A high-performing bottom-gate top-contact pentacene-based oTFT technology with an ultrathin (25-48 nm) and electrically dense photopatternable polymeric gate dielectric layer is reported. The photosensitive polymer poly((±)endo,exo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, diphenylester) (PNDPE) is patterned directly by UV-exposure (λ = 254 nm) at a dose typical for conventionally used negative photoresists without the need for any additional photoinitiator. The polymer itself undergoes a photo-Fries rearrangement reaction under UV illumination, which is accompanied by a selective cross-linking of the macromolecules, leading to a change in solubility in organic solvents. This crosslinking reaction and the negative photoresist behavior are investigated by means of sol-gel analysis. The resulting transistors show a field-effect mobility up to 0.8 cm2 V-1 s-1 at an operation voltage as low as -4.5 V. The ultra-low subthreshold swing in the order of 0.1 V dec-1 as well as the completely hysteresis-free transistor characteristics are indicating a very low interface trap density. It can be shown that the device performance is completely stable upon UV-irradiation and development according to a very robust chemical rearrangement. The excellent interface properties, the high stability and the small thickness make the PNDPE gate dielectric a promising candidate for fast organic electronic circuits.
Keywords: Dielectrics; Organic electronics; Organic field effect transistor; Photochemistry; Thin films.