This paper introduces a method for a broadband absorption enhancement in the LWIR range (8-12 μm), in single layer microbolometer pixels with 35 μm pitch. For the first time in the literature, this study introduces a very simple and low cost approach to enhance the absorption by embedding plasmonic structures at the same level as the already existing metallic layer of a microbolometer pixel. The metal layer comprises the electrode and the arm structures on the body. Even though the periodicity of the plasmonic structures is slightly disturbed by the placement of the electrodes and the connecting metal, the metal arms and the electrodes compensate for the lack of the periodicity contributing to the resonance by their coupling with the individual plasmonic resonators. Various plasmonic structures are designed with FDTD simulations. Individual, plasmonically modified microbolometer pixels are fabricated, and an increase in the average absorption due to surface plasmon excitation at Au/Si3N4 interfaces is observed. Plasmonic structures increase the average absorption from 78% to 82% and result in an overall enhancement of 5.1%. A good agreement between the simulation and the FTIR measurement results are obtained within the LWIR range. This work paves the way for integration of the plasmonic structures within conventional microbolometer devices for performance enhancement without introducing additional costs.
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%.
This paper introduces an analysis on the absorption enhancement in uncooled infrared pixels using resonant plasmon
modes in metal structures, and it reports, for the first time in literature, broad-band absorption enhancement using
integrated plasmonic structures in microbolometers for unpolarized long-wave IR detection. Different plasmonic
structures are designed and simulated on a stack of layers, namely gold, polyimide, and silicon nitride in order to
enhance absorption at the long-wave infrared. The simulated structures are fabricated, and the reflectance measurements
are conducted using an FTIR Ellipsometer in the 8-12 μm wavelength range. Finite difference time domain (FDTD)
simulations are compared to experimental measurement results. Computational and experimental results show similar
spectral reflection trends, verifying broad-band absorption enhancement in the spectral range of interest. Moreover, this
paper computationally investigates pixel-wise absorption enhancement by plasmonic structures integrated with
microbolometer pixels using the FDTD method. Special attention is given during the design to be able to implement the
integrated plasmonic structures with the microbolometers without a need to modify the pre-determined microbolometer
process flow. The optimized structure with plasmonic layer absorbs 84 % of the unpolarized radiation in the 8-12 μm
spectral range on the average, which is a 22 % increase compared to a reference structure with no plasmonic design.
Further improvement may be possible by designing multiply coupled resonant structures.