Study And Preparation Of Vanadium Oxide Films As Thermal Resistance

In this paper, vanadium oxide thin films were prepared through direct current magnetron sputtering method combined post annealing process with a pure vanadium metal target. The effect of the ratio of O₂/Ar, deposition temperature, sputtering time and power of vanadium and the power of tungsten target on properties of the films have been explored. The impact of annealing temperature, time and pressure on the structure, composition, valence, surface morphology and electrical properties of the films was also studied. Variation of properties with process parameters has been obtained and parameters of process have been optimized to prepare vanadium oxide thin film suitable for uncooled infrared detector. Sheet resistance of the obtained vanadium oxide thin film is lower than 100k?/?, temperature coefficient of resistance?TCR? is higher than 2.5%/K and noise of the film is low. The microstructure, composition, valence, surface microstructure and resistance of the thin film were characterized using XRD diffraction, X ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and temperature resistance tester. The results of the study are as follows:?1? Resistance and temperature coefficient of resistance?TCR? of the film is greatly affected by the ratio of oxygen and argon. The resistance of the films raise with increasing of the ratio of oxygen and argon. The sheet resistance of the film raised slightly with the increase of the ratio of O₂/Ar when the ratio of O₂/Ar is lower than 0.8/46. But as the ratio of O₂/Ar is higher than 0.8/46, the sheet resistance of the film increases greatly with increasing of the ratio of O₂/Ar. When the ratio of O₂/Ar rise from 0.8/46 to 1.1/46, the sheet resistance of the film increase from 70k?/? to 10M?/?; TCR of the film increase greatly with the increasing of the ratio of O₂/Ar. TCR increase from 1.6%/K to 2.6%/K when the ratio of O₂/Ar increase from 0.7/46 to 1.1/46. The prepared film tends to have more higher valence vanadium particles with increasing of O₂/Ar, and the ratio of O₂:Ar have slightly impact on the microstructure.?2? The deposition temperature has greatly effect on structure of the films. The film tends to be amorphous as the temperature is low. Some particles of the film deposited at high temperature tend to grow in column shape. Compared to the film deposited at low temperature, the film deposited at high temperature tend to have more lower valence vanadium particles; The deposited temperature have slight impact on the resistance and temperature coefficient of resistance of the film. The sheet resistance decrease from 800k?/? to 400k?/? and TCR change in the range of 2.3%/K-2.4%/K.?3? The vanadium power of sputtering have effect greatly on the sheet resistance and TCR of the film, the sheet resistance and TCR of the film decrease with increasing of the power of vanadium sputtering. The sheet resistance and TCR decrease from 6M?/? to 500k?/ ? and from 2.4%/K to 2.05%/K. Compared to the film deposited at lower sputtering power, the film deposited at higher sputtering power tends to have more lower valence vanadium particles.?4? Sputtering time has slightly effect on the temperature coefficient of resistance, sheet resistance, micromorphology and average valence.?5? As the sputtering power of tungsten increased to 20 w, the ratio of V/W decreased to 3.94. The sheet resistance and TCR first increase then decrease with the sputtering power of tungsten increase. The sheet resistance of the film is 7700k?/? and 180k?/? as the sputtering power of tungsten is 20 w and 30 w. The average valence of vanadium decreases with increasing of the sputtering power of tungsten. The sputtering power of tungsten has slightly effect on surface morphology.?6? Annealing make thin film to be crystallized. The sheet resistance, average valence and the content of oxygen first increase then decrease with the annealing temperature increasing, the extension of annealing time and the pressure of vacuum increasing.The optimized process parameters is as follows: the ratio of O₂/Ar is 1.2/46, deposition temperature is room temperature, sputtering time is 10 min, sputtering power is 80 w, the work pressure is 1pa,; annealing temperature is 480?, annealing time 500 s, annealing vacuum is 2000 pa. the prepared film is the mixture of crystal of V6O13 and noncrystal, and the of valence of vanadium is mainly include V4+ and V5+.in the film the ratio of content of O/V is 4.196. the thickness of film is 99 nm, the sheet resistance and TCR is 90K?/? and 2.57%/K respectively.