Patterning of single-walled carbon nanotubes and photosensitive polyimides

Abstract

Well-defined and high-density single-walled carbon nanotube (SWNT) patterns were fabricated using a combination of photolithographic and chemical assembling processes. To form the SWNT pattern, the substrate was treated with acid-labile group protected amine, and an amine prepattern was formed using a photolithographic process with a novel polymeric photoacid generator (PAG). The polymeric PAG contains a triphenylsulfonium salt on its backbone and was synthesized to obtain a PAG with enhanced efficiency and ease of spin-coating onto the amine-modified glass substrate. The SWNT monolayer pattern was then formed through the amidation reaction between the carboxylic acid groups of carboxylated SWNTs (ca-SWNTs) and the prepatterned amino groups. A high-density multilayer was fabricated via further repeated reaction between the carboxylic acid groups of the ca-SWNTs and the amino groups of the linker with the aid of a condensation agent. Unlike previously reported patterned SWNT arrays, this ca-SWNT patterned layer has high surface density and excellent surface adhesion due to its direct chemical bonding to the substrate. Well-defined polyimide patterns were also fabricated by the preparation of a chemically amplified photosensitive polyimide (PSPI). The positive-working PSPI developable with basic aqueous solutions was obtained from poly(amic acid ethoxymethyl ester) (PAAE) as a polyimide precursor and diphenyliodonium 5-hydroxynaphthalene-1-sulfonate (DINS) as a photo acid generator. The acid generated from DINS in the UV exposed region effectively deprotects the ethoxymethyl groups of PAAE by a chemical amplification mechanism. The resolution of the PSPI is excellent compared to those previously reported for chemically amplified PSPIs, and such a film can thus be used as a buffer coating in semiconductor packaging.