A plasmonically enhanced pixel structure for uncooled microbolometer detectors

Abstract

This paper introduces a method of broadband absorption enhancement that can be integrated with the conventional suspended microbolometer process with no significant additional cost. The premise of this study is that electric field can be enhanced throughout the structural layer of the microbolometer, resulting in an increase in the absorption of the infrared radiation in the long wave infrared window. A concentric double C-shaped plasmonic geometry is simulated using the FDTD method, and this geometry is fabricated on suspended pixel arrays. Simulation results and FTIR measurements are in good agreement indicating a broadband absorption enhancement in the 8 μm - 12 μm range for LWIR applications. The enhancement is attained using metallic geometries embedded in the structural layer of the suspended microbridge, where the metallic-dielectric interface increases the average absorption of a 35 μm pixel from 67.6% to 80.1%. © 2013 SPIE

Broadband absorption enhancement in an uncooled microbolometer infrared detector

“…While the S-2 and S-3 designs make relatively small contributions to the absorptions, 3.3%, and 1.8% respectively, S-1 results in a very distinct absorption enhancement (5.1%) in a complete microbolometer pixel and increase the absorption from 78% to 82%. The enhancement is much more pronounced between 8 and 9 μm where the silicon nitride is an inefficient absorber [13], the plasmonic features' surface plasmon excitations make a significant contribution to the pixels' performance with the other metal layers on the surface. Additionally, the absorption of S-1 between 8-12 µm range has a very good spectral uniformity compared to the reference pixel, which is also another desired property in the uncooled microbolometers.…”

“…On the other hand, the simulation results are in accord with the FTIR measurement results, the absorption starts to decrease at ~9 µm. The extinction coefficient of the silicon nitride layer around 9 µm clearly starts to increase faster and dominates absorption of the pixel [13], which prevents excitation of surface plasmons in the pixels. The strong material absorption in longer wavelengths overwhelms plasmonic effects.…”

“…The material database of the Lumerical is used during the simulations (except for the dielectric properties of silicon nitride and the active material). The dielectric properties of silicon nitride (deposited in the PECVD system) between 6-16 µm wavelength were given previously [13]. The absorption is calculated from the reflected power, Preflected, as 1-Preflected.…”

“…This paper studies the design and integration of plasmonic structures into a complete microbolometer pixel for improved absorption in the 8-12 µm spectral range. We have previously shown that plasmonic structures can be utilized for strong absorption in the infrared [12] and further demonstrated that plasmonic features can be utilized for strong absorption Si3N4 Ti Au NiCr Polyimide (PI) Active Material enhancement in the bolometric structures [13]. Here, we introduce plasmonic structures into a rather more complex microbolometer pixel which includes a resistive material, metal electrodes providing electrical contacts between the read-out circuitry and the resistive layer through the support arms, and a very thin metal film that is used as the absorber layer.…”

Resistance hysteresis loop characteristic analysis of VO2 thin film for high sensitive microbolometer

“…Therefore, almost all of practical microbolometers are fabricated into a kind of microbridge structure for microbolometric focal plane arrays to improve their sensitivities [4][5][6]. However, the normal microbridge structure is limited to improve the response sensitivity of microbolometer and some complicated conceptual microbridge structure for microbolometer are nearly unchallengeable to be fabricated [7,8].…”