Low-voltage and hysteresis-free N-type organic thin film transistor and complementary inverter with bilayer gate insulator

In this paper, we report on a low-voltage-operation n-type organic thin film transistor (OTFT) and a complementary inverter circuit using a thiazolothiazole derivative as an organic semiconductor (OSC). To achieve the low voltage and stable operation of the n-type OTFT, a bilayer structure consisting of a thin low-k polymer layer and a high-k Ta₂O ₅ layer was used and investigated as the gate insulator. Atomic force microscopy images of the OSC film on the hydrophobic polymer showed densely distributed small grains, and the corresponding OTFT exhibited hysteresis-free and excellent n-type performance, for example, an electron mobility of 0.23-0.35cm² V^-1 s^-1. In addition, the n-type OTFT with a thinner polymer layer exhibited a low operating voltage of less than 10 V while maintaining excellent characteristics. A complementary inverter based on the thiazolothiazole derivative and pentacene was also fabricated using the bilayer gate insulator. The switching operation of the inverter was achieved at a low voltage of 5-10 V.