Mid-infrared Based 1-D Porous Silicon Dioxide Photonic Crystal For Pyroelectric Sensor Application

Porous Silicon,a brand new optical material,is usually fabricated by anodization. Periodically alternative changes of high/low current densities may form alternative porosities in anodization in one dimension.Therefore,it consists of alternating layers of different refractive indices,resulting in considerable novel characters named photonic band gap(PBG),which means the light can't transmit in the photonic crystal when light's frequency locates in the PBG.Thus,it is also called 1-Dimension photonic crystal.Large refractive index variation with porosity,as well as relatively simple fabrication and low manufacturing cost,makes porous silicon a very promising candidate for photonic applications.Since after oxidation,the porous silicon can be oxidized into one of excellent thermal isolative properties,if its photonic band gap is designed at the mid/far infrared(IR)wavelength,this porous structure can be used as the substrate for non-cooling infrared pyroelectric thin film IR detector,which can not only block the radiation for mid-IR but also can isolate the heat.Non-cooling infrared pyroelectric thin film IR detector has attracted great interest due to its high sensitivity and can be applied at room temperature. Unfortunately,the thermal isolative structure of the substrate and its infrared radiation was the major factors that limit the resolution of non-cooling infrared pyroelectric thin film IR detector.This thesis focuses on this problem and tries to find a substrate material for non-cooling infrared pyroelectric thin film IR detector, based on the oxidation of one dimension porous silicon photonic crystal.The structure factors of the PBG material is discussed,which can influence the photonic crystal multilayer through computer simulation and be referenced for the anodization process.Rapid thermal oxidation(RTO)is applied to achieve a good thermal isolative layer with a photonic band gap at expected mid/far infrared range. Several factors have been discussed to optimize the properties to get a substrate for non-cooling infrared pyroelectric thin film IR detector.In ChapterⅠ,the basic knowledge of photonic crystal is introduced briefly, especially one dimension photonic crystal together with the development status of photonic crystal and the problems it has encountered.The aim of this paper is also listed.In ChapterⅡ,the basic theories and fabrication technique are described for the one dimension porous silicon photonic crystal.The influence of the factors,such as current density,HF concentration,the type of substrate,formation temperature and RTO time and temperature are discussed to obtain the promising substrate material.In ChapterⅢ,one dimension porous silicon photonic crystal is designed by means of the transfer-matrix method(TMM).The influence of the number of periods and the ratio of refractive indices are investigated on the wavelength of mid-gap to the reflectivity spectra.In ChapterⅣ,the optimization of one dimension porous silicon photonic crystal is discussed.Fourier transform infrared spectroscopy(FTIR)is applied to check the difference before and after oxidation,contrast and comparison with simulation.Parameters for obtaining photonic crystals with the PBG gap ranging in mid(5,6,7 microns)have been successfully achieved.Such a material has also good thermal isolative properties due to RTO process.In ChapterⅤ,the practical use of the substrate at far-IR(10 microns)is discussed and the fabrication procedure of the array for non-cooling infrared pyroelectric thin film IR detector has been addressed and achieved.SEM is applied to find its multilayer structure while FTIR for its optical properties.ChapterⅥwill summarize the work and discuss the future application for this promising substrate.