Tomohiko Edura

Graphoepitaxy of sexithiophene on thermally oxidized silicon surface with artificial periodic grooves

Graphoepitaxial growth of a sexithiophene (6T) thin film was achieved on a thermally oxidized silicon surface with artificial periodic grooves. The surface structure was fabricated by electron beam lithography and the thin film was grown by molecular beam deposition. A well-pronounced, in-plane oriented component ([010]6T‖grooves) was identified by grazing incidence x-ray diffraction, though there also existed some randomly oriented 6T grains. Presence of the graphoepitaxial component was also confirmed by results of the orientational analysis of atomic force microscopy images. It was shown that the in-plane orientation control of organic semiconductors is possible using graphoepitaxy.

Tunable Monolithic DWDM Band-Selection Interleaver Filter Switch on Silicon-on-Insulator Substrate

A tunable band-selection interleaver filter switch formed on a silicon-on-insulator (SOI) substrate for dense wavelength-division-multiplexing (DWDM) system was fabricated, and its fundamental performances were experimentally demonstrated. The device consists of monolithic integration of a Michelson interferometer (MI) structure with two arm-waveguides with different lengths, appropriately designed for ITU-grid separation, a phase-modulation electrode on one arm and tunable wideband Bragg gratings reflectors. An SOI rib waveguide structure with a medium mode size was adopted for low loss and easy fabrication. A bandwidth of the grating, formed by electron beam (EB) lithography and deep reactive-ion etching (Deep-RIE), was rather large of 4 nm at -10 dB transmission level, from which a large coupling coefficient of the Bragg grating of 105 cm-1 was evaluated. A large tuning range of the Bragg grating of 17 nm was obtained. An extinction ratio of the interleaver filter was about 18 dB, and the interleaving switching was also attained with an applied electric power of 50 mW and a switching speed of about 1 ms.

Fabrications of Micro-Channel Device by Hot Emboss and Direct Bonding of PMMA

We have fabricated and evaluated the mechanical, optical and fluidic characteristics a 50µm wide and a 30µm deep micro-channel device produced by hot emboss and direct bonding of PMMA plate with dimensions of 20mm × 20mm × 1mm. The fabricated micro-channel device was evaluated the bond strength, which was confirmed to be high enough for practical use as well as for quite severe cleaning conditions as ultrasonic cleaning in pure water. The optical loss around bonded interface was also evaluated and no increase in the light absorption was observed. The above results confirmed that the hot emboss and direct bonding technologies for micro-channel manufacturing using the PMMA plates realizes high performance micro channel devices.

Microfluidic White Organic Light-Emitting Diode Based on Integrated Patterns of Greenish-Blue and Yellow Solvent-Free Liquid Emitters.

We demonstrated a novel microfluidic white organic light-emitting diode (microfluidic WOLED) based on integrated sub-100-μm-wide microchannels. Single-μm-thick SU-8-based microchannels, which were sandwiched between indium tin oxide (ITO) anode and cathode pairs, were fabricated by photolithography and heterogeneous bonding technologies. 1-Pyrenebutyric acid 2-ethylhexyl ester (PLQ) was used as a solvent-free greenish-blue liquid emitter, while 2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetracene (TBRb)-doped PLQ was applied as a yellow liquid emitter. In order to form the liquid white light-emitting layer, the greenish-blue and yellow liquid emitters were alternately injected into the integrated microchannels. The fabricated electro-microfluidic device successfully exhibited white electroluminescence (EL) emission via simultaneous greenish-blue and yellow emissions under an applied voltage of 100 V. A white emission with Commission Internationale de l’Declairage (CIE) color coordinates of (0.40, 0.42) was also obtained; the emission corresponds to warm-white light. The proposed device has potential applications in subpixels of liquid-based microdisplays and for lighting.

Single grain and single grain boundary resistance of pentacene thin film characterized using a nanoscale electrode array

In this paper, we report on a less than 100-nm-wide nanoscale electrode array, with which the field-effect mobilities of a single grain and a single grain boundary in organic thin films are characterized. The method of fabricating the nanoscale electrode array and the evaluation results of the pentacene thin film are described. The nanoscale electrode array was fabricated by EB lithography and a liftoff process. The pentacene thin film was deposited by molecular-beam epitaxy (MBE). The resistances of a single grain and a single grain boundary were estimated to be around 10 and 100 MΩ, respectively, and the field-effect mobility was estimated to be around 1 cm2/(V s), which is almost comparable to the highest value ever reported. These results confirm that a single crystal is essential for high performance organic thin-film transistors.

Fabrication of planar nano-gap electrodes for single molecule evaluation

This paper aims is to fabricate planar nano-gap electrodes for single molecule characterization, which allow to measure the intrinsic nature of single molecule and to derive the number of molecules on them by atomic force microscopy (AFM), whereas conventional non-planar ones do not. Thus, the planar nano-gap electrodes are the essential tool for single molecule electronics research. Currently, the fabrication technology by anodic bonding realized planar electrodes with 300 nm in width and 200 nm in length. Insulation characteristics of the fabricated electrodes were evaluated and were in the order of 1012 Ω, which indicates that these electrodes are suitable for single molecule evaluation.

Investigation of Spatial Resolution in Current-Induced Magnetic Field Detection by Magnetic Force Microscopy

The magnetic field distribution around sub-µm-wide current paths was investigated by magnetic force microscopy (MFM) as a candidate for the current mapping in fine structures. In particular, an undesirable electrostatic force working between an MFM tip and the current path was dynamically eliminated utilizing an extra ac bias to observe the magnetic field correctly. We observed magnetic force signals around current paths consisting of branching or closely aligned metal wires, and the results were compared with results of the numerical simulation of the magnetic field. We found that spatial resolution of magnetic force detection by our method was better than 0.2 µm. The calculation results also indicate that the oscillatory motion of the MFM tip in tapping operation influences spatial resolution.

Implementation of tapered multimode interference lightwave combiner on silicon-on-insulator substrate with negligible back-reflection

We fabricated and experimentally evaluated 2×1 tapered multimode interference (MMI) combiners on silicon-on-insulator (SOI) substrates. The tapered MMI combiner we previously proposed is expected to be free from the reflection problem usually existed in a conventional rectangular MMI coupler, and such a negligible back-reflection property was actually verified. As one of its applications, we implemented a Mach–Zehnder (MZ) modulator using the tapered MMI combiner, which is often equipped with semiconductor optical amplifiers (SOAs) for ultrahigh-speed photonic switching devices and those SOAs are quite sensitive to the back-reflection.

Tunable wavelength-band switch using large coupling-coefficient Bragg grating on SOI rib waveguide

A tunable wavelength-band switch using a large coupling-coefficient Bragg grating on a silicon-on-insulator (SOI) rib waveguide is presented. The wavelength-band switch is promising in photonic networks because of its efficient signal routing of multi channels. The device with a simple structure was fabricated on an SOI substrate, which can provide a compact and low-cost functional switch.

Quantitative Evaluation of Current through Magnetic Field Observation by Magnetic Force Microscopy

Magnetic field around fine current paths has been investigated by magnetic force microscopy (MFM) for a purpose of current evaluation with high spatial resolution. In this paper, the MFM observation of magnetic field around an artificial current network to discuss ability in quantitative evaluation of current is discussed. In this method, the alternating current pass through the network, whose frequency is tuned to be coincident with the torsional resonant frequency of an MFM cantilever (typically, 300 kHz), and torsional displacement of the cantilever is extracted by a lock-in technique as a magnetic force signal, while vertical displacement due to mechanical vibration is used for height control of the tip. This allows us to observe a magnetic force image and a topographic image, simultaneously.