Flexible low-voltage organic thin-film transistors and circuits based on C ₁₀-DNTT

Using the recently developed organic semiconductor, 2,9-didecyldinaphtho[2, 3-b:2′,3′-f]thieno[3,2-b]thiophene (C ₁₀-DNTT), we have fabricated organic thin-film transistors and ring oscillators on flexible polymeric substrates. By utilizing a gate dielectric with a small thickness (5.3 nm) and a large capacitance (800 nF cm ^-2), the transistors can be operated with relatively low voltages of about 2 to 3 V. To improve the charge exchange between the organic semiconductor and the gold source and drain contacts, a thin layer of a non-alkylated organic semiconductor (DNTT) sandwiched between two thin layers of a strong organic dopant (NDP-9) was inserted between the C ₁₀-DNTT and the gold contacts. The optimized transistors have a field-effect mobility of 4.3 cm ² V ^-1 s ^-1, an on/off current ratio of 10 ⁸, and a subthreshold swing of 68 mV per decade. The ring oscillators have a signal propagation delay of 5 μs per stage at a supply voltage of 3 V, making these the fastest organic circuits at supply voltages below 7 V reported to date.