Ultralow resistivity in the surface direction of LB heterofilms

LB heterofilms of double layer consisting of arachidic acid and 2-pentadecyl-7, 7′, 8, 8′-tetracyanoquinodimethane (C₁₅ · TCNQ) LB films were sandwiched between Al and Au thin evaporated films. Such layer structures of Al/LB heterofilm/Au were deposited on the SiO₂ insulating film of silicon wafters. Resistance in the surface direction of the above layer structure was measured by the four-point probe technique. As a result, very low resistance of 10^?2 ～ 10^?3 Ω was obtained by the electrode system of gap 3.3 mm with width 10 mm. It was clarified in the experiments that the current flowed through the LB heterofilms of about 200 ～ 30 Å in thickness; accordingly the resistivity of LB heterofilms was calculated to be 10^?8 ～ 10^?9 Ω cm. Such a value of resistivity was much smaller than the metal resistivity of 10^?5 Ω cm. Furthermore, the current through the LB film, increased up to 1.3A, was equivalent to the very high current density of 4.1 ～ 10⁵ A/cm². However, the resistance was increased suddenly by 10⁶ times at that time and the current was decreased to 3 ～ 10^?4 A. Such a switching phenomenon could be observed repeatedly. The ultraflow resistance and the very high current density observed in the LB heterofilms will be explained by the model of the potential well filled with electron gas which was generated in the LB hetero-film by the polarization of C¹⁵ · TCNQ LB film.     

Microporous activated carbons from used coffee grounds for application to electric double‐layer capacitors

Electrochemical double‐layer capacitors (EDLCs) are devices that store enormous amounts of charge electrostatically when a potential is applied between electrodes of very high surface area (typically made of porous carbon) and an electrolyte. Wider commercialization of this technology has been held back by the lack of ultralow‐cost electrode materials. We demonstrate that used coffee grounds can be processed to form low‐cost electrodes. The surface and electrochemical characteristics of microporous activated carbons from used coffee grounds (CGCs) were measured. First, optimal times and temperatures for carbonization and activation were identified on the basis of Brunauer–Emmett–Teller (BET) surface area, pore volume, and pore size distribution. Second, CGCs were used as polarized electrodes in EDLCs, whose capacitances were evaluated using cyclic voltammetry. The results show that carbonization for 1 h at 600 °C with a heating rate of 300 °C/h, followed by CO₂ activation for 2 h at 1000 °C, affords the highest BET surface area (1867 m²/g) compared to other works. The produced CGCs have many micropores of less than 2 nm across, which contribute to the formation of an electric double layer. Capacitors made using these CGCs show the highest capacitance (103 F/g) in 0.8 M (C₂H₅)₄NBF₄/PC as an organic electrolyte, which is much higher than the ∼80 F/g typically used in organic‐electrolyte‐based commercial EDLCs, suggesting that coffee grounds are a useful electrode material. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Properties of anisotropic Ba‐Zn‐Cu system W‐type hexagonal ferrite magnets

Experiments were carried out to investigate the magnetic and physical properties of Ba‐Zn‐Cu W‐type hexagonal ferrites sintered without atmosphere control. Compositions were chosen according to the formula BaZn_2–xCu_xFe₁₆O₂₇, where x was varied 0 ˜ 0.5 and 1.0. The effect of BaO addition after semisintering treatment on magnetic properties of Ba‐Zn‐Cu compounds was examined. It was found that BaO addition for Ba‐Zn‐Cu compounds was very useful in stabilizing the W‐type hexagon. The optimum condition of making magnets and some properties of typical specimens are as follows: composition—BaZn_1.7Cu_0.3Fe₁₆O₂₇ with 4 wt% Ba added; semisintering conditions—1275 °C for 1.0 h in air; sintering conditions—1175°C for 0.5 h in air; magnetic properties and lattice constant are J_m = 0.405 T, J_r = 0.370 T, H_cJ = 88.15 kA/m, (BH)_max = 19.12 kJ/m³, T_c = 356 °C, H_A = 994.7 kA/m, K_A = 2.01 × 10⁵ J/m³, c = 32.928 × 10^–10 m, a = 5.927 × 10^–10 m, c/a = 5.556. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 36–42, 2001     

Magnetic properties of Pr‐Fe‐Co‐V‐W‐Si‐B system exchange spring magnets

The melt‐spun ribbons of Pr‐Fe‐Co‐V‐W‐Si‐B system alloys were prepared by single roller rapid‐quenching method. The effects of composition, surface velocity, and heat treatment on the magnetic properties were investigated. The P₉sFe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 alloy ribbons prepared at a surface velocity of 12.5 m/s were crystallized by heat treatment, and the optimum heat‐treatment condition was found to be at 575°C for 3 min, for which the magnetic properties were (BH)_max = 136.1 kJ/m³, J_r = 0.93 T, H_cJ = 652.2 kA/m, and H_cB = 528.3 kA/m. The temperature coefficients of J_r and H_cJ for the ribbons crystallized from melt‐spun ribbons of Pr₉Fe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 alloy were α(J_r)_ave = ?0.057%/°C and α(H_cJ) = ?0.450%/°C. The value of (B)_max for the compression molding Pr₉Fe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 isotropic bonded magnet prepared by using the ribbons annealed at 575°C for 3 min is 80.0 kJ/m³, and the density is 6.24 Mg/m³. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 10–16, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20211 Copyright © 2006 Wiley Periodicals, Inc.     

Interfacial electrostatic phenomena and capacitance–voltage characteristics of ultrathin polyimide Langmuir–Blodgett films

Capacitance–voltage (C–V) characteristic of ultrathin polyimide (PI) Langmuir–Blodgett (LB) films is discussed theoretically and experimentally taking into account the interfacial electrostatic phenomena and interfacial electronic states at the metal/PI LB film interface. It was found that the apparent film thickness decreases due to the charge exchange phenomena at the metal/film interface. It was also found that electrical insulating properties of the Au/PI LB film/Al device depended on the polarity of external voltage, probably due to the formation of the electrostatic interfacial electric field of 10⁸ to 10⁹ V/m. © 2000 Scripta Technica, Electr Eng Jpn 134(3): 9–15, 2001     

Analysis of domain structure in the Ce<Subscript>0.8</Subscript>Sm<Subscript>0.15</Subscript>Ca<Subscript>0.05</Subscript>O<Subscript>1.875</Subscript> sample

A Ce_0.8Sm_0.15Ca_0.05O_1.875 (S15C05DC) sample is synthesized by a solid-state reaction serving as a potential electrolyte material for intermediate-temperature solid oxide fuel cells. The sintered sample was found to be dense with a cubic fluorite structure. The addition of Ca²⁺ can act as a CeO₂ sintering aid for accelerating the process. The microstructures and properties of the sample were analyzed by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy, thermomechanical analysis, and transmission electron microscopy. Existing oxygen vacancies in the sample are indicated by a Raman peak at 558 cm^?1. The thermal expansion coefficient of the S15C05DC sample at 200–800 °C is approximately 12–14 × 10^?6 °C^?1. The control of domain size is an important factor for improving the conductivity of S15C05DC. Local clustered nano-domains, with higher Sm₂O₃ concentrations, were found to regularly arrange to induce the formation of a nanoscale C-type superlattice structure. While Ca doping decreased the formation of the C-type Sm₂O₃ structure.     

Monte Carlo analysis of dynamic characteristics and high‐frequency noise performances of nanoscale double‐gate MOSFETs

In this paper, a full‐band Monte Carlo simulator is employed to study the dynamic characteristics and high‐frequency noise performances of a double‐gate (DG) metal–oxide–semiconductor field‐effect transistor (MOSFET) with 30 nm gate length. Admittance parameters (Y parameters) are calculated to characterize the dynamic response of the device. The noise behaviors of the simulated structure are studied on the basis of the spectral densities of the instantaneous current fluctuations at the drain and gate terminals, together with their cross‐correlation. Then the normalized noise parameters (P, R, and C), minimum noise figure (NF_min), and so on are employed to evaluate the noise performances. To show the outstanding radio‐frequency performances of the DG MOSFET, a single‐gate silicon‐on‐insulator MOSFET with the same gate length is also studied for comparison. The results show that the DG structure provides better dynamic characteristics and superior high‐frequency noise performances, owing to its inherent short‐channel effect immunity, better gate control ability, and lower channel noise. Copyright © 2012 John Wiley & Sons, Ltd.     

Fabrication of flat micro‐gap electrodes for molecular electronics

Recently, organic molecular electronic devices such as molecular thin‐film transistors have received considerable attention as possible candidates for next‐generation electronic and optical devices. This paper reports on fabrication technologies of flat metallic electrodes on insulating substrates with a micrometer separation for high‐performance molecular device evaluation. The key technologies of fabricating planar‐type electrodes are the liftoff method by the combination of bilayer photoresist with overhang profile, electron beam evaporation of thin metal (Ti and Au) films, and SiO₂‐CMP (Chemical Mechanical Polishing) method of CVD (Chemical Vapor Deposition)‐deposited TEOS (tetraethoxysilane)–SiO₂ layer. The raggedness of the electrode/insulator interface and the electrode surface of the micro‐gap electrodes were less than 3 nm. The isolation characteristics of fabricated electrodes were on the order of 10¹³ ohms at room temperature, which is sufficient for evaluating electronic properties of organic thin‐film devices. Finally, pentacene FET (Field Effect Transistor) characteristics are discussed fabricated on the micro‐gap flat electrodes. The mobility of this FET was 0.015 cm²/Vs, which was almost on the order of the previous results. These results suggest that high‐performance organic thin‐film transistors can be realized on these advanced electrode structures. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 39–46, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20152     

Proposal of flux‐lock‐type fault current limiter with high‐TC superconducting element

This paper proposes a new type of fault current limiter (FCL), which consists of a high‐T_C superconducting (HTS) element and two coils wound on the same core without any leakage magnetic flux. In this FCL, either the limiting impedance or the initial limiting current level can be controlled by adjusting the inductances and the winding direction of the coils. Therefore, this FCL could relax the material restrictions on high‐T_C superconducting FCL. A current‐limiting experiment by a model FCL was carried out, and the limiting performance was observed. The initial limiting current level of the model FCL was 1.7 times higher than the critical current of the HTS element, and the fault current is suppressed to 52% immediately after the short‐circuit in the test. Considering voltage–current characteristics of a high‐T_C superconductor in a computer simulation, the calculated results almost agreed with the experimental results. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 31–38, 1999     

Impact of high‐κ gate dielectric and other physical parameters on the electrostatics and threshold voltage of long channel gate‐all‐around nanowire transistor

High‐κ gate‐all‐around structure counters the Short Channel Effect (SCEs) mostly providing excellent off‐state performance, whereas high mobility III–V channel ensures better on‐state performance, rendering III–V nanowire GAAFET a potential candidate for replacing the current FinFETs in microchips. In this paper, a 2D simulator for the III–V GAAFET based on self‐consistent solution of Schrodinger–Poisson equation is proposed. Using this simulator, capacitance–voltage profile and threshold voltage are characterized, which reveal that gate dielectric constant (κ) and oxide thickness do not affect threshold voltage significantly at lower channel doping. Moreover, change in alloy composition of In_xGa_1‐xAs, channel doping, and cross‐sectional area has trivial effects on the inversion capacitance although threshold voltage can be shifted by the former two. Although, channel material also affects the threshold voltage, most sharp change in threshold voltage is observed with change in fin width of the channel (0.005 V/nm for above 10 nm fin width and 0.064 V/nm for sub‐10 nm fin width). Simulation suggests that for lower channel doping below 10²³ m⁻³, fin width variation affects the threshold voltage most. Whereas when the doping is higher than 10²³ m⁻³, both the thickness and dielectric constant of the oxide material have strong effects on threshold voltage (0.05 V/nm oxide thickness and 0.01 V/per unit change in κ). Copyright © 2014 John Wiley & Sons, Ltd.     

A low‐voltage band‐gap reference circuit with second‐order analyses

A new band‐gap reference (BGR) circuit employing sub‐threshold current is proposed for low‐voltage operations. By employing the fraction of V_BE and the sub‐threshold current source, the proposed BGR circuit with chip area of 0.029mm² was fabricated in the standard 0.18µm CMOS triple‐well technology. It generates reference voltage of 170 mV with power consumption of 2.4µW at supply voltage of 1 V. The agreement between simulation and measurement shows that the variations of reference voltage are 1.3 mV for temperatures from ?20 to 100^°C, and 1.1 mV per volt for supply voltage from 0.95 to 2.5 V, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

High‐tuning‐range CMOS band‐pass IF filter based on a low‐Q cascaded biquad optimization technique

A design procedure for high‐order continuous‐time intermediate‐frequency band‐pass filters based on the cascade of low‐Q biquadratic cells is presented. The approach is well suited for integrated‐circuit fabrication, as it takes into account the maximum capacitance spread dictated by the available technology and maximum acceptable sensitivity to component variations. A trade‐off between noise and maximum linear range is also met. A novel, wide‐tuning‐range transconductor topology is also described. Based on these results, a 10‐pole band‐pass filter for a code division multiple‐access satellite receiver has been designed and tested. The filter provides tunable center frequency (f₀) from 10 to 70 MHz and exhibits a 28‐MHz bandwidth around f₀ = 70 MHz with more than 39‐dB attenuation at f₀/2 and 2f₀. Third‐order harmonic rejection is higher than 60 dB for a 1‐Vpp 70‐MHz input, and equivalent output noise is lower than 1 mV_rms. The circuit is fabricated in a 0.25‐µm complementary metal oxide semiconductor process, and the core consumes 12 mA from a 2.5‐V supply, offering the best current/pole ratio figure. The die area resulted to be 0.9 × 1.1 mm². Copyright © 2014 John Wiley & Sons, Ltd.     

Characteristics evaluation of a CO2‐capturing power generation system with reheat cycle utilizing regenerative oxygen‐combustion steam‐superheater

A new CO₂‐capturing power generation system is proposed that can be easily realized by applying conventional technologies. In the proposed system, the temperature of medium‐pressure steam in a thermal power plant is raised by utilizing an oxygen‐combusting regenerative steam‐superheater. The CO₂ generated by combusting the fuel in the superheater can be easily separated and captured from the exhaust gas at the condenser outlet, and is liquefied. The superheated steam is used to drive a steam turbine power generation system. Using a high‐efficiency combined cycle power generation system as an example, it is shown that the proposed system can increase the power output by 10.8%, and decrease the CO₂ emissions of the entire integrated system by 18.6% with a power generation efficiency drop of 2.36% compared with the original power plant without CO₂ capture, when the superheated steam temperature is 750 ^°C. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 35–41, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20575     

Formation and properties of nitrogen‐rich phases in austenitic stainless steel by plasma‐based ion implantation

Surface modification of austenitic stainless steel by plasma‐based ion implantation at elevated temperatures below 450°C has been studied experimentally. The nitrogen depth profile at room temperature was similar to that obtained by TRIM code simulation, but the depth of nitrogen penetration increases with target temperature and reaches a few micrometers at a treatment condition of 450°C and an implantation time of 2 h. High‐dose nitrogen implantation exceeding 10¹⁸ cm^?2 at temperatures above 350°C results in the formation of expanded austenite phase (supersaturated f.c.c. phase) with little CrN precipitation, leading to remarkable enhancement of surface hardness without loss of corrosion resistance. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(4): 9–16, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10340     

IC‐constrained optimization of continuous‐time Gm–C filters

This paper presents an automated synthesis procedure for integrated continuous‐time fully‐differential G_m?C filters. Such procedure builds up on a general extended state‐space system representation which provides simple matrix algebra mechanisms to evaluate the noise and distortion performances of filters, as well as, the effect of amplitude and impedance scaling operations. The proposed technique not only addresses the dynamic range optimization under power dissipation constraints, but also accounts for other relevant integrated circuit related features, such as transconductor decomposition in unitary instances, spread of capacitances and estimated area occupation, among other characteristics. The proposed approach, implemented in the MATLAB^® framework, can be also used as an exploratory tool to compare different circuit implementations for a given set of filter specifications. Copyright © 2010 John Wiley & Sons, Ltd.     

On the transposition of Gm–C filters to DC stabilized log‐domain filters

High‐order log‐domain filters could be designed by transposing the already known linear‐domain G_m–C filter topologies to the corresponding topologies in the log‐domain. This is achieved by using a non‐linear transconductor configuration, where the output current is exponentially related to its input and output voltages. A drawback of the non‐linear transconductor configuration already introduced in the literature is that a number of the transposed log‐domain filter topologies suffer from DC instability, while in some others a DC offset current appears at their output. In order to eliminate the aforementioned problems a modified non‐linear transconductor configuration for transposing G_m–C filter topologies to log‐domain filter topologies is introduced in this paper. The achieved improvements are demonstrated through a number of log‐domain filter configurations derived using the already introduced and the proposed transposition schemes. Copyright © 2006 John Wiley & Sons, Ltd.     

Magnetic properties of PLD‐fabricated ND‐Fe‐B film magnets and their applications to millimeter‐size motors

We succeeded in depositing 200‐ to 300‐µm‐thick Nd‐Fe‐B film magnets with (BH)_max of approximately 55 kJ/m³ on Fe substrates by the PLD method. In addition, we confirmed that a millimeter‐size motor, which was prepared from the obtained film, rotates at 15,160 rpm under a no‐load test. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(2): 1–6, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20215     

67 GHz three‐spiral transformer CMOS oscillator

This paper presents a 67GHz LC oscillator exploiting a three‐spiral transformer and implemented in 65nm bulk complementary metal–oxide–semiconductor technology by STMicroelectronics. The three‐spiral transformer allows operating with a lower voltage supply, still obtaining good phase noise performance, and achieving a compact design. Measured performances when supplied with 1.2 V are: oscillation frequency of 67 GHz, phase noise (PN) equal to ?96 dBc/Hz at 1 MHz frequency offset from the carrier, power consumption (P_C) equal to 19.2 mW and figure of merit (FOM) equal to ?179.7 dB/Hz. Measured performances when supplied with 0.6 V are: oscillation frequency of 67 GHz; PN equal to ?88.7 dBc/Hz at a 1 MHz frequency offset from the carrier; P_C equal to 3.6 mW and FOM equal to ?179.7 dB/Hz. Copyright © 2016 John Wiley & Sons, Ltd.     

Laser‐induced discharge in a rod–plane electrode in the presence of a negative dc electric field

Discharge induction experiments were performed between a plate and a rod on a plate electrode configuration with a gap length of 1 m using a high‐power CO₂ laser and a dc voltage generator. The electrodes are parallel planes. Each plate electrode consists of a central flat part having a diameter of 3 m with a circular edge on a cross section. The length of the rod is 10 cm. A chain of plasma beads of length 10 cm was created on the tip of the rod by the CO₂ laser and used for artificial triggering of negative high‐voltage sparkover. The behavior of streamer, leader, and return stroke was observed by an image converter camera. It was found that a positive upward traveling leader can be triggered from the tip of the rod on the lower plane to the upper plane by the chain of plasma beads created by the CO₂ laser. This apparatus is useful for study for realization of laser‐induced lightning. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 19–27, 2000