Patterning of oxide-hardened gold black by photolithography and metal lift-off

• We report the patterning of oxide-hardened gold black with standard photolithography and metal lift-off.
• The minimum pattern length-scale achieved was less than 10 μm after lift-off.
• Average ∼90% absorption in 3–5 μm wavelength window is observed on the patterns.
• For IR array detectors, we provide a method to selectively coat the active regions of individual pixels.
• This method will help improve the sensitivity of current generation micro-bolometers.

A method to pattern infrared-absorbing gold black by conventional photolithography and lift-off is described. A photo-resist pattern is developed on a substrate by standard photolithography. Gold black is deposited over the whole by thermal evaporation in an inert gas at ∼1 Torr. SiO2 is then deposited as a protection layer by electron beam evaporation. Lift-off proceeds by dissolving the photoresist in acetone. The resulting sub-millimeter size gold black patterns that remain on the substrate retain high infrared absorption out to ∼5 μm wavelength and exhibit good mechanical stability. This technique allows selective application of gold black coatings to the pixels of thermal infrared imaging array detectors.