Plasma-polymerized multistacked bipolar gate dielectric for organic thin-film transistors

A 10-layer stack of bipolar gate dielectric was formed by sequential layer-by-layer deposition using pulsed radio frequency (RF) plasma polymerization of allylamine and vinyl acetic acid monomers. Due to polar groups localized at the interfaces between each consecutive layer by alternating amine (–NH2) and carboxylic acid (–COOH) functional groups, a 60 nm thick multilayer structure demonstrated relatively high dielectric constant of 4.4 with extremely smooth and crack/pin-hole free surfaces. Without any post-deposition thermal annealing, a 10-layer stack of bipolar dielectric layers shows a low leakage current density (∼1 × 10−6 A/cm2 at 2 MV/cm) with high breakdown fields (>4 MV/cm). With a 10-layer stack of bipolar gate dielectrics, low supply voltage regioregular poly-(3-hexythiophene) (P3HT) organic thin-film transistors (OTFT) were tested. P3HT OTFTs demonstrated low-voltage operation and moderate field-effect mobility up to ∼3.4 × 10−3 cm2/V s in the saturation region with the drain voltage a −12 V. The threshold voltage in the saturation region and on–off current ratio were measured to be +1.4 V and ∼1.2 × 102, respectively.