Selectively apply near-unity absorptive gold-black to the pixels of thermal infrared (IR) imaging array detectors for use in night vision
In thermal IR sensors (bolometers), absorptive coatings convert IR power into heat. Absorptive coating gold-black has been used for many decades for IR bolometers, particularly for array detectors used in night vision for defense and security. Gold-black is a nanocrystalline deposit formed when an inert gas causes gold atoms to collide and bind with each other to form a web-like structure. While the material achieves near-unity absorption from visible to far IR, it is extremely fragile and cannot currently be patterned to selectively coat only the sensing elements of IR array detectors.
This gold-black coating for infrared sensors from UCF establishes a means of protecting the fragile layer of gold-black with an overcoat of evaporated dielectric, and of coating individual pixels to improve the sensitivity of micro-bolometers. For IR array detectors, only the sensing element should be coated leaving the spaces in between the pixels clear in order to avoid thermal and electrical bridging. Laser ablation has been used in the past to remove coatings deposited between the pixels, but this slow process is unsuited for mass production. This new method solves that problem by providing a means to selectively coat the active regions of individual pixels.
This new method of patterning gold-black reaches at least 90% absorption, but more often approaches 100%, in the mid-IR range using standard photolithography and metal lift-off. In the application process, gold-black is deposited on a photoresist by thermal evaporation in an inert gas at 1 Torr, followed by depositing SiO2 as a protection layer by electron beam evaporation. The photoresist then dissolves in acetone resulting in sub-millimeter size gold- black patterns that retain high IR absorption out to 5 μm wavelength and exhibit good mechanical stability.
- Over 90% absorption
- Improved sensitivity
- Night vision for defense and security