Magnetron Sputtering Growth And Photoelectric Properties Of Vanadium Oxide Thin Films

Vanadium dioxide?VO₂?is a phase change material.When the temperature reaches its phase transition point,VO₂ will undergo a reversible transition from a low temperature semiconductor state to a high temperature metal state.This change occurs between tens of nanoseconds,accompanied by sudden changes in electrical and optical properties,such as its sheet resistance?rate?and infrared-near-infrared optical transmittance and reflectance during phase transitions.Based on this series of excellent optoelectronic properties,the materials have high practical value and broad application prospects,so it has attracted the attention and research of many scholars in recent years.Vanadium?V?,as a metal element in the 3d transition zone,has multivalent properties.In addition to vanadium oxides of different valence states,there are many different crystal phases between vanadium dioxides in the same valence state.Therefore,the preparation of pure phase high quality vanadium dioxide film is still a challenge in this field.In this thesis,a series of high-quality VO₂,VO₂?B?and V₂O₃ films were prepared on silicon substrates and quartz substrates using vanadium oxides as research objects.It is intended to improve the crystallinity and purity of the film by a preparation process to enhance the photoelectric properties of the VO₂ films.The microstructure and phase structure of the samples were characterized by field emission scanning electron microscopy?FE-SEM?and X-ray diffractometry?XRD?.The variable temperature sheet resistance and transmittance of the samples were tested by a four-probe resistance tester and an visible-near-infrared-infrared spectrophotometer.The application of vanadium oxide thin films in micro-bolometers and thermochromic smart windows was studied.The effects of different preparation processes on the electrical sheet resistance and optical transmittance of vanadium oxide thin films with temperature were systematically discussed.The main content is as follows:1)The phase transition characteristics and valence structure of VO₂ thin films were analyzed,and the process flow of depositing VO₂ thin films was introduced.Using RF magnetron sputtering,after repeated trials,we finally obtained the process parameters of multiple groups of VO₂ thin films deposited on silicon and quartz substrates,and the samples prepared by each set of parameters have good crystallinity and high repeatability.In addition,there are different crystallization conditions on different substrates.Under the same process parameters,the diffraction samples of the film samples prepared on single crystal silicon are always stronger than those on the quartz substrate,and the crystallinity is better than that of the film prepared on the quartz substrate.2)According to the actual needs of the application and compatibility with CMOS technology,we prepared a series of VO₂ films by changing the oxygen flow rate on a single-spray silicon?100?substrate at a deposition temperature of 350�C.We systematically analyzed the crystallization condition and the sheet resistance as a function of temperature.The movement of the diffraction peaks of the crystal faces indicates that the increase in the oxygen flow rate causes a change in the internal lattice structure of the films.The increase in oxygen flow rate leads to a gradual increase in the grain size of the films.The samples obtained have excellent electrical properties and can be used as heat sensitive materials.3)The VO₂ films were sputtered directly on the quartz substrate by RF magnetron sputtering,which eliminates the need for an annealing process and simplifies the complicated preparation process.The effect of oxygen partial pressure on the phase structure,surface morphology and photoelectric properties of the films were investigated.The change of samples transmittance with temperature was analyzed emphatically.It was observed that the oxygen flow rate during sputtering has a significant influence on the formation of the crystal phase of the deposited films,thereby affecting the thermochromic properties of the films.Our high quality with pure phase VO₂ films grown on the quartz substrate has a great potential for smart windows.4)The preparation of thin-film materials such as metastable VO₂?B?and V₂O₃ was introduced in detail.The samples were characterized by phase structure,surface morphology and high-low temperature four-probe resistance test.The metastable VO₂?B?film does not undergo semiconductor-metal phase transition and thermal hysteresis at room temperature.It can be applied to uncooled infrared detectors.A single crystal and polycrystalline V₂O₃ film was obtained by deposition,which can be used as a seed layer to grow the VO₂ film to improve it crystallinity and thermochromic properties.