Micromachined Optical Readable Uncooled Thermal Imaging Technology Based On Fabry-Perot Interferential Principle

With the development of MEMS(Miro-electro-mechanical system) technology, the breakthrough of uncooled thermal imaging technology has been achieved in recent years. Optical readable uncooled thermal imaging technology is one of the most attractive topics in infrared detective field.In this dissertation, we first proposed a novel micromachined optical readable uncooled thermal imaging system based on Fabry-Perot interferential principle, which has many merits, for example, higher brightness, better modulation degree of interferential light and higher sensitivity. It consists of three parts: IR optic system, F-P MCIRDA (Fabry-Perot Mico-Cavity Infrared Detective Array) and visible light readout. This dissertation covers the optimization of F-P MCIRDA, the key part of the system, performance analysis of F-P MCIRDA and this system, F-P MCIRDA fabrication and its performance tests.F-P MCIRDA plays the roles of infrared sensing and optical readout. For the optimization design, the optical and thermo-mechanical analysis are involved. Optimal design of F-P MCIRDA has been achieved and structure parameters of movable micro-mirror has been determined by theoretical analysis. From thermal stress theory, the relation between the structure parameters and thermo-machanical sensitivity of bi-material beams supported movable micro-mirror was analyzed, and the optimal thickness ratio and its corresponding maximal thermo-mechanical sensitivity were determined by using thermal stress theory.In this dissertation, we theoretically analyzed opto-mechanical sensitivity, infraredMicromachined Optical Readable Uncooled Thermal Imaging Technology Based on Fabry-Perot Interferential Principletemperature response, time constant and so on of F-P MCIRDA, which helps us to find the the relations between structure parameters and performances of F-P MCIRDA. We also investigated two important aspects of infrared response ability of this system: system detectable temperature difference and noise analysis. The former with a value larger than 2500K can satisfy the requipment in most infrared detective cases. The latter analysis indicates that the visible light readout is the main noise source and the minimal NETD (noise equipment temperature difference) can reach uK level.The bulk micromachined F-P MCIRDA ensures that two reflective surfaces of Fabry-Perot micro-cavity are parallel with each other and larger array device can be easily realized. Some processes, for example, thin film etch and silicon-glass bonding and so on, were studied detailly and optimized; the carefully designed process flow was applied to develope a 50X50 Al/SiC^ movable micro-mirror array which successfully demonstrated the first but promising response to infrared signal.Several key factors that may affect device performance were investigated: infrared absorptive spectrum of SiC>2 and SiNx films that fabricated in our laboratory; the impacts of residual stress on the profile of movable micro-mirror by using ANSYS; the roughness of Fabry-Perot reflective surfaces; and the cause of destroyed metal surface occured in silicon-glass process.We built a testing system for thermo-mechanicai sensitivity. The achieved results for movable micro-mirror with Al/SiC2 bi-material beams include: the movable micro-mirror showed distinct displacement; measured data, theoretical and ANSYS modulation results of thermo-mechanicai sensitivity are 2.02xlO"8m/K, 3.30xlO"8m/K and 2.80* 10"8m/K, respectively, which are in good accordance within the error range and verify the validity of theoretical design.