Deposition and patterning of conductive carbon black thin films

Highly conductive carbon black-filled composite thin films were prepared using layer-by-layer assembly. Films were grown by alternately dipping a PET substrate into aqueous suspensions containing carbon black and polyethylenimine (PEI) or poly(acrylic acid) (PAA). Growth rate and sheet resistance of these films were tailored by varying the polymer concentration in the suspensions and completely removing carbon black from one solution or the other. Films made from an aqueous mixture containing 0.25 wt.% carbon black and 0.05 wt.% PAA and another solution containing 0.1 wt.% PEI grew at a rate of 735 nm per bilayer (BL) deposited and achieved the lowest sheet resistance at 10-BL (∼500 Ω/sq), with a thickness of 5.4 μm, making its bulk resistivity below 0.3 Ω cm. These composite thin films were patterned using a traditional photolithographic lift-off process that could be used to process them for a variety of electronics applications.