bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and Fabrication of a One-Transistor/One-Resistor Nonvolatile Binary Content-Addressable Memory Using Perpendicular Magnetic Tunnel Junction Devices with a Fine-Grained Power-Gating Scheme
Authors: Matsunaga Shoun , Natsui Masanori , Ikeda Shoji , Miura Katsuya , Endoh Tetsuo , Ohno Hideo , Hanyu Takahiro
Published: June 2011

A perpendicular magnetic tunnel junction (P-MTJ)-based one-transistor/one-resistor (1T–1R) binary content-addressable memory (CAM) is proposed for a high-density nonvolatile CAM. The proposed CAM cell performs an equality-search operation between an input bit and the corresponding stored bit by detecting the difference of a “cell resistance”, where the cell resistance is determined by the series connection of one metal–oxide–semiconductor (MOS) transistor and one P-MTJ device. This circuit structure makes it possible to implement a compact nonvolatile CAM cell circuit with 1.25 µm2 of a cell size in a 0.14 µm complementary MOS (CMOS)/P-MTJ process. Moreover, the equality-search operation in a bit-serial fashion is used for great reduction of the activity rate in the proposed CAM cell array, since most of the mismatched words in the CAM are detected by just several higher bits of comparison results in the word circuits. By applying a bit-level fine-grained power gating scheme, a fabricated 64-bit × 128-word nonvolatile CAM achieves high density with maintaining low search energy under 3.1% of activity rate in the cell array.
Physical Mechanism of Threshold Voltage Modulation by Ge Channel Ion Implantation in the TiN/HfO2 Gate Stack Systems
Authors: Tsuchiya Yoshinori , Berliner Nathaniel , Iijima Ryosuke , Tai Leo , Takayanagi Mariko , Paruchuri Vamsi
Published: June 2011

We extensively investigated the physical origin of the threshold voltage V
TH modulation by the Ge channel ion implantation (I/I) in HfO2/TiN/polycrystalline Si gate stack systems. The possible V
TH modulation factors were carefully distinguished from each other by changing the channel dopant concentration and the thickness of the gate dielectric films. It was found that the changes in energy-band offset and dopant concentration in the channel region are minor factors of the V
TH modulation. However, it was also found that ΔV
TH is sensitive to the oxidation condition of the interfacial oxide layer; a longer oxidation induces a larger ΔV
TH. From the X-ray spectroscopy, we found that a Ge pile-up at the interfacial layer/channel interface occurs, and that the V
TH modulation range correlates well with the amount of piled-up Ge.
Rapid Fabrication of Silver Nanowires through Photoreduction of Silver Nitrate from an Anodic-Aluminum-Oxide Template
Authors: Lin Yu-Hsuan , Chen Kun-Tso , Ho Jeng-Rong
Published: June 2011

A method for rapidly fabricating dense and high-aspect-ratio silver nanowires, with wire diameter of 200 nm and wire length more than 30 µm, is reported. The fabrication process simply involves filling the silver nitrate solution into the pores of an anodic-aluminum-oxide (AAO) membrane through capillary attraction and irradiating the dried template AAO membrane using a pulsed ArF excimer laser. Through varying the thickness and pore diameter of the employed AAO membrane, the primary dimensions of the targeted silver nanowires can be plainly specified; and, by amending the initial concentration of the silver nitrate solution and adjusting the laser operation parameters, laser fluence and number of laser pulses, the surface morphology and size of the resulting nanowires can be finely regulated. The wire formation mechanism is considered through two stages: the period of precipitation of silver particles from the dried silver nitrate film through the laser-induced photoreduction; and, the phase of clustering, merging and fusing of the reduced particles to form nanowires in the template pores by the thermal energy owing to photothermal effect. This approach is straightforward and takes the advantage that all the fabrication processes can be executed in an ambient environment and at room temperature. In addition, by the excellence in local processing that the laser possesses, this method is suitable for precisely growing nanowires.
A Study on the Plasmonic Properties of Silver Core Gold Shell Nanoparticles: Optical Assessment of the Particle Structure
Authors: Mott Derrick , Lee JaeDong , Thuy Nguyen Thi Bich , Aoki Yoshiya , Singh Prerna , Maenosono Shinya
Published: June 2011

This paper reports a qualitative comparison between the optical properties of a set of silver core, gold shell nanoparticles with varying composition and structure to those calculated using the Mie solution. To achieve this, silver nanoparticles were synthesized in aqueous phase from a silver hydroxide precursor with sodium acrylate as dual reducing–capping agent. The particles were then coated with a layer of gold with controllable thickness through a reduction–deposition process. The resulting nanoparticles reveal well defined optical properties that make them suitable for comparison to ideal calculated results using the Mie solution. The discussion focuses on the correlation between the synthesized core shell nanoparticles with varying Au shell thickness and the Mie solution results in terms of the optical properties. The results give insight in how to design and synthesize silver core, gold shell nanoparticles with controllable optical properties (e.g., SPR band in terms of intensity and position), and has implications in creating nanoparticle materials to be used as biological probes and sensing elements.
On Optical Properties of CdTe/ZnTe Quantum Rings
Authors: Hong Woo-Pyo , Park Seoung-Hwan
Published: June 2011

The optical properties of CdTe/ZnTe self-assembled quantum rings as functions of the height and inner diameter are investigated with a finite element method based on the linear elasticity theory of solids and the eight-band k·p Hamiltonian. We find that the quantum ring height significantly alters the bi-axial strain, while it has less effect on the hydrostatic strain. It was shown that the interband transition energy increases with increasing inner diameter (or decreasing quantum ring volume), while it decreases as the height increases. We find that the matrix element for thex-polarization is much larger than that of thez-polarization, in contrast to the result of the truncated quantum dot heterostructure. It is found that the gain peak is redshifted as the height of quantum ring increases, while it is blueshifted with increasing intensity as the inner diameter of quantum ring increases.
Sulfurization Growth of CuInS2 Thin Film Using Ditertiarybutylsulfide as a Less Hazardous Source
Authors: Sugiyama Mutsumi , Fujiwara Chika , Shoji Ryuki , Chichibu Shigefusa
Published: June 2011

Ditertiarybutylsulfide [(t-C4H9)2S: DTBS] was shown to be a promising, less hazardous alternative source for the sulfurization growth of CuInS2 films. Single-phase, polycrystalline CuInS2 films were formed in only 15 min when the sulfurization temperature was 575 °C. Photoluminescence spectra at a low temperature were dominated by characteristic emission bands at 1.34 and 1.37 eV, indicating that the films are a suitable material as a photoabsorbing layer of CuInS2-based solar cells. These results represent the first step toward realizing a solar cell using a CuInS2 film grown by sulfurization using an organometallic source and conventional, large-scale equipment.
Ce-Induced Reconstruction of Si(001) Surface Structures
Authors: Shindo Daisuke , Sakurai Shusaku , Fujimura Norifumi
Published: June 2011

The reconstructed surface structure of Ce-doped Si thin films on Si(001) was studied byin situreflection high-energy electron diffraction. We observed a reconstructed surface structure of Si(001) with three-fold periodicity by introducing Ce atoms during the film growth. The three-fold periodic surface structure was observed at the Ce concentration above 1.1 at. %. Moreover, the incubation time for emergence of the three-fold periodic surface structure changed depending on the deposition temperature and the Ce concentration, suggesting that the diffusion of the incorporated Ce atoms to the surface played an important role in the reconstruction of the Si(001) surface. This reconstructed surface with high Ce concentration should be available as a new technique to obtain a diluted magnetic semiconductor with high magnetic element.
Epitaxial Growth of V2O3 Thin Films on c-Plane Al2O3 in Reactive Sputtering and Its Transformation to VO2 Films by Post Annealing
Authors: Okimura Kunio , Suzuki Yasushi
Published: June 2011

Epitaxial growth of thin vanadium sesquioxide (V2O3) films on c-plane sapphire (c-Al2O3) substrates was achieved with reactive magnetron sputtering under restricted oxygen flow. Even with a film thickness of approximately 12 nm, highly c-axis textured growth of corundum V2O3 was realized because of the smaller mismatch of V2O3 against corundum Al2O3. Post annealing in O2 atmosphere for as-grown V2O3 films caused phase transformation to oxidized crystalline phases. At a moderate annealing temperature of 450 °C, the V2O3 thin films transformed to VO2 films, which show a resistivity change of over three orders of magnitude. The X-ray photoelectron spectroscopy spectra for the annealed VO2 film showed a single charge state of V4+, indicating a homogeneous crystalline structure, in contrast to the inhomogeneous feature with mixed charge states of V in addition to V3+ for as-grown V2O3 film. This method is promising to prepare thin VO2 films with metal–insulator transition in productive reactive sputtering and to examine crystalline phase transformation mechanisms, including phase coexistence.
Effect of the Laser Contrast Ratio within Picosecond Timescales on Generating a High-Quality Electron Beam by Laser–Plasma Interaction
Authors: Kotaki Hideyuki , Kando Masaki , Daito Izuru , Kameshima Takashi , Kawase Keigo , Chen Liming , Fukuda Yuji , Koga James K. , Kiriyama Hiromitsu , Kondo Shuji , Kanazawa Shuhei , Nakai Yoshiki , Shimomura Takuya , Tanoue Manabu , Akutsu Atsushi , Okada Hajime , Motomura Tomohiro , Bulanov Sergei V.
Published: June 2011

The laser contrast ratio within picosecond timescales is one of the important parameters for laser acceleration. For a high laser contrast ratio, a 140 MeV monoenergetic electron beam with a charge of 44 pC is obtained by using a 20 TW Ti:sapphire laser. For a low laser contrast ratio, a low quality electron beam or no electron beam is generated, because the pre-pulse blows out plasma electrons and puts the plasma into disorder before the main pulse interacts with the plasma. The laser contrast ratio should be high enough in order to generate a high quality electron beam with a large amount of charge.
Laser Direct Patterning of Organic Dielectric Passivation Layer for Fabricating Amorphous Silicon Thin-Film Transistors
Authors: Chen Chao-Nan , Su Kuo-Hui , Chen Yeong-Chin
Published: June 2011

In this study, a laser direct patterning process application in benzocyclobutene (BCB) organic dielectric passivation-based amorphous silicon (a-Si) thin film transistor (TFT) device fabrication has been carried out using a KrF excimer laser. A BCB organic photoresist material of 2000 nm with a dielectric constant = 2.7 served as the dielectric passivation layer in our device. Compared with conventional processes, laser direct patterning combining BCB organic photoresist dielectric passivation could eliminate at least four process steps. The etching depth of the BCB organic material passivation layer depends on the laser energy density and number of irradiation shots. The hydrogenated a-Si TFT devices are fabricated by replacing the passivation layer and contact hole patterning process. The mobility and threshold voltage reached 0.16 cm2 V-1 s-1 and -3.5 V, respectively. For TFT device performance, laser direct patterning technology is a potential method of replacing photolithography technology in the application of BCB organic dielectric passivation-based TFT manufacture.
Etching Characteristics and Mechanisms of Pb(Zr,Ti)O3, Pt, and SiO2 in an Inductively Coupled HBr/Cl2 Plasma
Authors: Kwon Kwang-Ho , Efremov Alexander , Kim Youngkeun , Lee Chi-Woo , Kim Kwangsoo
Published: June 2011

An investigation of the etching characteristics of Pb(Zr,Ti)O3 (PZT), Pt, and SiO2 in an inductively coupled HBr/Cl2 plasma as functions of gas mixing ratio at constant total gas pressure (6 mTorr), gas flow rate (40 sccm), input power (700 W), and bias power (300 W) was carried out. It was found that the PZT etching rate exhibits a maximum of 23.8 nm/min at 60% Cl2, while the highest PZT/SiO2 and PZT/Pt etching selectivities correspond to 20 and 40–60% Cl2, respectively. Plasma diagnostics by a double Langmuir probe and a global (zero-dimensional) plasma model provided the data on plasma parameters, densities and fluxes of plasma active species. It was considered that the PZT etching process appears in the neutral-flux-limited or transitional regime of an ion-assisted chemical reaction, and the nonmonotonic behavior of the PZT etch rate may result from the change in reaction probability.
Evaluation of a Single-Crystal-Silicon Microelectromechanical Systems Resonator Utilizing a Narrow Gap Process
Authors: Hashimoto Keita , Ito Kouzaburo , Tanigawa Hiroshi , Suzuki Kenichiro
Published: June 2011

To investigate a higher frequency microelectromechanical systems (MEMS) resonator, mechanical behaviors and electrical characteristics on a single-crystal-silicon MEMS resonator, utilizing a narrow gap process, have been evaluated. The size reduction for the resonators leads to a decrease in output signal. To overcome this problem, an increase in electromechanical coupling coefficient is required. To investigate the effect of the reduction of the gap between a beam and a driving electrode, two types of 100 kHz MEMS resonator with different gaps have been fabricated and compared. It has been observed that the resonator with a narrow gap (1 µm) has a larger displacement amplitude, as well as a larger phase transition, than that with a 4 µm gap, which suggests that the gap reduction is effective. Then, a 10 MHz MEMS resonator has been fabricated by using the narrow gap process with a focused-ion beam (FIB). The resonant vibration for the fabricated device has been observed at 11.262 MHz. To further improve the resonators, it is suggested that the substrate vibration near the beam resonant frequency should be suppressed and that a smooth surface of the gap should be fabricated.
Optical Absorption Properties of BaSi2 Epitaxial Films Grown on a Transparent Silicon-on-Insulator Substrate Using Molecular Beam Epitaxy
Authors: Toh Katsuaki , Saito Takanobu , Suemasu Takashi
Published: June 2011

We have grown 100-nm-thick BaSi2 films on transparent silicon-on-insulator (SOI) substrates using molecular beam epitaxy, for optical absorption measurements. The SOI substrate has a 0.7-µm-thick (111)-oriented Si layer on top of a fused silica substrate. Reflection high-energy electron diffraction and θ–2θ X-ray diffraction patterns showed that a-axis-oriented BaSi2 layers were grown epitaxially. The absorption spectrum of the film measured in a transmission configuration at room temperature revealed that BaSi2 has a large absorption coefficient of 3 ×104 cm-1 at 1.5 eV and an indirect optical absorption edge of 1.34 eV.
Lithography – Green and Getting Greener
Authors: Levinson Harry J.
Published: June 2011

Today, many energy-saving technologies and practices are enabled or made more effective through the use of nano-electronics. Such technologies include hybrid and all-electric cars, as well as controllers to increase the efficiency of photovoltaic panels. Telecommuting, which enables people to work without traveling from their homes, has been made possible by personal computers and the internet. Reducing the costs of nano-electronics will make possible increased opportunities for the use of products that reduce energy consumption. The most effective way to reduce costs is to improve efficiency. Increased efficiency also provides the benefit of reducing energy and material consumption in the manufacturing of nano-electronics. For example, reducing photochemical usage decreases costs but also reduces material consumption and the need for disposal. Reduction of scrap and rework are direct improvements in efficiency. Cycle time reduction enables greater responsiveness to demand, reducing the amount of material started in processing but never completed. Good process control reduces scrap and rework during manufacturing and results in circuits that have high performance, yet lower power consumption, when used. There are ready opportunities for making the most of the natural tendencies of businesses to innovate and improve efficiency. The semiconductor industry has historically adopted process improvements that have increased worker safety and reduced the consumption of hazardous materials. An early example was the transition from solvent to aqueous photoresist developers. Today, all types of development can be conducted in safer equipment that minimizes the release of hazardous chemicals to the air and water. Non-toxic solvents, such as ethyl lactate, have been widely adopted. There are many opportunities for further improvement. For example, over 90% of resist goes down the drain using conventional spin-coating process, so there is an opportunity for greatly improved efficiency in that operation. A lot of water is used to reduce defects when using chemically amplified resists, and the amount of water needed could be reduced by improved design of resists and substrate coatings. Thinking further into the future, directed self-assembly has the promise of a patterning technology that can be applied simply and with energy-efficiency. Once the fundamental challenges of creating high output extreme ultraviolet (EUV) light sources are overcome, there will be great opportunities for reducing electricity consumption.
Using FlexRay in Computational Lithography
Authors: Socha Robert , Shao Wenjin , Dommelen Youri van , Oorschot Dorothe , Meggens Henry , Vellanki Venu , Adrichem Paul van , Xie Xu , Gau Justin , Aldana Rafael , Du Fei , Goossens Ronald , Yu Zongchang , Reijnen Liesbeth , Knops Roel , Schreel Koen , Hsu Stephen , Chen Luoqi , Gronlund Keith
Published: June 2011

FlexRay programmable illumination and LithoTuner software is combined in several use cases. The first use case is source mask optimization (SMO) in which the process window is maximized for a static random access memory (SRAM) design. In a 55 nm half-pitch contact hole array (k
1 = 0.38, NA= 1.35, λ= 193 nm), the process window (PW) with FlexRay programmable illumination is twice as large as the PW with cQuad illumination defined through completely refractive illumination. The second use case is optical proximity error (OPE) minimization in which the large PW from SMO is realized on every scanner in the fab. The OPE error is reduced by 17% with LithoTuner and FlexRay. The third use case is matching two ArF scanners, a 1950i with FlexRay to a 1700i with diffractive optical element (DOE) illumination. With LithoTuner and FlexRay, the root means squared (rms) critical dimension (CD) error is reduced by 29% in this third use case. The last use case, intrafield dose optimization with DoseMapper is combined with FlexRay programmable source optimization to reduce the CD error on a wafer from a mean-to-target critical dimension (CD) error in the mask manufacturing process. This combination was optimized with LithoTuner to reduce the root mean square (rms) wafer CD error by 30%.
In-situ Contamination Thickness Measurement by Novel Resist Evaluation System at NewSUBARU
Authors: Matsuda Naohiro , Watanabe Takeo , Harada Tetsuo , Kinoshita Hiroo , Oizumi Hiroaki , Itani Toshiro
Published: June 2011

To reduce the influence of carbon contamination growth, which is the origin of the resist outgassing during extreme ultraviolet (EUV) exposure, it is necessary to study the relationship between the outgassing species from the resist and carbon contamination growth during EUV exposure. Thus a novel evaluation system which enable the measurement of the carbon contamination thickness on a Mo/Si multilayer witness sample by in-situ ellipsometry in the resist outgassing environment under EUV exposure was installed at the beamline in the NewSUBARU synchrotron radiation facility. The carbon contamination thickness on the witness sample measured by in-situ ellipsometry is in good agreement with those measured using an atomic microscope and by reflectivity measurement. In addition, it is found that the time dependence of the carbon growth on a witness sample is due to the difference in outgassing species from the resist samples during EUV exposure. Furthermore, for the model resist of poly(hydroxystyrene) containing the protectiive group of tertial butoxycarbonyl group with a photoacid generator (PAG) and a quencher, the time dependence of contamination thickness was mainly due to the decomposition of outgassing species of the tert-butoxycarbonyl group and the residual casting solvent, such as propyleneglycol monomethyl ether acetate. In order to evaluate the carbon contamination thickness measurement, the in-situ measurement system was moved to the 10.8-m-long undulator beamline. The EUV light intensity flux was estimated to be the same level as that required in high-volume manufacturing.
Improvement of Flare Modeling and Derivation for Extreme Ultraviolet Optics
Authors: Shiraishi Masayuki , Oshino Tetsuya , Murakami Katsuhiko , Chiba Hiroshi
Published: June 2011

Flare has a critical impact on extreme ultraviolet (EUV) lithography. Precise estimation and control of flare amount are important for optical proximity correction (OPC). Flare can be calculated by the convolution of a reticle pattern with a flare point spread function (PSF) containing total integrated scatter (TIS) and scatter PSF (PSF
SC) derived from the power spectral density (PSD) of the mirror surface. TIS is traditionally obtained by the integration of PSF
SC. However, a portion of scatter cannot reach the wafer. Hence, TIS should be defined as the total amount of as-scattered light, while PSF
SC should be defined as the amount of light reaching the wafer; i.e., TIS should be derived from PSF different from PSF
SC. We also had other considerations: the termination of linear approximation, the scatter extinction effect of multilayers, and the obscuration effect. With these considerations, we can calculate flare behaviors that agree well with the experiments.
Transmission Grating Fabrication for Replicating Resist Patterns of 20 nm and Below
Authors: Yamaguchi Yuya , Fukushima Yasuyuki , Harada Tetsuo , Watanabe Takeo , Kinoshita Hiroo
Published: June 2011

We proceed to develop the extreme ultraviolet (EUV) interference lithographic exposure tool to determine whether the obtained resist could satisfy the requirement for the 20 nm node and below down to the 11 nm node. Transmission grating fabrication is a key technology in EUV interference lithography (EUV-IL). To replicate a 20 nm line and space resist pattern, a 40 nm line and space (L/S) pattern is required for the transmission grating. In the hard mask process, by optimizing the resist thickness to 60 nm and the dry etching conditions, and improving the alignment procedure for back-side etching, the 40 and 35 nm L/S patterns of the transmission grating were successfully fabricated. In addition, by applying a chemically amplified resist to adopt the center stop process in the transmission fabrication process and optimizing the resist thickness to attenuate completely the 0th order light, which was transmitted through the absorber and membrane, we succeeded in increasing the light intensity of the interference fringes and in replicating the 20 nm L/S resist pattern on a wafer. Furthermore, the chemically amplified molecular resist in the positive tone was confirmed to have a 20 nm resolution.
Charge Modeling for Metal Layer on Insulating Substrate
Authors: Okai Nobuhiro , Yano Tasuku , Sohda Yasunari
Published: June 2011

A charging model for magnification variation in the observation of a metal pattern on an insulating substrate using a scanning electron microscope is proposed. To calculate the time evolution of charging, we replace electron trajectory with current. Negative charging of the metal layer is observed and is caused by the current from the anode, which is set above the sample, to the metal layer. The origin of the current is tertiary electrons produced by backscattered electrons colliding with the anode. By controlling tertiary-electron trajectories through the application of bias voltage to the anode, the magnification variation can be reduced to almost zero.
A New Method for Line Width Roughness Mitigation
Authors: Mayya K. Subramanya , Yool Kang , Kim Hochul , Cho Han-Ku
Published: June 2011

Demands of the continuous downscaling of device size impose stringent requirements on the RLS trade-off (R: resolution, L: line width roughness and S: sensitivity). Among the above, line width roughness (LWR) has to be controlled below 10% of critical dimensions (CD). While significant improvement in R&S was achieved, LWR has been relatively high for extreme ultra-violet lithography resists. Herein, we provide a new method for LWR mitigation that overcomes several shortcomings of previously known methods. Our new method is based on a double development method wherein, a polymeric solution in developer is coated on to the patterned surface. The wafer is then subjected to the standard development step during which LWR improvement is affected. In this paper we discuss the hypothesis of our method and provide relevant data to understand the conditions under which LWR improvement is observed. Effect of polymer/developer concentration ratio, solid content and bake temperatures will be discussed. Also, our method will be compared with currently available methods for LWR improvement on pattern transfer.
First-Principles Simulation on Piezoresistivity in Alpha and Beta Silicon Carbide Nanosheets
Authors: Nakamura Koichi , Toriyama Toshiyuki , Sugiyama Susumu
Published: June 2011

We have simulated strain gauge factors in some n-type alpha and beta silicon carbide (SiC) nanosheet models on the basis of first-principles calculations. Our original procedure of simulating piezoresistive properties was applied to the two-dimensional system with a multivalley conduction-band structure. The calculated gauge factors of the 2H-SiC(0001) nanosheet model for the [1100] tensile strain are very small at room temperature, but the longitudinal gauge factor shows a significant negative value at high temperatures. In the simulation of the gauge factors of the 4H-, 6H-, and 3C-SiC(0001) models, negative longitudinal gauge factors and positive transverse ones are clearly given at room temperature, and they are in good proportion to 1/T. The piezoresistivity of the 2H-SiC(0001) model increases rapidly as temperature rises, and it is expected that n-type 2H-SiC(0001) nanosheet will be useful for future high-temperature sensor applications, owing to its piezoresistivity at high temperatures.
Fabrication and Characteristics of Nanoscale Stacked-Tunneling-Junctions on Graphite Flake Using Focused Ion Beam
Authors: Venugopal Gunasekaran , Kim Gui Shik , Kim Sang-Jae
Published: June 2011

We report the successful fabrication and characteristics of a nanoscale stack of tunneling junctions formed along the c-axis of thin graphite flakes. The stack was made by a three-dimensional focused-ion-beam etching method. First, a submicron bridge was patterned in a required junction width by normal-direction etching. By tilting the sample stage to 90°, two grooves on the bridge were etched from the lateral direction in order to create the required stack size. The stacked junctions showed a perfect c-axis transport behavior and nonlinear current–voltage (I–V) characteristics at all studied temperatures. We discussed the nonlinear I–V characteristics in detail using the Schottky barrier model and Fowler–Nordheim (FN) tunneling theory. The stack transport characteristics showed good agreement with FN tunneling behavior.
Highly Sensitive Electrical Detection of Sodium Ions Based on Graphene Field-Effect Transistors
Authors: Sofue Yasuyuki , Ohno Yasuhide , Maehashi Kenzo , Inoue Koichi , Matsumoto Kazuhiko
Published: June 2011

We have fabricated graphene field-effect transistors (GFETs) to demonstrate highly sensitive electrical detection of sodium (Na) ions in electrolytes. Na ions in electrolytes affect the electrical potential of graphene channels, resulting in shifts toward a negative direction of the transfer curves in GFETs with increasing Na ion concentration. The transfer characteristics of GFETs indicated that Na ions in solutions were effectively detected over a wide range of concentrations from 1.0 nM to 1.0 mM. We also developed Na ion sensors based on GFETs to have a precise resolution of Na ion concentration to be utilized in the medical field. Time dependence measurement revealed that GFETs detected Na ions in real time. These results indicate that GFETs are potentially capable of being highly sensitive Na ion sensors.
Enormous Shrinkage of Carbon Nanotubes under Low-Energy Electron Beam Irradiation with Uniaxial Tensile Stress
Authors: Ueki Ryuichi , Hikata Takeshi , Ookubo Soichiro , Utsunomiya Risa , Matsuba Teruaki , Fujita Jun-ichi
Published: June 2011

We found that low-energy electron irradiation combined with uniaxial tensile stress strongly enhanced the shrinkage of carbon nanotubes (CNTs). The shrinking maximized at 5 keV, although some believe that the low-energy electron irradiation from 1 to 30 keV using a scanning electron microscope hardly induces structural deformation of CNTs. Such shrunk CNTs showed periodic and zigzag folding of their sidewalls, resulting in about 90% shrinkage from the original length. Such deformation could be induced in either single- or multi-walled nanotubes (MWNTs). The surface area per unit volume drastically increased up to 560% when a tube shrunk to 10% of its original length, a phenomenon observed in the shrinkage of MWNTs.
Organic Electrolyte Based Pulsed Nanoplating and Fabrication of Carbon Nanotube Network Transistors
Authors: Kang Myung Gil , Hwang Dong Hoon , Kim Tae Geun , Hwang Jong Seung , Ahn Doyeol , Whang Dongmok , Hwang Sung Woo
Published: June 2011

The formation of gold nanocontacts was performed using a pulsed electrochemical plating technique. The effect of various plating variables on the surface roughness of the plated electrodes was studied in the high frequency regime where the reduction reaction of gold complex becomes the bottleneck process. We demonstrated the selective contact formation of single wall carbon nanotube network field effect transistors (FETs) with this technique. The fabricated FETs exhibit usual p-type behavior with the performance comparable to usual network FETs.
Fabrication of p–n–p Graphene Structure and Observation of Current Oscillation
Authors: Konishi Keita , Yoh Kanji
Published: June 2011

We have studied transport characteristics through a lateral p–n–p graphene structure with relatively wide n-channel gate length. The source-to-drain length, gate width and gate length were 4, 0.5, and 0.2 µm, respectively. Although the tunnel barrier thickness of 2000 Å was comparable to the estimated mean free path, the observed conductance oscillation due to Fabry–Pérot resonance clearly indicated Klein tunneling.
Nonvolatile Resistive Memory Device Based on Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) Thin Film for Transparent and Flexible Applications
Authors: Lee Jungmoo , Kim Ohyun
Published: June 2011

In this paper, a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) thin-film memory device with both top and bottom indium tin oxide (ITO) electrodes was fabricated and the feasibility of this device was verified. The device showed a bipolar switching property. A write-read-erase-read memory cycle test and a data retention test were performed under ambient conditions. The turn on/off process occurred owing to the reduction and oxidation mechanism of the PEDOT chain, and each interface influenced the on and off voltages. Lastly, the switching characteristic of the flexible memory device was investigated.
Development of Hybrid Photovoltaic Cells by Incorporating CuInS2 Quantum Dots into Organic Photoactive Layers
Authors: Nam Minwoo , Lee Sehan , Park Jaehyun , Kim Sang-Wook , Lee Kee-Keun
Published: June 2011

Hybrid photovoltaic (PV) cells containing CuInS2 quantum dots (CIS QDs) incorporated into organic PV layers were developed through a simple solution process. Four types of such cells were fabricated by blending poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM) and CIS QDs in weight ratios of 1:1:0, 1:1:0.2, 1:1:0.5, and 1:1:1. The hybrid PV cell with CIS QDs exhibited increased light absorption and greater quantum efficiency than the purely organic PV cell. In cell performance tests under an air mass (AM) 1.5 solar simulator, the short-circuit current of the hybrid cells with CIS QDs reached up to 10.12 mA/cm2; the corresponding power conversion efficiency was 2.76%, which was 13% higher than that of purely organic PV cells. This indicates that the CIS QDs function as an additional light absorber encouraging device performance improvement.
Novel Nanowire-Based Flip-Flop Circuit Utilizing Gate-Controlled GaAs Three-Branch Nanowire Junctions
Authors: Shibata Hiromu , Shiratori Yuta , Kasai Seiya
Published: June 2011

A novel set-reset flip-flop (SR-FF) circuit integrating gate-controlled GaAs three-branch nanowire junctions (TBJs) is designed, fabricated, and characterized. Fundamental logic gates including AND, NOT, and NAND are constructed using Schottky wrap gate (WPG)-controlled TBJs together with inverter circuits that have the same configuration. The present SR-FF circuit is simply designed using a pair of cross-coupled TBJ-based NAND gates. The circuit is successfully fabricated on a GaAs-based hexagonal nanowire network. Its correct operation with a voltage transfer gain larger than unity is demonstrated. Reduction of circuit area and possible operation speed are also discussed.
Single-Electron Stochastic Resonance Using Si Nanowire Transistors
Authors: Nishiguchi Katsuhiko , Fujiwara Akira
Published: June 2011

We demonstrate stochastic resonance (SR) with single electrons (SEs) using nanoscale metal–oxide–semiconductor field-effect transistors (MOSFETs). Input signal applied to a MOSFET modulates SE transport in an average manner based on nonlinear characteristics. On the other hand, an individual SE goes through the MOSFET in a completely random manner, which corresponds to shot noise. SEs transferred to a storage node are counted precisely by the other MOSFET and used as an output signal. The correlation between the input and output signals is improved by taking advantage of extrinsic noise as well as the intrinsic shot noise composed of SEs. It is confirmed that the shot-noise-assisted SR allows fast operation with a simple system. Pattern perception utilizing SR is also demonstrated.
Enhanced Optical and Electrical Properties of Inorganic Electroluminescent Devices Using the Top-Emission Structure
Authors: Kim Jin-Young , Jeong Taewon , Park Shang Hyeun , Bae Min Jong , Song Sunjin , Lee Jeonghee , Han Intaek , Jung Donggeun , Liu Chunli , Yu SeGi
Published: June 2011

Alternating current inorganic powder electroluminescence (EL) devices with a top-emission structure were fabricated on glass substrates to investigate the structural dependence on EL. The EL performance was examined by comparing the top-emission structure with the conventional EL device, i.e., the bottom-emission structure. High performance, such as 50 and 40% increases in efficiency and brightness, respectively, was achieved. This enhanced EL performance was attributed to the structural change in the EL device, leading to reduced optical loss and enhanced electric field applied to the phosphor.
Nickel Nanocrystals Embedded in Metal–Alumina–Nitride–Oxide–Silicon Type Low-Temperature Polycrystalline-Silicon Thin-Film Transistor for Low-Voltage Nonvolatile Memory Application
Authors: Wang Terry Tai-Jui , Liu Yu-Cheng , Wu Chien-Hung , Lu Tien-Lin , Hsieh Ing-Jar , Kuo Cheng-Tzu
Published: June 2011

In this work, a nickel nanocrystal (Ni-NC) assisted metal–alumina–nitride–oxide–silicon (MANOS) thin-film transistor (TFT) nonvolatile memory (NVM) was fabricated by a standard low temperature polycrystalline silicon (LTPS) TFT process. The size range and density of Ni-NCs were approximately 5–13 nm and 5 ×1011 cm-2, respectively. The programming/erasing (P/E) voltages are decreased down to -10 and +8 V, respectively, by the Fowler–Nordheim tunneling mechanism from gate injection. In this P/E voltage condition, a large memory window (∼4.2 V) was observed by current–voltage measurement. Then, the speed and voltages of P/E were measured and discussed completely. The data retention of the Ni-NC assisted MANOS-LTPS-TFT-NVM is extracted to be 1.62 V of memory window after 104 s.
Electrical Characteristics of WSi2Nanocrystal Capacitors with Barrier-Engineered High-k Tunnel Layers
Authors: Lee Hyo Jun , Lee Dong Uk , Kim Eun Kyu , You Hee-Wook , Cho Won-Ju
Published: June 2011

Nanocrystal-floating gate capacitors with WSi2nanocrystals and high-ktunnel layers were fabricated to improve the electrical properties such as retention, programming/erasing speed, and endurance. The WSi2nanocrystals were distributed uniformly between the tunnel and control gate oxide layers. The electrical performance of the tunnel barrier with the SiO2/HfO2/Al2O3(2/1/3 nm) (OHA) tunnel layer appeared to be better than that with the Al2O3/HfO2/Al2O3(2/1/3 nm) (AHA) tunnel layer. When ΔVFBis about 1 V after applying voltage at ±8 V, the programming/erasing speeds of AHA and OHA tunnel layers are 300 ms and 500 µs, respectively. In particular, the device with WSi2nanocrystals and the OHA tunnel barrier showed a large memory window of about 7.76 V when the voltage swept from 10 to -10 V, and it was maintained at about 2.77 V after 104cycles.
Tunnel Field-Effect Transistors with Extremely Low Off-Current Using Shadowing Effect in Drain Implantation
Authors: Mori Takahiro , Yasuda Tetsuji , Maeda Tatsuro , Mizubayashi Wataru , O'uchi Shin-ichi , Liu Yongxun , Sakamoto Kunihiro , Masahara Meishoku , Ota Hiroyuki
Published: June 2011

Tunneling field-effect transistors (TFETs) were investigated. To realize the potentially low off-current characteristics of the TFETs, the offset drain structure is preferred. We have proposed an oblique drain implantation process utilizing the shadowing effect to fabricate the offset drain, and the effectiveness was studied by simulation and experiment. Extremely low off-currents of 40 fA/µm for the P-TFET and 15 fA/µm for the N-TFET have been demonstrated experimentally.
Patterning Strategy for Monoelectronic Device Platform in a Complementary Metal Oxide Semiconductor Technology
Authors: Pauliac-Vaujour Sebastien , Wacquez Romain , Vizioz Christian , Chevolleau Thierry , Pierre Mathieu , Previtali Bernard , Comboroure Corinne , Bove Nadine , Roche Benoit , Vinet Maud , Jehl Xavier , Sanquer Marc , Sixt Pierre
Published: June 2011

We report a patterning strategy for building the first monoelectronic device complementary metal oxide semiconductor (CMOS)-compatible platform, including a single-electron transistor (SET) and multiple coupled quantum dots. Aggressive hybrid lithography (e-beam and deep UV are combined) and plasma etching are used to form adapted silicon active areas and gates, with a minimum size of 14 nm and a pitch of 80 nm after etching. These aggressive dimensions enable the study of double dots, a key structure for the more complex quantum circuits emerging now.
Characterization of Low-Frequency Noise in GaAs Nanowire Field-Effect Transistors Controlled by Schottky Wrap Gate
Authors: Miura Kensuke , Shiratori Yuta , Kasai Seiya
Published: June 2011

Low-frequency noise in GaAs-based nanowire field-effect transistors (FETs) controlled by a Schottky wrap gate (WPG) is investigated focusing on the size dependence of 1/fnoise and the basic behavior of a gentle slope of the noise spectrum at a relatively high frequency. 1/fnoise is found to systematically depend on the nanowire widthWand gate lengthLG, which is explained by the conventional flicker noise model. The evaluated flicker noise coefficientKFis on the order of 10-23V2F, comparable to that of Si metal–oxide–semiconductor (MOS) FETs. The gentle slope close to 1/f0.5frequently appears in the noise spectrum from the fabricated devices. Its intensity is found to be proportional to gate leakage current, suggesting that electrons flowing through the AlGaAs barrier layer induce generation-recombination (GR) noise in the gate region.
Thermal Stability of Pd Gate in Pseudomorphic InGaAs Heterostructures
Authors: Ishikura Tomotsugu , Cui Zhixin , Matsuda Takashi , Yoh Kanji
Published: June 2011

The characterization of InAs is known to have high spin–orbit interaction as well as high electron velocity, high sheet carrier density. In order to realize Datta–Das type spin field effect transistor (FET), it becomes crucial to develop thermally stable Schottky gate metal process for achieving a non-alloyed ohmic contact with ferromagnetic electrode after gate formation process. We have investigated Pd-gate deposited on In0.81Ga0.19As-based pseudomorphic heterostructures structure in order to check Pd as a good candidate for thermally stable Schottky gate by verifying good Schottky characteristics while maintaining good transport properties during heat treatment. Characteristics of Pd gate on InAlAs barrier layer was found to have Schottky barrier height of around 0.68 and less than 1.10 of ideality factor. Moreover Pd gate was found to endure higher heat treatment than Ti/Pt/Au gate or Ti/Au gate.
Fabrication of Metal Embedded Nano-Cones for Single Quantum Dot Emission
Authors: Huh Jae-Hoon , Hermannstädter Claus , Akahane Kouichi , Sasakura Hirotaka , Jahan Nahid A. , Sasaki Masahide , Suemene Ikuo
Published: June 2011

High efficiency in the extraction, transmission and detection of single and entangled photons is one of the most significant factors to provide general usage and to suppress the bit-error rate in optical communication networks. We propose and realize metal embedded nanostructures with quantum dots (QDs) as photon sources to meet these challenges on the emitter side. Advantages of the process are the ability of fast nanometer-scale fabrication and the high reproducibility and yield. Mesas with typical taper angles of 20–30° and diameters between 100 nm and 1 µm were produced; these nanostructures are referred to as “cones” in this work. The dependence of the taper angle on the composition of the etched cone material is discussed, focusing on the contribution of indium. The nano-cones used as photon sources were embedded in highly reflective metal and turned upside down to provide efficient and partly directed photon extraction. We present the selection of 1.35 µm photons emitted from a single QD as a result of embedding only a small number of dots in a nanometer sized cone.
Orientation-Controlled and Long-Range-Ordered Self-Assembled Nanodot Array for Ultrahigh-Density Bit-Patterned Media
Authors: Akahane Takashi , Huda Miftakhul , Tamura Takuro , Yin You , Hosaka Sumio
Published: June 2011

In this study, we investigated the control of the orientation and ordering of self-assembled nanodots from a block copolymer (BCP) with the help of a guide pattern created by electron beam (EB) drawing. The guide pattern consisted of a post lattice and guide lines. The former is used to enable self-assembled nanodots from the BCP to be regularly arranged, while the latter is used to control the orientation of the nanodot arrays. It was demonstrated that the combined guide pattern was effective for controlling the BCP dot array to achieve long-range ordering and controlled orientation.
Annealing Effect of W Incorporated Diamond-Like Carbon Fabricated by Ga Focused Ion Beam Chemical Vapor Deposition
Authors: Wada Akira , Suzuki Tsuneo , Niibe Masahito , Ito Haruhiko , Kanda Kazuhiro
Published: June 2011

The effects of thermal annealing of W incorporated diamond-like carbon (W-DLC) films fabricated with focused ion beam chemical vapor deposition (FIB-CVD) were investigated using X-ray absorption fine structure near the carbon K-edge (C-K NEXAFS) and the combination of Rutherford backscattering (RBS) and elastic recoil detection analysis (ERDA). W-DLC films were annealed for 32 h at temperatures, T
a, between 673 and 1073 K. Comparing the T
a dependences of Ga and H contents obtained from RBS-ERDA and the sp2/(sp2 + sp3) ratios from C-K NEXAFS, it was found that even a trace amount of W incorporation into DLC films fabricated by Ga+ FIB-CVD may cause a significant sp3 →sp2 structural change.
Inductively Coupled Plasma Etching of Silicon Using Solid Iodine as an Etching Gas Source
Authors: Matsutani Akihiro , Ohtsuki Hideo , Koyama Fumio
Published: June 2011

We investigated the Si dry etching process by inductively coupled plasma (ICP) using solid I2 as an etching gas source. A vertical etching profile and a smooth etched surface, which satisfy the requirements for optical device fabrication, were obtained at a relatively higher substrate temperature. The etching rate of Si was approximately 90 nm/min at 1 Pa and at an ICP/bias RF power of 300/100 W. The I2 plasma etching technique is a very simple C-, CF-, and H-free process. In addition, we believe that this proposed process is useful for fabricating Si-based optical devices, such as photonic crystals, narrow optical waveguides, and micro-electro-mechanical systems (MEMS).
Morphological and Electrical Properties of Self-Textured Aluminum-Doped Zinc Oxide Films Prepared by Direct Current Magnetron Sputtering for Application to Amorphous Silicon Solar Cells
Authors: Kim Young Baek , Choi Bum Ho , Lee Jong Ho , Kim Jin Hyeok
Published: June 2011

Self-textured Al-doped zinc oxide (AZO) transparent conducting oxide (TCO) layers were grown by DC magnetron sputtering, and their morphological and electrical properties were investigated. The self-textured AZO layers were fabricated by controlling the deposition conditions, without employing wet or dry etching for surface texturing. The polycrystalline AZO layers with a high surface roughness (42 nm) were grown on a glass substrate at various DC plasma power. The lowest sheet resistance was 3.7×10-4Ω cm and the highest carrier mobility obtained was 30 cm2V-1s-1, which are comparable to those of chemically textured AZO layers. The electrical and optical characteristics of the self-textured AZO films are comparable to those of wet-etched AZO films that were etched using the conventional HCl solution. Our study suggests a possible way to inexpensively fabricate amorphous silicon thin-film solar cells.
Fabrication of Polymer Micropyramid/Nanolens Combined Structures Using Microstructured Nanodimpled Aluminum Stamp
Authors: Cha Kyoung Je , Lee Bong-Kee , Kim Dong Sung
Published: June 2011

In this study, we present an efficient and low-cost fabrication technique of polymer micropyramid/nanolens combined structures (MPNL-CS). The present fabrication technique is based on hot embossing of polymer substrates using a microstructured nanodimpled aluminum (MNA) stamp. The MNA stamp for the replication of polymer MPNL-CS was realized by combining three fabrication steps. (1) A nickel stamp with micropyramid array was manufactured by electroforming onto an anisotropically wet-etched silicon substrate. (2) A reverse micropyramid cavity array was transcribed on an electropolished aluminum substrate by microindentation with the nickel stamp. (3) The MNA stamp was finally realized by forming nanodimple arrays onto the reverse micropyramid array on the aluminum substrate through an electrochemical oxidation (anodization) process. In the final step, we have optimized the electrochemical oxidation process to realize nanodimple arrays at the sharp edge reverse micropyramid without defects. The MPNL-CS were successfully replicated on polymer substrates via a hot embossing process with the fabricated MNA stamp through investigating the effect of embossing pressure on the transcription quality of MPNL-CS. The present fabrication technique can be widely applied to the realization of various types of three-dimensional micro/nano combined structures.