Performance Analysis And Optimization Of The Substrate-free Focal Plane Array

Infrared (IR) imaging technique plays a critical role in military, industrial, medical, commercial applications. Optical readout uncooled IR imaging technique becomes a hotspot of research because of its low cost and high performance. Substrate-free focal plane array (FPA) is the key component of this technique and a series studies about it are carried out. This dissertation has proposed a new theoretical analysis model for thermal-mechanical behaviour of substrate-free FPA. FPA was designed and fabricated with new materials, with various optimizations to improve the deformation of FPA reflectors. Furthermore, a thermal infrared spectral analysis embedded software platform has been developed. The main achievements of this dissertation are as follows:(1) Finite element analysis (FEA) is convenient and accurate in predicting a response when the parameters of the geometrical design are given. However, FEA hardly provides an effective methodology for the design of an FPA when a performance goal for a system, such as the temperature gray response, is desired. This paper presented an analytical model, based on an analogy with electrical circuits and a holistic approach, to analyze the performance of substrate-free FPA, using metrics such as the temperature gray response and the response time of the FPA. This analytical model was validated by FEA results. A substrate-free FPA with a unit size of50μm×50μum was fabricated. Its infrared imaging experiments validated the model and indicated a noise equivalent temperature difference (NETD) value of170mK has been achieved. At the same time, theoretical model analysis of FPA with unit sizes of120μm×120μm and200μm×200μm verified that this model can apply to substrate-free FPA with any unit size.(2) Based on the material selection requirements of substrate-free FPA, a substrate-free Al/SiO2bi-material FPA with a unit size of50μm×50μm was fabricated under the constraint of MEMS manufacturing process,. Its thermal-mechanical performance was analysed by FEA and compared with that of a substrate-free Au/SiNx bi-material FPA with the same unit size, which showed the heat conversion efficiency and the thermo-mechanical efficiency of the Al/SiO2bi-material FPA were improved significantly. This material optimization enhanced the sensitivity of the system by up to5.8times of the original. (3) Three optimization schemes for reducing the initial deformation of the FPA reflector were proposed in this dissertation:A. Reducing the thickness of the Au layer on the reflector. Based on the theoretical analysis, a FPA with a unit size of200μm was fabricated and the thickness of the Au layer of its reflector was reduced. The reflector curvature radius and optical detection sensitivity for the system were increased by4.71times and5.2times repectively compared to that of the FPA without thinning process. B. Fabricating reflector with stiffeners. A FPA with a unit size of60μm was fabricated, with stiffeners. The reflector curvature radius and optical detection sensitivity for the system were increased by4.29times and1.18times respectively comppared that of the FPA without stiffeners. The experiments agreed with the anticipation of the theory. C. Two annealing methods on substrate-free Au/SiNx bi-material FPA with a unit size of50μm×50μm using Hot-Cold Stage were carried out:direct annealing process and circular annealing process. The second treatment enhanced the temperature-gray response by32%。(4) A thermal infrared spectral analysis embedded software platform was developed. This software platform integrated the motor control of a vertical focused platform and a variety of hardware devices and realized functions on the infrared imaging device, such as camera connecting, adjusting, data transmission, data analysis and processing, data display, etc. With an extra registration service module to contact the client and server, this embedded platform was ready for commercial sale. Further development on this platform was based on the advantage of the IR imaging technique on monitoring. A YaAn PTZ device was integrated for controlling the field of view of the IR imaging device. The PTZ controlling module and multichannel image processing (visible light camera and IR imaging device) module were also embedded in the platform. Considering the broad market prospects of the IR imaging, the commercial value and development potential of this embedded platform would be great.