Air-stable, low-voltage organic transistors: High-mobility thienoacene derivatives for unipolar and complementary ring oscillators on flexible substrates

The organic semiconductor DNTT (dinaphtho-[2,3-b:2',3'-f]thieno[3,2-b] thiophene) and its didecyl- and diphenyl derivatives C₁₀-DNTT and DPh-DNTT [1-3] have recently shown exceptionally large field-effect mobilities together with excellent air stability [4]. Here we present a detailed analysis of the mobility, contact resistance, air stability and signal delay (measured in unipolar as well as complementary ring oscillators) of low-voltage (∼3 V) thin-film transistors (TFTs) based on these semiconductors with channel lengths down to 0.5 μm on flexible plastic substrates. The TFTs were fabricated with an inverted staggered device structure and with Al gate electrodes, a gate dielectric composed of a plasma-grown AlO_x layer (3.6 nm thick) and a tetradecylphosphonic acid self-assembled monolayer (SAM), a vacuum-deposited organic semiconductor layer (25 nm), and Au source and drain contacts [4]. The fabrication of organic TFTs with channel lengths as short as 0.5 μm was accomplished using high-resolution silicon stencil masks [6,7]. All measurements were performed in ambient air.