Design and fabrication of thin film a-Si Al2O3 Infrared filter

Abstract EN

Long-wavelength infrared filter operated at various temperature are critical for imaging applications.

In this paper anew type of infrared filter is investigated, this infrared filter uses a crystalline silicon substrate coated with multi layers of aluminum oxide (AL2O3) and amorphous silicon (a-Si) to produce the multi layers thin film infrared filter a-Si / AL2O3 operating in the range (8-14)um.

Amorphous silicon is used in this paper due to its high refractive index, while AL2O3 due to its low refractive index material.

The a-Si / AL2O3 thin film structure were designed using the Thin Film Design software (TF Calc 3.5.6 version).

The simulated results obtained shows that the transmittance of the a-Si / AL2O3 infrared filter with 19 layers is about 90% for (8-12.5) μm wavelength, while it is about 95 % for 47 layers for (8.25-13.25) μm wavelength.

The investigated filter was fabricated using vacuum evaporation process and the results obtained were comparable with the simulated one.

The fabricated a-Si / AL2O3 filter is compared with the Ge / ZnS infrared filter and it is found that the results is comparable but the cost of the fabricated filter is small compared to the Ge / ZnS filter.