Hiroyuki Endoh

Highly Uniform Thin-Film Transistors Printed on Flexible Plastic Films with Morphology-Controlled Carbon Nanotube Network Channels

Carbon nanotube (CNT) transistor arrays were fabricated on plastic films by printing. All the device elements were directly patterned by maskless printing without any additional patterning process, and minimum materials were used. During fabrication, the morphology of the CNT random network was controlled by an adsorption mechanism on the surface to be printed, which resulted in excellent and uniform electrical properties. The field-effect mobility was further improved by post-treatment to modify the morphology of the CNT network. These results are promising for realizing printed electronics integrated with CNT transistors.

Noncritical phase‐matched second‐harmonic generation with an organic crystal, 4‐(isopropylcarbamoyl)nitrobenzene

This letter reports an organic crystal that can generate a second‐harmonic beam under type II noncritical phase‐matching conditions. The cleavage plane of a 4‐(isopropylcarbamoyl)nitrobenzene (PCNB) crystal was found by theoretical calculation to have a type II noncritical phase‐matched incident surface. This enables the PCNB crystal to convert Ti:sapphire laser light (930 nm) into 465 nm blue light with high conversion efficiency (1%/W at 5.5 mm path length).

Electrical property of printed transistors fabricated with various types of carbon nanotube ink

Printed electronics is expected to be a low-cost, eco-friendly, and on-demand fabrication technology because it decreases the number of process steps and the amount of waste materials. Carbon nanotube (CNT) transistor arrays were fabricated on plastic films by maskless printing without any additional pattering process, and minimum materials were used. During fabrication, the morphology of the CNT random network was controlled by an adsorption mechanism on the surface to be printed, which resulted in excellent and uniform electrical properties. Based on the fabrication technology, various types of CNT ink were examined. A guiding principle for developing CNT ink was shown to improve the TFT performance.

High Performance Vertical-Type Organic Transistors And Organic Light Emitting Transistors

We have fabricated organic static induction transistor (SIT) and organic light emitting transistor (OLET) combining SIT with organic light emitting diode (OLED). SIT and OLET have a grid-type Al gate electrode that was formed using a shadow evaporation mask in the organic semiconductor layers. The effective electrode area of SIT and OLET is approximately 4 mm2. By optimizing the device structure, excellent performances of SIT and OLET were obtained. The drain-source current (IDS) at a constant drain-source voltage (VDS) decreases with increasing the gate voltage (VG). The current is controlled by relatively small VG (-10 V) and a typical SIT characteristic is obtained in the OLET. The luminance of OLET also varies corresponding to the I-V characteristics. The maximum current and luminance values were approximately 10 mA and 10,000 cd/m2, respectively. We have also investigated the electrical characteristics of organic SITs having several gate gaps. The organic SIT with gate gap (Dg) less than 200 nm have much smaller off currents and much larger on/off ratios.

Evaluation of Dynamic Performance of CNT Random Network Transistors

A carbon nanotube (CNT) [1] random network channel was fabricated with dispenser printing on a substrate on which electrodes were patterned to reduce the gate capacitance by using super inkjet technology. The dynamic performance of the CNT thin-film transistor (CNT-TFT) was evaluated. As a result, on-off switching action up to 100 kHz was achieved. The authors demonstrated the high potential of CNTs as printable semiconductive materials.

Effect of dipole moment on hole transport in polymers doped with compounds containing two styryltriphenylamine units

Hole mobilities have been measured in molecularly doped polymers and polystyrene (PS). Both polymers were doped with a series of 1,1-bis(4-(N-styryl- phenyl)amino)phenyl)cyclohexane (BTAS) derivatives that have different dipole moments. The measured results are described within the framework of a formalism based on disorder in which it is assumed that charge transport occurs by hopping through a manifold of hopping sites subject to energetic and positional disorder. For each polymer doped with BTAS derivatives, the energy width of its hopping site manifold increased with increasing dipole moments of BTAS derivatives. The BTAS doped PC, which is a highly polar polymer, has a larger energy width than does the BTAS doped PS, and its energy width is also less dependent on the dipole moment. We measured the energy width dependence on BTAS concentration, and found that the energy width decreased with increasing BTAS concentration in the PC systems, but increased in the PS systems. These dependencies may have been attributed to the dipolar fields associated with the dipole moments of not only the BTAS derivatives but also the respective polymers. To explain these dependencies, we proposed a new model which dealt with the effects of the dipole moments of PC on energy width. By using this model, we estimated the dipole moment of a monomer unit of PC to be approximately 2.1 D, which corresponds roughly to that of the carbonyl group within a monomer unit.