The Mechanism Research And Development Of Multilayer Nanometal Decorated Black Silicon In Mid-infrared

Gas detectors have been widely used in environment protection,industrial monitoring and medical instruments.the requirements of non-dispersive infrared(NDIR)gas sensor have increased recently because of the advantages of high reliability,fast response speed and high selectivity.the performance of critical infrared detector is closely related to that of gas sensor.The pyroelectric infrared detector based on microelectromechanical system(MEMS)technology has the advantages of high detectivity and low noise signals,which can be applied to high-precision gas sensing.However,the absorber on the surface of the pyroelectric detector affects the output signal distinctly,which has the performance requirements of high absorption,low heat capacity and high reliability.Herein,based on the mechanism of light trapping resulted from black silicon and the electromagnetic loss caused by nanometal,we designed and fabricated black silicon decorated with multilayer nanometal for the higher absorption in mid-infrared.The research and development involved in this paper are as follows:(1)The infrared absorption mechanism of black silicon,nanometal and multilayer nanometal decorated black silicon was investigated.The contribution of light trapping to the infrared absorption of black silicon was verified by finite element simulation.The permittivity of Pt nanoparticles was calculated,and the infrared enhanced absorption of Pt nanoparticles was proved based on simulation.The simulation of the multilayer nanometal decorated black silicon had been completed to the absorption enhancement contributed by black silicon and Pt nanoparticles.Finally.the structure of Pt nanoparticles was optimized.(2)The black silicon was etched by inductively coupled plasma etch(ICP etch).Innovatively,black silicon was fabricated on a substrate surface using single-step etching of C4F8 and SF6 plasma By altering the gas flow ratio,the etch morphology changed from isotropic to anisotropic etching was realized.Characterized by scanning electron microscopy(SEM),a black silicon structure with a height of 892 nm was obtained.The multilayer nanometal was characterized by and transmission electron microscopy(TEM),and the particles with size ranging from 4 to 12 nm were insulated by SiO2 thin films.Finally,the absorptions of the black silicon with different heights and multi-nanostructures were measured,and the structure with 6 layers of Pt nanoparticles achieved 92%at the range of 2.5-20 μm by using a Fourier-transform infrared spectrometer with an integrating sphere.(3)In order to realize the application of the absorption material on the infrared device,the patterning process was simplified and optimized,and the number of etching and lithography processes was reduced.In order to stabilize the performance of photoresist in the process of patterning,the minimum temperature and time during thermal treatment in the preparation of multi-nanostructures were determined by experiments.In the end,the improved lift-off process has been developed to patterned the absorber on the surface of a 4inch thermal oxidation silicon wafer and the multi-physics simulation has been done.