bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of Uniformity of Resistive Switching Parameters by Selecting the Electroformation Polarity in IrOx/TaOx/WOx/W Structure
Authors: Prakash Amit , Maikap Siddheswar , Lai Chao Sung , Lee Heng Yuan , Chen W. S. , Chen Frederick T. , Kao Ming Jer , Tsai Ming Jinn
Published: April 2012

A route to improve the uniformity of key resistive switching memory parameters such as SET/RESET voltages, low/high-resistance states as well as switching cycles is demonstrated in an IrO
x
/TaO
x
/WO
x
/W simple resistive memory stack by selecting the electroformation polarity. The various stack layers are confirmed by high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy analyses. Cumulative probability plots of the key memory parameters show tight distribution. The oxygen vacancy filaments are formed/ruptured owing to polarity-dependent oxygen ion migration, which is the switching mechanism in the TaO
x
/WO
x
bilayers, and improved resistive switching parameters under positive formation polarity are observed. The fabricated device has shown good potential for multilevel capability with a low voltage operation of ±3 V. The device has shown an excellent read endurance of >105 cycles and data retention up to 10 years at 85 °C.
Scaling Trends and Tradeoffs between Short Channel Effect and Channel Boosting Characteristics in Sub-20 nm Bulk/Silicon-on-Insulator NAND Flash Memory
Authors: Miyaji Kousuke , Hung Chinglin , Takeuchi Ken
Published: April 2012

The scaling trends and limitation in sub-20 nm a bulk and silicon-on-insulator (SOI) NAND flash memory is studied by the three-dimensional (3D) device simulation focusing on short channel effects (SCE), channel boost leakage and channel voltage boosting characteristics during the program-inhibit operation. Although increasing punch-through stopper doping concentration is effective for suppressing SCE in bulk NAND cells, the generation of junction leakage becomes serious. On the other hand, SCE can be suppressed by thinning the buried oxide (BOX) in SOI NAND cells. However, the boosted channel voltage decreases by the higher BOX capacitance. It is concluded that the scaling limitation is dominated by the junction leakage and channel boosting capability for bulk and SOI NAND flash cells, respectively, and the scaling limit is decreased to 9 nm using SOI NAND flash memory cells from 13 nm in bulk NAND flash memory cells.
Areal and Structural Effects on Oxide-Based Resistive Random Access Memory Cell for Improving Resistive Switching Characteristics
Authors: Ryoo Kyung-Chang , Oh Jeong-Hoon , Jung Sunghun , Jeong Hongsik , Park Byung-Gook
Published: April 2012

A new technical improvement in understanding the resistive switching characteristics of unipolar resistive random access memory (RRAM) is investigated. It is possible to minimize reset current (I
RESET), set voltage variation, and forming voltage (V
FORMING), which results in a wide sensing margin and high density applications by using a conducting filament (CF) minimized structure up to a 10 nm technology node. Its structural advantages enable I
RESET to be tuned with excellent manufacturability. Numerical simulation is also performed using a random circuit breaker (RCB) model, showing that the proposed structure elucidates the resistive switching improvement.
Evaluation of the WOx Film Properties for Resistive Random Access Memory Application
Authors: Chen Yi-Yueh , Chien Wei-Chih , Lee Ming-Hsiu , Chen Yi-Chou , Chuang Alfred T. H. , Hong Tian-Jue , Lin Su-Jien , Wu Tai-Bor , Lu Chih-Yuan
Published: April 2012

The formation condition, microstructure, and growth kinetics of the WO
x
layer for WO
x
resistive random access memory are investigated. To understand the optimal condition for the rapid thermal oxidation process which forms the WO
x
layer, various annealing temperature and annealing time are systemically studied through transmission electron microscopy, X-ray diffraction, Raman spectra analyses and electrical characterizations. The growth kinetics for WO
x
under rapid thermal oxidation is found similar to the one for thermal oxidation on silicon. The electrical forming voltages of the WO
x
cells are also found independent from the oxide thickness, which further suggests the switching behavior of WO
x
resistive random access memory takes place at the interface but not the bulk.
Formation-Polarity-Dependent Improved Resistive Switching Memory Performance Using IrOx/GdOx/WOx/W Structure
Authors: Jana Debanjan , Maikap Siddheswar , Tien Ta Chang , Lee Heng Yuan , Chen Wei-Su , Chen Frederick T. , Kao Ming-Jer , Tsai Ming-Jinn
Published: April 2012

The formation-polarity-dependent improved resistive switching memory performance using a new IrO
x
/GdO
x
/WO
x
/W structure has been investigated. The memory device has been observed by both high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. The thicknesses of the GdO
x
and WO
x
layers are observed to be approximately 15 and 5.5 nm, respectively. All layers are also analyzed by X-ray photoelectron spectroscopy. The resistive switching mechanism is filament formation/rupture in the high-κ GdO
x
layer, which is controlled by the oxygen ion migration in bilayer GdO
x
/WO
x
films under negative and positive formation polarities. Excellent uniformity of SET/RESET voltages, low/high resistance states, and switching cycles have been observed under positive formation polarity owing to the charge trapping/detrapping in the high-κ GdO
x
switching layer. The memory device shows a long endurance of >104 times, and extrapolated 10-year data retention at 85 °C. This device shows great potential for future nonvolatile memory (NVM) applications.
High Speed Frequency-Mapping-Based Associative Memory Using Compact Multi-Bit Encoders and a Path-Selecting Scheme
Authors: Sasaki Seiryu , Yasuda Masahiro , Kawabata Akio , Koide Tetsushi , Mattausch Hans Jürgen
Published: April 2012

A compact multi-bit encoding concept for nearest-distance search-speed improvement of scalable and reliable associative-memories utilizing a mapping operation of the distances into frequency space is reported. The distance differences are transformed into signal delays which are finally detected with a time-domain winner-take-all (WTA) circuit. Ring oscillators programmable in discrete frequency steps are used for the distance–frequency mapping. This implementation enables to decrease the effects of process-induced variations, because the step size is a constraint-free design parameter. To further improve the search reliability, frequency dividers are used to enlarge the size of the frequency steps. The multi-bit encoder achieves a substantial search-time reduction by optimizing the basic-ring oscillator delay for distance zero with a path-selecting scheme. The proposed multi-bit encoding concept has been evaluated with two test-chip designs in 180 nm complementary metal oxide semiconductor (CMOS) technology. Search-time reductions by a factor 1.7 in typical search cases and a compact circuit implementation are verified.
An Inverter-Based Wideband Low-Noise Amplifier in 40 nm Complementary Metal Oxide Semiconductor
Authors: Dharmiza Dayang Nur Salmi , Oturu Mototada , Tanoi Satoru , Ito Hiroyuki , Ishihara Noboru , Masu Kazuya
Published: April 2012

Multistandard RF chips have been highly demanded for multipurpose wireless applications. However, in RF circuits, a low-noise amplifier (LNA) plays an important role in determining the receiver's performance. In this paper, we present a scalable wideband LNA based on complementary metal oxide semiconductor (CMOS) inverters, employing two bandwidth expansion techniques to achieve a large bandwidth without using inductors. Fabricated by the 40 nm CMOS process, the LNA attains 0.1–8.0 GHz of flat bandwidth with S
21=17.5 dB and S
11≤-10 dB. The minimum NF measured is 5.1 dB and the power consumption is 14.3 mW at 1.3 V. The LNA core circuit is as small as 0.001 mm2 since no large passive device is used. A study of LNA scalability has been conducted by comparing the performances of circuits with the same topology fabricated by the 65, 90, and 180 nm CMOS processes.
A Wide-Range Tunable Level-Keeper Using Vertical Metal–Oxide–Semiconductor Field-Effect Transistors for Current-Reuse Systems
Authors: Tanoi Satoru , Endoh Tetsuo
Published: April 2012

A wide-range tunable level-keeper using vertical metal–oxide–semiconductor field-effect transistors (MOSFETs) is proposed for current-reuse analog systems. The design keys for widening tunable range of the operation are a two-path feed-back and a vertical MOSFET with back-bias-effect free. The proposed circuit with the vertical MOSFETs shows the 1.23-V tunable-range of the input level with the 2.4-V internal-supply voltage (V
DD) in the simulation. This tunable-range of the proposed circuit is 4.7 times wider than that of the conventional. The achieved current efficiency of the proposed level-keeper is 66% at the 1.2-V output with the 2.4-V V
DD. This efficiency of the proposed circuit is twice higher than that of the traditional voltage down converter.
Low-Turn-on-Voltage Heterojunction Bipolar Transistors with a C-Doped InGaAsSb Base Grown by Metalorganic Chemical Vapor Deposition
Authors: Hoshi Takuya , Sugiyama Hiroki , Yokoyama Haruki , Kurishima Kenji , Ida Minoru
Published: April 2012

We demonstrate the low-turn-on-voltage InP-based heterojunction bipolar transistors (HBTs) with a C-doped InGaAsSb base grown by metalorganic chemical vapor deposition. As the solid In content of InGaAsSb increases, not only the near-band-edge emission peak energy in photoluminescence spectra of the InGaAsSb film but also the turn-on base–emitter voltage of the HBT with an InGaAsSb base decrease. These results are attributed to the reduction of the InGaAsSb band gap with the increase of solid In content. We obtain the turn-on voltage of 0.35 V at collector current density of 1 A/cm2 in the HBT with a In0.22Ga0.78As0.73Sb0.27 base, which is one of the lowest turn-on voltages ever reported.
High Integrity SiO2Gate Insulator Formed by Microwave-Excited Plasma Enhanced Chemical Vapor Deposition for AlGaN/GaN Hybrid Metal–Oxide–Semiconductor Heterojunction Field-Effect Transistor on Si Substrate
Authors: Kambayashi Hiroshi , Nomura Takehiko , Kato Sadahiro , Ueda Hirokazu , Teramoto Akinobu , Sugawa Shigetoshi , Ohmi Tadahiro
Published: April 2012

High quality SiO2gate insulator has been demonstrated for GaN metal–oxide–semiconductor (MOS) transistor which has high performance with normally-off operation. The SiO2films formed on GaN by microwave-excited plasma enhanced chemical vapor deposition (MW-PECVD) and annealed after deposition exhibits a low-interface state density between SiO2and GaN, a high-breakdown field, and a high charge-to-breakdown. The SiO2films have been also applied to the gate insulator of AlGaN/GaN hybrid MOS heterojunction field-effect transistor (HFET) on Si substrate. The MOS-HFET show excellent properties with the threshold voltage of 4.2 V and the maximum field-effect mobility of 161 cm2V-1s-1.
Deep levels in n-GaN Doped with Carbon Studied by Deep Level and Minority Carrier Transient Spectroscopies
Authors: Honda Unhi , Yamada Yujiro , Tokuda Yutaka , Shiojima Kenji
Published: April 2012

Electron and hole traps in the carbon doping of n-type GaN films grown by metal–organic chemical vapor deposition were investigated by deep level and minority carrier transient spectroscopies. Four electron traps were observed in the samples. Of these traps, the electron trap concentration of E2 (E
c-0.40 eV) rose with increasing C incorporation. Two hole traps H1 (E
v + 0.86 eV) and H2 also showed the dependence of C doping concentration. According to these results, traps E2, H1, and H2 correspond to C-related defects. Moreover, the energy level of H1 was consistent with an ionization energy of 0.9 eV of CN acting as a deep acceptor, which might give rise to conventional yellow luminescence and current collapse of GaN-based high electron mobility transistors (HEMTs). This was confirmed by photoluminescence (PL) spectra that the integrated intensity of yellow luminescence (YL) band was largely dependent on C incorporation. Therefore, we speculated that hole trap H1 might be responsible for a broad YL band in the samples.
Analysis of Phase Matching Conditions for Generating Second Harmonic in ZnO Channel Waveguides
Authors: Taira Yuta , Kita Tomohiro , Teraoka Edgar Yoshio Morales , Yamada Hirohito
Published: April 2012

We describe a phase-matching scheme for generating the second harmonic in ZnO channel waveguides using a modal phase-matching (MPM) method. We found that MPM can be achieved between the TM00 mode of the fundamental wave and the TM02 mode of the second-harmonic wave by using structural dispersion of the waveguide mode. Furthermore, we calculated the normalized conversion efficiency by taking the overlap integral of each waveguide mode and the effective area of the fundamental wave into account, and obtained a sufficiently high conversion efficiency. These results show that ZnO channel waveguides are very attractive for generating second-harmonic devices.
GaAs/AlAs Multilayer Cavity with Er-Doped InAs Quantum Dots Embedded in Strain-Relaxed InGaAs Barriers for Ultrafast All-Optical Switches
Authors: Ueyama Hyuga , Takahashi Tomoya , Nakagawa Yoshinori , Morita Ken , Kitada Takahiro , Isu Toshiro
Published: April 2012

Er-doped InAs quantum dots (QDs) embedded in strain-relaxed InGaAs barriers, which exhibit an extremely short carrier decay time of 3 ps due to the nonradiative process, are superior materials for ultrafast all-optical switches using a GaAs/AlAs multilayer cavity. The intensity of the nonlinear signal due to the absorption saturation in the 20-layer stack of the Er-doped QDs was increased by increasing the In composition in the strain-relaxed InGaAs barriers while keeping the extremely short decay time. The QD cavity structure, which consisted of GaAs/AlAs distributed Bragg reflector (DBR) multilayers and a half-wavelength cavity layer containing two layers of the Er-doped QDs was grown by molecular beam epitaxy. The transmission change signal was clearly observed in the time-resolved measurements at the cavity mode wavelength of 1.55 µm. The response time of 4 ps was observed for the Er-doped QD cavity, which was much shorter than that (12 ps) for the undoped QD cavity.
Electroluminescence from One-Dimensionally Self-Aligned Si-Based Quantum Dots with High Areal Dot Density
Authors: Makihara Katsunori , Deki Hidenori , Ikeda Mitsuhisa , Miyazaki Seiichi
Published: April 2012

Self-aligned Si-based quantum dots (QDs) with an areal density as high as ∼1013 cm-2 have been successfully fabricated on GeH4-adsorbed ultrathin SiO2 by the process sequence consisting of Si-QDs formation by controlling low-pressure chemical vapor deposition (LPCVD) using pure Si2H6, selective Ge-LPCVD from 5% GeH4 diluted with He, thermal oxidation of the dots, thermal desorption of Ge oxide, and subsequent formation of the Si-QDs. In semitransparent Au-gate diodes with self-aligned dots so-prepared, when carriers were injected to the self-aligned Si-QDs from the n-Si(100) substrate for electrons and from the Au top electrode for holes, electroluminescence (EL) in the near-infrared region at room temperature becomes observable with an increase in current at positive biases over a threshold voltage as low as ∼1.2 V at the Au top electrode. Note that, in the case of an areal dot density of ∼1013 cm-2, the EL threshold voltage was reduced down to ∼60% of that of ∼1011 cm-2 and emission intensity was enhanced markedly by a factor of ∼425 in comparison with the case of ∼1011 cm-2 under the same current density. This is clear evidence of not only an increase in radiative recombination rate in the self-aligned structure but also an improvement of recombination efficiency due to a decrease in current leakage with increasing dot density.
Light Detection and Emission in Germanium-on-Insulator Diodes
Authors: Tani Kazuki , Saito Shin-ichi , Lee Yong , Oda Katsuya , Mine Toshiyuki , Sugawara Toshiki , Ido Tatemi
Published: April 2012

We fabricated a germanium-on-insulator (GeOI) lateral p–i–n diode by a standard silicon process and characterized it as a photodetector and a light emitter. For the photodetector, we observed photosensitivity by an excitation light with the wavelength of 1550 nm. The experimental radio frequency response has completely agreed with simulated results, and the observed 3-dB bandwidth of 2 GHz was limited by contact resistances. For the light emitter, the electroluminescence spectra have broad peaks located at 1460 nm, much shorter than that of photoluminescence spectra located at 1600 nm. The difference was presumably attributable to the poor interface properties by the surface passivation. From these results, GeOI p–i–n diodes can be promising device candidates for silicon photonics by improving process conditions.
Light Output Enhancement of GaN-Based Light-Emitting Diodes by Optimizing SiO2 Nanorod-Array Depth Patterned Sapphire Substrate
Authors: Chiu Ching-Hsueh , Tu Po-Min , Chang Shih-Pang , Lin Chien-Chung , Jang Chung-Ying , Li Zhen-Yu , Yang Hung-Chih , Zan Hsiao-Wen , Kuo Hao-Chung , Lu Tien-Chang , Wang Shing-Chung , Chang Chun-Yen
Published: April 2012

In this study, we investigated high-efficiency InGaN/GaN light-emitting diodes (LEDs) grown on sapphire substrates with SiO2 nanorod arrays (NRAs) of different heights. The GaN film showed an improved crystal quality through X-ray diffraction (XRD) full-width at half-maximum (FWHM), photoluminescence (PL), and cathodoluminescence (CL) measurements. The light output power and internal quantum efficiency (IQE) of the fabricated LEDs were increased when compared with those of conventional LEDs. Transmission electron microscopy (TEM) images suggested that the voids between SiO2 nanorods and the stacking faults introduced during the nanoscale epitaxial lateral overgrowth (NELOG) of GaN can effectively reduce the threading dislocation density (TDD). We believe that the improvements could be attributed to both the enhanced light extraction by utilizing SiO2 NRAs and the improved crystal quality through the NELOG method. We found that the sample with SiO2 NRA structures of 200 nm height can increase the LED output power by more than 70% in our study.
Basic Study of Coupling on Three-Dimensional Crossing of Si Photonic Wire Waveguide for Optical Interconnection on Inter or Inner Chip
Authors: Furuya Katsumi , Takei Ryohei , Kamei Toshihiro , Sakakibara Youichi , Mori Masahiko
Published: April 2012

For speeding up of transmission and energy saving on inter or inner chips of semiconductors, hydrogenated amorphous silicon (a-Si:H), unlike conventional crystal Si (c-Si), promises optical multilevel wiring on a Si IC. For three-dimensional (3D) crossing of Si/a-Si:H photonic wire waveguides, the loss and crosstalk as S-parameters of the two propagation modes are evaluated by numerical analysis at the C-band when the waveguide core is 200 ×400 nm2. Whether the crosstalk can be suppressed to -50 dB or less is to be a criterion. Even at the crossing angle of 30°, when the distance between the waveguides of the crossing is 1 µm or less, the crosstalk is suppressed sufficiently, while the radiation loss is also small if a TE-like mode propagates. These quantitative results are derived for the first time and show that the photonic 3D crossing can rival the present electric multilevel wiring from the viewpoint of device height. An important index for the 3D waveguide crossing fabrication is obtained.
Experimental Analysis of Optical Fiber Multimode Interference Structure and its Application to Refractive Index Measurement
Authors: Taue Shuji , Matsumoto Yoshiki , Fukano Hideki , Tsuruta Kenji
Published: April 2012

We investigated a fiber-based multimode interference phenomenon in the wavelength domain by using a white light source and an optical spectrum analyzer. This phenomenon was produced by a larger-core optical fiber joined at both ends with smaller-core optical fibers. We examined the variation of interference wavelength with changes in the length of the larger-core fiber. The interference wavelengths were blue-shifted and the interference signals were sharpened with an increase in the length of the larger-core fiber. The calculated results agreed well with the measured results. Next, we investigated how the input and output fibers with a small core influence the interference signal characteristics. By comparing the amplitude differences of the interference signal we find the conditions of input and output (I/O) fibers for higher sensitivity. In addition, an interference-signal shift was observed by changing the medium surrounding an multimode interference (MMI) structure. The amount of shift increased at a longer wavelength. This leads to the sensitive detection of the refractive index. Finally, a demonstration of the optical fiber refractometer with a multimode interference structure was given by refractive-index measurements of ethanol/water solutions.
GaN-Based Metal–Insulator–Semiconductor Ultraviolet Photodetectors with CsF Current-Suppressing Layer
Authors: Chen Chin-Hsiang , Tsai Chia-Ming , Cheng Chung-Fu , Yen Shuo-Fu , Su Peng-Yin , Tsai Yu-Hsuan , Tsai Cheng-Nan
Published: April 2012

GaN metal–insulator–semiconductor (MIS) ultraviolet (UV) photodetectors (PDs) with the CsF current-suppressing layer were, for the first time, fabricated and characterized successfully. It was found that we can achieve a low dark current and large photocurrent-to-dark-current contrast ratio from the proposed devices with the use of the CsF current-suppressing layer. With a 5 V applied bias, it was found that the leakage current of the fabricated MIS PDs with the CsF current-suppressing layer was 7.1×10-10 A. This small leakage current should be attributed to the large barrier height caused by the insertion of the CsF current-suppressing layer. With a 5 V applied bias, the barrier height of ΦB = 0.942 can be calculated from the dark current–voltage (I–V) characteristics. We can also achieve a large UV-to-visible rejection ratio from the PDs with the CsF current-suppressing layer.
Effect of Phase Purity on Dislocation Density of Pressurized-Reactor Metalorganic Vapor Phase Epitaxy Grown InN
Authors: Iwabuchi Takuya , Liu Yuhuai , Kimura Takeshi , Zhang Yuantao , Prasertsuk Kiattiwut , Watanabe Haruna , Usami Noritaka , Katayama Ryuji , Matsuoka Takashi
Published: April 2012

The effect of the metastable zincblende (ZB) InN inclusion in the stable wurtzite (WZ) InN on the threading dislocation densities (TDDs) of an InN film grown by pressurized-reactor metalorganic vapor phase epitaxy has been studied by X-ray diffraction measurements. InN films are directly grown on c-plane sapphire substrates with nitrided surfaces at 1600 Torr with the different growth temperature from 500 to 700 °C. Films including ZB-InN show the correlation between the ZB volume fraction and the edge component of TDDs, not the screw component of TDDs. This result can be crystallographically understood by a simple model explaining how the ZB structure is included, i.e., ZB domains existing side-by-side with WZ domains and twined ZB domains. This can be clearly observed by electron backscatter diffraction.
Tuning Optical Properties of Two-Dimensional Ordered Arrays of Silica/Gold and Silver Core/Shell Structured Nanoparticles in Near-Infrared Region
Authors: Sugawa Kosuke , Sakai Tatsuya , Tanaka Daido , Akiyama Tsuyoshi
Published: April 2012

Core/shell type nanoparticles, in which the shell consists of a thin layer of metal and the core consists of monodispersed dielectric nanoparticles, are of great interest owing to their characteristic plasmonic properties. In this study, we have fabricated highly regular two-dimensional arrays of silica-core/gold (or silver)-shell nanoparticles protected with polyvinylpyrrolidone (PVP) by drop-casting their colloidal ethanol solutions onto tilted glass plates. The structure and plasmonic properties of the arrays were evaluated by visible/near-infrared transmission absorption spectroscopy and scanning electron microscopy (SEM). The characteristic broad plasmon band in the near-infrared wavelength region, derived from a hybridized mode of dipolar plasmon modes of the individual core/shell nanoparticle, appeared by changing the concentration of PVP added.
Strain Effects on Avalanche Multiplication in a Silicon Nanodot Array
Authors: Mori Nobuya , Minari Hideki , Uno Shigeyasu , Mizuta Hiroshi , Koshida Nobuyoshi
Published: April 2012

Strain effects on avalanche multiplication in a one-dimensional Si nanodot array have been theoretically studied. Compressive strain has two competing effects of the band-gap narrowing and the level-separation widening. The former reduces the ionization threshold and the latter reduces the impact ionization rate for higher energy region. Larger carrier multiplication factor is observed under compressive strain condition.
Bidirectional Two-Terminal Switching Device for Non-Volatile Random Access Memory
Authors: Kil Gyu-Hyun , Yang Hyung-Jun , Lee Gae-Hun , Lee Seong-Hyun , Song Yun-Heub
Published: April 2012

A two-terminal N+/P/N+ Si junction device that can replace the conventional selective transistor was studied as a bilateral switching device for spin transfer torque magnetic random access memory (STT-MRAM), by three-dimensional device simulation. An N+/P/N+ junction structure with 30×30 nm2 area provides sufficient bidirectional current flow to write data by a drain-induced barrier lowering (DIBL) under a reverse bias at the N+/P (or P/N+) junction, and high current on/off ratio of 106, which is acceptable for STT-MRAM. In this work, critical parameters such as P-length, P doping, and N+ doping are investigated to elucidate the optimal parameter condition in view of write current and current on/off ratio.
Structural and Ferroelectric Characterization of Uniaxially Oriented Vinylidene Fluoride Oligomer Thin Films
Authors: Kuroda Yusuke , Koshiba Yasuko , Misaki Masahiro , Horie Satoshi , Ishida Kenji , Ueda Yasukiyo
Published: April 2012

A uniaxially oriented film of ferroelectric vinylidene fluoride (VDF) oligomer was fabricated by vacuum deposition on a friction-transferred vinylidene fluoride–trifluoroethylene copolymer; i.e., P(VDF/TrFE), film as a structural template. Fourier transform infrared spectroscopy and scanning electron microscopy measurements revealed that the ultra thin P(VDF/TrFE) film induced the formation of the ferroelectric form I crystal phase and the uniaxial orientation of what to the VDF oligomer by epitaxial growth. The VDF oligomer/P(VDF/TrFE) films exhibit ferroelectric hysteresis loops with a coercive field and a remanent polarization of 150 MV/m and 77 mC/m2, respectively; however, VDF oligomer films without a structural template showed no ferroelectric properties.
Light-Emitting Field-Effect Transistors Having Metal Electrodes Modified with an Organic Thin Film
Authors: Okada Akinori , Fukaya Yoshihide , Hotta Shu , Yamao Takeshi
Published: April 2012

We have improved the emission properties and the carrier mobilities of organic light-emitting field-effect transistors (OLEFETs) by modifying the metal electrode(s) with a thin film of n-type thiophene/phenylene co-oligomer (TPCO). Their semiconductor layer was a p-type TPCO crystal. When we used the modified electrode for electron injection, the device exhibited eight times higher emission intensity than a device with unmodified electrodes. By contrast, employing the modified electrode as the hole injection contact, we achieved the maximum hole mobility of 0.11 cm2·V-1·s-1 under the hole-enhancement mode. The modified electrodes effectively functioned for injecting both electrons and holes into the p-type crystal. The origin of this is briefly discussed.
Fundamental Study on Organic Solar Cells Based on Soluble Zinc Phthalocyanine
Authors: Yamada Ichiko , Umeda Masashi , Hayashi Yasuhiko , Soga Tetsuo , Shibata Norio
Published: April 2012

We investigated the potential of trifluoroethoxy-coated phthalocyanine [(4TFEO)4-ZnPc] as an organic thin-film solar cell material. (4TFEO)4-ZnPc dissolves well in several organic solvents, thus a fluorinated phthalocyanine (Pc) thin film can be fabricated by a wet process. Additionally, (4TFEO)4-ZnPc has lowest unoccupied molecular orbital (LUMO) energy level close to that of a fullerene derivative owing to the electron-withdrawing effect of fluorine substituents. We fabricated two types of fluorinated Pc solar cells by spin casting “(4TFEO)4-ZnPc single-layer solar cells” and “two-layer heterojunction solar cells” consisting of a (4TFEO)4-ZnPc layer and a poly(3-hexylthiophene) (P3HT) layer. P3HT is a common donor solar cell material. On the other hand, we used (4TFEO)4-ZnPc as an acceptor material. For the single-layer solar cells, the (4TFEO)4-ZnPc film acts as the photoactive layer of the solar cells, and P3HT/(4TFEO)4-ZnPc solar cell properties were improved as compared with that of P3HT or (4TFEO)4-ZnPc single-layer solar cells. Additionally, the photovoltaic properties of these solar cells were significantly improved by annealing treatment.
Silicon Based System for Single-Nucleotide-Polymorphism Detection: Chip Fabrication and Thermal Characterization of Polymerase Chain Reaction Microchamber
Authors: Majeed Bivragh , Jones Ben , Tezcan Deniz S. , Tutunjyan Nina , Haspeslagh Luc , Peeters Sara , Fiorini Paolo , Beeck Maaike Op de , Hoof Chris Van , Hiraoka Maki , Tanaka Hiroyuki , Yamashita Ichiro
Published: April 2012

A single nucleotide polymorphism (SNP) is a difference in the DNA sequence of one nucleotide only. We recently proposed a lab-on-a-chip (LoC) system which has the potentiality of fast, sensitive and highly specific SNP detection. Most of the chip components are silicon based and fabricated within a single process. In this paper, the newly developed fabrication method for the silicon chip is presented. The robust and reliable process allows etching structures on the same chip with very different aspect ratios. The characterization of a crucial component to the LoC SNP detector, the microreactor where DNA amplification is performed, is also detailed. Thanks to innovative design and fabrication methodologies, the microreactor has an excellent thermal isolation from the surrounding silicon substrate. This allows for highly localized temperature control. Furthermore, the microreactor is demonstrated to have rapid heating and cooling rates, allowing for rapid amplification of the target DNA fragments. Successful DNA amplification in the microreactor is demonstrated.
Design of a Compact Nonvolatile Four-Input Logic Element Using a Magnetic Tunnel Junction and Metal–Oxide–Semiconductor Hybrid Structure
Authors: Suzuki Daisuke , Natsui Masanori , Endoh Tetsuo , Ohno Hideo , Hanyu Takahiro
Published: April 2012

A nonvolatile logic element (NV-LE) using a magnetic tunnel junction (MTJ) and metal–oxide–semiconductor (MOS)-hybrid structure is proposed for a high-density field-programmable gate array with an instant-on capability. Since the output current level of a multiplexer tree including MTJ devices is directly evaluated and amplified by a single differential amplifier on the final stage of the LUT circuit, the number of wasted sense amplifiers is greatly reduced and a compact 4-input NV-LE can be implemented. Moreover, the use of dynamic current-mode logic based circuitry makes it possible a high-speed operation with low-active power dissipation due to the elimination of steady current-path. In fact, the proposed 4-input NV-LE reduces transistor counts to 63% with no performance degradation compared to those of a conventional complementary-MOS-based implementation.
Physics-Based SPICE Model of Spin-Torque Oscillators
Authors: Lim Hyein , Ahn Sora , Lee Seungjun , Shin Hyungsoon
Published: April 2012

The spin-torque oscillator (STO) is a new compact device operating as a tunable RF oscillator in the tens of gigahertz range whose characteristics are determined by the applied current and magnetic field. In this paper, we present a physics-based empirical circuit-level model of an STO that is compatible with circuit-level simulators such as SPICE. The characteristics of an STO are modeled as physics-based analytic functions of the applied current and external magnetic field. The validity of our model was verified by the HSPICE simulation of a current mirror circuit that contains an STO element. The simulation results are in good agreement with the experimental data in the normal operation range. High-order nonlinear effects at large currents are not included in our model because there is no theoretical equation available yet that can precisely explain these effects.
Relative Vortex State Control in a Co/Cu/Co Pseudo-Spin-Valve Ring
Authors: Demiray Ahmet S. , Miyawaki Tetsuya , Watanabe Yusuke , Kohda Makoto , Saito Kesami , Mitani Seiji , Takanashi Koki , Nitta Junsaku
Published: April 2012

The magnetization reversal process of a Co/Cu/Co pseudo-spin-valve ring structure has been investigated by magneto-resistance measurements and micromagnetic simulations. Major-loop measurement reveals four distinct magnetic configurations between the top and bottom Co rings. We conducted minor-loop measurements with a fixed vortex configuration in the bottom Co ring while the magnetic state of the top Co ring was changed between the onion and vortex states. It was found that the parallel vortex between the top and bottom rings shows a stable magnetization state when the top Co ring is not fully saturated in the onion state, in which the local vortex remains at the ring edge. Micromagnetic simulations also confirm that the local vortex remaining in the top ring contributes to the control of the magnetic parallel vortex state.
Growth of Horizontally-Aligned Single-Walled Carbon Nanotubes on Sapphire Surface by Needle-Scratching Method
Authors: Ago Hiroki , Kayo Yasumichi , Tsuji Masaharu
Published: April 2012

We report the growth of single-walled carbon nanotubes (SWNTs) over metal nanoparticles which are formed by scratching sapphire surface with metal wires. The chemical vapor deposition over sapphire substrate scratched with Fe and Co metal wires gives horizontally aligned SWNTs, while no nanotube growth is observed for Au, Mo, and Ni wires. This result suggests that the nanoparticles scattered from Fe and Co wires act as the catalyst for SWNT growth, being different from the previously proposed substrate-catalyzed reaction mechanism. Further, we study the effects of the flow rates of CH4–H2 gases during the SWNT growth on the nanotube density and diameter.
Plasma Treatment to Improve Chemical Vapor Deposition-Grown Graphene to Metal Electrode Contact
Authors: Kwon Taesoo , An Hyosub , Seo Young-Soo , Jung Jongwan
Published: April 2012

We show that contact properties of chemical vapor deposition (CVD)-grown graphene to metal electrode can be improved with Ar plasma treatment before metal electrode deposition. The Ar plasma treatment reduced the baseline signal of the Raman spectrum of graphene without changing main peaks of 2D and G peak and increasing D peak, supporting its effectiveness to reduce the polymer residue. Transfer length method (TLM) patterns for the plasma-treated samples exhibit more linear and neat current–voltage curve, and lower contact resistance compared with the control one (no plasma treated sample). These results support that plasma treatment is effective to improve the graphene–metal contact properties by reducing interface polymer residue.
Effect of Solid-Phase-Epitaxy Si Layers on Suppression of Sb Diffusion from Sb-Doped n+-BaSi2/p+-Si Tunnel Junction to Undoped BaSi2 Overlayers
Authors: Du Weijie , Saito Takanobu , Khan Muhammad Ajmal , Toko Kaoru , Usami Noritaka , Suemasu Takashi
Published: April 2012

A new method is proposed for the growth of undoped BaSi2 overlayers on a Sb-doped n+-BaSi2/p+-Si tunnel junction with reduced Sb diffusion. Samples with the structure of undoped-BaSi2/Si/Sb-doped n+-BaSi2/p+-Si were prepared; the inserted Si layer was grown by solid phase epitaxy and used to prevent Sb diffusion during the growth of undoped BaSi2 overlayers. Secondary ion mass spectrometry measurements indicated that Sb diffusion was effectively suppressed when the growth temperature of the undoped BaSi2 overlayers was 500 °C and lower. The X-ray diffraction (XRD) rocking curves revealed that the full width at half maximum for the BaSi2(600) intensity increased significantly for BaSi2 grown at 440 °C, indicating that the growth temperature should be higher than this temperature.
Extraction Enhanced Lateral Insulated Gate Bipolar Transistor: A Super High Speed Lateral Insulated Gate Bipolar Transistor Superior to Lateral Dobule Difused Metal Oxide Semiconductor Field-Effect Transistor
Authors: Ashida Youichi , Takahashi Shigeki , Shiraki Satoshi , Tokura Norihito , Nakagawa Akio
Published: April 2012

We have successfully developed novel extraction enhanced lateral insulated gate bipolar transistors (E2LIGBTs) in conventional silicon on insulator (SOI) wafers, which exhibit super-high speed switching of 34 ns turn-off time and a low on-state voltage of 3.7 V at 84 A/cm2 simultaneously with a high breakdown voltage of 738 V. This is the first report showing its superior switching speed and on-resistance compared to conventional lateral double diffused metal oxide semiconductor field-effect transistor (LDMOS). The superior performance is achieved by a new anode structure designed with the proposed E2 concept, which simultaneously achieves enhanced electron extraction and suppression of hole injection at the anode region without life time control. The E2 concept is realized using the anode structure, consisting of a narrow p+-injector and a wide Schottky contact on a lightly doped p-layer over an n-buffer. The switching speed can be controlled by the area ratio of the Schottky area over the injector area.
High Voltage and High Reliability Silicon-on-Insulator Power IC Technologies and Their Application to 750 V 4.5 A Micro-Inverter IC
Authors: Shiraki Satoshi , Takahashi Shigeki , Yamada Akira , Yamamoto Masahiro , Senda Koji , Ashida Youichi , Hiruma Atsuyuki , Tokura Norihito
Published: April 2012

We have successfully developed the record high blocking voltage of 750 V and the largest current capability of 4.5 A silicon-on-insulator (SOI) micro-inverter IC, which is made possible by the newly developed high voltage reliability technology and high-speed and low-dissipation extraction enhanced lateral insulated gate bipolar transistor (E2LIGBT). It has been found, for the first time, that the stable and reliable high blocking voltage of 760 V is assured by controlling the sheet-resistance of the polycrystalline silicon (poly-Si) layer of the scroll-shaped resistive field plate (SRFP). The high voltage and high reliability SOI power IC technology is expected as the key technology enabling 750 V 4.5 A micro-inverter IC for harsh applications such as automotive electronics.
Optimization of Amorphous Si/Crystalline Si Heterojunction Solar Cells by BF2 Ion Implantation
Authors: Tsai Tzong-Han , Wu Yung-Chun , Yang Shih-Sian , Chen Chun-Hao
Published: April 2012

In this study we evaluated two approaches to improving the efficiency of amorphous Si/crystalline Si (a-Si/c-Si) heterojunction solar cells by BF2 ion implantation. First, emitter layer formation was compared for the cases of B and BF2 ion implantation when using the same 7° tilt angle. Second, emitter layer formation was compared between a 7° tilt angle and a 60° tilt angle when using BF2 ion implantation. The experimental results reveal that the fluorine in BF2 passivates the defects at the a-Si and a-Si/c-Si interface, and ion implantation at a high 60° tilt angle forms a shallow solar cell junction. The emitter layer formed by BF2 ion implantation with a 60° tilt angle in an a-Si/c-Si heterojunction solar cell achieves the highest short circuit current density (J
SC) of 36.85 mA/cm2 with a conversion efficiency (η) of 14.41%.
Sat1 is dispensable for active oxalate secretion in mouse duodenum
Authors: Ko Narae , Knauf Felix , Jiang Zhirong , Markovich Daniel , Aronson Peter S.
Published: April 2012

Mice deficient for the apical membrane oxalate transporter SLC26A6 develop hyperoxalemia, hyperoxaluria, and calcium oxalate stones due to a defect in intestinal oxalate secretion. However, the nature of the basolateral membrane oxalate transport process that operates in series with SLC26A6 to mediate active oxalate secretion in the intestine remains unknown. Sulfate anion transporter-1 (Sat1 or SLC26A1) is a basolateral membrane anion exchanger that mediates intestinal oxalate transport. Moreover, Sat1-deficient mice also have a phenotype of hyperoxalemia, hyperoxaluria, and calcium oxalate stones. We, therefore, tested the role of Sat1 in mouse duodenum, a tissue with Sat1 expression and SLC26A6-dependent oxalate secretion. Although the active secretory flux of oxalate across mouse duodenum was strongly inhibited (>90%) by addition of the disulfonic stilbene DIDS to the basolateral solution, secretion was unaffected by changes in medium concentrations of sulfate and bicarbonate, key substrates for Sat1-mediated anion exchange. Inhibition of intracellular bicarbonate production by acetazolamide and complete removal of bicarbonate from the buffer also produced no change in oxalate secretion. Finally, active oxalate secretion was not reduced in Sat1-null mice. We conclude that a DIDS-sensitive basolateral transporter is involved in mediating oxalate secretion across mouse duodenum, but Sat1 itself is dispensable for this process.
Increased endogenous H2S generation by CBS, CSE, and 3MST gene therapy improves ex vivo renovascular relaxation in hyperhomocysteinemia
Authors: Sen Utpal , Sathnur Pushpakumar B. , Kundu Sourav , Givvimani Srikanth , Coley Denise M. , Mishra Paras K. , Qipshidze Natia , Tyagi Neetu , Metreveli Naira , Tyagi Suresh C.
Published: April 2012

Hydrogen sulfide (H2S) has recently been identified as a regulator of various physiological events, including vasodilation, angiogenesis, antiapoptotic, and cellular signaling. Endogenously, H2S is produced as a metabolite of homocysteine (Hcy) by cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3MST). Although Hcy is recognized as vascular risk factor at an elevated level [hyperhomocysteinemia (HHcy)] and contributes to vascular injury leading to renovascular dysfunction, the exact mechanism is unclear. The goal of the current study was to investigate whether conversion of Hcy to H2S improves renovascular function. Ex vivo renal artery culture with CBS, CSE, and 3MST triple gene therapy generated more H2S in the presence of Hcy, and these arteries were more responsive to endothelial-dependent vasodilation compared with nontransfected arteries treated with high Hcy. Cross section of triple gene-delivered renal arteries immunostaining suggested increased expression of CD31 and VEGF and diminished expression of the antiangiogenic factor endostatin. In vitro endothelial cell culture demonstrated increased mitophagy during high levels of Hcy and was mitigated by triple gene delivery. Also, dephosphorylated Akt and phosphorylated FoxO3 in HHcy were reversed by H2S or triple gene delivery. Upregulated matrix metalloproteinases-13 and downregulated tissue inhibitor of metalloproteinase-1 in HHcy were normalized by overexpression of triple genes. Together, these results suggest that H2S plays a key role in renovasculopathy during HHcy and is mediated through Akt/FoxO3 pathways. We conclude that conversion of Hcy to H2S by CBS, CSE, or 3MST triple gene therapy improves renovascular function in HHcy.
Transient receptor potential vanilloid type 1 channels contribute to reflex cutaneous vasodilation in humans
Authors: Wong Brett J. , Fieger Sarah M.
Published: April 2012

Mechanisms underlying the cutaneous vasodilation in response to an increase in core temperature remain unresolved. The purpose of this study was to determine a potential contribution of transient receptor potential vanilloid type 1 (TRPV-1) channels to reflex cutaneous vasodilation. Twelve subjects were equipped with four microdialysis fibers on the ventral forearm, and each site randomly received 1) 90% propylene glycol + 10% lactated Ringer (vehicle control); 2) 10 mM l-NAME; 3) 20 mM capsazepine to inhibit TRPV-1 channels; 4) combined 10 mM l-NAME + 20 mM capsazepine. Whole body heating was achieved via water-perfused suits sufficient to raise oral temperature at least 0.8°C above baseline. Maximal skin blood flow was achieved by local heating to 43°C and infusion of 28 mM nitroprusside. Systemic arterial pressure (SAP) was measured, and skin blood flow was monitored via laser-Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was calculated as LDF/SAP and normalized to maximal vasodilation (%CVCmax). Capsazepine sites were significantly reduced compared with control (50 ± 4%CVCmax vs. 67 ± 5%CVCmax, respectively; P < 0.05). l-NAME (33 ± 3%CVCmax) and l-NAME + capsazepine (30 ± 4%CVCmax) sites were attenuated compared with control ( P < 0.01) and capsazepine ( P < 0.05); however, there was no difference between l-NAME and combined l-NAME + capsazepine. These data suggest TRPV-1 channels participate in reflex cutaneous vasodilation and TRPV-1 channels may account for a portion of the NO component. TRPV-1 channels may have a direct neural contribution or have an indirect effect via increased arterial blood temperature. Whether the TRPV-1 channels directly or indirectly contribute to reflex cutaneous vasodilation remains uncertain.
Synergistic effect of obesity and lipid ingestion in suppressing the growth hormone response to exercise in children
Authors: Oliver Stacy R. , Hingorani Sunita R. , Rosa Jaime S. , Zaldivar Frank P. , Galassetti Pietro R.
Published: April 2012

Diet plays an important role in modulating exercise responses, including activation of the growth hormone (GH)/insulin-like growth factor-I (IGF-1) axis. Obesity and fat ingestion were separately shown to reduce exercise GH responses, but their combined effect, especially important in children, has not been studied. We therefore measured the GH response to exercise [30-min intermittent cycling, ten 2-min bouts at ∼80% maximal aerobic capacity (V̇o2max), separated by 1-min rest], started 45 min after ingestion of a high-fat meal (HFM) in 16 healthy [controls; body mass index percentile (BMI%ile) 51 ± 7], and 19 obese (Ob, BMI%ile 97 ± 0.4) children. Samples were drawn at baseline (premeal), and at start, peak, and 30 min postexercise. In the Ob group, a marked ∼75% suppression of the GH response (ng/ml) to exercise was observed (2.4 ± 0.6 vs. 10.6 ± 2.1, P < 0.001). This level of suppression was also significantly greater compared with age-, fitness-, and BMI-matched historical controls that had performed identical exercise in fasting conditions. Our data indicate that the reduction in the GH response to exercise, already present in obese children vs. healthy controls, is considerably amplified by ingestion of fat nutrients shortly before exercise, implying a potentially downstream negative impact on growth factor homeostasis and long-term modulation of physiological growth.