| Electromagnetic waves in the millimetre wave and terahertz bands have safety,metallic reflection properties,non-ionising properties and non-polar material penetration that other wavelengths do not have,and their relatively short wavelengths allow for higher imaging resolution.Therefore,research into imaging systems in the millimetre wave and terahertz bands is of great importance for military surveys,medical imaging and human security screening.Among the many imaging systems,focal plane(FPA)imaging requires no additional mechanical scanning and has the characteristics of portability and real time,making it the main imaging modality.However,traditional focal plane imaging is bulky,costly and difficult to achieve real-time imaging,and there are some urgent problems to be solved.In recent years,structural functional materials have been applied to various fields with the advantage of artificially modulating the desired properties.In addition to this,the use of micro-opto-electro-mechanical systems(MOEMS)to achieve highly integrated,low-cost and small volume designs has become a major focus of scientific researchers.In this paper,the cross-fertilisation of two technologies,structural functional materials and MOEMS,is applied to the study of focal plane chips,a key component of imaging systems,with the following specific findings.(1)The working mechanism of the focal plane chip is investigated: starting from the imaging framework,the overall structure and imaging principles are studied.Then the focal plane is analysed from two parts: electromagnetic absorption principle and cantilever detection principle.It is pointed out that the focus of focal plane research is to achieve ultra-high absorption at ultra-thin thicknesses,which in turn causes large mechanical strains in the focal plane.(2)The study of highly absorbing focal plane chips at ultra-thin thicknesses is carried out: The innovative separation-inversion structure was proposed to solve the problem of the limitation of the thickness of the structural functional material and to reduce the thickness of the dielectric substrate of the focal plane chip to a scale of two thousandths of a wavelength.A FPA chip has been designed for the 94 GHz and 220 GHz bands respectively.For the 94 GHz focal plane chip,the electromagnetic simulation results show that the absorption rate at 94 GHz is greater than 99%;the thermomechanical study shows that the thermal response time per unit temperature rise of the FPA chip is 1.14 s and the maximum mechanical deflection is 1.17 um.The measured results show that the absorption rate at 94 GHz is 96.7%.For the 220 GHz focal plane simulation,the absorption rate at 220 GHz is greater than 99%,the thermal response time per unit temperature rise is 0.3s,and the maximum mechanical deflection is 0.22um;due to the limitation of processing technology,the measured absorption frequency point is shifted to 226.3GHz,and the absorption rate is 98%.(3)Research on an ultra-thin,high-absorption focal plane chip based on indium tin oxide(ITO)film: using a transmissive indium tin oxide film,the high transmission and metal-like properties of the film can be used to achieve high absorption and a side transmissive design,solving the problem of visible light source incidence in optical readout systems.In addition,the first version of the structure was improved by drilling holes to reduce the effect of self-weight,optimising the corner structure to reduce processing difficulties,and adding a silicon support frame to improve the mechanical capacity of the structure.Simulation results show that the 94 GHz focal plane chip based on ITO film achieves near perfect absorption at 94 GHz.The test results show that the overall absorption band is red-shifted,with the perfect absorption peak moving to92.04 GHz,and the absorption rate at the designed 94 GHz frequency point is about 90%. |
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