Study On The Key Techniques Of Silicon-Based Thermo-Optical Tunable Thin Film Filter

Silicon-based thermo-optical tunable Fabry-Perot filter film has a very impressive application prospect in the field of infrared detection based on the wavelength conversion and the field of optical signal demultiplexing due to its high resolution, the wide tuning range, low-cost and flexible design. The reasonable structural design of thin film filter, the excellent uniformity and optical properties of silicon-based monolayer, and the stability of multilayer film microstructure during the preparation process, and so on, these are the key factors affecting the performance of the silicon-based multilayer filter. Therefore, this paper theoretically analyzed and optimized the structure of the filter, and then experimentally explored the controlled technology of the silicon-based monolayer film performance and inquired into the preparation technology of multilayer DBR and filter.Firstly, this paper selected two suitable preparation material, and then theoretically simulated the key factors affecting multilayers DBR and filter and analyzed the effect of thermo-optic tunable. Results showed that the filter with symmetric DBR structure can get better transmission performance, the larger of the optical thickness of cavity and the number of DBR cycles will get a smaller FWHM of the filter.Secondly, completed the preparation and characterization of a-Si:H and a-Si Nx:H thin films under different conditions of PECVD processes, and then studied the controlled technology of the optical properties and uniformity of these silicon-based film. For the a-Si:H, the uniformity and optical properties become more even and ideal as increasing the gas pressure; it will get a better performance on both uniformity and optical properties as the increase of power density at first, but the thin film will get a very poor performance with the continued increase of power density. For the a-Si Nx:H, the trends of the film properties by increasing the power density and the ratio of ammonia are similar to the change of a-Si:H performance as increasing the power density. The best process conditions of monolayer are obtained for the preparation of infrared filter, which are the 0.17 W/cm2 and 80 Pa for the a-Si:H thin film and the 0.51 W/cm2 and the 1:2(Si H4/NH4 ratio) for the a-Si Nx:H thin film.Then, the multilayer DBR structures with high reflectivity at 1550 nm were designed in theory and verified in preparation. Experimental results show that the reflectivity of 5 cycles of a-Si:H/a-Si Nx:H structure can up to 99.3 % in the stop band, the maximum stop band bandwidth is 742 nm. The defects appeared in the 5th cycle film can be found from SEM cross section, which is presumed caused by the temperature of growing surface. The Si-N bond absorption peak increased significantly as the number of cycles up to 5 which can be observed from FTIR spectra, to some extent, it explains the formation of defects from the perspective of micro-structural components.Finally, this paper designed, prepared and tested two kinds of multilayer film filters based on based on the experience in preparation of multilayer film by PECVD process. The filter with the 0l/ 2 cavity optical thickness is fully met the expectations index, the transmittance can up to 75.77 % at 1550 nm, the FWHM and FSR is 45 nm and 354 nm respectively. In addition to the blue shift of the transmission peak, the filter with the 0l cavity optical thickness is also reached the target. These two kinds of multilayer filters reveal a remarkable uniformity, surface roughness and density observed from the SEM cross section.