Improved organic thin film transistor performance using chemically-modified gate dielectrics

We report on the use of silicon dioxide gate dielectric chemically-modified with vapor-deposited octadecyltrichlorosilane (OTS) monolayers for improved organic thin film transistor (OTFT) performance. To date, silicon dioxide gate dielectric chemically-modified with OTS monolayers deposited from solvent solution have demonstrated the highest reported OTFT performance using the small-molecule organic semiconductor pentacene as the active layer. Vapor treatment is an attractive alternative, especially for polymeric substrates that may be degraded by solvent exposure. Using our OTS vapor treatment we have fabricated photolithographically defined pentacene OTFTs on flexible polymeric substrates with field-effect mobility greater than 1.5 cm²/V-s. We find the performance of pentacene as well as several other small-molecule organic active layer materials can be significantly improved using silicon dioxide gate dielectric chemically-modified with vacuum vapor prime OTS. Pentacene, naphthacene, Cu-phthalocyanine, and alpha-sexithienyl OTFTs fabricated on thermally oxidized silicon substrates with photolithographically defined "bottom" contacts typically show a factor of 2 to 5 improvement in field-effect mobility and reduced subthreshold slope when using silicon dioxide gate dielectric vacuum vapor treated with OTS compared to OTFTs on untreated gate dielectric.