Block copolymers for high-performance transistors
Use of polymer materials is an innovative and low-cost technique for producing structures on nanoscale lengths. It involves simple mixing in a proper solution. With block copolymers, one can take two or more monomers that are chemically different and link them together into one chain; the system then will self-assemble at the nanoscale. The ability to self-assemble them in a controlled fashion is the cornerstone of this approach. Within XLIM (Well-defined conjugated block copolymer nanofibers and their applications in photovoltaic devices), scientists synthesised block copolymers containing poly(3-hexylthiophene) (P3HT) to prepare complex, functional nanoscale objects through low-cost solution processing. Importantly, the polymer blocks were found to be conductive, thus being suitable for use in electronic devices. The project team used a synthetic methodology to produce block copolymers consisting of two different conjugated segments. When self-assembled, these two blocks with different properties allowed the formation of ordered structures in the form of cylindrical micelles with a crystalline core. Using the crystallisation-driven self-assembly method, scientists effectively controlled their length, which ranged from tens of nanometres to more than 800. These cylindrical micelles were then successfully incorporated in the active semiconducting layer of field-effect transistors. A remarkable finding was that the cylinder length influenced the charge-carrier mobility and thus the transistor performance. Using a modified approach, scientists also reported synthesis of a triblock copolymer. Semiconductive polymers are particularly important for the electronics industry. Tailoring the length of copolymers can make these materials self-assemble into complex patterns that can serve as templates for etching nanoscale circuitry in transistors. This approach can be used to create the ever-smaller and denser parts in transistors.
Keywords
Block copolymers, nanoscale structures, self-assemble, field-effect transistors