Solution-Processed, Low-Voltage Polycrystalline Organic Field-Effect Transistor Fabricated Using Highly Ordered Liquid Crystal With Low- Gate Dielectric

Abstract

Low-voltage operable organic field-effect transistors (OFETs) of 2-decyl-7-phenyl-[1] benzothieno[3,2-b][1] benzothiophene (Ph-BTBT-10) with low- $k$ polystyrene/SiO2 hybrid gate dielectric are fabricated using highly ordered smectic E (SmE) liquid crystalline phase. SmE phase helps organic molecules form a well-aligned crystalline thin film during spin-coating process and gives it high thermal stability. Low- $k$ gate dielectric is especially favorable for practical device applications, because it decreases parasitic capacitance in the device circuitry, leading to low-power dissipation. Despite the polycrystalline nature of Ph-BTBT-10 and low- $k$ gate dielectric, the solution-processed, bottom-gate, bottom-contact Ph-BTBT-10 OFET exhibits saturation mobility up to 4.9 cm2/( $\text {V}\cdot \text {s}$ ) with the subthreshold swing of 79 mV/decade, which is very close to the theoretical limit of 60 mV/decade at room temperature. These outstanding characteristics can be attributed to the asymmetric molecule structure of Ph-BTBT-10, which forms a bilayer structure with quasi-2-D growth mode that allows for excellent carrier transport properties with little effect of grain boundaries.