Study On Thermal And Mechanical Properties Of Porous Silicon Thermal Isolation Layer Used In Uncooled Infrared Microbolometer

Uncooled infrared detector is widely studied around the world, since its immense potential value in both military and civilian area. At present, microbolometer is the kind of uncooled infrared detector which is mostly studied and applied. The author's laboratory proposed a new type of microbolometer which uses porous silicon as heat-insulating layer based on the consideration of adiabaticity, mechanical stability and compatibility to silicon technology.This thesis builds the theoretical mathematical model to study the thermal and mechanical properties of porous silicon heat-insulating layer. Specifically, how pore existing way, pore distribution and film thickness affect the thermal and mechanical properties of porous silicon heat-insulating layer is analysed and explained. The validity of mathematical model is verified by comparing the model result with experimental data measured before. Furthermore, ANSYS finite element simulation is used to prove the correctness of mathematical medal as well. Properties of porous silicon's thermal conductivity and Young modulus areattributed to its structure factors, such as the existence and distribution of pores. Porous silicon is viewed as a compound microstructure piece, which is constructed by both silicon continuous material and pore continuous material medium, connecting in parallel and series pattern. Therefore, an understandable and simpler explanation to thermal and mechanical properties of porous silicon is given. The influence of porosity to equivalent thermal conductivity and equivalent Young modulus can be broken down to two parts, vertical and horizontal. In addition, by observing the semi-quantitative mathematical model under different pore structures and distributions, the correlation between the porosity and equivalent thermal conductivity and Young modulus will be explained.Through the theoretical and simulation analysis in this thesis, the relationship between thermal and mechanical properties of porous silicon and its pores structure will be clearly explained; the current relevant theories are perfected and supplemented; the theoretical instruction to prepare satisfactory porous silicon is proposed. Therefore, this thesis has practical significance to porous silicon heat-insulating layer preparation.