Defect-Free Copolymer Gate Dielectrics for Gating MoS₂ Transistors

In this study, the poly(2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane-co-cyclohexyl methacrylate) [p(V4D4-co-CHMA)] copolymer was developed for use as a gate dielectric in molybdenum disulfide (MoS₂) field-effect transistors (FETs). The p(V4D4-co-CHMA) copolymer was synthesized via the initiated chemical vapor deposition (iCVD) of two types of monomers: 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4) and cyclohexyl methacrylate (CHMA). Four vinyl groups of V4D4 monomers and cyclohexyl groups of CHMA monomers were introduced to enhance the electrical strength of gate dielectrics through the formation of a highly crosslinked network and to reduce the charge trap densities at the MoS₂-dielectric interface, respectively. The iCVD-grown p(V4D4-co-CHMA) copolymer films yielded a dielectric constant of 2.3 and a leakage current of 3.8 × 10^-11 A/cm² at 1 MV/cm. The resulting MoS₂ FETs with p(V4D4-co-CHMA) gate dielectrics exhibited excellent electrical properties, including an electron mobility of 35.1 cm²/V s, a subthreshold swing of 0.2 V/dec, and an on-off current ratio of 2.6 × 10⁶. In addition, the environmental and operational stabilities of MoS₂ FETs with p(V4D4-co-CHMA) top-gate dielectrics were superior to those of devices with SiO₂ back-gate dielectrics. The use of iCVD-grown copolymer gate dielectrics as demonstrated in this study provides a novel approach to realizing next-generation two-dimensional electronics.