A Fiber-Si3N4 Composite Nanoforest with High 7.6 to $11.6\ \mu\mathrm{m}$ Absorption for MEMS Infrared Sensors

In this work, a fiber-Si3N4 composite nanoforest with high absorption in 7.6 to $11.6\ \mu \mathrm{m}$ wavelength range is presented. Especially, when thickness of a Si3N4 coating reaches 300 nm, the nanoforest can achieve an average absorption as high as 88.12%. Such a composite nanoforest is fabricated based on an extremely simple process, including spin-coating and plasma treating of a polyimide layer, followed by deposition of a Si3N4 film. The process is fully compatible with conventional micromachining, thus the nanoforest can be integrated onto MEMS infrared (IR) sensors as an additional absorber. Furthermore, with such a composite nanoforest-based absorber, the IR sensors are expected to achieve higher performance, especially for human IR sensing.