Atomic layer deposited HfO2 gate dielectrics for low-voltage operating, high-performance poly-(3-hexythiophene) organic thin-film transistors

Here we report on low-supply voltage and high-performance regioregular poly-(3-hexythiophene) (P3HT) organic thin-film transistors (OTFT) using a thin atomic layer deposited (ALD) HfO2 gate dielectric. For the capacitance–voltage characteristics, the measured gate capacitance was ∼392 nF/cm2 at 1 kHz and the dielectric constant was estimated ∼18.5 for a 40 nm thick ALD HfO2 gate dielectric. The gate dielectric showed breakdown fields >5 MV/cm with the leakage current density less than 10−7 A/cm2 at 2 MV/cm. With octadecyltrichlorosilane-treated ALD HfO2 gate dielectrics, P3HT OTFTs demonstrated high field-effect mobilities up to ∼0.01 ± 0.002 cm2/V s in the saturation region with the drain voltage of −5 V, which is at least one order of magnitude higher than typically reported mobilities particularly for low-voltage regioregular P3HT OTFTs using high-k inorganic gate dielectrics. The threshold voltage in the saturation region and on–off current ratio were measured to be −1.2 ± 0.2 V and ∼1.1(±0.1) × 104, respectively.