bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of Source/Drain Doping Level of Carbon Nanotube Field-Effect Transistors to Suppress OFF-State Leakage Current while Keeping Ideal ON-State Current
Authors: Algul Berrin Pinar , Uchida Ken
Published: June 2012

The effects of doping concentration variation in source/drain junctions on the characteristics of carbon nanotube field-effect transistors (CNFETs) have been studied in order to realize high performance CNFETs, where suppressed OFF-state leakage current and ideal maximum ON-state current were obtained. The characteristics of CNFETs with doped source/drain regions have been studied by solving the Poisson and carrier transport equations self-consistently. The transmission coefficient through the bandgap (Eg) has been calculated using the Wentzel–Kramers–Brillouin (WKB) approximation in order to take into account the band-to-band tunneling (BTBT) leakage current. The doping is characterized by the Fermi level (Ed) in a doped region which is measured from the conduction band edge. In this study, it is demonstrated that, when the power supply voltage (Vdd) is greater than the bandgap of carbon nanotubes (CNTs), optimized doping levelEdofVdd-Egshows the lowest OFF-state current (IOFF). On the other hand, whenVddis smaller thanEg,IOFFmonotonically decreases asEddecreases, although the aggressively lowered doping concentration results in lower ON-state current. We also demonstrated that CNFETs with low source/drain doping concentration exhibit current saturation at higher gate voltages. The current saturation results from the fact that the injection velocity to the channel is limited by the velocity in the source region which is determined by the source doping level. We showed that, in order to avoid the current saturation, doping level should be higher than 0.3 eV, regardless of carbon nanotube diameter.
Single-String Carbon Nanotube Field Effect Transistors Fabricated by Two-Step Dielectrophoresis
Authors: Kim Tae Geun , Hwang Jong Seung , Yu Yun Seop , Kang Myung Gil , Hwang Sung Woo
Published: June 2012

Carbon nanotube field effect transistors (CNT FETs) with a long, single channel are an essential ingredient for gas and bio sensors, because a single spot modification of the channel can change the conductivity of the whole device. Herein, the two-step dielectrophoresis (DEP) technique was used to fabricate single string, single wall CNT FETs with a length longer than 10 µm. The single string FET showed an on/off ratio and transconductance which are larger than those of the network FET on the same substrate. The observed characteristics were explained by a circuit simulation. We also demonstrated that our method could be applied to flexible substrates.
Effects of Aluminium Doping and Electrode Distance on the Performance of Aligned Zinc Oxide Nanorod Array-Based Ultraviolet Photoconductive Sensors
Authors: Mamat Mohamad Hafiz , Khusaimi Zuraida , Zahidi Musa Mohamed , Bakar Suriani Abu , Yusop Mohd Zamri , Tanemura Masaki , Mahmood Mohamad Rusop
Published: June 2012

Metal–semiconductor–metal (MSM) ultraviolet (UV) photoconductive sensors were fabricated using undoped and aluminium (Al)-doped zinc oxide (ZnO) nanorod arrays prepared via the sonicated sol–gel immersion method. Notably, the nanorod diameter decreased with Al-doping, varying in the size range of 30 to 70 nm, compared with undoped ZnO, which had a size range of 80–120 nm. The Al-doped nanorod arrays exhibited optical properties superior to those of the undoped ZnO, with an average transmittance of 85% in the visible region; the Al-doped arrays also showed good UV absorption properties. Photoluminescence measurements indicate that the suppression of defects was observed for the Al-doped ZnO nanorod, as shown by a biggerIUV/Ivisof 1.24 compared to that of undoped ZnO (0.97). According to the experimental results, the UV responsivity was significantly improved by the Al-doping, with the highest value of 373 A/W obtained at an inter-electrode distance of 0.07 mm under UV light (365 nm, 750 µW/cm2) with a 10 V bias. In addition, the responsivity of the UV sensor also significantly improved when the inter-electrode distances were reduced from 2.00 to 0.07 mm.
Novel Protruded-Shape Unipolar Resistive Random Access Memory Structure for Improving Switching Uniformity through Excellent Conductive Filament Controllability
Authors: Ryoo Kyung-Chang , Kim Sungjun , Oh Jeong-Hoon , Jung Sunghun , Jeong Hongsik , Park Byung-Gook
Published: June 2012

Resistive random access memory (RRAM) with a new structure which can effectively control switching area and electric field is proposed. It has been verified that the decrease in area of resistive material with the new structure increases electric field of switching area, and that such increased electric field makes initial forming at unipolar switching rather easier, resulting in effective decrease in forming voltage. Also, as the area in switching area is effectively reduced, decrease in reset current and set voltage in a limited area has also been verified. Excellent resistive switching characteristics are possible by decrease of conductive filament (CF) area in our structure. Random circuit breaker (RCB) simulation model which can effectively explain percolation switching similar to unipolar switching verifies such structural effect.
Design Guideline of Si-Based L-Shaped Tunneling Field-Effect Transistors
Authors: Kim Sang Wan , Choi Woo Young , Sun Min-Chul , Kim Hyun Woo , Park Byung-Gook
Published: June 2012

In this work, novel L-shaped tunneling field-effect transistors (TFETs) have been proposed. The proposed L-shaped TFETs feature higher on-current (I
on) and lower subthreshold swing (SS) than conventional TFETs. It is because L-shaped TFETs have large cross-sectional area of band-to-band tunneling junction which is perpendicular to the channel direction and their tunneling barrier width (W
t) is defined by the length of an intrinsic silicon region. As the devices are based on the Si without any other material, it can be fabricated with well-established Si process technology. In addition, it can moderate some issues come from scaling down and enlarging tunneling area due to its mesa structure. Simulation results have confirmed the superiority of L-shaped TFETs over conventional TFETs. Additionally, the effect of some device parameters on device performance has been investigated for the clear verification of its operation mechanism and the optimization.
Experimental Test of Landauer's Principle at the Sub-kBT Level
Authors: Orlov Alexei O. , Lent Craig S. , Thorpe Cameron C. , Boechler Graham P. , Snider Gregory L.
Published: June 2012

Landauer's principle connects the logical reversibility of computational operations to physical reversibility and hence to energy dissipation, with important theoretical and practical consequences. We report the first experimental test of Landauer's principle. For logically reversible operations we measure energy dissipations much less than k
B
Tlog
2, while irreversible operations dissipate much more than k
B
Tlog
2. Measurements of a logically reversible operation on a bit with energy 30 k
B
T yield an energy dissipation of 0.01 k
B
T.
Heterojunction Photodiodes Based on Honeycomb Structures for Ultraviolet Detection
Authors: Tsai Shu-Yi , Lee Jian-Hong , Hon Min-Hsiung
Published: June 2012

The p-NiO/n-ZnO heterojunction device based on honeycomb structures was fabricated by RF sputtering method. The structural and optical properties of the p-NiO/n-ZnO heterojunction were characterized by X-ray diffraction (XRD), UV–visible spectroscopy, field-emission scanning electron microscope (FE-SEM), and current–voltage (I–V) photocurrent measurements. The XRD spectra indicate that ZnO films were of hexagonal wurtzite structures, preferentially (002) oriented. SEM show that the spherical polystyrene stacking on hexagonal close-packing lattice structure. Optical measurements showed that the honeycomb structures exhibited the maximum haze values up to 50% at wavelength range 380–800 nm. TheI–Vcurve of the heterojunction demonstrates obvious rectifying diode behavior in a dark environment. The lowest of leakage current is 8.23×10-9A/cm2for p-NiO/n-ZnO heterojunction device.
Speed Enhancement of WSi2 Nanocrystal Memory with Barrier-Engineered Si3N4/HfAlO Tunnel Layer
Authors: Lee Dong Uk , Lee Hyo Jun , Kim Eun Kyu , You Hee-Wook , Cho Won-Ju
Published: June 2012

WSi2 nanocrystal nanofloating gate capacitors with multistacked Si3N4/HfAlO high-k tunnel layers were fabricated and their electrical properties were characterized. The thicknesses of the Si3N4 and HfAlO tunnel layers were 1.5 and 3 nm, respectively. The asymmetrical Si3N4/HfAlO tunnel layer was modulated to enhance the tunneling efficiency to improve program and erase speeds. The flat-band voltage shift of the WSi2 nanofloating gate capacitor was about 7.2 V after applied voltages swept were from -10 to 10 V and from 10 to -10 V. Then, the program/erase speeds and the memory window under programming and erasing at ±7 V were 300 µs and 1 V, respectively. As demonstrated in the results, the WSi2 nanocrystal memory with barrier-engineered Si3N4/HfAlO layers could be applied to enhance the program and erase speeds at low operating voltages for nanocrystal nonvolatile memory application.
Vertical-Electrical-Field-Induced Control of the Exciton Fine Structure Splitting in GaAs Island Quantum Dots for the Generation of Polarization-Entangled Photons
Authors: Ghali Mohsen , Ohtani Keita , Ohno Yuzo , Ohno Hideo
Published: June 2012

We report on the polarization-resolved photoluminescence spectroscopy of a single GaAs island quantum dot (QD) formed by the monolayer thickness fluctuation of a GaAs/Al0.3Ga0.7As quantum well and embedded in a Schottky device. By applying a forward vertical electric field between the top metallic contact and the sample substrate we suppress the QD excitonic fine structure splitting to ≈1.5 µeV. These results open the door toward the possible generation of visible entangled photon pairs using GaAs island QDs.
Control Theory of Near-Field Optical Energy Transfer in One-Dimensional Waveguide Consisting of Metallic Nanoparticles by Vibrating External Field
Authors: Tanaka Shin , Hattori Hironori , Hidaka Shimpei , Vy Nguyen Duy , Iida Takuya
Published: June 2012

We have theoretically investigated the properties of optical energy transfer (OET) along an array of metallic nanoparticles (MNPs) on a one-dimensional chain consisting of organic materials under the local excitation by near-field light in these states. Remarkably, under the telescopic motion of organic chain induced by an external field resonant with its vibration, we have clarified that the efficiency of OET can be drastically modulated for particular wavelength region depending on the size of MNPs. Obtained results would provide an unconventional way to wavelength-tunable OET and signal processing.
Fabrication and Characterization of NOR-Type Tri-Gate Flash Memory with Improved Inter-Poly Dielectric Layer by Rapid Thermal Oxidation
Authors: Kamei Takahiro , Liu Yongxun , Matsukawa Takashi , Endo Kazuhiko , O'uchi Shinichi , Tsukada Junichi , Yamauchi Hiromi , Ishikawa Yuki , Hayashida Tetsuro , Sakamoto Kunihiro , Ogura Atsushi , Masahara Meishoku
Published: June 2012

Floating-gate (FG)-type tri-gate flash memories with an improved inter-poly dielectric (IPD) layer have been successfully fabricated by introducing a newly developed rapid thermal oxidation (RTO) process, and their NOR-mode operation including threshold voltage (V
t) variations before and after one program/erase (P/E) cycle have been systematically investigated. It was experimentally confirmed that the gate breakdown voltage (BVg) is greatly increased from 12 to 19 V by introducing the RTO process thanks to the high quality and thin thermal silicon dioxide (SiO2) formation on the FG surface and etched edge regions, which effectively blocks the leakage pass of the IPD layer. A source–drain (SD) breakdown voltage (BVDS) as high as 4.5 V was obtained even when the gate length (L
g) was as small as 117 nm. It was also experimentally confirmed that the memory window increases with increasing gate voltage (V
g) in NOR-mode programming thanks to the increased efficiency of channel hot electron (CHE) injection. The developed tri-gate flash memory with improved IPD layer is useful for the further scaling of NOR-type flash memory.
Extraction Method for Substrate-Related Components of Vertical Junctionless Silicon Nanowire Field-Effect Transistors and Its Verification on Radio Frequency Characteristics
Authors: Shin Sunhae , Kang In Man , Kim Kyung Rok
Published: June 2012

In this paper, we propose a radio-frequency (RF) model and parameter extraction method for vertical junctionless silicon nanowire (VJL SNW) field-effect transistors (FETs) using three-dimensional (3D) device simulation. We introduce the substrate-related components such as the substrate resistance (R
sub) and drain-to-substrate capacitance (C
sub), and evaluate the RF performance such as f
t, f
max, gate input capacitance, and transport time delay. A quasi-static (QS) RF model has been used in simulation program with integrated circuit emphasis (SPICE) circuit simulator to simulate VJL SNW FETs with RF parameters extracted from 3D device simulated Y-parameters. We confirmed the validity of our RF model by the well-matched results between HSPICE and 3D device simulation in terms of the Y-parameters and the S
22-parameter up to 100 GHz.
Carrier Transport Mechanisms of the Programming and Retention Characteristics for TaN–Al2O3–Si3N4–SiO2–Si Flash Memory Devices
Authors: Kim Dong Hun , You Joo Hyung , Lee Dea Uk , Kim Tae Whan , Lee Keun Woo
Published: June 2012

Carrier transport mechanisms of the programming and retention characteristics for TaN–Al2O3–Si3N4–SiO2–Si (TANOS) flash memory devices were theoretically investigated by using the one-band model taking into account Shockley–Reed statistics, the continuity equation, and the Pöisson equation. The simulation results showed that the dominant tunneling mechanism during the programming operation in the TANOS memory devices was varied from the Fowler–Nordheim (FN) tunneling to the direct tunneling (DT) processes and from the DT to the modified FN tunneling processes. The dominant tunneling mechanism in TANOS memory devices at the retention operation mode without gate bias voltage was DT process. Simulation results showed that the retention time increased with increasing tunneling oxide thickness. The threshold voltage shifts, as determined from the theoretical calculation during the programming and retention process, were in reasonable agreement with the threshold voltage shifts obtained from experimental results.
Evaluation of Chemical Bonding Features and Resistance Switching Behaviors of Ultrathin Si Oxide Dielectric Sandwiched Between Pt Electrodes
Authors: Ohta Akio , Goto Yuta , Nishigaki Shingo , Murakami Hideki , Higashi Seiichiro , Miyazaki Seiichi
Published: June 2012

We investigated the chemical bonding features and resistance switching properties of ultrathin Si-rich oxides sandwiched between Pt electrodes to evaluate the feasibility of SiO
x
-based resistance random access memories (ReRAMs). In the early stages of SiO
x
deposition on Pt by radio-frequency (RF) sputtering in Ar + O2 gas mixture at 300 °C, the formation of a PtO
x
layer at the interface between SiO
x
and the Pt bottom electrode was observed. This interfacial PtO
x
layer decreased in thickness with increasing SiO
x
thickness. With decreasing as-deposited SiO
x
thickness down to 3.3 nm, the initial electrical state changed from the high resistance state (HRS) to the low resistance state (LRS), and resistance switching behavior was observed without the forming process. To gain a better understanding of the resistance switching mechanism, especially the role of oxygen deficiency in the SiO
x
network, we investigated the impact of O2 annealing after SiO
x
deposition on the switching behavior. The resistance switching behaviors were barely detectable for the samples at O2 annealing temperatures of over 500 °C. The results imply that the oxygen vacancies in the SiO
x
play an important role in resistance switching.
Thickness-Dependent Characteristics of Aluminium-Doped Zinc Oxide Nanorod-Array-Based, Ultraviolet Photoconductive Sensors
Authors: Mamat Mohamad Hafiz , Ishak Nurul Izzah , Khusaimi Zuraida , Zahidi Musa Mohamed , Abdullah Mohd Hanapiah , Muhamad Salina , Sin Nor Diyana Md , Mahmood Mohamad Rusop
Published: June 2012

Aluminium (Al)-doped zinc oxide (ZnO) nanorod arrays were prepared on a seed-layer-coated glass substrate by a sonicated sol–gel immersion method. We have shown, for the first time, that the thickness of the nanorod arrays can be increased incrementally without greatly affecting the diameter of the nanorods, by increasing the number of immersions. The field-emission scanning electron micrographs and thickness measurements revealed that the nanorods had diameters within the range from 40 to 150 nm and thicknesses from 629 to 834 nm with immersion times ranging from 1 to 5 h. The photoluminescence (PL) spectra revealed that the ZnO nanorod quality was enhanced with long immersion times as shown by an improvement in the ratio of the UV peak intensity to the visible emission peak intensity, or I
UV/I
vis. The thickness-dependent characteristic of Al-doped ZnO nanorod-array-based, UV photoconductive sensors was studied; minimising the thickness of the nanorod arrays was found to provide high responsivity and good performance. Our experiments showed that a decrease in the thickness of the nanorod arrays improved the responsivity and response time of the UV sensors, with a maximum responsivity of 2.13 A/W observed for a 629-nm-thick nanorod film.
Epitaxial-Template Structure Utilizing Ge-on-Insulator Stripe Arrays with Nanospacing for Advanced Heterogeneous Integration on Si Platform
Authors: Hashim Abdul Manaf , Anisuzzaman Mohamad , Muta Shunpei , Sadoh Taizoh , Miyao Masanobu
Published: June 2012

A possible Ge-on-insulator (GOI) structure, namely, stripe arrays with nanospacing, was proposed as a promising epitaxial template structure for the Ge epitaxial layer. Agglomeration-free single-crystalline GOI stripe arrays with thickness of 50 nm and spacing down to 0.5 µm were successfully grown by the Si-seeded rapid-melting growth technique. The growth of GOI stripe arrays with a spacing of 0.1 µm was not achieved owing due to the severe agglomeration of Ge during the heat treatment. This may be due to the small adhesion area of the capping layer between the stripes where it could not withstand the force caused by Ge agglomeration. From the electron backscattering diffraction (EBSD) measurement, the rotational growth was confirmed by the observation of various orientations when the thickness of the Ge layer was reduced to 20 nm. This is probably due to the decrease in the bulk effects that basically act to prevent the slip of lattice planes. These preliminary results provide a breakthrough towards the realization of heterogeneous integration on Si platforms with multifunctionalities.
Fabrication of Nanocone Subwavelength Antireflection Structures on Quartz Substrates
Authors: Tang Yu-Hsiang , Huang Mao-Jung , Su Jien-Yin , Shiao Ming-Hua
Published: June 2012

This study combined self-assembled nanosphere lithography (SANL) and inductively coupled plasma reactive ion etching (ICP-RIE) for fabricating orderly arranged quartz nanocone arrays. We reported a simple process for successfully fabricating quartz subwavelength structure (SWS) substrate, achieving broadband antireflection (AR) and increasing the transmittance of incident light across the quartz glass. This combined process arranged a monolayer of nanospheres onto 2×2 cm2 test specimen. In addition, we evaluated various etching times of ICP-RIE for producing SWS surfaces, which resulted in various specific surface areas for the quartz substrates. Consequently, smoothly tapered SWS surfaces with a width of 105 nm and a height of 190 nm could be produced on quartz wafer. This fabricated SWS decreased the surface reflectance to less than 6.75% in the visible light spectrum.
Electronic State Formation by Surface Atom Removal on a MoS2 Surface
Authors: Kodama Nagisa , Hasegawa Tsuyoshi , Tsuruoka Tohru , Joachim Christian , Aono Masakazu
Published: June 2012

Removal of a sulfur atom from the topmost layer of a MoS2 surface forms electronic states in the band-gap of an inherently semiconducting material. Scanning tunneling spectroscopy measured at sulfur vacancies, which were made by sulfur atom removal using the high electrical field of a scanning tunneling microscope, shows stepwise increases in the current in a band-gap region, corresponding to the formation of electronic states. The periphery of sulfur vacancies also show linear current–voltage (I/V) characteristics, suggesting that electronic states in the periphery are modified due to the removal of sulfur atoms.
Additional Electrochemical Treatment Effects on the Switching Characteristics of Anodic Porous Alumina Resistive Switching Memory
Authors: Otsuka Shintaro , Takeda Ryouta , Furuya Saeko , Shimizu Tomohiro , Shingubara Shouso , Iwata Nobuyuki , Watanabe Tadataka , Takano Yoshiki , Takase Kouichi
Published: June 2012

We have investigated the current–voltage characteristics of a resistive switching memory (ReRAM), especially the reproducibility of the switching voltage between an insulating state and a metallic state. The poor reproducibility hinders the practical use of this memory. According to a filament model, the variation of the switching voltage may be understood in terms of the random choice of filaments with different conductivities and lengths at each switching. A limitation of the number of conductive paths is expected to lead to the suppression of the variation of switching voltage. In this study, two strategies for the limitation have been proposed using an anodic porous alumina (APA). The first is the reduction of the number of conductive paths by restriction of the contact area between the top electrodes and the insulator. The second is the lowering of the resistivity of the insulator, which makes it possible to grow filaments with the same characteristics by electrochemical treatments using a pulse-electroplating technique.
Silver Embedded Nanomesas as Enhanced Single Quantum Dot Emitters in the Telecommunication C Band
Authors: Huh Jae-Hoon , Hermannstädter Claus , Akahane Kouichi , Jahan Nahid A. , Sasaki Masahide , Suemune Ikuo
Published: June 2012

We use high-density InAs quantum dots, which were grown by molecular beam epitaxy on InP(311)B substrates, as photon sources in the telecommunication C band at approximately 1.55 µm. To select a small numbers of dots, we fabricate sub-micrometer sized mesas by electron beam lithography and reactive ion etching. The benefit of using high-density quantum dot samples is that at least one optically active quantum dot can be expected in every single mesa. We show that the etching rate and resulting mesa shape of the In0.53Al0.22Ga0.25As epitaxial layer can be varied with the chamber pressure during the etching process. Furthermore, under constant pressure and with increasing etching time, the sequential etching of the epitaxial layer and the underneath substrate leads to a significant modification in the mesa shape, too. We demonstrate that the isolation of a small number of quantum dots within one mesa results in the appearance of single quantum dot emission with a narrow line width and minimal spectral overlap between different emission lines. We moreover present significant enhancement of the luminescence collected from single dots in silver-embedded nanomesas when compared with as-etched mesas.
Two-Color Photoexcitation in a GaNAs/AlGaAs Quantum Well Solar Cell
Authors: Elborg Martin , Jo Masafumi , Ding Yi , Noda Takeshi , Mano Takaaki , Sakoda Kazuaki
Published: June 2012

We demonstrate an efficient two-color photoexcitation process in a GaNAs/AlGaAs multiple quantum well (MQW) solar cell. The introduction of N into the GaAs MQW induces a marked reduction in bandgap energy, forming a large conduction band offset, and the formation of localized states. Owning to this deep confinement, the thermal escape of photogenerated carriers from the QWs is greatly suppressed even at room temperature, resulting in a reduction in photocurrent. An additional photocurrent is generated by a two-color absorption process of sub-bandgap photons.
Fabrication and Electrochemical Characterization of Nanoporous Silicon Electrode for Amperometric Urea Biosensor
Authors: Yun Donghwa , Song Min-Jung , Hwang Sungwoo , Hong Suk-In
Published: June 2012

We describe a new type of biosensor that employs a modified gold electrode based on nanoporous silicon (NPSi) for the electrochemical detection of urea. Urease (Urs) was covalently immobilized onto an Au/NPSi electrode functionalized with 3-mercaptopropionic acid (3-MPA). Amperometric calibration curves for both NPSi and planar silicon (PLSi)-based urea sensitive electrodes were compared in the range of 0.3 to 4.5 mM urea concentrations. The Michaelis–Menten constant (K
m) was determined using the amperometric method. The electrochemical active area (A
ea) of the 3-MPA/Au/NPSi electrode was evaluated using cyclic voltammetry (CV) and the result was compared with the 3-MPA/Au/PLSi electrode. Measured sensitivity of the Urs/SAMs/Au/NPSi electrode is ca. 2.05 µA mM-1 cm-2 and that of the Urs/SAMs/Au/PLSi electrode is ca. 1.10 µA mM-1 cm-2. About 1.8 times of sensitivity increase is obtained in the Au/NPSi electrode.
Photoluminescence and X-ray Absorption Fine Structure Analysis of Sm-Doped TiO2Thin Films
Authors: Sakurai Junpei , Harako Susumu , Ohtsuki Takuya , Komuro Shuji , Hirao Norie , Kasahara Rei , Zhao Xinwei
Published: June 2012

The local structure of samarium-doped titanium dioxide (TiO2:Sm) thin films fabricated by laser ablation and post annealing has been investigated by Sm L III-edge X-ray absorption fine structure (XAFS) analysis using a synchrotron radiation. The TiO2:Sm samples at annealing temperatures lower than 1000 °C showed an anatase (A-)TiO2:Sm crystal structure and transferred into a rutile (R-)TiO2:Sm phase at annealing temperature of 1100 °C. All the A-TiO2:Sm phase samples showed intense Sm-related photoluminescence (PL) at room temperature. It was shown that the samples which showed intense PL have shorter coordination distance for the first nearest neighbor of Sm than that of the samples which did not show PL after the crystal phase transition.
Differential-Mode Biosensor Using Dual Extended-Gate Metal–Oxide–Semiconductor Field-Effect Transistors
Authors: Choi Jinhyeon , Lee Hee Ho , Ahn Jungil , Seo Sang-Ho , Shin Jang-Kyoo
Published: June 2012

In this paper, we present a differential-mode biosensor using dual extended-gate metal–oxide–semiconductor field-effect transistors (MOSFETs), which possesses the advantages of both the extended-gate structure and the differential-mode operation. The extended-gate MOSFET was fabricated using a 0.6 µm standard complementary metal oxide semiconductor (CMOS) process. The Au extended gate is the sensing gate on which biomolecules are immobilized, while the Pt extended gate is the dummy gate for use in the differential-mode detection circuit. The differential-mode operation offers many advantages such as insensitivity to the variation of temperature and light, as well as low noise. The outputs were measured using a semiconductor parameter analyzer in a phosphate buffered saline (PBS; pH 7.4) solution. A standard Ag/AgCl reference electrode was used to apply the gate bias. We measured the variation of output voltage with time, temperature, and light intensity. The bindings of self-assembled monolayer (SAM), streptavidin, and biotin caused a variation in the output voltage of the differential-mode detection circuit and this was confirmed by surface plasmon resonance (SPR) experiment. Biotin molecules could be detected up to a concentration of as low as 0.001 µg/ml.
Synthesis of TiO2Nanowires via Hydrothermal Method
Authors: Nor Asiah Mohd , Achoi Mohd Faizal , Mamat Mohamad Hafiz , Zabidi Musa Mohamed , Abdullah Saifollah , Mahmood Mohamad Rusop
Published: June 2012

Titanium dioxide (TiO2) nanowires have been successfully synthesized by a simple, rapid, inexpensive, and novel approach based on a hydrothermal method. The use of hydrothermal treatment on TiO2nanopowder as a precursor with highly concentrated sodium hydroxide for 6 h produced a novel nanostructure of TiO2nanowires. The field-emission scanning electron microscopy (FESEM) image shows that the synthesized TiO2nanowires are very abundant in quantity with diameters ranging from 8.0–14 nm and are extra long. X-ray diffraction (XRD) result indicates that the synthesized TiO2nanowires are mainly composed of anatase phase with a minor of rutile phase. These properties of nanowires promise a broad range of applications in electronic devices.
Carrier Transport Mechanisms of Organic Bistable Devices Fabricated Utilizing Hybrid C60/Poly(methyl methacrylate) Nanocomposites
Authors: Yoo Chan Ho , Ko Seong Hoon , Kim Tae Whan
Published: June 2012

Organic bistable devices (OBDs) based on nanocomposites consisting of C60embedded in the poly(methyl methacrylate) (PMMA) layer were fabricated by using a spin coating method. The current density–voltage (J–V) curves of the Al/C60embedded in PMMA layer/indium–tin-oxide devices exhibited an electrical bistability with a low-conductivity state, a transition state, and a high-conductivity state. TheJ–Vcurves for OBDs containing hybrid C60and PMMA except a low voltage range were reasonably fitted by using the space-charge-limited current conduction model. The trapped electron densities of the OBDs were attributed to the space charge relative to the internal electric field.
Oxygen Vacancy Chain Formation in TiO2 under External Strain for Resistive Switching Memory
Authors: Yoo Dong Su , Ahn Kiyong , Cho Sung Beom , Lee Minho , Chung Yong-Chae
Published: June 2012

The electronic structure and vacancy formation energy of rutile TiO2 with ordered oxygen vacancies were calculated using the density functional theory with on-site Coulomb corrections between Ti 3d orbital and O 2p orbital (LDA+Ud+Up). The calculated band gaps are about 3 eV, using LDA+Ud+Up, and a hybrid functional proposed by Heyd–Scuseria–Ernzerhog. The ordered oxygen vacancies were introduced along the [001] direction within a 3×3×4 supercell of rutile TiO2-x
that consisted of 72 Ti and 136 O atoms. Biaxial strain was induced in the rutile TiO2 along the x- and y-directions up to ±5%. The lowest formation energy of ordered oxygen vacancies was found in 5% compressive strain and deemed as a thermodynamically favorable structure.
Optical Studies of GaAs Nanowires Grown on Trenched Si(001) Substrate by Cathodoluminescence
Authors: Lee Ling , Chien Kun-Feng , Fan Wen-Chung , Chou Wu-Ching , Ko Chih-Hsin , Wu Cheng-Hsien , Lin You-Ru , Wan Cheng-Tien , Wann Clement H. , Hsu Chao-Wei , Chen Yung-Feng , Su Yan-Kuin
Published: June 2012

The strains in GaAs nanowires, which were grown from 1700- to 80-nm-wide trenches on the Si(001) wafer with SiO2masks, were investigated by cathodoluminescence. For 1700- to 500-nm-wide trenches, the in-plane tensile strain at 15 K decreases with the decreasing trench width. The strain increases abruptly when the trench width is 300 nm, and then decreases as the trench width is further decreased. The results revealed that the stress induced by the SiO2sidewalls dominates when the width is less than the depth of the trench. This approach provides an effective technique to measure the strain of a single nanowire and helps for the demonstration of selectively-grown GaAs with a designed strain.
Highly Sensitive Detection of Target Biomolecules on Cell Surface Using Gold Nanoparticle Conjugated with Aptamer Probe
Authors: Kim Hyonchol , Terazono Hideyuki , Hayashi Masahito , Takei Hiroyuki , Yasuda Kenji
Published: June 2012

A method of gold nanoparticle (Au NP) labeling with backscattered electron (BE) imaging of field emission scanning electron microscopy (FE-SEM) was applied for specific detection of target biomolecules on a cell surface. A single-stranded DNA aptamer, which specifically binds to the target molecule on a human acute lymphoblastic leukemia cell, was conjugated with a 20 nm Au NP and used as a probe to label its target molecule on the cell. The Au NP probe was incubated with the cell, and the interaction was confirmed using BE imaging of FE-SEM through direct counting of the number of Au NPs attached on the target cell surface. Specific Au NP-aptamer probes were observed on a single cell surface and their spatial distributions including submicron-order localizations were also clearly visualized, whereas the nonspecific aptamer probes were not observed on it. The aptamer probe can be potentially dislodged from the cell surface with treatment of nucleases, indicating that Au NP-conjugated aptamer probes can be used as sensitive and reversible probes to label target biomolecules on cells.
Theoretical Study of Mechanical Control of Micro- and Nano-Mechanical Systems by Cavity-Induced Radiation Force
Authors: Vy Nguyen Duy , Ooka Ryu , Iida Takuya
Published: June 2012

We theoretically investigate the possibility of controlling the vibration amplitude of a cantilever used in scanning probe microscopy (SPM) by cavity-induced radiation force (CIRF) exerted on the cavity mirror attached to it. It has been clarified that the amplitude of the cantilever can be decreased by one order of magnitude owing to the nonlinear dynamics induced by CIRF under weak laser irradiation of 30 to 50 µW. This mechanism would be applied to, for example, dynamical control of micro- and nano-mechanical systems, and high-sensitivity SPM based on small amplitude metrology.
Large-Area Nanotemplate Process and Its Application to Roll Imprint
Authors: Choi Jun-Hyuk , Lee Soon-Won , Lee Ji-Hye , Choi Dae-Geun , Jeong Jun-Ho , Lee Eung-Sug
Published: June 2012

This study developed a stitching process for unit element nanotemplates based on step and repeat imprinting for use in enlarged soft mold fabrication. This mold was subsequently used for the custom-developed roll-to-plate UV nanoimprint process. The distinctive features of roll UV imprinting include the following: (1) the UV source is embedded within a roll mold made of quartz so that it can illuminate a resist coated on either a transparent or an opaque substrate, (2) the press-contact between the resist and soft mold wrapped around the quartz mold was designed to synchronize the rolling operation with the linear motion of the substrate, which helped minimize the residue thickness, and (3) a compressed pneumatic force was applied along the contact line of the roll imprint, which helped attenuate any possible level mismatch on the stitched mold surface.
Transfer Printing Method to Obtain Polarized Light Emission in Organic Light-Emitting Device
Authors: Noh Hee Yeon , Park Chang-sub , Park Ji-Sub , Kang Shin-Won , Kim Hak-Rin
Published: June 2012

We demonstrate a transfer printing method to obtain polarized light emission in organic light-emitting devices (OLEDs). On a rubbed self-assembled monolayer (SAM), a spin-coated liquid crystalline light-emissive polymer is aligned along the rubbing direction because of the anisotropic interfacial intermolecular interaction. Owing to the low surface energy of the SAM surface, the light-emissive layer was easily transferred to a patterned poly(dimethylsiloxane) (PDMS) stamp surface without degrading the ordering. Finally, a polarized light-emissive OLED device was prepared by transferring the patterned light-emissive layer to the charge transport layer of the OLED structure.
Impact of Resist Shrinkage and Its Correction in Nanoimprint Lithography
Authors: Horiba Akira , Yasuda Masaaki , Kawata Hiroaki , Okada Makoto , Matsui Shinji , Hirai Yoshihiko
Published: June 2012

Relative critical dimension (CD) errors in nanoimprint lithography are estimated by numerical simulation for various pattern sizes. From the results, transfer functions to estimate the CD errors are proposed, which are expressed similarly to a low- or high-pass filter in terms of the spatial frequency. Using the transfer functions, the mold pattern sizes are corrected to compensate the shrinkage.
Simulation of Resist Filling Properties under Condensable Gas Ambient in Ultraviolet Nanoimprint Lithography
Authors: Nagaoka Yoshinori , Suzuki Ryosuke , Hiroshima Hiroshi , Nishikura Naoki , Kawata Hiroaki , Yamazaki Noboru , Iwasaki Takuya , Hirai Yoshihiko
Published: June 2012

Resist filling characteristics under a condensable gas ambient in UV nanoimprint lithography are firstly verified by numerical simulation for nanoscale patterns with various resist properties. The resist filling time in condensable gas ambient is compared with that in a vacuum ambient and the result shows that the filling times are almost the same. Also, the filling time for various pattern sizes are investigated. The filling time decreases in proportion to the feature size for a microscale pattern; however, it increases in a nano scale pattern due to the surface tension of the resist. Nevertheless, the resist filling time is sufficiently short for practical use.
Step and Repeat Ultraviolet Nanoimprinting under Pentafluoropropane Gas Ambient
Authors: Iyoshi Shuso , Okada Makoto , Katase Tetsuya , Tone Katsuhiko , Kobayashi Kei , Kaneko Shu , Haruyama Yuichi , Nakagawa Masaru , Hiroshima Hiroshi , Matsui Shinji
Published: June 2012

In the UV nanoimprinting process an antisticking layer such as fluorinated self-assembled monolayer (F-SAM) is grafted on the mold surface to diminish the demolding impact. These layers are supposed to deteriorate as the imprint steps mount up, resulting in defects in the cured resist layer. In this work, continuous multiple shots of UV nanoimprint were conducted in the air and in pentafluoropropane (PFP) gas environment and demolding forces in every imprint step were determined. The experiments revealed that the demolding forces for the imprint in PFP atmosphere drastically reduced compared with those in the air. Water contact angles of the mold surface were also determined in every 225 imprint steps to observe the degree of degradation of the antisticking layer. It was found that the antisticking layer was less damaged or contaminated in the PFP environment than it was in the air after a certain number of imprint steps.
Throughput of Ultraviolet Nanoimprint in Pentafluoropropane Using Spin Coat Films under Thin Residual Layer Conditions
Authors: Hiroshima Hiroshi , Suzuki Kenta
Published: June 2012

In UV nanoimprint, UV-curable resin is usually supplied as droplets, but, from the viewpoint of throughput, it is not the best approach in some cases. When the pattern density of a given layout can be regarded as uniform, UV-curable resin should be supplied as a film with a uniform thickness if no other critical problems occur. Fine line-and-space (L/S) patterns with widths of 45, 65, and 90 nm were successfully fabricated with a residual layer thickness of 20 nm by UV-NIL in pentafluoropropane (PFP) using a spin coat UV-curable resin, PAK-01, and the throughput of UV-NIL in PFP for the fabrication of such fine L/S patterns with a thin residual layer was investigated. The resin filling of UV-NIL in air was not completed in 15 s but that of UV-NIL in PFP was completed in 0.6 s. The filling speed of UV-NIL in PFP is 80 times higher than that of UV-NIL in air. This value is one order of magnitude larger for the fabrication of patterns with a width of 300 µm in our previous work, and the high-throughput process is presumably due to the large capillary pressure, which may be canceled out for UV-NIL in air, of fine grooves of the L/S patterns. Simulation revealed that a virtual imprint pressure of 2.2 MPa should be produced by the capillary pressure for UV-NIL in PFP. Simulations also revealed that the complete filling time is proportional to the square of the space width and that the resin filling would be completed in 0.1 s for a space width of less than 40 µm.
Microchip-Based Organophosphorus Detection Using Bienzyme Bioelectrocatalysis
Authors: Han Yong Duk , Jeong Chi Yong , Lee Jun Hee , Lee Dae-Sik , Yoon Hyun C.
Published: June 2012

We have developed a microsystem for the detection of organophosphorus (OP) compounds using acetylcholine esterase (AchE) and choline oxidase (ChOx) bienzyme bioelectrocatalysis. Because AchE is irreversibly inhibited by OP pesticides, the change in AchE activity with OP treatment can be traced to determine OP concentration. Polymer-associated ChOx immobilization on the working electrode surface and magnetic microparticle (MP)-assisted AchE deposition methods were employed to create an AchE–ChOx bienzyme-modified biosensing system. ChOx was immobilized on the micropatterned electrodes using poly(L-lysine), glutaraldehyde, and amine-rich interfacial surface. AchE was immobilized on the MP surface via Schiff's base formation, and the enzyme-modified MPs were deposited on the working electrode using a magnet under the microfluidic channel. The bioelectrocatalytic reaction between AchE–ChOx bienzyme cascade and the ferrocenyl electron shuttle was successfully used to detect OP with the developed microchip. This provides a self-contained and relatively easy method for OP detection. It requires minimal time and a small sample size, and has potential analytic applications in pesticides and chemical warfare agents.
Importance of Thickness in Human Cardiomyocyte Network for Effective Electrophysiological Stimulation Using On-Chip Extracellular Microelectrodes
Authors: Hamada Tomoyo , Nomura Fumimasa , Kaneko Tomoyuki , Yasuda Kenji
Published: June 2012

We have developed a three-dimensionally controlled in vitro human cardiomyocyte network assay for the measurements of drug-induced conductivity changes and the appearance of fatal arrhythmia such as ventricular tachycardia/fibrillation for more precise in vitro predictive cardiotoxicity. To construct an artificial conductance propagation model of a human cardiomyocyte network, first, we examined the cell concentration dependence of the cell network heights and found the existence of a height limit of cell networks, which was double-layer height, whereas the cardiomyocytes were effectively and homogeneously cultivated within the microchamber maintaining their spatial distribution constant and their electrophysiological conductance and propagation were successfully recorded using a microelectrode array set on the bottom of the microchamber. The pacing ability of a cardiomyocyte's electrophysiological response has been evaluated using microelectrode extracellular stimulation, and the stimulation for pacing also successfully regulated the beating frequencies of two-layered cardiomyocyte networks, whereas monolayered cardiomyocyte networks were hardly stimulated by the external electrodes using the two-layered cardiomyocyte stimulation condition. The stability of the lined-up shape of human cardiomyocytes within the rectangularly arranged agarose microchambers was limited for a two-layered cardiomyocyte network because their stronger force generation shrunk those cells after peeling off the substrate. The results indicate the importance of fabrication technology of thickness control of cellular networks for effective extracellular stimulation and the potential concerning thick cardiomyocyte networks for long-term cultivation.
Measurement of Nonlinear Mechanical Properties of Surfactant-Added Poly(dimethylsiloxane)
Authors: Kim Hea Teak , Jeong Ok Chan
Published: June 2012

This paper presents a measurement of the nonlinear mechanical property of the surfactant-added poly(dimethylsiloxane) (PDMS) elastomer. The tension test samples with the different concentrations of the surfactant were prepared using a simple mixing, coating, curing, and cutting process. A 10 times cyclic tension test with a fixed magnitude of applied strain and a single-pull-to-failure tension test were sequentially performed with a micro-tensile tester at room temperature. Compared with the pure PDMS, the surfactant-added PDMS was more flexible and its yield strain also greatly increased. From the measured stress–strain relationship, the stress softening and the residual strain was observed in the first cyclic tension tests. Such a hysteresis was highly related with the concentration of the surfactant in preparing PDMS film. As the concentration of the surfactant increased, the hysteresis increased remarkably. From second cyclic tension test, a hysteresis dramatically reduced and the strain–stress curves were almost converged in 10 times cyclic test. Three nonlinear mechanical models like a Neo–Hookean, Mooney–Rivlin, and Ogden were computed from the experimentally measured stress–strain data. The Ogden model for the surfactant-added PDMS showed a good agreement with the experimental data. In the case of the Neo–Hookean and Mooney–Rivlin models, they could be preferable for the structural analysis of the micro device with the surfactant-added PDMS in the small strain region. This could provide the useful and reasonable nonlinear mechanical models of the surfactant-added PDMS for rapid computational prototyping from the hydrophilic PDMS.
Cell-Sorting System with On-Chip Imaging for Label-Free Shape-Based Selection of Cells
Authors: Terazono Hideyuki , Hayashi Masahito , Kim Hyonchol , Hattori Akihiro , Yasuda Kenji
Published: June 2012

We have developed a novel cell-sorting system involving microscopic imaging using a poly(methyl methacrylate) (PMMA)-based microfluidic chip with a pair of gel electrodes and real-time image-processing procedures for the quantification of cell shapes. The features of this system are as follows. 1) It can recognize cells both by microscopic cell imaging with a 10,000 event/s high-speed camera and by the photodetection of fluorescence. 2) Multistage sorting is used to reduce errors to an infinitesimally low level by using a pair of wide agarose-gel electrodes. 3) Carry-over-free analysis can be performed using a disposable microfluidic chip. 4) An field programmable gate array (FPGA) 10,000 event/s real-time image analysis unit for quantifying the cell images in cell sorting. To separate the target cells from other cells on the basis of the cell shape, we adopted an index of roughness for the cell surface R, which compares the actual perimeter of cell surface and the estimated perimeter of cross-sectional view of cell shape by approximating the cell as a sphere. Sample cells flowing through microchannels on the chip were distinguished by the dual recognition system involving optical analysis and a fluorescence detector, and then separated. Target cells could be sorted automatically by applying an electrophoretic force, and the sorting ability depended on the precision with which cells were shifted within the laminar flow. These results indicate that the cell-sorting system with on-chip imaging is practically applicable for biological research and clinical diagnostics.
Sensitive Fluorescence Microscopy of Neurons Cultured on a Plasmonic Chip
Authors: Yasui Chikara , Tawa Keiko , Hosokawa Chie , Nishii Junji , Aota Hiroyuki , Matsumoto Akira
Published: June 2012

A plasmonic chip with a periodic structure coated with thin metal films was fabricated and applied to bioimaging under a fluorescence microscope. By using the enhanced electric field of surface plasmon resonance excited on the chip, an enhanced fluorescence of samples was observed by conventional fluorescence microscopy. In this study, neurons were cultured on a plasmonic chip, which was used instead of a glass-bottomed dish or cover glass; the received fluorescence images of neuron dendrites were more than four times brighter than those obtained from similar specimens cultured on a glass-bottomed dish and observed using an upright fluorescence microscope.