Solution-processable organic dielectrics for graphene electronics.

We report the fabrication, at low-temperature, of solution processed graphene transistors based on carefully engineered graphene/organic dielectric interfaces. Graphene transistors based on these interfaces show improved performance and reliability when compared with traditional SiO(2) based devices. The dielectric materials investigated include Hyflon AD (Solvay), a low-k fluoropolymer, and various organic self-assembled monolayer (SAM) nanodielectrics. Both types of dielectric are solution processed and yield graphene transistors with similar operating characteristics, namely high charge carrier mobility, hysteresis free operation, negligible doping effect and improved operating stability as compared to bare SiO(2) based devices. Importantly, the use of SAM nanodielectrics enables the demonstration of low operating voltage ( < |1.5| V), solution-processable and flexible graphene transistors with tunable doping characteristics through molecular engineering of the SAM's molecular length and terminal group. The work is a significant step towards graphene microelectronics where large-volume and low-temperature processing are required.

Bias-stress effects in organic field-effect transistors based on self-assembled monolayer nanodielectrics.

The electrical stability of low-voltage organic transistors based on phosphonic acid self-assembled monolayer (SAM) dielectrics is investigated using four different semiconductors. The threshold voltage shift in these devices shows a stretched-exponential time dependence under continuous gate bias with a relaxation time in the range of 10(3)-10(5) s, at room temperature. Differences in the bias instability of transistors based on different self-assembled monolayers and organic semiconductors suggest that charge trapping into localized states in the semiconductor is not the only mechanism responsible for the observed instability. By applying 1-5 s long programming voltage pulses of 2-3 V in amplitude, a large reversible threshold voltage shift can be produced. The retention time of the programmed state was measured to be on the order of 30 h. The combination of low voltage operation and relatively long retention times makes these devices interesting for ultra-low power memory applications.

Effect of rapid thermal annealing on the electrical properties of GaAs Schottky diodes embedded with self-assembled InAs quantum dots.

After rapid thermal annealing (RTA), deep levels were found to be generated in Au/GaAs Schottky diodes embedded with InAs quantum dots grown by migration enhanced molecular beam epitaxy (MEMBE). From the corner frequency of the 1/f2 part of the low-frequency noise specrtral density, the locations of the deep levels were estimated to be 0.58, 0.61, and 0.66 eV below the conduction band edge for the samples without quantum dot layer, with quantum dot layer and capping layer thickness of 0.8 microm, and with quantum dot layer and the capping layer thickness of 0.4 microm, respectively. RTA also lowered the Schottky barrier height.