Study of the Characteristics of Organic Thin Film Transistors with Plasma-Polymer Gate Dielectrics

Abstract

The effects of gate dielectrics material in organic thin film transistors (OTFTs) were investigated. The gate dielectrics were deposited by plasma enhanced chemical vapor deposition (PECVD) with cyclohexane and tetraethylorthosilane (TEOS) respectively used as organic and inorganic precursors. The gate dielectrics (gate insulators) were deposited as either organic plasma-polymer or organic–inorganic hybrid plasma-polymer thin film by using cyclohexane or cyclohexane with TEOS, respectively. Additionally, hydrogen and argon were used as precursor bubbler gases. A polyimide (PI) substrate was used in the fabrication of pentacene OTFTs with a plasma-polymer gate insulator, an Au source–drain (S/D), and Cu gate electrodes. Different gate dielectrics were investigated. The as-grown plasma-polymer thin films were first analyzed using Fourier-transform infrared (FT-IR) spectroscopy. Also, they were analyzed by nano-indentation and capacitance measurements. The electrical properties, such as mobility and threshold voltage of the pentacene field-effect transistors with the plasma-polymer gate-dielectrics were investigated. Transistor with cyclohexane gate dielectric had a higher field-effect mobility, µFET = 0.84 cm2 V-1 s-1, and a smaller threshold voltage, VT= -6.8 V, than the transistor with the hybrid gate-dielectric.