Research On Fabrication,modification And Application Of Porous SiO₂ Film

The structure of porous SiO₂ aerogel film is similar to its bulk material which is composed of SiO₂ skeleton and large amount of nano-sized open pores.This makes it the kind of material with low density,high porosity and high specific surface area.Therefore,it has some remarkable properties such as low thermal conductance,low acoustic velocity,low permittivity,tunable refractive index,et.al.In addition,SiO₂ aerogel film is compatible with micro-electronic device fabrication,easy for large size deposition and easy to transfer.Therefore,it has great potential in micro-electronic devices and micromachining.Till now,SiO₂ aerogel film has already been used in acoustic impedance matching devices,uncooled infrared detectors,organic light emitting diode and semiconductor power devices.However,SiO₂ aerogel film produced from traditional sol-gel endures complicated procedures and long processing time.The physical fragility,poor structural controllability and hydroscopicity of SiO₂ aerogel film hinder its further development and application.This work is aiming to solve those problems found during sol-gel process and during applications.Firstly,the fabrication processes of SiO₂ aerogel film through sol-gel method were investigated.Single layer and bilayer SiO₂ aerogel film with different thicknesses were fabricated.Deeper research was carried out to understand the effects of different catalysts during reaction and how the viscosity of precursor affects the morphology of SiO₂ aerogel film.Transient hotwire and ANSYS simulation were conducted to judge the thermal insulation property of the porous film.The pyroelectric infrared detectors were fabricated on SiO₂ aerogel films with different thicknesses.The excellent thermal insulation was proved.Integrated techniques were applied and pyroelectric infrared sensor array with different unit sizes was achieved.Homogeneous detectivity has been verified according to the testing results.Further research was conducted to know the structural use of SiO₂ aerogel film.It was used as nano-template to fabricate sub-micrometer range resistive switching cells.The transport properties of the cell and its conducting mechanism were measured and analyzed deeply.1?Multi-step catalytic reaction was used to produce SiO₂ aerogel film with high porosity?>90%?.The reaction speed was adjusted by different kind of catalysts.The viscosity of sol precursor and the spin parameters are crucial for the structure of SiO₂ aerogel film.Hydrophobic SiO₂ aerogel films derived from surface modification were fabricated at ambient pressure with different thicknesses?300-1000nm?,surface morphologies and refractive indexes?1.04-1.18?.Extremely low thermal conductance was obtained from transient hotwire measurement.The vertical heat conduction of device was simulated by ANSYS,which proved that 800 nm SiO₂ aerogel film had good thermal insulating effect.2?Due to the excellent thermal insulation property,the SiO₂ aerogel films were applied in pyroelectric infrared detector as thermal insulation layer.Difficulties such as multi-layer structure fabrication and unstable detectivity are solved during the research.The detective properties of sensor units with different thicknesses of porous film were compared.Infrared detector on 780 nm porous SiO₂ film possessed the best detectivity,proving that 780 nm SiO₂ aerogel film had good insulating effect.Pyroelectric infrared array with sensor units of different sizes has also been obtained.A buffer SiO₂ layer was introduced above porous SiO₂ film in order to improve its flatness.The pyroelectric composite material was imaged by wet etching with the mask of top electrode.In addition,the property uniformity of pyroelectric infrared sensor with different unit sizes has been proved.3?SiO₂ aerogel films with different pore sizes and porosities were fabricated on various kind of materials.Therefore,it is an ideal material for nano-template casting.Dot matrix of sub-micrometer resistive switching units was uniformly fabricated on Si substrate assisted by SiO₂ aerogel template.The cylindrical shapes and sizes of the units perfectly match the morphology of pores in SiO₂ aerogel film.The outstanding resistive switching properties including high on/off ratio?>10⁴?,good retention?>600min?and extremely low SET voltage?<0.1V?were observed in the devices.Microstructure and chemical state of the sample were measured and the resistive switching mechanism was analyzed and elaborated accordingly.A conducting model was established for further understanding.In addition,this model perfectly explains the multi-level switching behavior observed in the device.