Printed dual-gate organic thin film transistors and PMOS inverters on flexible substrates: Role of top gate electrode

We report printed single and dual-gate organic thin film transistors (OTFTs) and PMOS inverters fabricated on 125 µm-thick flexible polyethylene naphthalate (PEN) substrate. All the electrodes (gate, source, and drain) are inkjet-printed, while the parylene dielectric is formed by chemical vapor deposition. A dispenser system is used to print the active channel material using a blend of 2,7-dihexyl-dithieno[2,3-d;2',3'-d']benzo[1,2-b;4,5-b']dithiophene (DTBDT-C6) and polystyrene (PS) in tetralin solvent, which gives highest mobility of 0.43 cm2/Vs. Dual-gate OTFTs are characterized by keeping the other gate electrode either in grounded or floating state. Floating gate electrode devices shows higher apparent mobility and current ratio due to additional capacitance of the parylene dielectric. PMOS inverter circuits are characterized in terms of gain, trip point and noise margin values calculated from the voltage transfer characteristics (VTC). Applied top gate voltage on the load OTFT control the conductivity or threshold voltage (VTh) of the bottom TFT and shift the trip point towards the middle of the VTC curve, and hence increase the noise margin.

Electromechanical Characteristics by a Vertical Flip of C70 Fullerene Prolate Spheroid in a Single-Electron Transistor: Hybrid Density Functional Methods

In this study, the B3LYP hybrid density functional theory was used to investigate the electromechanical characteristics of C70 fullerene with and without point charges to model the effect of the surface of the gate electrode in a C70 single-electron transistor (SET). To understand electron tunneling through C70 fullerene species in a single-C70 transistor, descriptors of geometrical atomic structures and frontier molecular orbitals were analyzed. The findings regarding the node planes of the lowest unoccupied molecular orbitals (LUMOs) of C70 and both the highest occupied molecular orbitals (HOMOs) and the LUMO of the C70 anion suggest that electron tunneling of pristine C70 prolate spheroidal fullerene could be better in the major axis orientation when facing the gate electrode than in the major (longer) axis orientation when facing the Au source and drain electrodes. In addition, we explored the effect on the geometrical atomic structure of C70 by a single-electron addition, in which the maximum change for the distance between two carbon sites of C70 is 0.02 Å.