title: Methacrylate Copolymers with Liquid Crystalline Side Chains for Organic Gate Dielectric Applications.
abstract: Polymers for all-organic field-effect transistors are under development to cope with the increasing demand for novel materials for organic electronics. Besides the semiconductor, the dielectric layer determines the efficiency of the final device. Poly(methyl methacrylate) (PMMA) is a frequently used dielectric. In this work, the chemical structure of this material was stepwise altered by incorporation of cross-linkable and/or self-organizing comonomers to improve the chemical stability and the dielectric properties. Different types of cross-linking methods were used to prevent dissolution, swelling or intermixing of the dielectric e.g. during formation processes of top electrodes or semiconducting layers. Self-organizing comonomers were expected to influence the dielectric/semiconductor interface, and moreover, to enhance the chemical resistance of the dielectric. Random copolymers were obtained by free radical and reversible addition-fragmentation chain transfer (RAFT) polymerization. With 6-[4-(4'-cyanophenyl)phenoxy]alkyl side chains having hexyl or octyl spacer, thermotropic liquid crystalline (LC) behavior and nanophase separation into smectic layers was observed, while copolymerization with methyl methacrylate induced molecular disorder. In addition to chemical, thermal and structural properties, electrical characteristics like breakdown field strength (EBD) and relative permittivity (k) were determined. The dielectric films were studied in metal-insulator-metal setups. EBD appeared to be strongly dependent on the type of electrode used and especially the ink formulation. Cross-linking of PMMA yielded an increase in EBD up to 4.0 MV/cm with Ag and 5.7 MV/cm with
  PSS electrodes because of the increased solvent resistance. The LC side chains reduce the ability for cross-linking resulting in decreased breakdown field strengths.
authors.affiliation: †Organic Chemistry of Polymers, Technische Universität Dresden, 01069 Dresden, Germany.|‡Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Straße 6, 01069 Dresden, Germany.|§Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden, 01062 Dresden, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Berndt
authors.affiliation: ‡Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Straße 6, 01069 Dresden, Germany.|§Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden, 01062 Dresden, Germany.
authors.forename: Doris
authors.initials: D
authors.lastname: Pospiech
authors.affiliation: ‡Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Straße 6, 01069 Dresden, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Jehnichen
authors.affiliation: ‡Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Straße 6, 01069 Dresden, Germany.
authors.forename: Liane
authors.initials: L
authors.lastname: Häußler
authors.affiliation: †Organic Chemistry of Polymers, Technische Universität Dresden, 01069 Dresden, Germany.|‡Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Straße 6, 01069 Dresden, Germany.|§Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden, 01062 Dresden, Germany.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Voit
authors.affiliation: ∥Physics Department, The University of Jordan, Amman 11942, Jordan.
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Al-Hussein
authors.affiliation: §Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden, 01062 Dresden, Germany.|⊥Institute of Semiconductors and Microsystems, Microsystems Technology, Technische Universität Dresden, 01069 Dresden, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Plötner
authors.affiliation: §Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden, 01062 Dresden, Germany.|⊥Institute of Semiconductors and Microsystems, Microsystems Technology, Technische Universität Dresden, 01069 Dresden, Germany.
authors.forename: Amit
authors.initials: A
authors.lastname: Kumar
authors.affiliation: §Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden, 01062 Dresden, Germany.|⊥Institute of Semiconductors and Microsystems, Microsystems Technology, Technische Universität Dresden, 01069 Dresden, Germany.
authors.forename: Wolf-Joachim
authors.initials: WJ
authors.lastname: Fischer
keywords: breakdown field strength; dielectric layer; liquid crystalline side chain polymers; methacrylate copolymers; relative permittivity