To realize a single or several molecule device, the following are necessary: (1) an electrical wiring method that is not destructive to the molecular aggregates and does not affect the electronic state of the molecules, (2) noncontact and controllable molecular manipulation technology, (3) oriented growth techniques especially to prepare a nanodevice employing an anisotropic molecular system. In this paper, recently developed electric-field assisted growth and its application to molecular device fabrication are presented.

View full abstract

In this review, we introduce a variety of surface sensitive techniques for the study of organic thin films, and applications to organic devices. These studies include surface plasmon emission light, organic thin film transistors, combination of quartz crystal microbalance and optical waveguide spectroscopy, evaluation of alignment of liquid crystal molecules at surfaces, and biosensor applications.

View full abstract

Dye-sensitized solar cells are expected to be used as future clean energy. Most of the researchers in the field of the dye-sensitized solar cells use Ruthenium complex as dye. On the other hand, we have proposed the dye-sensitized solar cells using natural dyes, such as dye of red-cabbage and curcumin. In this paper, we use new electrolyte solution for the solar cells using dye of curcumin. As a result, a conversion efficiency of about 1.3% has been obtained (light source: halogen lamp).

View full abstract

Current density-voltage (J-V) and capacitance-voltage (C-V) characteristics of P3HT/n⁻-silicon heterojunction diodes were investigated to clarify the carrier conduction mechanism at the organic/inorganic heterojunction. The J-V characteristics of the P3HT/n⁻-Si junctions can be explained by a Schottky diode model with an interfacial layer. Diode parameters such as Schottky barrier height and ideality factor were estimated to be 0.78eV and 3.2, respectively. The C-V analysis suggests that the depletion layer appears in the n⁻-Si layer with a thickness of 1.2 µm from the junction with zero bias and the diffusion potential was estimated at 0.40eV at the open-circuit condition. The present heterojunction allows a photovoltaic operation with power conversion efficiencies up to 0.38% with a simulated solar light exposure of 100mW/cm². The forward bias current was enhanced by coating the Si surface with a SiC layer, where the ideality factor was improved to be the level of 1.45∼1.50.

View full abstract

We fabricated solution-processed organic complementary inverters based on α, ω-bis (2-hexyldecyl)sexithiophene (BHD6T) for p-channel and C60-fused N-methylpyrrolidine-meta-dodecyl phenyl (C60MC12) for n-channel. The BHD6T and C60MC12 thin-film transistors showed high field-effect mobilities of 0.035 and 0.057cm²/Vs, respectively. The complementary inverter with a supply voltage of 50V exhibited inverting voltages of 26.8V for forward and 27.0V for backward sweeps and a high gain of 76.

View full abstract

We designed and synthesized alkoxyphenyl group containing starburst host materials 1. Using 1 as a host material, efficient phosphorescent OLEDs with the power efficiencies of 32lm W^-1 for blue, and 85lm W^-1 for green at 100cd m^-2 were developed.

View full abstract

Ridge optical waveguides (OWGs) of fluorinated polyimides were deposited on a quartz crystal microbalance (QCM), and a hybrid sensor employing the OWG spectroscopy and the QCM technique was prepared. A polyvinyl alcohol (PVA) film with CoCl₂ was deposited on the OWG, and humidity sensing characteristics were investigated. White light was entered into the waveguide and the output light spectra was observed. The output light intensity markedly changed because of the chromism of CoCl₂ by humidity sorption. During the output light measurement, the QCM frequency was monitored simultaneously. The humidity dependences of the QCM frequency and output light were also investigated in a range from 10% to 70%. Furthermore, the response to hydrofluoroether (HFE) was observed, and the change in the output light was hardly observed because CoCl₂ does not exhibit chromism in HFE sorption.

View full abstract

Thin film glucose biosensors were fabricated with organic/inorganic hybrid films based on glucose oxidase (GOx) and Prussian Blue nano-clusters. The biosensors composed of hybrid films were characterized by the low operating potential and the advantage to interference-free detection. In this research, we employed two kinds of thin films for GOx immobilization: Langmuir-Blodgett (LB) and self-assembled monolayer (SAM). The LB film immobilizes GOx in its inside through the electrostatic force, while the SAM immobilizes GOx with the covalent bond. The sensors with LB film produced a relatively high current signal, while the non-linear behavior and a low stability were recognized. On the other hand, the sensors with SAM presented a good linear relationship and a very stable performance.

View full abstract

Polymer multimode optical waveguides were fabricated from optically-sensitive hybrid silicone using the ultraviolet laser drawing method. The waveguide loss values were measured as 0.069dB/cm with a laser diode, 0.069dB/cm with a vertical-cavity surface-emitting laser, and 0.128dB/cm with a light-emitting diode. The cross waveguide on a curved waveguide was drawn by overlapped direct laser drawing. The crosstalk and excess loss at the cross angle of 50° in the cross waveguide were measured as 47dB and 0.5dB, respectively.

View full abstract

We propose a novel technique to grow the single-walled carbon nanotubes (SWNTs) with specific chirality at the desired position using free electron laser (FEL) irradiation during growth and surface treatment. As a result, only the semiconducting SWNTs grew at the area between triangle electrodes, where the ozone treatment was done to be hydrophilic when an alcohol chemical vapor deposition (ACCVD) process was carried out with the 800nm FEL irradiation. Although the number of possible chiral index is 22 in the SWNTs grown without the FEL irradiation, the number is much reduced to be 8 by the FEL.

View full abstract

To estimate the field emission current associated with an array of carbon nanowalls (CNWs), the model of the floating rods between anode and cathode plates was proposed. An approximate formula for the enhancement factor was derived, showing that the interwall distance of the CNW array critically affects the field emission. The field enhancement factor was almost one order of magnitude less than that of vertically aligned CNTs. Considering the field emission current density, the field emission can be optimized when the interwall distance is comparable with the wall height. For same separation distance, the macroscopic field strength of the CNW array is almost one order of magnitude higher than that of vertical CNT array to obtain the emission current of 1mA from the cathode surface of 1cm².

View full abstract

To characterize and predict the dynamics of the nonlinear polarization rotation in SOAs, an experimental method based on the frequency response technique and a model based on the density matrix and effective index formalisms are presented. Both determine the angular displacement, at the Poincare Sphere, that produces the evolution of the polarization of the output signal.

View full abstract

The noise performance of common source and cascode topology 60GHz LNAs is analyzed and verified. The analysis result shows that the noise performance of the cascode topology is degraded at high frequency due to the inter-stage node capacitance. The analysis result is verified by experimental results. A three-stage LNA employing two noise-matched CS stages and a cascode stage is proposed. For comparison a conventional two-stage cascode LNA is also been studied with the measurement-based model. The measured results of the proposed LNA show that an input and output matching of less than -10dB, a maximum gain of 9.7dB and a noise figure (NF) of 3.2dB are obtained with a power consumption of 30mW from a 1.2-V supply voltage. Compared to the conventional cascode LNA, an improvement of 2.3-dB for NF and 1.9-dB for power gain are realized. Both the proposed and conventional LNAs are implemented in 65nm CMOS process.

View full abstract

We propose a capacitive averaging technique applied to a double-tail latched comparator without a preamplifier for an offset reduction technique. Capacitive averaging can be introduced by considering the first stage of the double-tail latched comparator as a capacitive loaded amplifier. This makes it possible to reduce the offset voltage while preventing an increase in power dissipation. A positive feedback technique is also used for the first stage, which maximizes the effectiveness of the capacitive averaging. The capacitive averaging mechanism and the relationship between the offset reduction and the linearity of the amplifier is discussed in detail. Simulation results for a 90-nm CMOS process show that the proposed technique can reduce the offset voltage by 1/3.5 (3mV) at a power dissipation of only 45µW.

View full abstract

In this paper, we propose a two-step TDC with phase-interpolator and time amplifier to satisfy high resolution at 2.4GHz input frequency by implementing delay time less than that of an inverter delay. The accuracy of phase-interpolator is improved for process variation using the resistor automatic-tuning circuit. The gain of time amplifier is improved using the delay time difference between two delay cells. It is implemented in a 0.13µm CMOS process with a die area of 0.68mm². And the power consumption is 14.4mW at a 1.2V supply voltage. The resolution and input frequency of the TDC are 0.357ps and 2.4GHz, respectively.

View full abstract

Based on the substrate integrated waveguide (SIW) technology, a new type of varactor-tuned radial power divider has been developed with a single bias supply. The varactors are used as tuning elements and allow for a frequency agile behavior. In addition, bandwidth characteristics have been analysed with group-delay. It has been measured with a single bias supply ranging from 6V to 12V that the center frequency of the power divider can be adjusted from 6.6GHz to 7.2GHz (600MHz, 11.5%) while maintaining a low insertion loss (< 1dB) in the passband.

View full abstract

A simple analytical model to predict the DC MOSFET behavior under electromagnetic interference (EMI) is presented. The model is able to describe the MOSFET performance in the linear and saturation regions under EMI disturbance applied to the gate. The model consists of a unique simple equivalent circuit based on a voltage dependent current source and a reduced number of parameters which can accurately predict the drift on the drain current due to the EMI source. The analytical approach has been validated by means of electric simulation and measurements and can be easily introduced in circuit simulators. The proposed modeling technique combined with the nth-power law model of the MOSFET without EMI, significantly improves its accuracy in comparison with the n-th power law directly applied to a MOSFET under EMI impact.

View full abstract

A readout circuit incorporating a pixel-level analog-to-digital converter (ADC) is studied for 2-dimensional microbolometer infrared focal plane arrays (IRFPAs). The integration time and signal-to-noise ratio (SNR) is improved using the current-mode bias and MSB skimming. The proposed pixel-level ADC is a two-step configuration, so its power consumption is very low. The readout circuit was designed using a 0.35µm 2-poly 4-metal CMOS process for a 320×240 microbolometer array with a pixel size of 35μm × 35μm. The noise equivalent temperature difference (NETD) was estimated to be 47mK, with a power consumption of 390nW for a pixel-level ADC.

View full abstract

A carbonaceous thin film was deposited on a tungsten single emitter by electrolysis of liquid methanol. The carbonaceous single emitter was thermally treated under vacuum conditions, and changes in its field emission characteristics were examined. The field emission characteristics obeyed the Fowler-Nordheim relationship for all annealing temperatures. The turn-on voltage decreased from 1640V to 790V with annealing up to 1373K.

View full abstract