IEICE Transactions on Electronics - current issue

Special Section on The Forefront of 21st Century Organic Molecular Electronics

Onoda, M. — 2008-12-19

Characterization of Zinc Oxide and Pentacene Thin Film Transistors for CMOS Inverters

IECHI, H., WATANABE, Y., YAMAUCHI, H., KUDO, K. — 2008-12-19

We fabricated both thin film transistors (TFTs) and diodes using zinc oxide (ZnO) and pentacene, and investigated their basic characteristics. We found that field-effect mobility is influenced by the interface state between the semiconductor and dielectric layers. Furthermore, the complementary metal oxide semiconductor (CMOS) inverter using a p-channel pentacene field-effect transistor (FET) and an n-channel ZnO FET showed a relatively high voltage gain (8–12) by optimizing the device structure. The hybrid complementary inverters described here are expected for application in flexible displays, radio frequency identification cards (RFID) tags, and others.

Control of P3HT-FET Characteristics by Post-Treatments

IIZUKA, M., YAMAUCHI, H., KUDO, K. — 2008-12-19

The control of the organic field-effect transistor characteristics is necessary to produce the integrated circuits using organic semiconductors. Variations in the poly (3-hexylthiophene) field-effect transistor characteristics upon post-treatment such as thermal treatment and voltage treatment in N₂ atmosphere have been investigated. The controllability and reproducibility of the threshold voltage and mobility were achieved as a result of the post-treatments.

Characterization of Organic Static Induction Transistors with Nano-Gap Gate Fabricated by Electron Beam Lithography

YAMAUCHI, H., WATANABE, Y., IIZUKA, M., NAKAMURA, M., KUDO, K. — 2008-12-19

Organic static induction transistor (OSIT) is a promising driving device for the displays, since it shows high-speed, high-power and low-voltage operation. In this study, the OSIT with fine gate electrode patterned by electron beam exposure were fabricated. We investigated the basic electrical characteristics of copper phthalocyanine OSIT and compared with the calculation results obtained by two-dimensional (2D) device simulator. The experimental results show that the gate modulation improved by reducing the electrode gap and on/off current ratio depends on the gate gap.

Potential Drop at Electrode Contact of Organic Field-Effect Transistors Evaluated by Optical Second Harmonic Generation

MANAKA, T., NAKAO, M., LIM, E., IWAMOTO, M. — 2008-12-19

Time-resolved microscopic optical second harmonic generation (TRM-SHG) imaging measurement revealed quantitatively the potential drop at the electrode contact of pentacene field effect transistors (FET). An activation of the SH signal at the edge of Ag-source electrode indicates the presence of large potential drop at pentacene-Ag contact during device operation, whereas negligible potential drop was observed at pentacene-Au contact. These findings agree with the injection characteristics of electrodes owing to the relationship between the work function of the metal and the HOMO level of pentacene.

Organic Photodetectors Using Triplet Materials Doped in Polyalkylfluorene

HAMASAKI, T., MORIMUNE, T., KAJII, H., OHMORI, Y. — 2008-12-19

The characteristics of violet-sensitive organic photodetectors (OPDs) utilizing polyalkylfluorene and triplet materials have been studied as a host and a dopant material, respectively. For the photo absorption layer, poly(9,9-dioctylfluorene) [PFO] and a phosphorescent iridium complex (Iridium (III) bis(2-(4,6-difluorophenyl)pyridinato-N,C²) [FIrpic] or Iridium (III) bis(2-(2'-benzothienyl)pyridinato-N,C³')(acetyl-acetonate) [(btp)₂Ir(acac)]) were used as a host and a dopant material, respectively. PFO: (btp)₂Ir(acac) device showed less photocurrent than PFO device because (btp)₂Ir(acac) enhances recombination of the photo generated carriers in the photo absorption layer. On the other hand, PFO : FIrpic device showed larger photocurrent than PFO device due to triplet energy transfer from FIrpic to PFO. A cutoff frequency of 20 MHz was observed using a sinusoidal modulated violet laser light illumination under the reverse bias of 8 V.

An Amperometric Sensor for Chemical Imaging Using Photoconductive Organic Film

HAGIWARA, T., TAKAZAWA, M., UCHIDA, H., HASEGAWA, Y., YAJI, T. — 2008-12-19

We have developed an amperometric sensor employing a photoconductive organic thin film that enables the measurement of the two-dimensional distribution of redox current on a sensor surface. The sensor simply consists of photoconductive film and transparent electrode. A focused light beam through the transparent electrode excites the photoconductive film that leads to detect local redox current at the beam position. Intensity of the redox current depends on local concentration of redox species of solution on the sensor. We investigated several materials for the photoconductive film and found a suitable structure is Cu-phthalocyanine doped polyvinylcarbazole film/indium tin oxide/glass substrate. Compared with a conventional two-dimensional chemical sensor, our newly developed sensor can be prepared by lower cost fabrication methods without complex semiconductor processes. The sensor showed a good signal dependence on the concentration of K₃Fe(CN)₆/K₄Fe(CN)₆ in an aqueous solution at 15.4 nA/dec at a constant bias voltage of 0.8 V. We measured the two-dimensional distribution of ions in an agarose gel of 2 mm thickness. The result showed a photograph of the diffusion process of redox species. We also discuss the discrimination of redox species like voltammetry.

Evanescent-Field Modulation of Amplified Spontaneous Emissions from {pi}-Conjugate Polymer Film by a One-Dimensional Photonic Crystal

KAMIYAMA, Y., TOMIOKA, A., MIZUTANI, T., YAMAZAKI, M., MORIMOTO, K. — 2008-12-19

One-dimensional photonic crystal (PC) with alternating layers of TiO₂ and SiO₂ was fabricated with spin coating and low temperature baking, resulting in a successful tuning of the PC stop band so as to block the amplified spontaneous emission (ASE) of a -conjugate polymer film. Single PC as a substrate, not a cavity with two PC's, of the polymer film was sufficient to shift the tangential ASE to the energy at PC stop band edge, indicating that the tangential ASE propagating along the interface was modulated by its evanescent-field tail in the PC, which opens the new pathway for low-threshold coherent luminescence from an ultrathin -conjugate polymer film with ultimate mode volume.

Novel Humidity and Gas Detector Using Langmuir-Blodgett Cellulose-Thin-Film Coated Quartz Crystal Oscillator

KUSANO, H., KITAGAWA, M. — 2008-12-19

We have developed novel humidity and gas detector system using quartz crystal oscillators (QCO) deposited with cellulose Langmuir-Blodgett (LB) films. We have realized stable humidity detection by the LB-based QCO sensor for extremely high humidity subsequent to the water dipping condition. Also, specific gaseous molecules such as alcohol could have been sensitively detected.

Electrocatalytic Oxidation Properties of Ascorbic Acid at Poly(3,4-ethylenedioxythiophene) Films Studied by Electrochemical-Surface Plasmon Resonance Spectroscopy

BABA, A., SANO, Y., OHDAIRA, Y., SHINBO, K., KATO, K., KANEKO, F. — 2008-12-19

In this report, we demonstrate electrocatalytic oxidation properties of ascorbic acid at poly(3,4-ethylenedioxythiophene) (PEDOT) thin films in view of their potential application for bio-sensing devices. PEDOT thin films were deposited on gold thin films by electropolymerization of EDOT monomer in acetonitrile solvent. In-situ electrochemical-surface plasmon resonance spectroscopy (EC-SPR) was used to detect both electrochemical and optical signals upon an injection of ascorbic acid.

Surface Plasmon Excitation and Emission Light Property for Otto/Kretschmann Configuration with MEH-PPV Film

2008-12-19

Attenuated total reflection (ATR) property utilizing surface plasmon (SP) excitation was investigated for BK-7 prism/Mg₂/Ag film/fluorescent organic dye film structure. In the structure, it is expected that SPs are excited at MgF₂/Ag and Ag/dye film interfaces by Otto and Kretschmann configurations, respectively. In the experimental ATR curve, reflection dips for the SP excitations at the interfaces could be detected. Furthermore, SP emission lights were observed by irradiation of Ar ion laser beam from the dye film side. The SP emission light curve with two peaks was observed and it was also considered that the peaks corresponded to the SP excitation of Otto and Kretschmann configurations. The SP emission light spectra indicated the excited fluorescent dyes induced the SP emission lights. Intense emission light of Otto configuration was observed in this sample.

In-situ Measurement of Photoelectron Spectroscopy in Air of Polypyrrole during Electrochemical Undoping

TADA, K., MIYOSHI, Y., ONODA, M. — 2008-12-19

In-situ measurement of photoelectron spectra of polypyrrole during electrochemical undoping/doping cycles has been carried out by using an open-type electrochemical cell. It has been observed that the ionization potential decreases with decreased electrochemical potential. This result seems to be reasonable because the decreased electrochemical potential corresponds to the undoping or recovery of electrons into vacant state of valence band.

Electrochromic Thin Film of Water-Dispersible Prussian-Blue Nanoparticles

2008-12-19

The insoluble Prussian-blue (PB) pigment becomes possible to disperse in aqueous solution by covering their surfaces with ferrocyanide anions. The thin film fabricated with these water-dispersible PB nanoparticles shows evident electrochromic color changes between +0.8 V to –0.4 V on an ITO substrate. The mass change of the thin film during an electrochemical reaction is measured by means of electrochemical quartz crystal microbalance (EQCM). According to the EQCM analysis, the filling rate of water-dispersible PB nanoparticles in the film is 37.7% as compared with an assumed perfect crystal PB film.

Conducting Polymer Based Nucleic Acid Sensor for Environment Monitoring

MALHOTRA, B. D., PRABHAKAR, N., SOLANKI, P. R. — 2008-12-19

Nucleic acid sensor based on polyaniline has been fabricated by covalently immobilizing double stranded calf thymus (dsCT) DNA onto perchlorate (ClO₄^– doped polyaniline (PANI) film deposited onto indium-tin-oxide (ITO) glass plate using 1-(3-(dimethylamino) propyl)-3-ethylcarbodiimide hydrochloride (EDC)/N-hydroxyl succinimide (NHS) chemistry. These dsCT-DNA-PANI/ITO and PANI/ITO electrodes have been characterized using square wave voltammetry, electrochemical impedance, and Fourier-transform-infra-red (FTIR) measurements. This disposable dsCT-DNA-PANI/ITO bioelectrode is stable for about four months, can be used to detect arsenic trioxide (0.1 ppm) in 30 s.

High-k Dielectric Layers for Bioelectronic Applications

BORSTLAP, D., SCHUBERT, J., ZANDER, W., OFFENHAUSSER, A., INGEBRANDT, S. — 2008-12-19

In many different bioelectronic applications silicon field-effect devices such as transistors or nanowires are used. Usually native or thermally grown silicon oxides serve as interfacing layer to the liquid. For an effective voltage to current conversion of the devices, the main demands for interface layers are low leakage current, low defect density, and high input capacitance. In this article we describe the fabrication and characterization of ultra-thin silicon oxide/high-k material stacks for bioelectronics. A combination of ultra-thin silicon oxide and DyScO₃ revealed the best results. This material stack is particularly interesting for future fabrication of field-effect devices for bioelectronic applications.

In Situ Observation of Time Dependent Electrochemical Activity of Cytochrome c at Bare Indium-Tin-Oxide Electrodes by Cyclic Voltammetry and Slab Optical Waveguide Spectroscopy

AYATO, Y., TAKATSU, A., KATO, K., MATSUDA, N. — 2008-12-19

In situ observation of electrochemical activity and time dependent characteristics of cytochrome c (cyt c) was carried out in 0.01 M phosphate buffered saline (PBS, pH 7.4) containing 20 µM cyt c solutions at bare indium-tin-oxide (ITO) electrodes by using a cyclic voltammetry (CV) and a slab optical waveguide (SOWG) spectroscopy. The bare ITO electrodes could retain the electrochemical activity of cyt c in the PBS solutions, indicating the great advantage of using ITO electrodes against other electrode materials, such as gold (Au). The CV curves and simultaneously observed the time-resolved SOWG absorption spectra in the consecutive cycles implied that the cyt c molecules could retain its own electrochemical function for a long time.

Analyzing Bioelectric Potential Response of Plants Related to Photosynthesis under Blinking Irradiation

ANDO, K., HASEGAWA, Y., MAEKAWA, H., KATSUBE, T. — 2008-12-19

The bioelectric potential of plants is generated by ion concentration difference between inside and outside of plant cells. It has been reported that the bioelectric potential of leaves changes at the beginning of steady irradiation and intensity of the potential response increases with the photosynthetic rate. Although it has been reported that photosynthesis is accelerated by blinking irradiation, the potential response under the blinking irradiation have not been fully clarified. In this study, we measured the bioelectric potential and CO₂ consumption of plants under various types of the blinking irradiation. This result showed that the potential response under the blinking irradiation has various behaviors and intensity of the response related to photosynthetic rate. We conclude that our method is suitable for monitoring the biological activity of plants such as photosynthesis.

Step Width Tolerable for Offset of the Aperture in a Millimeter-Wave Transducer between Post-Wall and Hollow Standard Waveguides

LEE, J., HIROKAWA, J., ANDO, M. — 2008-12-19

A transducer with a wide step from a post-wall waveguide to a hollow waveguide width is proposed which is tolerant against the aperture offset. The modes in the step width of about 1.50 wavelengths are stable for the aperture offset and the fields are not so perturbed while in the conventional stepped structure with step width of about 1.00 wavelength, the higher evanescent mode of TE₃₀ is excessively enhanced by the aperture offset. The operation of the transducer with the wider step is robust for the fabrication errors in the millimeter wave band. It is also suggested that the anti-symmetrical TE₂₀ mode which is excited only by non-zero offset or the misalignment of the aperture exists in both structures and can not be the dominant factor for the improvement. The transducers are designed and fabricated at 61.25 GHz using PTFE substrate with glass fiber of _r = 2.17. The bandwidth for the reflection lower than –15 dB is almost unchanged (6.30–6.60 GHz) for the offset from –0.2 mm to 0.2 mm, while it is degraded in the conventional stepped structure, from 7.65 GHz for no offset to 3.30–5.70 GHz for the same range of the offset.

Active Frequency Selective Surfaces Using Incorporated PIN Diodes

CHANG, K., KWAK, S. i., YOON, Y. J. — 2008-12-19

In this paper, active frequency selective surfaces (FSS) having a squared aperture with a metal plate loading are described. Active FSS elements using switched PIN diodes are discussed with an equivalent circuit model. A unit cell consists of a square aperture element with metal island loading and one PIN diode placed at the upper gap, considering the vertical polarization. The electromagnetic properties of the active FSS structure are changed by applying dc bias to the substrate, and they can be estimated by the equivalent circuit model of the FSS structure and PIN diode. This active FSS design enables transmission to be switched on or off at 2.3 GHz, providing high transmission when the diodes are in an off state and high isolation when the diodes are on. The equivalent circuit model in the structure is investigated by analyzing transmission and reflection spectra. Measurements on active FSS are compared with numerical calculations. The experimentally observed frequency responses are also scrutinized.

Driving Voltage Analysis for Fast Response of Waveguide Optical Switch Based on Movement of Liquid Droplet Driven by Electrostatic Force

IKEMOTO, T., KOKUBUN, Y. — 2008-12-19

The electrostatic force required for the driving of liquid droplet injected in a microchannel was studied to obtain the guiding principle to reduce the driving voltage of waveguide optical switch based on the movement of droplet. We analytically calculated the relation between the threshold voltage and velocity of droplet and the surface roughness of microchannel, and clarified some unconfirmed parameters by comparing experimental results and aeromechanical analysis. The driving of droplet in a microchannel was best analyzed using the Hagen-Poiseuille flow theory, taking into account the movement of both ends of the droplet. When the droplet is driven by some external force, a threshold of the external force occurs in the starting of movement, and hysteresis occurs in the contact angle of the droplet to the side wall of the microchannel. The hysteresis of contact angle is caused by the roughness of side wall. In our experiment, the threshold voltage ranged from 200 to 350 V and the switching time from 34 to 36 ms. The velocity of droplet was evaluated to be 0.3–0.4 mm/s from these experimental results. On the other hand, the measured angle distribution of side wall roughness ranged from 30 to 110 degrees, and the threshold voltage was evaluated to be 100–320 V, showing a good agreement with experimental results. The reduction of threshold voltage can be realized by smoothing the side wall roughness of microchannel. The switching time of 10 ms, which is required for the optical stream switch, can be obtained by shortening the horizontal spot size down to 1.5 µm.

Thermal Gain Variation Compensation Technique Using Thermistor on HPA Module for W-CDMA System

2008-12-19

The thermal gain variation of a high-power amplifier (HPA) module for a wide-band code division multiple access (W-CDMA) system application was reduced to within ±1 dB by applying a thermistor to compensate the gain variation. Two techniques for gain variation compensation with respect to temperature were investigated: base bias control according to temperature, and use of a thermistor in a matching network. Experimental comparison of two techniques indicated that the thermistor-based technique was more effective in reducing the gain variation without affecting linearity. A fabricated two-stage HPA module with a thermistor in its input matching network achieved a small gain variation within ±1 dB and ±5 MHz offset adjacent channel leakage power ratio (first ACLR) below –36 dBc over the temperature range from –10 to +85°C, where the first ACLR was measured under a load-mismatched condition with a voltage standing wave ratio (VSWR) of 1.4:1.

Highly Accurate and Efficient Current-Mode PWM CMOS DC-DC Buck Converter with On-Chip Current-Sensing

CHENG, K.-H., SU, C.-W., KO, H.-H. — 2008-12-19

In this paper, a high accuracy, high efficiency, and wide current-sensing range current-mode PWM buck converter with on-chip current-sensing technique is presented. The proposed current-sensing circuit uses simple switch technique to achieve high accuracy, high power efficiency, and high line regulation. The test chip is fabricated using TSMC 0.18 µm 1P6M 3.3 V CMOS process. The measurement results show that the buck converter with on-chip current-sensing circuit can operate from 700 kHz to 3 MHz with a supply voltage of 1.5–5 V and the output voltage of 0.5–4.5 V for lithium ion battery applications. The accuracy of the proposed current-sensing circuit is exceeds 89.8% for load current from 50 mA to 500 mA and for temperature from 0°C to 100°C. The peak power efficiency of the buck converter is up to 95.5%.

Eliminating the Reverse Charge Sharing Effect in the Charge-Transfer-Switch (CTS) Converter

SHIAU, M.-S., LIU, D.-G., LIAO, S.-S. — 2008-12-19

A novel voltage level controller for low-power charge pump converters will be presented in this paper. The proposed voltage level controller would react according to the pumped voltage in the charge-transfer-switch (CTS) converter. For the CTS circuit, the pumping operation would be degraded by the charge sharing effect in the auxiliary switch path. In this study, a voltage shifter was used as the voltage level controller to overcome this serious problem without consuming too much chip area. The simulation results showed that the converter can accept a rated input of 1.5 V and generated an output up to 8 V based on the TSMC 0.35-µm CMOS technology. The layout consumed an area of 125*160 µm². The highest output obtained in measuring the real chip was 5.5 V which is primarily due to the limitation that the transistor could tolerated. The largest load was estimated as high as 6 mW which is large enough for on-chip application.

An Experimental Study of Head Instabilities in TMR Sensors for Magnetic Recording Heads with Adaptive Flying Height

TONGSOMPORN, D., AFZULPURKAR, N., BARGMANN, B., LEKAWAT, L., SIRITARATIWAT, A. — 2008-12-19

We did an experimental study to investigate the effect of the thermal stress due to the heater for adjusting adaptive flying height (AFH) on the readability and instability of tunneling magnetoresistance (TMR) sensors. The slider head consists of a small heater nearby the read/write elements for controlling the clearance between the read/write elements and the recording medium of the magnetic recording system. It is firstly reported that the thermal stress from the AFH heater induces instabilities and caused head degradation. The thermal stress degrades the reader performance by inducing voltage fluctuations and large noise spikes that causes the magnetic recording system having poor bit error rate (BER). The open loop of the transfer curve indicates that the flipping of a synthetic antiferromagnet (SAF) edge magnetization causes these instabilities. The thermal stress reduces the exchange bias field and the energy barrier to flop the SAF edge magnetization. The dispersion and thermal stability of the antiferromagnetic (AFM) layer are the potential root causes of these SAF instabilities because the larger AFM dispersion in these heads gives less net stabilizing field to SAF layers that lowers the energy barrier to flop the SAF edge magnetization. Scanning electron microscope (SEM) images of these weak heads show rough surface and scratches close to the sensor element. The mechanical stress due to these scratches may additionally impact to the stabilizing field of the SAF.

Wide Band Metallic Waveguide with Asymmetric In-Line Dielectric Rods

KOKUBO, Y., KAWAI, T. — 2008-12-19

A system that has an array of dielectric rods at the center of a waveguide was previously suggested for single mode propagation with a wide frequency range. However, it is difficult to introduce the wave source from a coaxial cable, due to use of the TE₁₀-like and TE₂₀-like modes. In this investigation, an asymmetric setup of the dielectric rods is proposed for better coupling efficiency of the TE₁₀ mode.

A CMOS RF Power Detector Using an Improved Unbalanced Source Coupled Pair

PARK, H., LEE, J., LEE, J., NAM, S. — 2008-12-19

This paper presents the design of a CMOS RF Power Detector (PD) using 0.18 µm standard CMOS technology. The PD is an improved unbalanced source coupled pair incorporating an output differential amplifier and sink current steering. It realizes an input detectable power range of –30 to –20 dBm over 0.1–1 GHz. Also it shows a maximum data rate of 30 Mbps with 2 pF output loading under OOK modulation. The overall current consumption is 1.9 mA under a 1.5 V supply.

A Novel Fast-Lock-in Digitally Controlled Phase-Locked Loop

CHEN, X., YANG, J., SHI, L.-x. — 2008-12-19

A novel fast lock-in digitally controlled phase-locked loop (DCPLL) is proposed in this letter. This DCPLL adopts a novel frequency search algorithm to reduce the lock-in time. Furthermore, to reduce the power consumption, the frequency divider is reused as a frequency detector during the frequency acquisition, and reused as a time-to-digital converter module during the phase acquisition. To verify the proposed algorithm and architecture, a DCPLL design is implemented by SMIC 0.18 µm 1P6M CMOS technology. The Spice simulation results show that the DCPLL can achieve frequency acquisition in 3 reference cycles and complete phase acquisition in 11 reference cycles when locking to 200 MHz. The corresponding power consumption of DCPLL is 3.71 mW.