| Vanadium oxides exist in a large variety of structures with mixed valencies. Most of the VOx materials have the transition properties with low temperature semiconductor phase to high temperature metal phase. As a heat-sensing material, VOx thin films have promising prospect for thermal detectors and IR imaging due to their outstanding physical and chemical properties.In this dissertation, vanadium oxide (VOx) thin films were studied. The VOx thin films for heat-sensing applications were deposited by DC magnetron sputtering method. Preparation, microstructure, and characterization of the VOx thin films were studied. The outline of this dissertation was outspread by the optimization of the preparation technology for the VOx thin films.In the experiments, X-ray photoelectron spectrometer (XPS), X-ray diffraction (XRD), scanning electron microscope (SEM), and atomic force microscope (AFM) were employed to analyze the microstructures and chemical states of the VOx films. The square resistance (R□) and temperature coefficient of square resistance (TCR) were emphasis measured. Moreover, the refractive index (n) and extinction coefficient (k) of the VOx films prepared were investigated. The dissertation was narrated from six aspects as follows:(1) Microstructures of the VOx films have great influence on the film properties. In the dissertation, composition, chemical state, crystallization, and micro-features were first analyzed by XPS, XRD, SEM, and AFM. In this way, the micro-properties of the VOx films were acquainted, which help us to optimize the technology process.(2) In the optimization of the deposition conditions of the VOx films, we first systematically investigated the effects of gas flux of Ar, O2, and Ar/O2 on the deposition rate and sputtering voltage. On the basis of the investigations, a new controlling method—sputtering controlling method was proposed. By adjusting the sputtering voltage, the reproductability and stability of the technology were improved obviously. VOx films were deposited under different sputtering voltage by our new method and the properties of the films were analyzed. The results revealed that when the sputtering voltage is 304～318 V, the R□and TCR of the VOx films is 30～150 KΩ/□and -4%/℃～-5%/℃, respectively, and the O/V ratio is 1.91～2.13.(3) The growth mode and texture of VOx films grown on different substrates, including Si, glass, Si3N4/Si, were studied. Experiment results demonstrated that both the growth mode and texture are clearly different for the VOx films deposited on different substrates. For the VOx films grown on Si3N4/Si substrate, the grain sizes are small and the film is flat. However, for the films grown on glass substrate or Si substrate, the grain sizes are large, and the column-like growth mode is obvious. Moreover, it was confirmed that film thickness has great influence on the film grain size, and the film thermal electrical properties are greatly influenced by the film thickness and the grain size. In addition, the grain size and the crystallization extent increase with increasing the film thickness from 80nm to 1000nm. The growth mode of the VOx was demonstrated an obvious club-shape or spindle-shape for the thick films. With increasing the film thickness, the R□decreases, the TCR increases, and the metal-semiconductor phase transition becomes obvious. These suggest that substrates have great influence on the microstructure and properties of VOx films.(4) The optical and electrical properties were investigated for the VOx films with different thickness. Results proved that the refractive index and extinction coefficient of vanadium oxide thin films are correlated with the film thickness. In the dissertation, the Preisach theory model was adopted to analyze the asymmetrical thermal electrical hysteresis loop. Based on this theory, the interrelations of the film resistance, temperature, and grain volume were determined.(5) On the basis of the studies above, VOx thin films were deposited in pure Ar condition by DC magnetron sputtering method. The target material was vanadium pentoxide. The vanadium oxide thin films deposited were post-annealed with high temperature in high vacuum. Crystallization of the samples was analyzed by XRD and the results showed that the thin films prepared exhibit preferred orientation of VO2 crystalline plane before and after annealing. XPS results verified the phase analysis obtained by XRD. XRD analysis and square resistance measurements proved that the thin films are VO2 (B). Based on these and the theory of grain boundary scattering, the electrical properties of the samples can be controlled by changing the film thickness and grain size.(6) Moreover, we deposited the VOx thin films by a two-step procedure method. In this method, the pure vanadium thin films were first deposited onto the substrates, and then they were post-oxidized to form the VOx thin films. The results suggested that the appropriate oxidation process is helpful to optimize the R□and TCR of VOx thin films, and TCR of VOx films are higher than -2 %/℃. Moreover, the chemical states and V/O ratio of VOx can also be controlled by optimizing the annealing conditions.On the basis of the above researches, preparation, microstructure, and characterization of the VOx thin films were further acquainted and comprehended by us, which are beneficial for the application of the VOx thin films.
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