bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of High-Quality Carbon Nanotubes by Grid-Inserted Plasma-Enhanced Chemical Vapor Deposition for Field Emitters
Authors: Kojima Yoshihiro , Kishimoto Shigeru , Ohno Yutaka , Sakai Akira , Mizutani Takashi
Published: July 2005

The effect of a grid inserted between the anode and the cathode in plasma-enhanced chemical vapor deposition (PECVD) on carbon nanotube (CNT) growth was studied. The optimum grid-cathode distance and grid-cathode voltage were 4 mm and 2–10 V, respectively. Long small-diameter nanotubes were grown under these conditions. The smallest nanotube diameter obtained was 3 nm. However, when the grid-cathode voltage was higher than 10 V, short large-diameter nanotubes were grown. The field emission characteristics of CNTs with a low ON voltage and a high current density were explained by Fowler-Nordheim (FN) tunneling.
Magnetic and Electrical Properties of (La,Sr)MnO3 Sputtered on SrTiO3-Buffered Si Substrate
Authors: Uemura Tetsuya , Sekine Kenji , Matsuda Ken-ichi , Yamamoto Masafumi
Published: July 2005

LaSrMnO3 (LSMO) thin films were grown on SrTiO3(STO)-buffered Si(001) substrates by RF magnetron sputtering, and their magnetic and electrical properties as well as their crystalline structures were characterized. The LSMO film exhibited a polycrystalline nature with a strong preferred orientation to the c-axis. Compared with single-crystalline samples, the electrical and magnetic properties of the LSMO films on STO-buffered Si substrates obtained in this study were different in the following points. (1) A lower metal-insulator transition temperature than the Curie temperature, T
C, determined from magnetization measurements. (2) A large negative magnetoresistance with a clear hysteresis below T
C. (3) An increased coercivity in the low temperature region below 170 K. These features can be explained by the existence of localized ferromagnetic regions and spin-polarized tunneling between them.
Fabrication and Characterization of lateral Field Emission Device Based on Carbon Nanotubes
Authors: Juan Chuan-Ping , Tsai Chun-Chien , Chen Kuei-Hsien , Chen Li-Chyong. , Cheng Huang-Chung
Published: July 2005

We have proposed and fabricated a vertical lateral field emission device (LFED) based on carbon nanotubes (CNTs). It combines high-performance nanomaterials with mature solid-state fabrication technology to produce miniaturized vacuum devices with superior field emission characteristics. The techniques employed are very simple and allow for good reproducibility in controlling the short distance from the polysilicon anode to the CNTs cathode inter-electrode distance. The inter-electrode gap can be easily fabricated to be less than 1 µm by a wet etching process without using fine lithography. The CNTs were selectively grown using a microwave-plasma enhanced chemical vapor deposition system (MPCVD). The anode-to-emitter gap distance and the length of carbon nanotubes are well controlled to enable investigation of their effect on the field emission properties. The turn-on voltage of the fabricated device with an inter-electrode gap of 0.53 µm is as low as 0.2 V, and the emission current is as high as 9.72 mA at 10 V. The emission current fluctuation is approximately ±3.5% for 1500 s.
Complementary Self-Biased Logics Based on Single-Electron Transistor (SET)/CMOS Hybrid Process
Authors: Song Ki-Whan , Lee Yong Kyu , Sim Jae Sung , Kim Kyung Rok , Lee Jong Duk , Park Byung-Gook , You Young Sub , Park Joo-On , Jin You Seung , Kim Young-Wug
Published: July 2005

We propose a complementary self-biasing method which enables the single-electron transistor (SET)/complementary metal-oxide semiconductor (CMOS) hybrid multi-valued logics (MVLs) to operate well at high temperatures, where the peak-to-valley current ratio (PVCR) of the Coulomb oscillation markedly decreases. The new architecture is implemented with a few transistors by utilizing the phase control capability of the sidewall depletion gates in dual-gate single-electron transistors (DGSETs). The suggested scheme is evaluated by a SPICE simulation with an analytical DGSET model. Furthermore, we have developed a new process technology for the SET/CMOS hybrid systems. We have confirmed that both of the fabricated devices, namely, SET and CMOS transistors, exhibit the ideal characteristics for the complementary self-biasing scheme: the SET shows clear Coulomb oscillations with a 100 mV period and the CMOS transistors show a high voltage gain.
Electrical Transport Properties of Au-Doped Deoxyribonucleic Acid Molecules
Authors: Hwang Jong Seung , Hong Su Heon , Kim Hyung Kwon , Kwon Young Whan , Jin Jung Il , Hwang Sung Woo , Ahn Doyeol
Published: July 2005

Deoxyribonucleic acid (DNA) molecules were doped with Au atoms and their electrical transport properties were measured. The Au doping was carried out by incubating a mixture of HAuCl4·3H2O and DNA solutions. The binding of Au atoms to DNA bases was identified using Fourier transform infrared spectroscopy and X-ray photoemission spectroscopy. The Au-doped DNA molecules were deposited on nanoelectrodes and the presence of the molecules between the electrodes was determined by both scanning electron microscopy and atomic force microscopy. Measurement of the current-voltage characteristics showed that the Au-doped DNA molecules exhibited a higher conductivity than undoped DNA molecules. Detailed analysis of the chemical composition shows that there is a strong possibility of reliably controlling the conductivity of DNA molecules using this method.
Silicon Nanowires as pH Sensor
Authors: Hsu Jung-Fu , Huang Bohr-Ran , Huang Chien-Sheng , Chen Hsin-Li
Published: July 2005

Silicon nanowires (SiNWs) have been used as a sensing layer in an extended-gate field-effect transistor (EGFET) for the measurement of solution pH. SiNWs were synthesized directly from silicon substrates via a catalytic reaction in N2 atmosphere at 955°C. The SiNWs have an average diameter of approximately 30–50 nm and a length of up to a few tens of micrometers. Here, silicon bulk materials and SiNWs were used alternately as the sensing layer in an extended-gate field-effect transistor in measuring solution pH. Experimental results showed that the pH sensitivity of silicon bulk materials is poor. However, good pH sensing properties of SiNWs, with a sensitivity of 58.3 mV/pH, was observed. Therefore, it was suggested that the pH sensitivity of silicon bulk materials was greatly improved by downsizing them to the nanoscale.
Structural Study of Initial Growth of Nickel on Yttria-Stabilized Zirconia by Coaxial Impact-Collision Ion Scattering Spectroscopy
Authors: Saito Akira , Yamasaki Kazuki , Takami Kazuhiro , Ohnisi Shuji , Akai-Kasaya Megumi , Aono Masakazu , Kuwahara Yuji
Published: July 2005

The atomic structure of yttria-stabilized ZrO2 (YSZ) surfaces was investigated by coaxial impact-collision ion scattering spectroscopy (CAICISS). After a simple treatment to clean the surface, the outermost plane of the clean YSZ (001) surface was found to be a Zr layer. Compared with the clean surface, the initial stage of Ni/YSZ interface formation was studied after the vapor deposition of nickel at room temperature in ultrahigh vacuum (UHV). It was revealed that Ni atoms grow in order even at a thickness of 2 monolayers (MLs) in UHV. The Ni growth conserved the 4-fold symmetry of the YSZ (001) substrate structure, suggesting a certain interaction between the Ni and Zr atoms. However, after air exposure, the ordering structure disappeared and changed into a random phase.
New Operating Mode of Nanocrystalline Silicon Ultrasonic Emitters for Use as Audio Speakers
Authors: Kiuchi Akira , Koshida Nobuyoshi
Published: July 2005

To extend the technological potential of thermally induced ultrasonic emissions from the nanocrystalline silicon (nc-Si) devices we reported previously a driving mode suitable for operation in the audio-band has been studied. The device is composed of a patterned surface electrode, an nc-Si layer, and a single-crystalline silicon substrate. The acoustic emission is based on efficient heat exchange at the surface-air interface in which the surface temperature fluctuations induced by electrical input are quickly transferred to air due to the complete thermal insulating properties of the underlying nc-Si layer. In the proposed driving mode, a dc-superimposed input is sent into the surface electrode. In contrast to the conventional driving mode using a simple ac-signal input, the device efficiently emits the acoustic output signal at the same frequency as the input signal. A linear relationship between the input voltage and the output amplitude has been confirmed as expected. This driving mode is applicable to the operation of an audio-band speaker.
Fluoride Resonant Tunneling Diodes on Si Substrates Improved by Additional Thermal Oxidation Process
Authors: Watanabe So , Maeda Motoki , Sugisaki Tsuyoshi , Tsutsui Kazuo
Published: July 2005

An oxidation process was applied to the fabrication of fluoride resonant tunneling diodes (RTDs) on Si substrates. The oxidation process was carried out after the growth of an ultrathin CaF2 layer on Si, and expected to passivate the Si surface in pinholes generated in the CaF2 layer. Leakage currents of Au/Al/CaF2/Si(111) metal insulator semiconductor (MIS) diodes were extremely reduced by introducing this process. Au/Al/CaF2/CdF2/CaF2/Si(111) double-barrier RTDs were also fabricated by introducing this process, the leakage currents of which were extremely reduced and a very large peak to valley current ratio (PVCR) of 1500 was obtained. It was also shown that the chemical reaction between a CdF2 well layer and the Si substrate was suppressed by the oxidation process. Owing to this effect, high-temperature growth (up to 300°C) of the CdF2 well layer was realized for the first time in the fluoride RTDs, and resulted in the reduction of undesirable current drift.
Optimum Compositions for Pb(Zn1/3Nb2/3)O3–PbTiO3 Single Crystal for High-Performance Applications
Authors: Rajan Kalidindi K. , Zhang Michelle J. , Lim Leong-Chew
Published: July 2005

Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals of (6–7) mol% PbTiO3 (PT) grown by the high-temperature flux technique under near-equilibrium conditions exhibit improved composition homogeneity, superior and consistent dielectric and piezoelectric properties which are also the least sensitive to PT content variation in the material, and a depolarization temperature of approximately 100°C. This composition holds promise for the production of large-size high-homogeneity high-performance relaxor single crystals for commercial use.
Transition Energies of Vertically Coupled Multilayer Nanoscale InAs/GaAs Semiconductor Quantum Dots of Different Shapes
Authors: Li Yiming
Published: July 2005

The energy spectra of vertically coupled multilayer nanoscale semiconductor quantum dots (QDs) are theoretically studied using a unified three-dimensional (3D) model. The model formulation includes (1) the position-dependent effective mass Hamiltonian in a nonparabolic approximation for electrons, (2) the position-dependent effective mass Hamiltonian in a parabolic approximation for holes, (3) the finite hard wall confinement potential, and (4) Ben Daniel-Duke boundary conditions. To solve a nonlinear problem, a nonlinear iterative method is further improved in our developed 3D QD simulator. At an applied magnetic field (B), we explore the transition energy and the energy band gap of disk (DI)-, ellipsoid (EL)- and cone (CO)-shaped vertically coupled multilayer nanoscale semiconductor quantum dots. We find that the electron transition energy of vertically coupled multilayer InAs/GaAs QDs depends on their shape and is strongly dominated by the number of stacked layers (N). The interdistance (d) among InAs QDs plays a crucial role in the tunable states of these QDs. In DI-shaped vertically coupled 10-layer QDs at B=0 T and d=1.0 nm, we find approximately 40% variation in electron ground state energy, which is larger than that (∼20% variation) in CO-shaped QDs. In QDs at a nonzero magnetic field, the electron transition energy decreases with increasing N. In QDs with d=1 nm, the rate of decrease is low when N>6. This results in QDs with energy band gaps having similar dependences on N. This study implies different applications in magnetooptical phenomena and quantum optical structures.
Electronic Structures and Carrier Correlation in Single Pair of Coupled Quantum Dots
Authors: Yamauchi Shohgo , Komori Kazuhiro , Morohashi Isao , Goshima Keishiro , Sugaya Takeyoshi
Published: July 2005

The electronic structures and carrier correlation in a single pair of InAs/GaAs coupled quantum dots (QDs) are investigated by performing photoluminescence (PL), one-color photoluminescence excitation (PLE) and two-color PLE measurements. Luminescence from the bonding (X+) and anti-bonding (X-) states due to the wave function coupling was observed in the micro-PL (µ-PL) spectra of the coupled QDs. One-color PLE spectra reveal the electronic structures of the coupled QD system in which there is the coexistence of both common excited level series between the X+ and X- states and individual excited level series for each state. In two-color PLE measurement, the suppression of PLE peak intensity at the energy separation of the longitudinal optical (LO) phonon suggests a carrier correlation through the screening effect of the carrier–LO-phonon interaction in the coupled QD system. Additionally, we demonstrate the control of the energy state in the coupled QDs using two-color excitations.
Cross-Sectional Evolution and Its Mechanism during Selective Molecular Beam Epitaxy Growth of GaAs Quantum Wires on (111)B Substrates
Authors: Tamai Isao , Sato Taketomo , Hasegawa Hideki
Published: July 2005

The mechanism of the cross-sectional evolution during the selective growth of GaAs quantum wires (QWRs) on (111)B-patterned substrates was studied in detail both experimentally and theoretically. For this purpose, growth experiments were carried out on <-1-12>-oriented wires by systematically changing growth conditions and pattern sizes. A detailed investigation on cross sections of wires has shown that the lateral wire width is determined by facet boundaries (FBs) within AlGaAs layers separating growth regions on top facets from those on side facets of mesa structures. FBs were found to be planar or curved, depending on initial pattern sizes and growth conditions. Computer simulation based on a phenomenological growth model was attempted, taking account of the facet-angle-dependent lifetime of adatoms. The simulation well reproduced the experimentally observed growth features including the evolution of FBs, indicating that the cross sections of wires grown on (111)B-patterned substrates are kinetically controlled by the pattern sizes and growth conditions.
Fabrication and Micro-Photoluminescence Investigation of Mg-Doped Gallium Nitride Nanorods
Authors: Chang Ya-Hsien , Hsueh Tau-Hung , Lai Fang-I , Chang Chun-Wei , Yu Chang-Chin , Huang Hung-Wen , Lin Chia-Feng , Kuo Hao-Chung , Wang Shing-Chung
Published: July 2005

High-density magnesium (Mg)-doped gallium nitride (GaN) nanorods were fabricated by inductively coupled plasma reactive ion etching from a GaN film and had a mean length of approximately 50 nm. A large blue-shift was observed in the photoluminescence (PL) peak energy of Mg-doped GaN nanorods under HeCd laser (325 nm) excitation. The PL spectra of the nanorods show a typical donor-acceptor-pair (DAP) emission at approximately 3.0 eV with a large blue-shift compared to that of the Mg-doped GaN film. The blue-shift energy increases from 8 meV to 67 meV as the excitation intensity varies from 12 kW/cm2 to 56 kW/cm2. Possible reasons for the power dependence of the spectral shift in the PL emission energy are discussed.
Characterization of InGaN/GaN Multiple Quantum Well Nanorods Fabricated by Plasma Etching with Self-Assembled Nickel Metal Nanomasks
Authors: Hsueh Tao-Hung , Huang Hung-Wen , Kao Chih-Chiang , Chang Ya-Hsien , Ou-Yang Miao-Chia , Kuo Hao-Chung , Wang Shing-Chung
Published: July 2005

High-density (3.0×1010 cm-2) InGaN/GaN multiple quantum well (MQW) nanorods were fabricated from an as-grown bulk light-emitting diode structure by inductively coupled plasma dry etching with self-assembled nickel metal nanomasks. The self-assembled nickel metal nanomasks were formed by rapid thermal annealing of a nickel metal film at 850°C for 1 min. The influence of the thicknesses of the Ni metal film on the dimensions and density of the nanorods was also investigated. The structural and optical properties of the InGaN/GaN MQW nanorods were established using field emission scanning electron microscopy, transmission electron microscopy and photoluminescence measurements. The diameters and heights of nanorods were estimated to be 60 to 100 nm and more than 0.28 µm, respectively. The peak emission wavelength of the nanorods showed a blue shift of 5.1 nm from that of the as-grown bulk. An enhancement by a factor of 5 in photoluminescence intensity of the nanorods compared with that of the as-grown bulk was observed. The blue shift is attributed to strain relaxation in the wells after dry etching, the quantum confinement effect, or a combination of the two, which results in the enhancement of emission intensity.
Control of Self-Formed GaAs Nanoholes Combined with Embedded InAs Quantum Dots
Authors: Satoh Takayuki , Yamaguchi Koichi
Published: July 2005

We investigated the self-formation of GaAs nanoholes combined with embedded InAs quantum dots (QDs), grown by molecular beam epitaxy using the Stranski-Krastanov growth mode. After GaAs capping growth of uniform InAs QDs, GaAs nanoholes were naturally fabricated just above the embedded InAs dots by thermal annealing at 500°C. The self-formation of GaAs nanoholes is attributed to the detachment of unstable GaAs due to tensile strain during annealing. The nanohole structures affected the photoluminescence (PL) properties of InAs QDs and were strongly dependent on the thickness of the GaAs capping layer and the annealing time.
Electroluminescence Enhancement Assisted with Ballistic Electron Excitation in Nanocrystalline Silicon Diodes
Authors: Gelloz Bernard , Kanda Takayuki , Uchida Tetsuya , Niibe Masao , Kojima Akira , Koshida Nobuyoshi
Published: July 2005

The novel structure of a light-emitting device has been investigated in terms of the optical and electrical activities of nanocrystalline silicon (nc-Si). The device is composed of a semitransparent top electrode, a luminescent nc-Si layer, a bottom nc-Si layer for ballistic-transport, and a substrate. The two types of nc-Si layer are sequentially formed by electrochemical anodization under appropriate conditions. When a positive bias voltage is applied to the top electrode, electrons injected into the bottom nc-Si layer from the substrate are accelerated toward the outer surface, excite the luminescent nc-Si layer to generate electron-hole pairs, and induce visible luminescence through their radiative recombination. From the optoelectronic measurements of the fabricated devices with or without the ballistic transport layer, it is shown that the intrinsic electroluminescence (EL) of the nc-Si diode is significantly enhanced by the introduction of the ballistic excitation mode.
Two-Dimensional Quantum-Mechanical Modeling and Simulation of Strained-Si Fin Field Effect Transistor (FinFET) on SiGe-On-Insulator
Authors: Park Il-soo , Kim Kidong , Won Taeyoung
Published: July 2005

A strained-Si fin field effect transistor (SSFinFET) on SiGe-on-insulator is modeled and using two-dimensional Schrödinger and Poisson equations quantum-mechanically simulated in a self-consistent manner. The quantum electron concentration in an SS fin is then obtained using a two-dimensional Schrödinger equation. The field-dependent mobility in SS fin is calculated using the doping-dependent mobility which considered strain and velocity overshoot effects. These effects give rise to an enhancement in the drain current of SSFinFET by up to 25% compared with the conventional FinFET using relaxed Si-on-insulator (RSFinFET). For the gate length 1.5 times longer than fin width, the drain induced barrier lowering (DIBL) and subthreshold swing are below 0.1 V/V and 60 mV/dec, respectively, regardless of whether Si-fin experiences a strain. These results indicate that the ratio of gate length to fin width should be above approximately 1.5 to suppress short channel effects and DIBL in both SSFinFET and RSFinFET.
Observation of Bonding States in Single Pair of Coupled Quantum Dots Using Microspectroscopy
Authors: Goshima Keishiro , Komori Kazuhiro , Yamauchi Shohgo , Morohashi Isao , Shikanai Amane , Sugaya Takeyoshi
Published: July 2005

The electronic structures of InAs/GaAs single and coupled quantum dots have been studied using photoluminescence (PL) and photoluminescence excitation (PLE) spectra obtained by microspectroscopy. We observed two peaks located at the band-edge energy region of the PL spectrum of single quantum dots, which originated from exciton ground states and resonance states associated with one longitudinal optical (1LO) phonon. There was no peak in the energy area between the two peaks in the single quantum dot spectrum (This area is referred to as the zero-absorption region). However, in the case of coupled quantum dots, we found new peaks in the zero-absorption region in PL and PLE spectra that are due to coupled states of coupled dots. Moreover, we found that the energy difference between the bonding and anti-bonding states depends on dot size. These results can provide the first step towards realizing quantum logic gate devices using coupled quantum dots with scalability.
Characteristics of Partially Disordered Gallium Nitride Nanodots Synthesized by Pulsed-Laser Ablation
Authors: Shim Seung Hwan , Yoon Jong-Won , Koshizaki Naoto , Won Jong Han , Hirotsu Yoshihiko , Shim Kwang Bo
Published: July 2005

GaN nanodots were synthesized at room temperature in an Ar atmosphere by a laser ablation technique under a pressure of 100 Pa. The synthesized nanodots were found to be smaller than 10 nm and the GaN phase was Ga-rich. High-resolution transmission electron microscopy and its Fourier transform confirmed that these GaN nanodots contained partially disordered crystallites. In spite of this structural instability, their medium ranged atomic order resulted in quantum-shifted luminescence due to the confinement of electrons in the photoluminescence spectra, which is consistent with theoretical calculations on the size-dependent band gap of crystalline GaN.
Ge2Sb2Te5 Confined Structures and Integration of 64 Mb Phase-Change Random Access Memory
Authors: Yeung Fai , Ahn Su-Jin , Hwang Young-Nam , Jeong Chang-Wook , Song Yoon-Jong , Lee Su-Youn , Lee Se-Ho , Ryoo Kyung-Chang , Park Jae-Hyun , Shin Jae-Min , Jeong Won-Cheol , Kim Young-Tae , Koh Gwan-Hyeob , Jeong Gi-Tae , Jeong Hong-Sik , Kim Kinam
Published: July 2005

Phase-change random access memory is considered a potential challenger for conventional memories, such as dynamic random access memory and flash memory due to its numerous advantages. Nevertheless, high reset current is the ultimate problem in developing high-density phase-change random access memory (PRAM). We focus on the adoption of Ge2Sb2Te5 confined structures to achieve lower reset currents. By changing from a normal to a GST confined structure, the reset current drops to as low as 0.8 mA. Eventually, our integrated 64 Mb PRAM based on 0.18 µm CMOS technology offers a large sensing margin: R
reset ∼200 kΩ and R
set ∼2 kΩ, as well as reasonable reliability: an endurance of 1.0×109 cycles and a retention time of 2 years at 85°C.
Programming Characteristics of Phase Change Random Access Memory Using Phase Change Simulations
Authors: Kim Young-Tae , Hwang Young-Nam , Lee Keun-Ho , Lee Se-Ho , Jeong Chang-Wook , Ahn Su-Jin , Yeung Fai , Koh Gwan-Hyeob , Jeong Heong-Sik , Chung Won-Young , Kim Tai-Kyung , Park Young-Kwan , Kim Ki-Nam , Kong Jeong-Taek
Published: July 2005

We present a new simulation methodology for analyzing programming characteristics of a chalcogenide based phase-change device, phase change random access memory (PRAM), which is a next-generation non-volatile memory. Using the new simulation methodology, we analyze the initialization of chalcogenide material (ICM) of the mechanism and propose the next generation PRAM scheme. From the results of the phase change simulation, the process conditions for ICM for stable operation are presented. Also, the self-heating confined structure to overcome the inherent limitation of high operation power is proposed that resolves the operating power limitation associated with PRAM development.
Robust Three-Metallization Back End of Line Process for 0.18 µm Embedded Ferroelectric Random Access Memory
Authors: Kang Seung-Kuk , Rhie Hyoung-Seub , Kim Hyun-Ho , Koo Bon-Jae , Joo Heung-Jin , Park Jung-Hun , Kang Young-Min , Choi Do-Hyun , Lee Sung-Young , Jeong Hong-Sik , Kim Kinam
Published: July 2005

We developed ferroelectric random access memory (FRAM)-embedded smartcards in which FRAM replaces electrically erasable PROM (EEPROM) and static random access memory (SRAM) to improve the read/write cycle time and endurance of data memories during operation, in which the main time delay retardation observed in EEPROM embedded smartcards occurs because of slow data update time. EEPROM-embedded smartcards have EEPROM, ROM, and SRAM. To utilize FRAM-embedded smartcards, we should integrate submicron ferroelectric capacitors into embedded logic complementary metal oxide semiconductor (CMOS) without the degradation of the ferroelectric properties. We resolved this process issue from the viewpoint of the back end of line (BEOL) process. As a result, we realized a highly reliable sensing window for FRAM-embedded smartcards that were realized by novel integration schemes such as tungsten and barrier metal (BM) technology, multilevel encapsulating (EBL) layer scheme and optimized intermetallic dielectrics (IMD) technology.
Strained Thick p-InGaN Layers for GaN/InGaN Heterojunction Bipolar Transistors on Sapphire Substrates
Authors: Makimoto Toshiki , Yamauchi Yoshiharu , Kido Takatoshi , Kumakura Kazuhide , Taniyasu Yoshitaka , Kasu Makoto , Matsumoto Nobuo
Published: July 2005

Thick p-InGaN layers were grown on GaN by metalorganic vapor phase epitaxy to investigate the strain inside p-InGaN using a reciprocal space map of X-ray diffraction intensity. It was found that a large part of p-InGaN grows coherently on the GaN buffer layer, even though it is much thicker than the calculated critical thickness. This result means that few dislocations are generated at the InGaN/GaN interface. Using this strained thick p-InGaN as a base, a GaN/InGaN heterojunction bipolar transistor was fabricated on a sapphire substrate. Its maximum current gain was as high as 1000 and its offset voltage as low as 0.2 V, which matches that calculated from the conduction-band discontinuity between the n-GaN emitter and the p-InGaN base.
Pulsed Current-Voltage-Temperature Characteristics of AlGaN/GaN High Electron Mobility Transistor under Isothermal Conditions
Authors: Her Jin-Cherl , Lee Kang-Min , Lee Seung-Chul , Lee Jae-Hak , Oh Jae-Eung , Han Min-Koo , Seo Kwang-Seok
Published: July 2005

AlGaN/GaN high electron mobility transistors (HEMTs) have great potential, because of the material advantages. However, there are still some problems with AlGaN/GaN HEMTs, such as current collapse (power slump), the self-heating effect and the power scaling problem. In this paper, we have studied the self-heating effect using pulsed current-voltage (IV) and current-voltage-temperature (IVT) measurement under `the same dc bias power condition'- the isothermal condition. It was shown how self-heating affects the AlGaN/GaN HEMT's operation. It can be thought that a reason for the power slump problem of the GaN-based HEMT using a sapphire substrate and the power scaling difficulty is a thermal problem caused by the self-heating effect.
Comparison of AlGaN/GaN Insulated Gate Heterostructure Field-Effect Transistors with Ultrathin Al2O3/Si3N4Bilayer and Si3N4Single Layer
Authors: Wang Chengxin , Maeda Narihiko , Hiroki Masanobu , Tawara Takehiko , Makimoto Toshiki , Kobayashi Takashi , Enoki Takotomo
Published: July 2005

Device performances have been compared between two types of AlGaN/GaN metal-insulator-semiconductor heterostructure field effect transistors (MIS-HFETs) with Al2O3/Si3N4bilayers and a Si3N4single layer. Al2O3/Si3N4bilayer-based MIS-HFETs have much lower gate current leakage than Si3N4-based MIS devices by more than 3 orders of magnitude under reverse gate biases. An ultralow gate leakage of 1×10-11A/mm at -15 V has been achieved in the Al2O3/Si3N4bilayer-based MIS devices though higher maximum drain-source current has been obtained in the Si3N4-based MIS devices. A maximum transconductance of more than 180 mS/mm with ultra-low gate leakage has been achieved in the ultrathin Al2O3/Si3N4bilayer-based MIS-HFET device with a gate length of 1.5 µm, which is much higher than that of less than 130 mS/mm in the Si3N4-based MIS devices. The reduction in the transconductance of Al2O3/Si3N4bilayer-based devices was much smaller than that in the Si3N4-based MIS devices due to the employment of ultrathin bilayers with a large dielectric constant.This work demonstrates that an Al2O3/Si3N4bilayer insulator is a superior candidate for nitride-based MIS-HFET devices.
94-GHz fT, 0.4-dB NFmin HBT with Optimized Si Cap and Extrinsic Base Using Blanket SiGeC Epitaxy
Authors: Kiyota Yukihiro , Yamagata Hideo , Bairo Masaaki , Yanagawa Shusaku , Komoto Takeyoshi , Ohishi Masato , Arai Chihiro
Published: July 2005

The profile design methodology of heterojunction bipolar transistors (HBTs) using a blanket SiGeC epitaxial layer is presented from the viewpoint of a Si cap and an extrinsic base design. Although important, it is difficult to optimize the intrinsic and extrinsic base regions of a HBT using blanket epitaxy since these regions are simultaneously grown and their profiles cannot be controlled independently. In accordance with the optimum Si cap thickness, extrinsic base implantation and cobalt silicidation were carried out to obtain a low base resistance and a high maximum oscillation frequency ( f
max). A cobalt silicide process for the extrinsic base was optimized to accommodate the Si cap thickness without forming highly resistive layers caused by a reaction between Ge and Co. This design led us to realize HBTs with a 94 GHz cutoff frequency ( f

T
) and an 81 GHz f
max, and a 0.4 dB NF
min at 2 GHz, which could be used for consumer electronic products operating within a 2–5 GHz frequency range.
Resonant Tunneling Diode/HBT D-Flip Flop ICs Using Current Mode Logic-Type Monostable-Bistable Transition Logic Element with Complementary Outputs
Authors: Kim Taeho , Lee Bangkeun , Choi Sunkyu , Yang Kyounghoon
Published: July 2005

A current mode logic (CML)-type resonant tunneling diode (RTD)/heterojunction bipolar transistor (HBT) monostable-bistable transition logic element (MOBILE) IC with complementary outputs is proposed, which can simplify logic designs on the basis of complementary logic operation. Using the CML-type current modulator in the MOBILE IC, both the noninverted and inverted outputs are simultaneously generated with a single input signal. The CML-type MOBILE IC with complementary outputs has been fabricated using an InP-based RTD/HBT technology, and the operation of the fabricated circuit has been confirmed up to 10 Gb/s as a MOBILE with the complementary outputs. Moreover, the operation of a non-return-to-zero (NRZ) D-flip flop circuit, integrated with a set/reset latch (SR latch) using the CML-type complementary MOBILE IC has been for the first time confirmed up to 8 Gb/s with a low power consumption of 86 mW.
Application of Spatial Multiresolution Analysis and Synthesis to Piezoelectric Inhomogeneous Drive Systems
Authors: Ohki Michio
Published: July 2005

The method of multiresolution analysis and synthesis is applied on a space wave-number basis to investigate the frequency characteristics of a piezoelectric transducer with a spatially inhomogeneous `piezoelectric drive ability', with which conventional methods such as the electrical equivalent circuit method cannot deal easily and systematically. The inhomogeneous distribution of the piezoelectric drive ability is analyzed into some spatial functions with different resolutions, and then the synthesis of these components is performed on a circuit structure in the framework of `complex series dynamics'. The circuit structure reflects the electrical and mechanical boundary conditions of the transducer, and the frequency characteristics can be calculated easily and systematically using a recursive procedure up to the desired resolutions.
Efficient Design of Integrated Antennas on Si for On-Chip Wireless Interconnects in Multi-Layer Metal Process
Authors: Rashid A. B. M. H. , Sultana Nasrin , Khan M. Rezwan , Kikkawa T.
Published: July 2005

In this study it has been shown that the transmission gain of an integrated dipole antenna on a Si chip used for an on-chip wireless interconnect is drastically reduced in a multi-layer metal interconnect scheme when a second metal layer is placed above the antenna at the usual interlayer metal distance. The best way to preserve high gain of the integrated antenna in such a multi-layer metal process is to design an antenna with excitation vertically through the Si substrate. In the presence of the upper metal layers, the vertically excited field mode propagating through the Si substrate does not cause any significant reduction in the power transmission of the antenna. Simulations of the structures have been carried out using the ANSOFT high frequency structure simulation (HFSS) program employing the three dimensional finite element method. A simple analytical model has also been developed, and the results are presented for comparison.
Small-Area Inductor for Silicon CMOS Chips
Authors: Sugawara Hirotaka , Okada Kenichi , Masu Kazuya
Published: July 2005

This study proposes a small-area inductor on a Si CMOS chip. The inductor is evaluated using simulated and measured results. From the viewpoint of device area, a solenoid-type inductor is known to be superior to the other conventional on-chip inductors. The area of a proposed snake-type inductor is smaller than that of a solenoid-type inductor. Two types of snake inductor have been fabricated. Thier measured inductances are 1.46 nH at 10 GHz and 2.09 nH at 5.25 GHz. The maximum values of the quality factors are 1.76 at 10 GHz and 1.13 at 5.25 GHz.
Twisted Differential Transmission Line Structure for Global Interconnect in Si LSI
Authors: Ito Hiroyuki , Gomi Shinichiro , Sugita Hideyuki , Okada Kenichi , Masu Kazuya
Published: July 2005

This paper investigates the twisted differential transmission line structure to achieve high-speed signal transmission and electromagnetic interference (EMI) noise reduction of global interconnects in Si LSIs. The differential transmission line in Si LSIs can transmit a 12 Gbps pulse signal and has the capability of reducing EMI noise. The proposed twisted-diagonal-pair line provides high-speed, low-EMI-noise, high-crosstalk-robustness and high-density global interconnects in Si LSIs.
Effect of Ligand Carboxylation on Adsorption and Photosensitization in Ru(II)-Complex Dye-Sensitized Nanocrystalline TiO2 Solar Cell
Authors: Ishihara Taishi , Tokue Jyunya , Sano Tatsuji , Shen Qing , Toyoda Taro , Kobayashi Naoki
Published: July 2005

The kinetics of dye adsorption onto a mesoporous TiO2 film is compared between Ru(II) complex dyes with and without carboxy groups in the bipyridyl ligand, by diffuse reflectance spectroscopy at room temperature. Both dyes show adsorption saturation, and the dye without carboxy groups simply obeys the Langmuir isotherm equation. The dye with carboxy groups exhibits the same kinetics as the dye without carboxy groups in the period up to 20 min. However, in contrast to the latter, it increases its adsorption rate after this time, suggesting a change of the adsorption mode from physisorption to chemisorption. The carboxy group in the dye-sensitized solar cell is assumed to play a role in the chemical modification of the TiO2 surface via a two-step adsorption from physisorption to chemisorption.
Improved Performance of 2,3-Dibutoxy-1,4-Phenylene Vinylene Based Polymer Light-Emitting Diodes by Thermal Annealing
Authors: Tu Ming-Lung , Su Yan-Kuin , Chang Shoou-Jinn , Fang Te-Hua , Chen Wen-Hua , Yang Henglong
Published: July 2005

2,3-dibutoxy-1,4-phenylene vinylene (DB-PPV) thin films were used to fabricate polymer light emitting diodes (PLEDs). Before the PLEDs were fabrication, DB-PPV thin films were annealed at various temperatures. The surface morphologies of the films were measured by atomic force microscopy (AFM). From the measured J–V and L–I curves, the performance of PLED was found to have been improved. The best operational properties were observed for the DB-PPV based PLED annealed at 150°C.
Red Phosphorescent Organic Light-Emitting Diodes Using Mixture System of Small-Molecule and Polymer Host
Authors: Hino Yuichi , Kajii Hirotake , Ohmori Yutaka
Published: July 2005

We study two types of polymer materials, poly(n-vinylcarbazole) (PVK) and starburst small-molecule 1,3,5-tris[4-(diphenylamino)phenyl]benzene (TDAPB), as the host for electrophosphorescent organic light-emitting diodes (PHOLEDs) doped with red-emitting phosphor tris(1-phenylisoquinoline) iridium (III) [Ir(piq)3]. PHOLEDs employed a PVK and TDAPB blend as the host exhibited a maximum red light emission at a wavelength of 630 nm. The external quantum efficiency of 6.3% and power efficiency of 3.0 lm/W have been achieved. The electroluminescent (EL) spectra were not changed at high current and the luminance reached 8,800 cd/m2 at the voltage of 13 V. We found that the roughness of the surface as estimated by means of atomic force microscopy (AFM) smoothened with increasing TDAPB doping concentration, and a slight exciplex emission between TDAPB and an electron transport material 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4,-oxadiazole (PBD) was observed at the wavelength of approximately 530 nm.
Structural Characterization and Photocurrent Properties of cis-di(thiocyanato)-bis(4,4'-dicarboxy-2,2'-bipyridine) Ruthenium(II) Monolayers on the Gold Surfaces
Authors: Terasaki Nao , Nitahara Satoshi , Akiyama Tsuyoshi , Yamada Sunao
Published: July 2005

A self-assembled monolayer of cis-di(thiocyanato)-bis(4,4'-dicarboxy-2,2'-bipyridine) ruthenium(II) (denoted as N3) was prepared on a gold electrode. Immobilization of N3 on the gold electrode through Au (electrode)-S (NCS ligands in N3) bonding was confirmed from electrochemical and X-ray photoelectron spectroscopy (XPS) measurements. In an acetonitrile solution containing methylviologen (MV) and oxygen as electron acceptors, the cathodic photocurrent, based on the photoexcitation of N3, was clearly observed, and the incident photon-to-current conversion efficiency (IPCE) was estimated to be ∼0.1% at 520 nm. Photocurrent responses were compared between the nanostructured gold electrode prepared from gold nanoparticles and the planar electrode; the former gave larger photocurrents than the latter, especially in the longer wavelength region around the localized surface plasmon bands of gold nanoparticles.
Solid-State Solar Cells Consisting of Polythiophene-Porphyrin Composite Films
Authors: Akiyama Tsuyoshi , Matsushita Miho , Kakutani Keitaro , Yamada Sunao , Takechi Kensuke , Shiga Tohru , Motohiro Tomoyoshi , Nakayama Hideki , Kohama Keiichi
Published: July 2005

Sandwich-type solid-state solar cells using polythiophene-porphyrin composite films were fabricated. A spin-coated film of poly(3-dodecylthiophene) (P3DT) was fabricated on a gold electrode. Next, an electropolymerized polythiophene film was superimposed on the surface of the spin-coated P3DT film by electrochemical polymerization of bithiophene (BiTh) with repeated redox cycles in the 0–+2 V region. Then, tetrathienylporphyrin (TThP) was further assembled on the polythiophene-modified electrode by using the same electrochemical polymerization procedure (1 or 10 cycles), to obtain polythiophene-porphyrin-modified gold electrodes. Finally, an aluminum electrode was deposited on the polythiophene-porphyrin modified gold electrode by vacuum deposition, forming the sandwich-type solid-state solar cells. The morphological characterizations of the films were carried out by scanning electron microscopy. The thickness of the organic layer decreased from ∼5 µm m to ∼3 µm by performing TThP polymerization. The amount of porphyrin moiety in the composite film was larger for the modified electrode after 10 cycles of electrochemical TThP polymerization than for that after 1 cycle of TThP polymerization. The resultant photocurrent increased with scanning cycle of TThP polymerization in the 400–600 nm region. The combination of polythiophene and porphyrin in the electrochemically modified electrode is one of the useful systems for photocurrent generation.
Analytical Model of Electrodiffusion of Metals in Fullerene Thin Films
Authors: Kaflé Bhim P. , Rubinstein Isaak , Katz Eugene A.
Published: July 2005

This paper presents a theoretical model of doping of C60 thin films by the diffusion of ions from metal electrodes under the action of external electric bias. In the case of Au diffusion, the final nonlinear parabolic partial differential equation for the concentration of mobile metal ions was solved numerically by the finite difference method for a given electric current (galvanostatic operation). This yields the time evolution of ionic concentration profiles for different currents. A significant increase in the rate of Au ion penetration into C60 films with increasing electric current is predicted by these calculations in agreement with the published experimental observations.
Tight-Binding Quantum Chemical Calculations of Electronic Structures of Indium Tin Oxide
Authors: Lv Chen , Wang Xiaojing , Govindasamy Agalya , Tsuboi Hideyuki , Koyama Michihisa , Kubo Momoji , Ookawa Hideyuki , Miyamoto Akira
Published: July 2005

We report a theoretical study on the electronic structures of indium oxide (In2O3) and indium tin oxide (ITO) carried out using our original tight-binding quantum chemical calculation program “Colors”, which is over 5,000 times faster than the conventional first-principles quantum chemical calculation method. The calculated band gap of In2O3 is in good agreement with the experimental results, although the value obtained by conventional first-principles calculation is less than half the experimental one. The electronic structures of In2O3 calculated by our tight-binding method are consistent with those obtained by first-principles calculations. Furthermore, the doping of tin atoms into In2O3 increased the band gap, which is also in good agreement with the experimental tendency. Hence, we confirmed that our tight-binding quantum chemical calculation method was very effective for investigation and predicting the electronic structures of In2O3 and ITO crystals with high accuracy and reliability in spite of its high calculation speed.
Vapor Deposition Polymerization of a Polyimide Containing Perylene Units Characterized by Displacement Current Measurement
Authors: Usui Hiroaki , Watanabe Megumi , Arai Chizuru , Hibi Katsusuke , Tanaka Kuniaki
Published: July 2005

Polyimide thin films that have perylene units in the main chain were prepared by vapor deposition polymerization of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and 1,12-diaminododecane (DADD). Codeposition of PTCDA and DADD formed thin films of polyamic acid, which was converted to polyimide by annealing in air. The PTCDA-DADD polyimide thin films have uniform amorphous structure in contrast to the PTCDA evaporated films that have polycrystalline grains. Optical absorption and photoluminescence characteristics suggested that the intermolecular interactions can be reduced and luminescence quenching can be avoided by forming the polyimide. Electrical characterization showed that the polyimide film has lower conductivity than the PTCDA monomer film. The displacement current was measured for an aluminum/polyimide/Teflon AF diode on an indium-tin oxide substrate. The result suggested that the PTCDA-DADD polyimide has electron-transporting properties. The measurement also suggested presence of electron traps.
Semitransparent Organic Photodetectors Utilizing Sputter-Deposited Indium Tin Oxide for Top Contact Electrode
Authors: Morimune Taichiro , Kajii Hirotake , Ohmori Yutaka
Published: July 2005

Semitransparent organic photodetectors with the heterostructure of copper phthalocyanine (CuPc) and N,N'-bis(2,5-di-tert-butylphenyl) 3,4,9,10-perylenedicarboximide (BPPC) were fabricated using sputter-deposited indium tin oxide (ITO) for a top contact electrode, and the I–V and frequency characteristics were investigated. To prevent ITO penetration into an organic layer, an amorphous carbon nitride (a-C:N) buffer layer was placed between the organic layer and an ITO electrode. A cutoff frequency of more than 2 MHz was obtained for a semitransparent photodetector by applying a reverse bias voltage of -2 V under visible light illumination. We demonstrated that the fabricated semitransparent organic photodetectors can be applicable to a photoreflector with light-emitting diodes for integrated devices with organic light-emitting devices.
Organic Bi-function Matrix Array
Authors: Matsushita Yohsuke , Shimada Hiroyuki , Miyashita Takuya , Shibata Miki , Naka Shigeki , Okada Hiroyuki , Onnagawa Hiroyoshi
Published: July 2005

We have proposed and demonstrated a “bi-function matrix array (Bi-Matrix)” with a stacked layer of organic electroluminescent device (OELD) and organic photodiode (OPD) matrix arrays. Independent operations of emission and photodetection can be achieved for the multilayered array, where, the maximum luminance of OELD was 1,290 cd/m2 and the ratio of photoconductivity to dark conductivity was 103. A prototype 4×4 Bi-Matrix was also demonstrated.
Top-Absorption Organic Photodiodes Suitable for Device Integration
Authors: Shimada Hiroyuki , Naka Shigeki , Okada Hiroyuki , Onnagawa Hiroyoshi
Published: July 2005

We have fabricated top-absorption organic photodiodes (TA-OPDs) using sputtered indium zinc oxide (IZO) electrodes and compared their photodiode characteristics with conventional bottom-absorption organic photodiodes (BA-OPDs). In poly ([2-methoxy-5-(2'-ethylhexyloxy)]-1,4-phenylenevinylene) (MEH-PPV) films sandwiched between Al and IZO electrodes, the ratio of photoconductivity to dark conductivity, σ
R
, was approximately 103 for both BA- and TA-OPDs. In a TA-type Al/td-PTC/α-NPD/CuPc/IZO device, the σ
R
and the short-circuit photocurrent I

P
were 3.4×102 and 5.3×10-2 mA/cm2, respectively. The lower value of σ
R
in TA-OPDs compared to BA-OPDs in this structure is ascribed to sputtering damage during IZO film preparation. We were able to prevent successfully this damage by inserting the MoO3 hole-injecting and sputter buffer layer instead of the CuPc layer. We have also investigated the frequency characteristics of several TA-OPDs and obtained relatively good response in the TA-OPDs with a MoO3 buffer layer. In terms of frequency characteristics, the cut-off frequency of the TA-OPDs with a MoO3 buffer layer was as high as 300 kHz.
Enhancement of Luminance Yield of Blue Organic Light-Emitting Diode
Authors: Juang Fuh-Shyang , Chang Shan-Chou , Su Chiu-Yen , Chen Yen-Fong
Published: July 2005

In this study, a buffer layer of polytetrafluoroethylene (Teflon) was inserted between the indium tin oxide (ITO) and hole-transport layers of blue organic light-emitting diodes to improve their luminance efficiency. The thicknesses of the hole-transport layer, N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) and the Teflon and dopant layers, 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl (ADS080) were varied to obtain a high luminance yield. The dopant concentration in the host-emitting layer was also investigated. With a Teflon buffer layer of 1 nm, the organic light-emitting diode (OLED) emission became more stable. The luminance intensity and efficiency increased from 931 to 1734 cd/m2 at 8 V and from 1.6 to 2.25 cd/A at 40 mA/cm2, respectively. A double separately doped structure with optimum separation between its two doped layers shows apparent improvement on the luminance yield.