Numerical and Experimental Investigation into LWIR Transmission Performance of Complementary Silicon Subwavelength Antireflection Grating (SWARG) Structures

This paper presents a detailed comparison between the long wave infrared (LWIR) transmission performances of binary, silicon based, structurally complementary pillar and groove type antireflective gratings that can be used for wafer level vacuum packaging (WLVP) of uncooled microbolometer detectors. Both pillar and groove type gratings are designed with various topological configurations changing in various period sizes (Λ) from 1.0 μm to 2.0 μm, various heights/depths (h) from 0.8 μm to 1.8 μm, and various pillar/groove width-to-period (w/Λ) ratios from 0.6 to 1.0. The transmission performance of gratings is simulated with a hybrid simulation technique based on the modification of the reflection term within the Fresnel transmission equation, which combines both numerical and analytical approaches in a unique way for the first time in literature. Simulation results are experimentally verified with 19 different fabricated structures where a spectral agreement is achieved with an absolute root-mean-square (RMS) error less than 5.4% within the subwavelength (SW) regime, proving the effectiveness of the proposed hybrid technique. These results show first time in the literature that both pillar and groove type silicon based gratings present similar spectral IR transmission characteristics, and they are also structurally complementary when optimum configurations are employed to maximize the transmission.