Investigation of the Dielectric and Electrical Properties of Poly(chloro-p-xylylene) (Parylene-C) Layers for Controlling Charge Transport in Organic Field-Effect Transistors

Polymer dielectric-based organic field-effect transistors (OFETs) have attracted significant attention due to their potential applications in transparent and flexible electronics, intelligent labels for smart packaging, and chemical and biosensors. Herein, we demonstrate OFETs incorporating poly(chloro-p-xylylene) (parylene-C) as the gate dielectric with variable thickness in the range of 250–450 nm in 50 nm increments, with careful investigation of their electrical characteristics. The results showed that an optimal dielectric thickness of parylene-C (350 nm) significantly enhanced device performance compared to a standard SiO₂ dielectric, achieving a low threshold voltage (V_Th) (0.23 V), a higher on/off ratio (I_on/off) (7.27 × 10³), and increased hole mobility (µ_h) (1.29 × 10⁻² cm²V⁻¹s⁻¹). To understand how the thickness of the parylene-C dielectric layer influences the performance of OFETs, a variety of analyses were conducted, including capacitance-voltage and water contact angle measurements, atomic force microscopy, and grazing incidence wide-angle X-ray scattering. Furthermore, X-ray absorption spectroscopy was employed to analyze the electronic structure and molecular orientation of parylene-C and the PBTTT-C14 layer deposited on it. This study offers valuable insights for optimizing OFETs with parylene-C dielectric layers, paving the way for the development of next-generation flexible and low-power electronic devices.