Sol - Gel Preparation Of Porous Silica Films

In recent years, the research of preparation and characterization of porous silica thin films has become one of the hot areas in materials related fields. In many applications, porous silica thin films have an extremely important significance as the application of thermal insulation material. Porous SiO2 films are used as a thermal-insulation layer to block the diffusion of heat flow from the pyroelectric layer to the silicon substrate.This paper introduced the main technology and principle of preparation of silicon dioxide insulation thin film currently, compare a variety of process technologies, explored the experimental process. Porous silica thin films which have the effect of insulation have been prepared by Sol-gel process on silicon. Silicate solutions is obtained from tetraethoxysilane (TEOS) as raw materials and ethanol, ethylene glycol ethyl ether, isopropyl alcohol, water as solvents in addition of organic additives, on base catalysis system. Porous silica thin films on silicon wafers were prepared by spinning coating, then put it in vacuum oven to aging at 60℃for hours, in the end, put it in the high-temperature resistance furnace tube, to have the products through control the cooling and warming speed by artificial temperature controller to process heat-treated.Different thin films have been prepared with various parameters through different experimental condition, The impact of some factors has been analyzed, such as the quantity of water, sol ratio, annealing temperature, aging time to the film. The best technology method of the preparation had been discussed. After discussion of the experimental analysis, TEOS:H2O=1:1.5 is the best mol radio of the water adding. Method of mixed solvents, catalytic method with alkali, using a vacuum drying oven to accelerate the sol-speed, the use of sub-methods of heating, can be consistent with the requirements of thin-film heat insulation.To analyze the thin films composition and surface morphology by using FTIR detector, differential thermal analysis(DTA), scanning electron microscopy(SEM), Ellipsometer etc. The sol viscosity test has been tested by viscosimeter, the aging time under different catalytic method and the thermal conductivity has been tested by using home-made equipment. Differential thermal analysis(DTA) show that there are a large number of exothermic peak from room temperature to 250℃, means that it's the critical time to remove water and–OH group in the heat treatment, control the warming spend of this time to 0.5℃/min. Infrared spectral analysis showed that the major components of the thin films are SiO2. Ellipsometer and scanning electron microscopy (SEM) analysis showed that the thickness of thin films are from 700~800nm. Scanning electron microscopy (SEM) analysis showed that the thin films were buildup by closely SiO2 particles, spherical particles showed a diameter of about 30~50nm. By using the refractive index that form the text of ellipsometer, the porosity of the film has been calculated that more than 50%.In a word, SiO2 thin films with heat insulation effect is successful made by the sol-gel method, the process has been optimized, and the adhesion property with silicon substrate is great, which will be found wide use in the civil and military filed.