Single-crystal field-effect transistors of new Cl2-NDI polymorph processed by sublimation in air.

Physical properties of active materials built up from small molecules are dictated by their molecular packing in the solid state. Here we demonstrate for the first time the growth of n-channel single-crystal field-effect transistors and organic thin-film transistors by sublimation of 2,6-dichloro-naphthalene diimide in air. Under these conditions, a new polymorph with two-dimensional brick-wall packing mode (ß-phase) is obtained that is distinguished from the previously reported herringbone packing motif obtained from solution (α-phase). We are able to fabricate single-crystal field-effect transistors with electron mobilities in air of up to 8.6 cm(2) V(-1) s(-1) (α-phase) and up to 3.5 cm(2) V(-1) s(-1) (ß-phase) on n-octadecyltriethoxysilane-modified substrates. On silicon dioxide, thin-film devices based on ß-phase can be manufactured in air giving rise to electron mobilities of 0.37 cm(2) V(-1) s(-1). The simple crystal and thin-film growth procedures by sublimation under ambient conditions avoid elaborate substrate modifications and costly vacuum equipment-based fabrication steps.

High-performance ZnO nanowire transistors with aluminum top-gate electrodes and naturally formed hybrid self-assembled monolayer/AlO(x) gate dielectric.

A method for the formation of a low-temperature hybrid gate dielectric for high-performance, top-gate ZnO nanowire transistors is reported. The hybrid gate dielectric consists of a self-assembled monolayer (SAM) and an aluminum oxide layer. The thin aluminum oxide layer forms naturally and spontaneously when the aluminum gate electrode is deposited by thermal evaporation onto the SAM-covered ZnO nanowire, and its formation is facilitated by the poor surface wetting of the aluminum on the hydrophobic SAM. The hybrid gate dielectric shows excellent electrical insulation and can sustain voltages up to 6 V. ZnO nanowire transistors utilizing the hybrid gate dielectric feature a large transconductance of 50 µS and large on-state currents of up to 200 µA at gate-source voltages of 3 V. The large on-state current is sufficient to drive organic light-emitting diodes with an active area of 6.7 mm(2) to a brightness of 445 cd/m(2). Inverters based on ZnO nanowire transistors and thin-film carbon load resistors operate with frequencies up to 30 MHz.

High-yield transfer printing of metal-insulator-metal nanodiodes.

Nanoscale metal-insulator-metal (MIM) diodes represent important devices in the fields of electronic circuits, detectors, communication, and energy, as their cutoff frequencies may extend into the "gap" between the electronic microwave range and the optical long-wave infrared regime. In this paper, we present a nanotransfer printing method, which allows the efficient and simultaneous fabrication of large-scale arrays of MIM nanodiode stacks, thus offering the possibility of low-cost mass production. In previous work, we have demonstrated the successful transfer and electrical characterization of macroscopic structures. Here, we demonstrate for the first time the fabrication of several millions of nanoscale diodes with a single transfer-printing step using a temperature-enhanced process. The electrical characterization of individual MIM nanodiodes was performed using a conductive atomic force microscope (AFM) setup. Our analysis shows that the tunneling current is the dominant conduction mechanism, and the electrical measurement data agree well with experimental data on previously fabricated microscale diodes and numerical simulations.

Contact resistance and megahertz operation of aggressively scaled organic transistors.

Bottom-gate, top-contact organic thin-film transistors (TFTs) with excellent static characteristics (on/off ratio: 10(7) ; intrinsic mobility: 3 cm(2) (V s)(-1) ) and fast unipolar ring oscillators (signal delay as short as 230 ns per stage) are fabricated. The significant contribution of the transfer length to the relation between channel length, contact length, contact resistance, effective mobility, and cutoff frequency of the TFTs is theoretically and experimentally analyzed.

Top-gate ZnO nanowire transistors and integrated circuits with ultrathin self-assembled monolayer gate dielectric.

A novel approach for the fabrication of transistors and circuits based on individual single-crystalline ZnO nanowires synthesized by a low-temperature hydrothermal method is reported. The gate dielectric of these transistors is a self-assembled monolayer that has a thickness of 2 nm and efficiently isolates the ZnO nanowire from the top-gate electrodes. Inverters fabricated on a single ZnO nanowire operate with frequencies up to 1 MHz. Compared with metal-semiconductor field-effect transistors, in which the isolation of the gate electrode from the carrier channel relies solely on the depletion layer in the semiconductor, the self-assembled monolayer dielectric leads to a reduction of the gate current by more than 3 orders of magnitude.

Unipolar sequential circuits based on individual-carbon-nanotube transistors and thin-film carbon resistors.

A fabrication process for the monolithic integration of field-effect transistors based on individual carbon nanotubes and load resistors based on vacuum-evaporated carbon films into fast unipolar logic circuits on glass substrates is reported for the first time. The individual-carbon-nanotube transistors operate with relatively small gate-source and drain-source voltages of 1 V and combine large transconductance (up to 6 µS), large ON/OFF ratio (>10(4)), and short switching delay time constants (12 ns). The thin-film carbon load resistors provide linear current-voltage characteristics and resistances between 300 kΩ and 100 MΩ, depending on the layout of the resistors and the thickness of the vacuum-evaporated carbon films. Various combinational circuits (NAND, NOR, AND, OR gates) as well as a sequential circuit ( ̅S ̅R NAND latch) have been fabricated and characterized. Although these unipolar circuits cannot compete with optimized complementary circuits in terms of integration density and static power consumption, they offer the possibility of realizing air-stable, low-voltage integrated circuits with promising static and dynamic performance on unconventional substrates for large-area electronics applications, such as displays or sensors.

Logic circuits based on individual semiconducting and metallic carbon-nanotube devices.

Nanoscale transistors employing an individual semiconducting carbon nanotube as the channel hold great potential for logic circuits with large integration densities that can be manufactured on glass or plastic substrates. Carbon nanotubes are usually produced as a mixture of semiconducting and metallic nanotubes. Since only semiconducting nanotubes yield transistors, the metallic nanotubes are typically not utilized. However, integrated circuits often require not only transistors, but also resistive load devices. Here we show that many of the metallic carbon nanotubes that are deposited on the substrate along with the semiconducting nanotubes can be conveniently utilized as load resistors with favorable characteristics for the design of integrated circuits. We also demonstrate the fabrication of arrays of transistors and resistors, each based on an individual semiconducting or metallic carbon nanotube, and their integration on glass substrates into logic circuits with switching frequencies of up to 500 kHz using a custom-designed metal interconnect layer.

Highly reliable carbon nanotube transistors with patterned gates and molecular gate dielectric.

The prospect of realizing nanoscale transistors using individual semiconducting carbon nanotubes offers enormous potential, both as an alternative to silicon technology beyond conventional scaling limits and as a way to implement high-speed devices and circuits on flexible substrates. A significant challenge is the realization of low-voltage nanotube transistors with individually addressable gate electrodes that display large transconductance, steep subthreshold swing, and large on/off ratio. Their integration into circuits with large signal gain and good stability still needs to be demonstrated. Here, we demonstrate that these important goals can be achieved with the help of a bottom-gate device structure that combines patterned metal gates with a thin gate dielectric based on a molecular self-assembled monolayer. The obtained transistors operate with a gate-source voltage of 1 V and have a transconductance of 5 microS, a subthreshold swing of 68 mV/decade, and an on/off ratio of 10(7). To verify the excellent operational and shelf life stability, we show that the device performance does not degrade during 10,000 switching cycles and during storage under ambient conditions for more than 300 days. We also demonstrate that the device structure allows the implementation of unipolar logic circuits with good switching characteristics.