Design and optimization of microbolometer multilayer optical cavity

Abstract

Microbolometers are the most widely used detectors in long-wave infrared uncooled thermal imagers. An optical cavity is required within a microbolometer structure to increase its optical absorption. In this work we present a detailed study on the design and optimization of a microbolometer optical cavity using Essential-Macleod package. In the simulations, the cavity is considered as thin film multi-layers that form cascaded Fabry-Perot optical cavities. In the design phase, the layers structures are selected including materials and initial thickness. The absorbing layers are chosen to be vanadium-pentoxide (V2O5) and titanium (Ti). In the optimization phase, the designed layer thicknesses are varied to maximize optical absorption within the absorbing layers. The simulations show that Ti layer absorption dominates over V2O5 layer. Also, the optimization proves that the air-gap cavity thickness is not simply quarter-wavelength because of the complex cascaded Fabry-Perot structure. The optimized air-gap thickness here is ≈3.5 µm at 10.6µm wavelength.