Organic field effect transistors with structured 3D gates

TitleOrganic field effect transistors with structured 3D gates
Publication TypeConference Paper
Year of Publication2012
AuthorsMeredith, Paul, Burn P. L., Aljada M., Pandey A. K., M. Velusamy, and Namdas E.
Conference NameProc. MRS Spring Meeting J1.4
Conference LocationSan Francisco

Organic field-effect transistors (OFETs) have attracted significant fundamental and applied attention due to their potential to realize circuitry for low cost portable electronic devices such as active-matrix displays, radio frequency tags and smart cards. However, the low carrier mobility and carrier densities of organic semiconductors compared to conventional inorganic materials such as silicon currently limits the potential of OFETs to expand into a wider range of applications. One of the main challenges in OFETs is to achieve sufficient source-drain current at practically reasonable voltages for lower power operation. For over a decade efforts have been directed towards the quest for higher-performance organic semiconductors – one may consider these as “material-centric” strategies. However, typical values of carrier mobility remain comparable to or lower than amorphous inorganic semiconductors and below that required for most electronic control circuitry applications. Therefore, the development of conceptually different OFET architectures must also be of a high priority with in particular a clear goal to increase source-drain current without sacrificing the simplicity of the fabrication process or compromising the other benefits of organic semiconductors We report the fabrication and electrical characteristics of structured gate (3D) organic field effect transistors consisting of a gate electrode patterned with three-dimensional pillars. The pillar gate electrode was over-coated with a gate dielectric (SiO2) and solution processed organic semiconductors producing both unipolar p-type and bipolar behavior. We show that this new 3D gated architecture delivers higher source-drain currents, higher gate capacitance per unit equivalent linear channel area, and enhanced charge injection (both electron and holes) versus the conventional planar structure in all modes of operation. The maximum source-drain current enhancements in p- and n-channel mode were > 600% and 28% respectively. This assists in better matching of carrier mobilities which is advantageous for creating organic logic circuit elements such as inverters and amplifiers. The structuring appears to have no detrimental effect upon the underlying electronic properties of the organic semiconducting channel materials. Hence, the method represents a facile and generic strategy for improving standard OFET performance and also has the potential to assist in engineering channel properties in light emitting or sensing field effect transistor applications.