bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Au underlayers on perpendicular magnetic anisotropy of CoOx films
Authors: Hiratsuka Nobuyuki , Taguchi Kazuhiro , Ichikawa Tomonori , Fujita Minoru , Sugimoto Mitsuo
Published: July 2007

Partially oxidized cobalt films were deposited by the reactive evaporation method on an underlayer Au film and on a polymer film with a rough surface. The purpose of this study is to investigate the influence of these underlayers on the structure and perpendicular magnetic anisotropy of the partially oxidized cobalt films. The gold film was sputter‐deposited by using an Au target. The acceleration voltage and sputtering period for Au deposition were varied to form an Au film with different surface textures, i.e., island‐like, mesh‐like, and flat surfaces.

CoOx films were deposited on these underlayers. The measurement of the magnetic properties and the SEM observation of the film cross section were carried out. When a CoOx film was deposited on an Au film with an island‐like surface texture, the CoOx film had a columnar structure perpendicular to the underlayer surface and the diameters of the columns were small. Because of this columnar structure, the perpendicular magnetic anisotropy was improved. When a CoOx film was deposited on a polymer film whose surface was roughened by sputter‐etching, the CoOx film had a columnar structure with a small columnar diameter.

From the foregoing results, it was found that the columnar structure and perpendicular magnetic anisotropy of a CoOx film can be controlled by changing the surface condition of the underlayer.
A composite process for eprom and eeprom and its reliability
Authors: Shiba Kazuyoshi , Kubota Katsuhiko , Kuroda Ken‐Ichi , Hara Yuji
Published: July 2007

A process to form an IC with an EPROM (erasable programmable ROM) and EEPROM (electrically erasable PROM) was a developed and a module was tested. Fabricating a floating‐gate type EEPROM and the process to achieve high reliability in write/erase performance and the high data‐retention characteristic were investigated. The write/erase endurance is higher when the tunnel oxidation is carried out by wet oxidation than when carried out by dry oxidation.

As the temperature for forming the inter‐polyoxide increases, the leakage current decreases but the write/erase endurance decreases. As the tunnel oxide film becomes thinner, the write/erase endurance decreases. The passivation layer has a great influence on the Vth window and data‐retention characteristics. When the passivation layer is a P‐SiN, the foregoing characteristics are poorer than when a PSG film is used. However, if PSG and P‐SiO films are formed under the P‐SiN film, the degradation of the forementioned characteristics decreases.
Fiber optic pattern recognition sensor using neural network
Authors: Aisawa Shigeki , Noguchi Kazuhiro , Matsumoto Takao
Published: July 2007

A novel method for remote pattern recognition sensing through a multimode optical fiber using neural networks is proposed and tested experimentally. A neural network is used to recognize the original image from a pattern transmitted through the optical fiber. The experimental results show that the 26 alphabetic character patterns can be recognized correctly after transiting 30 m of multimode fiber (core diameter = 400 μm, numerical aperture = 0.39). To increase the tolerance for displaced patterns and recognition ability for rotational symmetrical patterns, the wavelength division multiplex method also is proposed. Experimental results confirm the efficiency of this method.
Semiconductor or vibration sensors using multiple cantilever beams with different lengths
Authors: Member Hideo Muro, , Member Shigeo Hoshino,
Published: July 2007

Semiconductor vibration sensors incorporating ten polycrystalline silicon cantilever beams with different lengths and the detection circuitry on the same substrate have been developed. The sensors were designed to detect a resonance of each beam by capacitance change and to discriminate knockings precisely by outputting the vibration spectrum.

This paper describes the structure of the sensors, the analysis of the characteristics, the fabrication process, and the measured results. The cantilever beams consist of triply stacked layers of Si3N4/p4poly‐Si/Si3N4 and are released from the substrate by etching a sacrificial layer of an undoped poly‐Si, where the warps of the beams are adjusted through thickness control of the upper silicon nitride layer. The measured resonant frequencies of the fabricated sensors were 5 to 14 kHz for the 1‐μm thick, 100‐μm wide beams with lengths of 510 to 310 μm, which agreed approximately with the values calculated using a simple model. The sensitivity at resonance depended on the ambient pressure and was about 10mV/G with Q of 100 at 5 × 10−6 torr. In the test using a one‐cycle engine, remarkable outputs were observed for knocking vibrations with peak frequencies near the resonant frequencies of the beams.
Characterization and design method for asymmetrical‐structure offset‐type broadside‐coupled strip lines having thick strip conductors and dielectric substrate
Authors: Nakajima Masayuki , Yamashita Eikichi
Published: July 2007

For asymmetrical‐structure offset‐type broadside‐coupled strip lines used for a tightly coupled directional coupler and a high‐Qtransmission line, an analysis method and a design method are proposed in which the strip conductor thickness and the presence of a dielectric substrate are taken into account. In the analysis, the rectangular boundary division method is used within the range of the quasi‐TEM approximation. By combining this analysis method with an algorithm using the secant method, the forementioned directional coupler is designed. A systematic optimization method for each design parameter needed in the design is described. Further, by means of the capacitance difference method, the attenuation constant due to the conductor loss of the offset‐type broadside‐coupled strip line is derived. The numerical results are presented graphically in the form of a coupling coefficient, mode impedance, effective relative permittivity and attenuation constant due to the conductor loss.
Properties of SiN films deposited by photo CVD and memory characteristics of MNOS structure
Authors: Kim Taehong , Ohnishi Kazunori
Published: July 2007

Silicon nitride (SiN) film was deposited at substrate temperature of 100–400°C using a photo CVD technique with NH3 and SiH2Cl2 gases and ultraviolet (UV) light from a low‐pressure mercury lamp.

Based on ESCA analysis, it has been clarified that the film is relatively Si‐rich, that the binding energy of Si2p changes from SiN bond to SiNO bond at the oxygen content of 23 percent and that the film deposited at 100°C changes from SiN to SiO2 structure after the deposition.

In the measurement of I–V characteristics using metal‐SiN‐Si (MNS) structure, the film leakage current was small, but the film deposited at high‐substrate temperature had a large leakage current although the interface characteristics improved.

From the characteristics as a nonvolatile memory using a metal‐SiN‐SiO2‐Si (MNOS) structure, it has been found that the SiN film deposited by the photo CVD method is useful for memory devices and the electron trap density increases with deposition temperature.
A simulation of high‐frequency mutually coupled circuit using bipolar transistors
Authors: Shigehiro Takanori , Nakamura Masataka , Yoneda Syojiro
Published: July 2007

As electronic and transmission circuits have decreased in size and been implemented as integrated circuits, a number of methods for simulating active inductors has been proposed. However, the simulation of an ideal transformer and a mutual induction circuit has not been fully realized. In particular, there is no method which deals with high‐frequency simulation of a mutual induction circuit that actually realizes the variable double‐tuned responses with a varying element that are related to the coupling coefficient.

This paper proposes a new high‐frequency simulation circuit which has the following advantages:

All the transistors used in the circuit are of the npn type.

Two inductances (the self‐and mutual‐inductances) are realized using a bi‐directional differential current flowing in a single capacitor. These inductances can be independently set and adjusted.

(3) The circuit is configured symmetrically, whereby the right and left circuits are coupled using buffer transistors, in order to minimize their effect on one another.

In this paper we will first describe the fundamental principles of the proposed circuit. Then, taking into account the imperfection of the transistors, we will perform a circuit analysis over a high‐frequency range and discuss the results. As an application example we will use a double‐tuned circuit with a center frequency of 1 MHz. Finally, the feasibility of the proposed circuit will be confirmed using an experiment. Results indicate that the measured responses coincide with the calculated ones for single‐peak, maximum‐flat, and double‐humped cases.
Soft magnetic properties of CoNbZrN microcrystalline films produced by dc magnetron sputtering
Authors: Shimada Yutaka , Miyakawa Choji
Published: July 2007

Previously, it was stressed that the magnetically soft amorphous films lose their softness when nitrogen or oxygen is doped in the fabrication process. However, it has been reported that composition‐modulated nitride films maintain magnetic softness and exhibit remarkably high thermal stability. Furthermore, it has been reported that uniform nitride films with magnetic softness can be obtained when deposited by ion beam sputtering.

In this paper, uniform nitride films deposited by dc magnetron sputtering are studied. DC magnetron sputtering is expected to have an effect similar to that of the nitride films in improvement of magnetic softness. The results of the analysis of nitrogen content and its chemical bonding and magnetic softness of the films are described. Furthermore, the transition process from the amorphous phase to the nanocrystalline phase and the structure of the crystalline phase are studied. The results suggest that the films have a magnetic structure different from that of the magnetically soft nanocrystalline materials reported so far.
Ir sensor using functional semiconducting fiber and application to human detection
Authors: Muto Norio , Miyayama Masaru , Yanagida Hiroaki , Kajiwara Teijiro , Mori Norihisa , Imai Yoshikazu , Harada Hirofumi , Ichikawa Hiroshi
Published: July 2007

The infrared (IR) sensor has recently become more important in many fields, and development of a conventional IR sensor with a fast IR response is needed. Both SiC fiber and carbon fiber have been found to be therm‐stor materials that have rapid thermal response. The present paper reports on the development of fibers for use in IR sensors, including the measurement of the fundamental fiber properties and thermal response characteristics to the IR radiation of IR sensors using fibers. Application in intelligent IR sensors, human body detection, and future developments are also reported.

The IR response was affected markedly by fiber structure. A thermal time constant of 1.24 ms was observed in response to IR radiation from a 600‐K black‐body furnace. The thermistor constant of the fiber increased linearly with an increase in the electrical resistivity of the fiber; the output voltage of the IR sensor using a semiconducting fiber increased with an increasing thermistor constant. The IR sensor using functional semiconducting fiber with a larger thermistor constant detected intelligently in a room‐temperature environment both an immobile and a mobile human body, each of which had body temperatures that were lower and higher than the room temperature. The functional semiconducting fiber was found to be a promising material for intelligent IR sensor.
Geometrical theory of diffraction including corner diffractions with application to radiation pattern analysis of major angle corner reflector antenna
Authors: Zhang Xu , Inagaki Naoki , Kikuma Nobuyoshi
Published: July 2007

The major angle corner reflector antenna is characterized by a large half‐power value width in the magnetic plane and a large front‐to‐back ratio. This antenna is considered a candidate for the fixed‐state antenna for radio communication within a limited space being studied by the authors. The analysis of radiation patterns of antennas of this type traditionally has been carried out by the induced electromotive force (EMF) method. In such calculations, the errors in the sidelobes have been substantial.

In the analysis of the radiation pattern in this paper, the corner diffraction formula derived previously and the approximate corner diffraction formula for a hollow wedge corner which is newly derived by an asymptotic calculation from the equivalent edge electric and magnetic currents in the UTD are included in the application of the GTD (Geometric Theory of Diffraction). It is shown that by this approach an accurate analysis can be performed in both the E‐ and H‐planes. It is confirmed that the results by the GTD, by the MM (moment method), and by the experiments agree well.
Neural network hardware with learning function using pulse‐density modulation
Authors: Eguchi Hirotoshi , Furuta Toshiyuki , Horiguchi Hiroyuki , Oteki Sugitaka
Published: July 2007

To adequately demonstrate the parallel distributed processing and self‐learning capabilities of neural networks, a realization in hardware is the most appropriate approach. Therefore, a pulse‐density type neuron model was proposed in view of its ease of implementation in hardware. In this model, symbols are transmitted as streams of pulses, and symbol values are represented by the pulse densities. In addition, symbol calculations are all done digitally. An algorithm was developed which enables learning by backpropagation in layered networks, and the efficacy of the proposed neuron model was established through a software simulation. Next, a hardware neuron is constructed on a digital circuit board and its feedforward and learning processes as well as its error backpropagation capability are demonstrated. Using this board, a prototype hardware neural network was constructed which does not require any software and which performed handwritten digit recognition and learning. Finally, this neuron board capabilities were integrated in LSI using a gate array. The possibility of its use in implementing future large‐scale networks is discussed.
Surface plasmon immunosensors
Authors: Sun Xiaochun , Matsui Yoshikazu , Shiokawa Showko , Kubota Hiroshi
Published: July 2007

A surface plasmon is a charge density wave propagating along the interface between a metal on dielectric medium. Since the energy is concentrated at the interface, sensors that utilize the surface plasmon are extremely sensitive to both the charges in the dielectric properties and the geometry of the interface.

A surface plasmon immunosensor to detect antibody and antigen immunoresponse has been developed. Here the sensitivity of the sensor is theoretically investigated and the experimental results of sensor sensitivity, the real‐time measurements and the problem of repeated utilization of the sensors are evaluated using α‐Feto‐protein (α‐FP) and goat IgG. In addition, the problem of deciding whether to use antibody or antigen as immobilized sensing medium is discussed based on the characteristics of surface plasmon and biomolecules. As a result, it is concluded that with an antigen immobilized sensor, the sensitivity is higher and the real‐time response can be detected.
Observation of the bonding interface between ALN ceramics and metal base with the ultrasonic imaging system
Authors: Takahashi Masaaki , Kurihara Yasutoshi , Yamada Kazuji , Musha Yoshinori
Published: July 2007

During the thermal cycle test of semiconductor modules with Si chips, AlN ceramics and metal bases for heat sink connected to each other by soldering, the thermal resistance of some specimens increased in a comparatively short test period. By observing the interiors of these specimens using an ultrasonic survey imaging system, a strong reflected wave was observed at the solder connection joints of the AlN and the metal base. The area of this reflected wave was in the circumferential part of the sample at the initial stage but extended to the center with the thermal cycles.

The reflected wave observed in these specimens was caused by a gap due to the breakage of solder because of the difference in thermal expansion coefficients between AIN and the metal base. It has been clarified that the reduction of the observed connection area agreed with the analytical estimation based on the thermal fatigue failure of solder, and the relationship between the reduction of the connection area and the increase of the thermal resistance also was clarified empirically. Moreover, it was confirmed that the ultrasonic imaging system is applicable to evaluation of the connecting conditions between semiconductor chips, ceramics substrate and metal bases because it can observe clearly the voids inside the solder which cause thermal resistance fluctuation.
A study of a resonant condition of symmetric triple‐barrier structures by using circuit theory
Authors: Ohtani Naoki , Nagai Nobuo , Suzuki Masakiyo , Miki Nobuhiro
Published: July 2007

Recently, quantum effect devices have been studied extensively and new functional devices not observed in the conventional devices are expected. As a result, the necessity of developing a design method for superlattices is enhanced.

The authors have proposed a method in which the multiple barrier structures are replaced with complex equivalent circuits. Using this method, it is now possible to treat the resonant tunneling effect from the viewpoint of circuit theory. It was shown that the network synthesis theory can be applied to the design of the superlattice. Although the resonant tunneling effect of a double‐barrier structure has been studied extensively for device applications, little attention has been given to the triple‐barrier structures.

In this paper, numerical experiments are carried out with this complex‐valued equivalent circuit model so that the resonant conditions of the symmetric triple barrier are studied. To this end, the matching condition valid for a circuit symmetric right to left is applied to the equivalent circuit of a symmetric triple‐barrier structure so that its resonant condition is investigated. It is found that the electron energy that makes the impedance viewed at the center of the equivalent circuit purely resistive is the complete resonant level. It is shown also that this resonant condition can be understood easily by the use of the Smith chart.
Evaluation of cohesive property of carbon black in epoxy resin composite from the equivalent circuit in high‐frequency region
Authors: Nakamura Shuhei , Ito Atsushi , Sawa Goro , Kitagawa Keiichi , Tsubota Kazunari , Ikeda Masayuki
Published: July 2007

When carbon black (CB) with high cohesiveness is used for a carbon‐black resin composite, the temperature coefficient of resin resistivity is negative and the increase in resin resistivity due to humidity is small. These symptoms are due to the balance between the mechanical change, such as thermal expansion and volume increase caused by humidity absorption and the bond strength between CBs. The bond strength between CBs is dependent on curing temperature. In this study, the cohesiveness of CBs which scatter in resin will be investigated by evaluating the electrical property in the high‐frequency region.

The impedance of a CB‐resin composite was measured at frequencies up to 3 GHz and was expressed by the parallel equivalent circuit with resistance Rs and static capacitance Ce. Since residual resistance is present at frequencies up to 3 GHz, the equivalent circuit was replaced with the circuit with series resistance Rs and a parallel circuit with resistance RC and static capacitance CC. This equivalent circuit was investigated by the S parameter method.

As the concentration CB increased, RS and RC rapidly decreased and CC increased. When CB particles were easily bonded together, RC was small and CC was high even if the concentration of CB was low. From the dependencies of RC and CC on the CB concentration and the temperature dependence of resistance, it was concluded that RC and CC provided information on the cohesiveness of CB.
Electrification properties of human body for walking‐motion
Authors: Fujiwara Osamu , Okazaki Masaru , Azakami Takashi
Published: July 2007

Digital equipment with various high‐speed, low‐power ICs is vulnerable to electrostatic discharge (ESD) and a method to avoid this problem should be developed. Since ESD often is generated by a human while walking, the ESD generating mechanism must be well understood to prevent ESD.

This paper proposes a method to estimate the generated charge by evaluating the potential of the human body while walking. Assuming that the basic human motions consist of the up and down movement of the feet, the potential of the human body and generated charges for every step were measured. As a result, it was found that the potential and charges in the human body caused by steps reach a steady state within 800 ms, the potential is lower than 700 V, and the charges are less than 100 nC.

The capacitance of the human body changes according to motion and is around 200 pF. When one foot is raised, the body capacitance is 70 percent of that when both feet are grounded. The body potential is dependent on the kind of foot motion, that is, in continuous walk, the body potential is negative and its absolute value increases continuously. In stepping, the potential vibrates with a constant amplitude. These characteristics can be explained from the charging characteristics for the basic body motions.
Design and fabrication of a shielded‐velocity‐matched Ti:LiNbO3 optical modulator
Authors: Kawano Kenji , Nozawa Toshinori , Kitoh Tsutomu , Yanagibashi Mitsuaki , Jumonji Hiromichi , Noguchi Kazuto
Published: July 2007

This paper describes a shielded‐velocity‐matched Ti:LiNbO3 optical modulator which realizes a wide bandwidth with the velocity matching between the optical wave and the modulation microwave by placing a shielding conductor close to the coplanar waveguide traveling electrode through an air overlay.

In the design of the traveling‐wave electrode, a quasi‐TEM approximation and a spectral domain approach with hybrid mode are used. From numerical analysis it has been found that the effective refractive indices of the microwave and the light wave can be matched by optimally setting the overlay thickness. It has also been found that the increase in the microwave propagation loss or decrease in the characteristic impedance can be suppressed by increasing the thickness of the SiO2 buffer layer. As for the optical waveguide, the design parameters have been clarified by using a newly developed modified step segment method.

Based on these examinations, a Mach‐Zehnder intensity modulator and a phase modulator for the 1.5‐μm wavelength band have been designed and fabricated. As a result of measurement, the optical modulation bandwidth has been improved greatly to 20 GHz. As for the drive voltage, the intensity modulator uses 4.7 V and the phase modulator uses 6 V. The total insertion loss including the connector loss is 2.2 dB for the intensity modulator and 2 dB for the phase modulator. It has also been verified that the modulators have superior ambient stability.
A possibility of superhigh‐speed photodetection through frequency conversion
Authors: Choi Young‐Kyu , Wai Yee Mun , Nakajima Masamitsu
Published: July 2007

It is shown that even if the modulating frequency of a light is too high for direct detection, the signal can be extracted by frequency conversion at the same time as the detection by means of the nonlinearity of the APD. When this frequency conversion detection is applied to an optical receiver, the detection bandwidth can be increased while the configuration of the optical detection circuit and the signal processing in the subsequent stages are simplified. A fundamental analysis is carried out with an APD which is confirmed experimentally.
Design and performance of optical transfer splicing system using multifiber connectors
Authors: Kobayashi Hideo , Shimizu Masatoshi , Watanabe Ichiro , Maki Terufumi , Uenoya Takuya
Published: July 2007

The transfer splicing of optical fiber cables is performed at night using released circuits; this involves time‐consuming manual work. To achieve highly efficient optical cable transfer splicings, development of low‐loss transfer components is expected to speed up transfer operations. This in turn reduces interruption time and identification of cable fibers and also controls synchronization of each function and details required.

This paper proposes an efficient system for the optical transfer splicing of the existing cables to the new ones. This system uses single‐mode multifiber connectors. The design method and related details of rapid transfer, fiber identification and synchronous transfer control are described. The transfer splicing characteristics of this newer, more efficient system are evaluated and it is verified experimentally that satisfactory results are possible.
A fast pull‐in PLL IC using two‐mode pull‐in technique
Authors: Sato Hideo , Kato Kazuo , Sase Takashi , Ikushima Ichiro , Kojima Shin‐ichi
Published: July 2007

The phase‐locked loop (PLL) circuit used in the timing recovery of high‐speed digital communications and high‐density digital recordings must have a fast pull‐in time and low jitter. One way to satisfy both characteristics is to use a two‐mode PLL in which the loop gain is switched in the pull‐in state and the steady state. However, in the PLL with a conventional procedure, the time constant of the loop filter cannot be reduced in the pull‐in state; hence the time for phase locking after frequency locking cannot be reduced.

This paper proposes a method in which the time constant of the loop filter and the loop gain are both switched. The loop gain is switched by the gain of the smoothing filter to eliminate ripple in the output from the phase comparator while the time constant is switched by the resistor in the loop filter. This method realizes a pull‐in time one‐tenth that in the PLL with conventional two‐mode operation.

A PLL IC using the forementioned method was fabricated by 2‐μm BiCMOS process technology. Its capture range was ±2 percent, the pull‐in time was 100 μs, and the noise bandwidth was 128 kHz in 64‐MHz operation.
An intelligent sensor architecture with fuzzy associative memory system
Authors: Yamaguchi Toru , Takagi Tomohiro , Tanabe Minoru
Published: July 2007

In realizing the intelligent sensor which flexibly transforms input information into the information required by the user employing such knowledge processing as fuzzy inference, the following points are especially important: (1) the representation of the knowledge as well as the acquisition of the knowledge should be easy; and (2) the inference should be executed with a high speed.

This paper proposes a sensor construction which satisfies both of the forementioned requirements. The intelligent sensor proposed in this paper employs the if‐then type knowledge representation as the fuzzy rule with a high affinity to human thought. The sensor is composed of three independent neural nets: the input (if) part, the output (then part), and the input/output relation (if‐then) part.

In the input part, the learning vector quantization (LVQ) network evaluates the features of the input waveform, and the result is mapped directly on the concept represented in the condition part of the fuzzy rule. LVQ executes self‐learning without a supervisor based on the features of the input waveform and automatically generates the membership function needed in the condition part of the fuzzy rule. This simplifies the knowledge acquisition process.

In the input/output relation part, the fuzzy inference is executed with a high speed by the parallel processing of the associative memory network. Thus, the intelligent sensor based on the fuzzy associative memory can improve the forementioned two points (1) and (2). Furthermore, to demonstrate the high versatility of the proposed construction, this paper considers the problem in which two entirely different sample problems are realized by the same construction. The realization example is shown by a simulation.
Monolithic integrated magnetic sensor realizing omnidirectional measurement
Authors: Maenaka Kazusuke , Ohgusu Tatsuro , Nakamura Tetsuro
Published: July 2007

A monolithic integrated magnetic sensor realizing omnidirectional measurement is presented. This monolithic integrated sensor consists of three Hall cells which detect magnetic components in x, y, and z directions and the bipolar circuit which converts the output signal of Hall cells VX, VY, and VZ into its absolute value (=(V2X + V2Y + V2Z)1/2).

For the magnetic detector, a new “lateral Hall cell” is proposed to detect the magnetic components parallel to the chip surface (x, y directions). The three‐dimensional (3‐D) magnetic detection has been realized by combining two lateral Hall cells and a conventional epitaxial (lateral) Hall cell (for z direction).

The signal conversion circuit uses a Gilbert multiplier for square calculation and a translinear circuit for a root circuit, with a total device count of 158 elements. The test device realized an omnidirectional magnetic measurement with a maximum error of ±4 percent, sensitivity of 14 V/T, and a temperature coefficient of 2100 ppm/°C in the magnetic flux range of −250 to +250 mT.
A high‐speed, large‐capacity BiCMOS SRAM with bipolar current switch logic
Authors: Douseki Takakuni , Ohmori Yasuo
Published: July 2007

BiCMOS SRAM has high speed comparable to that of the bipolar ECL RAM. In the realization of the SRAM by previous technology, the useful SRAM architecture employs the bipolar current switching circuit for all the peripheral circuits and CMOS for the cell array.

This paper discusses the construction of the bipolar peripheral circuit to apply the forementioned architecture to large‐capacity memory. First, the decoding scheme using the emitter‐follower is proposed for the selector circuit which contains the bipolar current switching circuit and the selection function. It is shown that the delay time and the power consumption can be suppressed even if the memory capacity is increased. The word driver which employs the current switching level converter and the CMOS converter is proposed. The relation between the current of the level converter and the inverter size is clearly indicated, and it is shown that a high‐speed operation is realized. Then the three‐stage multiplexer is proposed for the read‐out circuit. where the output buffer is provided with the selection function. The number of multiplexing in each stage is determined which minimizes the delay time of the read‐out circuit. Finally, the proposed structure is applied to the 256‐kbit SRAM and the usefulness is demonstrated.
Resistor and dielectric properties of carbon‐black epoxy resin composites
Authors: Nakamura Shuhei , Ito Atushi , Sawa Goro , Kitagawa Keiichi
Published: July 2007

In this paper, the change in carbon black (CB) coherence with CB loading in CB resin composites has been studied from the viewpoint of resistance characteristics (resistivity, temperature coefficient of resistance) and dielectric properties by using HS 500 as CB. Equivalent circuit parameters (Rs, Rc, and Cc) for these composites also are used for comparison.

The dielectric properties have been obtained from a complex relative dielectric constant evaluated from the reflection and transmission coefficients at the frequency of 300 kHz to 3 GHz. The parameters for the equivalent circuit have been obtained from the frequency dependence of relative dielectric constant and the dc conductivity. As the CB loading increases, the dc resistivity decreases and Rs and Rc also decrease. This corresponds to the increase in the number of conductive paths formed by the CB structure bridging the electrodes.

From the decrease of the positive TCR value, it is considered that a mechanically strong coherence was formed between the CB structure with an increase of the CB loading. Also, from the increase in the strength of relaxation and Cc with the CB loading, the branching of the CB structure which branches out of the conduction path bridging the electrodes has been found to increase. In this case, a parameter βd which is a measure of the distribution of the relaxation time increased.
Optical computed tomography for biomedical objects based on coherent detection imaging method
Authors: Toida Masahiro , Ichimura Tsutomu , Kondo Makoto , Inaba Humio
Published: July 2007

This paper summarizes a series of studies aiming at realization of computed tomography imaging (CT) by laser beam for actual in vitro biological samples, which is the first successful trial achieved in the world. The method is realized first by image reconstruction, which detects and selects only the weak transmitted light component buried in stronger multiple scattered light, using the optical heterodyne detection with a very high directivity and sensitivity. This is called coherent detection imaging (CDI).

To realize the optical CT using the laser light based on the projection theorem, the following three conditions should essentially be satisfied:

(1) The direct‐transmitted light component in the biological system with multiple scattering should accurately be selected and detected.

(2) The Lambert‐Beer law should be applied to the selectively detected direct‐transmitted light component.

(3) There must exist a direct‐transmitted light component in the medium with complex distribution of refraction index as well as complex boundaries. The authors examined the medium in which the sample is buried and cannot be observed, not only by the naked eye but also by the traditional direct detection method. It was verified experimentally that the three conditions for the realization of the optical CT are applicable, and it was demonstrated that optical CT imaging is feasible for actual samples using the CDI method.
Ultrafast optical processes in DC‐field biased quantum‐well structures
Authors: Yamanishi Masamichi
Published: July 2007

This paper describes one of the ultrafast optical processes in the dc‐biased quantum‐well structure, ultrafast switching of light emission controlled by electric field effect, and its application for light‐emitting devices. In the fabricated device, injection current for device operation is extremely low (10 A/cm2) and high‐speed switching of light emission (switching time of 300 ps) can be achieved without the influence of a recombination life‐time.

Utilizing the amplification of light emission in the microcavity, the external efficiency of the light‐emitting device can be improved, indicating that a switching time of 10 ps with an external efficiency of 10 percent can be achieved.

The paper also discusses the ultrafast optical nonlinearity due to virtual charge polarization caused during optical excitation of the quantum‐well structure by nonresonant light, and the physics and applications of utlrafast electric pulse caused by the nonlinerity. In addition, the possibility is discussed of optical detection without optical detection without optical absorption using the virtual excitation.
Optical switching effects using excited state absorption of Er3+ ‐doped fibers
Authors: Maeda Yoshinobu , Migitaka Masatoshi
Published: July 2007

When a 787‐nm signal light with constant optical intensity is superimposed with a control light of the same wavelength in an Er‐doped optical fiber, optical switchoff occurs. The optical intensity of the control light for switch‐off is 1.4 and 25 W/cm2. As the optical intensity increases, the optical transmission of the fiber decreases. When the optical intensity is 25 W/cm2, the optical transmission is lowest.

A numerical analysis based on the four‐level double absorption model indicates that this nonlinear transmission characteristic takes place because the excited absorption due to the 2H11/2‐4I13/2 transition of Er3+ is predominating in the 4I9/24I15/2 and 2H11/2‐4H13/2 double absorptions. The optical switch‐off phenomenon is regarded as the first‐order phase transition phenomenon due to complex saturable absorbers with negative optical intensity dependence in optical transmission.
Optical fiber local‐light injection and detection coupling system for identification of fiber transmission operation lines
Authors: Shimizu Masatoshi , Kobayashi Hideo
Published: July 2007

The development of optical fiber cable transfer splicing systems is being advanced to increase the speed of connection of in‐use circuits to new ones, an operation that has been necessary in cable joints, branches, etc. In the construction of these systems, the conservation of the action‐objectives of the in‐use fiber between two different points must be confirmed and, therefore, the fiber identification techniques play the most important role.

In this paper, considering the identification of in‐use fibers, the conditions of bent fiber light injection and detection and their coupling systems are discussed. As to the bent fiber light injection, the relations among the ray angle of incidence which results in the injected optical signal to propagate as a core mode, the bending radius, the thickness deviations of the UV coat and the refractive index of the matching material are investigated.

The bent‐injection coupling efficiency in relation to the axial displacement between the identifying fiber and the injected one also is investigated. It is found that large coupling efficiencies can be achieved if the incident light beam spot‐size is reduced and the light‐source wavelength is increased. As to the condition of the bent fiber light detection system, the detection efficiency in regard to the source wavelength when the detected optical signal inside the core corresponds to the injected light is discussed. It is shown that large detection efficiency can be achieved if the optical source‐wavelength is increased and the bending radius is kept below 6 mm.
Characteristics of high‐speed bipolar RAMs under address‐skew condition
Authors: Yamaguchi Kunihiko , Homma Noriyuki
Published: July 2007

This paper considers a high‐speed bipolar RAM with the integration density of 4 kb, as an example. The access time and the operational margin are examined by simulation and actual measurement in representing the effect of the timing difference between address input signals (called skew) on the characteristics of the memory.

First, it is shown that the access time increases by approximately 0.9 ns (17 percent) by the skew. This is due to the operation of the sense amplifier producing the differential output. As a result of the skew, the switching of the sensing current is delayed and the period is produced in which the differential sense outputs are kept at the same potential. This equipotential period lasts longer due to the skew than in the case without a skew, which produces a waveform distortion in the data output signal. This waveform distortion increases the access time. However, the increase is suppressed by optimizing the timing design of the internal circuit.

Next, the memory cell potential in the transient state is considered and the relation between the skew and the operational margin is examined. It is shown as a result that when a skew exists, the circuit experiences a special transient state which is not observed when there is no skew. It is shown that the operational margin in this state is determined by the particular memory, cell with a large variation in the forward voltage VF of Schottky Barrier Diode (SBD). It has been proven useful to reduce the variation of VF and to increase the SBD capacitance to reduce the dependency on the skew.

Finally, the relation between the two forementioned skew dependencies and the internal address latch function is discussed.
Ultralow‐frequency oscillator with switched capacitors
Authors: Miyazaki Tomoyuki , Lim Siew Thong , Minamitake Chikara , Takeishi Taisuke
Published: July 2007

A very high and stable equivalent resistance can be realized if switched capacitors (SC) are used. The operating characteristics of a three‐phase SC oscillator are measured in which SCs are used in place of resistors in a low‐frequency CR oscillator. The amplitude of the phase shifter outputs is designed to be equal. From the squared sum of the instantaneous values of the outputs, a dc voltage proportional to the square of the oscillation amplitude is obtained to be used as the control voltage of the amplitude stabilizing circuit. The clock frequency of the SC and the oscillation frequency have a linear relationship. The experimental values agree well with the theoretical values.

For constant circuit parameters, the oscillation frequency has been varied over more than five digits by changing only the clock frequency. A stable oscillation is observed at an extremely low frequency (10 μHz). A possibility of oscillation at frequencies lower than this value is demonstrated. The condition for steady‐state oscillation condition is given by the two sets of capacitance ratios. For the capacitors made with identical materials, the temperature coefficients are expected to be canceled. The problem of a long rise time of the oscillation at an extremely low frequency is resolved by reduction of the clock frequency after the amplitude has been stabilized within a short time by a high clock frequency. The effect of the equivalent parallel resistance on the characteristics of the ultralow‐frequency SC oscillator is discussed.
Temperature compensation methods for junction‐isolated analog integrated circuits and their applications
Authors: Otsuka Masanori , Hyogo Akira , Sekine Keitaro
Published: July 2007

This paper proposes temperature compensation methods used to improve circuit construction and to realize integrated circuits even at temperatures exceeding 200°C.

The main purpose of a temperature compensation method is to maintain stability of dc bias in the high‐temperature range.

The method is applied to the operational amplifier (OP‐AMP) to increase efficiency and to facilitate application to other circuits.

A new OP‐AMP which can operate at high temperature is presented.
Three‐dimensional nonstationary calculation of Quasi‐phase‐matched guided‐wave, second‐harmonic generation using weighted‐index method
Authors: Yanagawa Kazunori , Hayata Kazuya , Koshiba Masanori
Published: July 2007

A three‐dimensional (3‐D) nonstationary analysis method is proposed for the quasi‐phase‐matched (QPM) second‐harmonic generation in an optical waveguide with a periodic domain‐inversion structure. In this method, a 3‐D modeling of a waveguide‐type QPM is made possible by combining the mode coupling theory with the weighted‐index method (WIM) which is a highly accurate approximate analysis method for an optical channel waveguide. As an example of application, the effect of the channel dimensions on the conversion efficiency is studied for a proton‐exchanged LiNbO3 waveguide with a rectangular‐shaped inverted domain. The actual domain‐inversion shape is expected to be different, depending on the type of substrate material and inversion process. The present method is also applicable to an arbitrary inverted‐domain shape. Hence, the method is considered to be extremely useful for an actual device design.
Centralized system level redundancy scheme for large‐capacity memory systems
Authors: Sasaki Toshio , Shimohigashi Katsuhiro , Etoh Tsuyoshi , Sugano Toshio , Ozeki Tomotaka
Published: July 2007

To cope with the deterioration of the yield of the memory LSI due to the microstructured design, this paper considers the centralized system‐level redundancy scheme, where, by providing the spare memory chip and the rescue control circuit to the semiconductor memory system, the fault is rescued in a centralized way. In this scheme, the fault bits are memorized in the nonvolatile memory for each word/bit line, and the normal and the spare memories are switched at the I/O terminal of the system by the parallel access.

As the method of access to the spare memory, this paper proposes the indirect address input method, where the external address is converted by the control circuit, and the direct address input method, where the external address is directly used. In the former, the external address is converted into the internal address and the ratio of the spare memory to the normal memory decreases with the increase of the system scale, which is favorable to low‐cost applications.

The method is applied to the 20‐Mbit file memory using partially good 1 MSRAM, and it is verified that the defect word/bit lines of up to 35 line/chip can be rescued, thereby improving the yield by approximately three times.

In the latter method, the addresses to the normal and the spare memories are input simultaneously in parallel, which is favorable for the high‐speed operation. This method is applied to the 4‐Mbit memory module using partially good 4 MDRAM and it is verified that the defect can be rescued while minimizing the deterioration of the access time.
Ultrahigh‐speed multiquantum well‐distributed feedback semiconductor lasers
Authors: Uomi Kazuhisa , Tsuchiya Tomonobu , Aoki Masahiro , Suzuki Makoto , Nakano Hiroyuki , Chinone Naoki
Published: July 2007

With regard to a 1.55‐μm InGaAsP multiquantum well (MQW) distributed feedback semiconductor laser which is promising for its applications to high‐capacity, long‐distance optical fiber communication systems with transmission rate above 10 Gb/s, the relaxation oscillation frequency and nonlinear damping phenomena determining the high‐speed capability and the amount of chirping determining the long‐distance capability are examined both theoretically and experimentally.

First, by optimizing the number of wells in the MQW active layer and the barrier layer thickness, the relaxation oscillation frequency has been increased to 1.6 ∼ 1.7 GHz/√mA, which is almost twice the conventional value. A distinct xL dependence of the chirping at 10 Gb/s modulation has been clarified and explained by the spatial hole burning effect in the axis direction. A minimum chirp width of 3.4 Å has been obtained at 10 Gb/s large swing modulation, which is the world record. Furthermore, the physical mechanism of the nonlinear damping phenomenon has been considered from the dependences of the damping K factor and gain saturation coefficient on laser structure and oscillation wavelength and has been explained by the spectral hole burning theory.

Finally, p‐type doping of the MQW active layer has been shown to be effective as a means to increase the maximum modulation bandwidth which is limited by the damping phenomenon, and the modulation above 40 GHz has been shown to be possible.
High‐speed InGaAs/InAlAs multiple‐quantum‐well optical modulator
Authors: Kotaka Isamu , Mitomi Osamu , Wakita Koichi , Kawamura Yuichi , Asai Hiromitsu
Published: July 2007

An external modulator shows promise in the large‐capacity long‐repeater‐interval optical communication system. This paper investigates the following characteristics to realize an electric‐field absorbing‐type modulator with a low‐loss 1.5μm band InGaAs/InAlAs multiple‐quantum‐well (MQW) structure with a high‐speed response.

To reduce the device capacitance: (1) the separated pn structure is used in which the pn junction is separated from the MQW layers; (2) a polyimide is embedded into the bonding pad section; and (3) the dry etching method with a small side etch is used for formation of a good ridged waveguide. Also, to reduce the propagation loss, a ridged waveguide with a low mesa structure is formed.

As a result, the frequency response at 3‐dB bandwidth is 40 GHz, the extinction ratio is 10 dB with the driving voltage of 6 V, and the insertion loss is 13 dB including the coupling loss (including the Fresnel loss) with the fiber. The bandwidth of the frequency response is limited by the device capacitance and the bonding wire inductance. Most of the insertion loss is found to be the coupling loss.