Study On Thermal Isolation Layer And Mechanical Property Of Porous Silicon In MEMS Uncooled Infrared Bolometer

Uncooled infrared (IR) bolometer based on thermistor is a dominant low-cost uncooled thermal infrared detector,which has attached more and more attention by researchers around the world in recent years. In this paper, study on the material property and detector microstructure was carried out in order to improve the performance of the detector in the two aspects.The significance of thermal isolation structure and the characteristic of thermal isolation structure in mictro-detector were analyzed; the technique process of uncooled infrared bolometer was designed and a porous silicon (PS) thermal isolation layer was proposed; the mask was designed using L-EDIT software and 4 pieces masks (2.5 inch) were fabricated. In addition, the influence of the preparation condition of PS on its mictrostructure and the relationship between mictrostructure and thermal isolation property of PS was analyzed, the mechanical property of different porosities of PS and Vanadium oxide thin films deposited on PS/Si were compared.The thermal isolaton layer PS was prepared by electrochemical etching method, vanadium oxide thin films was deposited on silicon surface and PS by facing targets direct current reactive sputtering in super high vacuum method. The microstructures of PS samples were observed by Field Emission Scanning Electron Microscope (FESEM), and the three-dimensional topological image of PS was captured by Nano Profilometry (NP); the thermal conductivity is measured by micro-Raman spectrum method; Nano-indentation instrument (MTS Nano Indenter XP) was used to measure the hardness and Young's modulus of PS and vanadium oxide thin film。The results show that the thermal conductivity of PS with porosity of 50%, 55%, 65% are 8.16/W/mK,7.28/W/mK,0.624/W/mK, respectively; which drops with the porosity rises. The average hardness and Young's modulus of PS are in the range of 0.478GPa ~1.171GPa and 10.912GPa ~17.15GPa, which rises with the current density. The hardness and Young's modulus of vanadium oxide thin films deposited on PS with porosity of 50%, 55%, 65% are 1.917 GPa, 0.928 GPa, 0.13GPa, and 31.087 GPa, 16.921 GPa, 2.285 GPa, respectively; which have great difference compared to sample deposited on silicon substrate (10.919 GPa and 193.792 GPa). The dependence of PS thermal isolation and mechanical performance on its microstructure are obtained, which affords a certain thermal and mechanical parameters for the manufacture of uncooled infrared bolometer.