeatability is an important factor, and therefore, evaluation of VO 2 film properties at varied fabrication conditions is of great significance.…”

“…This method, however, requires long‐time thermal reduction firing at reduced pressure, while film composition is very sensitive to fluctuations of pressure; as a result, it was difficult to appropriately control VO 2 composition. This problem has been recently resolved, and VO 2 films were directly fabricated; for this purpose, carbon was intentionally left in precursor films, and these precursor films were not thermally reduced at a reduced pressure, but calcined under atmospheric pressure in nitrogen, using the remaining carbon 20 . However, though VO 2 has been obtained by carbon thermal reduction, characteristics of thin films fabricated at varied temperature, time, and other calcination parameters have not been yet explored.…”

Fabrication of V1−x Ti x O2 microbolometers on Si3N4/SiO2 membranes

“…The Ti content x in the thin films was in good agreement with a molar ratio x m = [Ti/(V+Ti)] in the MOD solution containing dissolved V-and Ti-metal carboxylates. 15,16) Relatively high TCR of ∼−4%/K over a wide temperature range of 10 °C-90 °C was obtained from the thin films with x = 0.25. 15) In order to increase the grain size in the VTO thin film suitable for bolometers, we find the two-step fabrication process as follows: (1) growth of a TiO 2 thin film with large grains by MOD, and (2) growth of a VO 2 thin film on the TiO 2 thin film and interdiffusion between V and Ti atoms by MOD.…”