bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhancement-Mode Metal Organic Chemical Vapor Deposition-Grown ZnO Thin-Film Transistors on Glass Substrates Using N2O Plasma Treatment
Authors: Remashan Kariyadan , Choi Yong-Seok , Kang Se-Koo , Bae Jeong-Woon , Yeom Geun-Young , Park Seong-Ju , Jang Jae-Hyung
Published: April 2010

Thin-film transistors (TFTs) were fabricated on a glass substrate with a metal organic chemical vapor deposition (MOCVD)-grown undoped zinc oxide (ZnO) film as a channel layer and plasma-enhanced chemical vapor deposition (PECVD)-grown silicon nitride as a gate dielectric. The as-fabricated ZnO TFTs exhibited depletion-type device characteristics with a drain current of about 24 µA at zero gate voltage, a turn-on voltage (Von) of -24 V, and a threshold voltage (VT) of -4 V. The field-effect mobility, subthreshold slope, off-current, and on/off current ratio of the as-fabricated TFTs were 5 cm2V-1s-1, 4.70 V/decade, 0.6 nA, and 106, respectively. The postfabrication N2O plasma treatment on the as-fabricated ZnO TFTs changed their device operation to enhancement-mode, and these N2O-treated ZnO TFTs exhibited a drain current of only 15 pA at zero gate voltage, aVonof -1.5 V, and aVTof 11 V. Compared with the as-fabricated ZnO TFTs, the off-current was about 3 orders of magnitude lower, the subthreshold slope was nearly 7 times lower, and the on/off current ratio was 2 orders of magnitude higher for the N2O-plasma-treated ZnO TFTs. X-ray phtotoelectron spectroscopy analysis showed that the N2O-plasma-treated ZnO films had fewer oxygen vacancies than the as-grown films. The enhancement-mode device behavior as well as the improved performance of the N2O-treated ZnO TFTs can be attributed to the reduced number of oxygen vacancies in the channel region.
Characteristics of Transparent ZnO-Based Thin-Film Transistors with High-k Dielectric Gd2O3 Gate Insulators Fabricated at Room Temperature
Authors: Liu Kou-Chen , Tsai Jung-Ruey , Li Chi-Shiau , Chien Po-Hsiu , Chen Jyun-Ning , Feng Wen-Sheng
Published: April 2010

A full room-temperature-fabricated ZnO-based thin-film transistor (TFT) has been demonstrated in this study using a gate dielectric of gadolinium oxide (Gd2O3) thin films. This is the first report on the use of Gd2O3 films as the gate insulator for a metal-oxide-based TFT. The properties of ZnO and Gd2O3 films deposited by pulsed laser deposition (PLD) at room temperature have also been studied under different oxygen pressures. In the high-oxygen-pressure region, the resistivity of the ZnO films was predominated by carrier concentration, while it is controlled by carrier mobility in the low-oxygen-pressure region. The on/off current ratio, field-effect mobility, and subthreshold swing of gate voltage obtained were approximately 105, 1.12 cm2 V-1 s-1, and 0.4 V/decade, respectively.
Strong Sum Frequency Generation in a GaAs/AlAs Coupled Multilayer Cavity Grown on a (113)B-Oriented GaAs Substrate
Authors: Tanaka Fumiya , Takahashi Tomoya , Morita Ken , Kitada Takahiro , Isu Toshiro
Published: April 2010

A strong sum frequency generation (SFG) has been demonstrated using two cavity modes realized in a GaAs/AlAs coupled multilayer cavity structure in which two GaAs half-wavelength cavity layers are coupled by an intermediate distributed Bragg reflector multilayer. The coupled multilayer cavity structure was grown on a (113)B GaAs substrate by molecular beam epitaxy. Two cavity modes with an optical frequency difference of 3.3 THz were clearly observed at 1514 and 1540 nm in the optical reflection spectrum. The room-temperature SFG and second-harmonic generation (SHG) signals were measured by the simultaneous excitation of two cavity modes using 100 fs laser pulses. The peak intensity of the SFG signal was more than 400 times larger than that of the SHG signal from a (113)B GaAs substrate alone, indicating that the effective second-order nonlinearity of GaAs was strongly enhanced by the cavity effect.
GaAs/AlAs Multilayer Cavity with InAs Quantum Dots Embedded in Strain-Relaxed Barriers for Planar-Type Optical Kerr Gate Switches
Authors: Takahashi Tomoya , Mukai Takuya , Morita Ken , Kitada Takahiro , Isu Toshiro
Published: April 2010

A GaAs/AlAs multilayer cavity containing self-assembled InAs quantum dots (QDs) embedded in strain-relaxed In0.35Ga0.65As barriers has been studied for planar-type optical Kerr gate switches. The multilayer cavity structure with smooth GaAs/AlAs interfaces was successfully grown on a (001) GaAs substrate by molecular beam epitaxy despite the lattice strain relaxation induced in the half-wavelength (λ/2) cavity layer. Time-resolved optical measurements at the cavity mode (λ= 1.46 µm) were performed by a pump–probe method at room temperature. Although only two layers of the InAs QDs were inserted into the λ/2 cavity layer, a large transmission change caused by the absorption saturation in the resonant QDs was clearly observed. The temporal profile was dominated by a fast (∼16 ps) decay component, which comes from carrier relaxation into the nonradiative centers arising from the lattice strain relaxation. We have also shown that an ultrafast response time (<1 ps) of the strongly enhanced optical Kerr signal is determined by the photon lifetime in the multilayer cavity.
Quantum Dot Optical Frequency Comb Laser with Mode-Selection Technique for 1-µm Waveband Photonic Transport System
Authors: Yamamoto Naokatsu , Akahane Kouichi , Kawanishi Tetsuya , Katouf Redouane , Sotobayashi Hideyuki
Published: April 2010

An optical frequency comb was generated from a single quantum dot laser diode (QD-LD) in the 1-µm waveband using an Sb-irradiated InGaAs/GaAs QD active medium. A single-mode-selection technique and interference injection-seeding technique are proposed for selecting the optical mode of a QD optical frequency comb laser (QD-CML). In the 1-µm waveband, a wavelength-tunable single-mode light source and a multiple-wavelength generator of a comb with 100-GHz spacing and ultrafine teeth are successfully demonstrated by applying the optical-mode-selection techniques to the QD-CML. Additionally, by applying the single-mode-selection technique to the QD-CML, a 10-Gbps clear eye opening for multiple-wavelengths in 1-µm waveband photonic transport over a 1.5-km-long holey fiber is obtained.
Influence of Heterointerface Abruptness on Electrorefractive Effect in InGaAs/InAlAs Five-Layer Asymmetric Coupled Quantum Well
Authors: Iseri Yuji , Arakawa Taro , Tada Kunio , Haneji Nobuo
Published: April 2010

An InGaAs/InAlAs five layer asymmetric coupled quantum well (FACQW) is expected to produce a large electrorefractive index change and is a promising structure for high-performance phase modulators. However, because an FACQW is composed of ultrathin layers, poor abruptness in heterointerface may deteriorate the electrorefractive effect. We therefore investigated theoretically the influence of abruptness of heterointerfaces in an FACQW on the electrorefractive effect of the FACQW. In the analysis, it is assumed that the composition profile in a heterointerface is exponential, and the thickness of the transition layer L is defined. With the increase in L, the absorption edge is blue-shifted, which deteriorates the electrorefractive index change of the FACQW especially in the case of L≥3 monolayer (ML). In addition, we propose an improved FACQW structure, which is expected to exhibit a large electrorefractive index even in the case of L=3 ML.
Divergent Far-Field III–Nitride Ultrathin Film-Transferred Photonic Crystal Light-Emitting Diodes
Authors: Lai Chun-Feng , Chao Chia-Hsin , Kuo Hao-Chung , Yu Peichen , Yen His-Hsuan , Yeh Wen-Yung
Published: April 2010

The divergent far-field distribution of III–nitride ultrathin film-transferred light-emitting diodes (FTLEDs) with ellipse holes of triangular photonic crystal (PhC) lattice have been experimental and theoretical studies. Angular-and-spectral-resolved measurement revealed guided modes extraction behaviors which obtain good agreement with theoretical model according to two-dimensional free photon band structure. The azimuthal evolution of the guided modes' diffraction behavior according to Bragg's diffraction has also been discussed by angular-resolved monochromatical mapping. Finally, the PhC FTLEDs show light enhancement with the divergence far-field pattern that exhibited 130% at a driving current of 200 mA as compared with non-PhC (without PhC) FTLEDs. This could lead to promising LEDs with unusual divergent far-field properties for specific applications.
GaN Thickness Effect on Directional Light Enhancement from GaN-Based Film-Transferred Photonic Crystal Light-Emitting Diodes
Authors: Lai Chun-Feng , Chao Chia-Hsin , Kuo Hao-Chung , Yu Peichen , Yen His-Hsuan , Yeh Wen-Yung
Published: April 2010

Directional light enhancement behavior including collimated far-field patterns sensitively depending on both photonic crystal (PhC) lattice constant and GaN thickness from GaN film-transferred light-emitting diodes (FTLEDs) with a triangular PhC lattice has been experimentally studied. Far-field pattern measurement in the Γ–M and Γ–K directions of GaN PhC FTLEDs with various lattice constants and GaN thicknesses revealed different far-field profiles as detemined on the basis of guided mode extraction of Bragg's diffraction. Additionally, three-dimensional (3D) far-field measurement revealing the PhC diffraction patterns was also demonstrated. We also used the 3D finite-different time-domain method to confirm the experimental results.
Thermal Analysis of InGaN/GaN Multiple Quantum Well Light Emitting Diodes with Different Mesa Sizes
Authors: Lee Hee Kwan , Yu Jae Su
Published: April 2010

We analyze experimentally and theoretically the thermal characteristics of 470 nm InGaN/GaN light emitting diodes (LEDs) with different mesa sizes for efficient heat dissipation. For various mesa sizes, the junction temperature is measured as a function of injection current by the diode forward voltage method. The junction temperature (T
j) increases linearly with injection current and it rises rapidly with the reduction in mesa size. The thermal parameters, such as the junction temperature, temperature profile, and thermal resistance (R
th), are obtained from thermal simulations with the heat source density, determined from the measured light–current–voltage data, using a three dimensional heat dissipation model. At 200 mA, the T
j values of LEDs are theoretically calculated as 392.7 and 578 K for 450 ×450 and 250 ×250 µm2, respectively. The thermal resistance is kept nearly constant due to a linear relationship between junction temperature and injection current and it is reduced as the mesa size increases, indicating a low R
th of < 75 K/W for 450 ×450 µm2 LED. The R
th values obtained by the thermal simulation are fairly consistent with the experimental data. The use of the substrate with a relatively high thermal conductivity can also improve significantly the R
th of LEDs.
Light-Emitting Diode Based on ZnO by Plasma-Enhanced Metal–Organic Chemical Vapor Deposition Employing Microwave Excited Plasma
Authors: Asahara Hirokazu , Takamizu Daiju , Inokuchi Atsutoshi , Goto Tetsuya , Hirayama Masaki , Teramoto Akinobu , Ohmi Tadahiro
Published: April 2010

In this paper we describe the growth of nitrogen doped zinc oxide (ZnO) films on single crystal ZnO substrates by plasma-enhanced metal–organic chemical vapor deposition (PE-MOCVD) employing microwave excited high-density plasma. We used Dimethylzinc (DMZ) as a Zinc precursor, and six different types of oxygen and nitrogen precursors: O2+N2, NO, N2O, O2+NH3, NO2, and O2. This paper considers the effects of nitrogen precursor material and utilizing the plasma on the structural properties and the nitrogen concentration by atomic force microscope and secondary ion mass spectrometry. It was only when using plasma and NO2that the nitrogen (N) doped ZnO film with the steps and terraces surface structure of two-dimensional growth could be formed by our growth method. Furthermore, we fabricated a homostructural LED comprising the N-doped ZnO film and n-type ZnO substrate, and we achieved electroluminescence (EL) in forward bias at room-temperature (RT) and the current–voltage rectifying characteristics.
Compact and Polarization-Independent Variable Optical Attenuator Based on a Silicon Wire Waveguide with a Carrier Injection Structure
Authors: Nishi Hidetaka , Tsuchizawa Tai , Watanabe Toshifumi , Shinojima Hiroyuki , Yamada Koji , Itabashi Sei-ichi
Published: April 2010

We developed a Si variable optical attenuator (VOA) with low-polarization-dependent loss (PDL). We designed the core dimensions to reduce PDL originating from free-carrier absorption. In the core dimensions, there is a big margin for which the PDL is less than 1 dB when attenuation is -20 dB. On the basis of calculations, we fabricated the Si VOAs and evaluated them. A fabricated Si VOA exhibited PDL of 0.2 dB due to free-carrier absorption when the attenuation was -20 dB. Moreover, we verified that the PDL is less than 1 dB in a wide range of core widths, it is tolerant to fabrication error.
Integrated SiO2/SiON/SiO2 Thermo-Optical Switch Based on the Multimode Interference Effect
Authors: Chuang Ricky W. , Hsu Mao-Teng , Liao Zhen-Liang
Published: April 2010

We propose the design of an integrated SiO2/SiON/SiO2 2 ×2 multimode interference (MMI) based optical switch. The entire switching mechanism is based on the thermo-optic (TO) effect of SiO2/SiON dielectric layers. The heating power of ∼0.89 W is required to switch the optical beam from bar to cross state. The experimental crosstalk of the switch as determined between the cross and bar states is in the excess of 12 dB. Furthermore, the rise and fall times of approximately 314 µs are also experimentally realized for this device.
Improvements in Optical Power and Emission Angle of Blue Light Emitting Diodes Using Patterned Sapphire Substrates with Low Threading Dislocation Densities
Authors: Jeong Seong-Muk , Kissinger Suthan , Ra Yong-Ho , Yun Seok-Hyo , Kim Dong-Wook , Lee Seung Jae , Ahn Haeng-Keun , Kim Jin-Soo , Lee Cheul-Ro
Published: April 2010

GaN blue light-emitting diodes (LEDs) with a peak emission wavelength of approximately 461 nm were fabricated on a c-face lens patterned sapphire substrate (PSS) and an unpatterened sapphire substrate (UPSS) by metal organic chemical vapor deposition (MOCVD). The crystal structure of an epitaxial GaN film was improved by using the PSS. The peak wavelengths with electroluminescence intensities of 462 and 464 nm were measured for PSS and UPSS LEDs using a 20 mA injection current. It was found that the electroluminescence intensity of the LEDs grown on the lens PSS was about 61% higher than that of the LEDs prepared on the UPSS. The emission angle of the PSS LED increased by 1.5 times compared with that of the UPSS LED. The luminous intensities of both LEDs increased similarly on both circular and square reflectors. The output power of the PSS LED was 33% greater than that of the LED UPSS. In addition, the reduction in full width at half maximum (FWHM) in the ω-scan rocking curves of GaN on the PSS suggested an improved crystal quality. These significant improvements in output power and emission angle resulted from the enhanced light extraction and the reduced threading dislocation (TD) density using the PSS method.
Direct Growth of a-Plane GaN on r-Plane Sapphire by Metal Organic Chemical Vapor Deposition
Authors: Hsu Hsiao-Chiu , Su Yan-Kuin , Huang Shyh-Jer , Wang Yu-Jen , Wu Chun-Ying , Chou Ming-Chieh
Published: April 2010

In this study, we had demonstrated the direct growth of nonpolar a-plane GaN on an r-plane sapphire by metal organic chemical vapor deposition (MOCVD) without any buffer layer. First, in this experiment, we had determined the optimum temperature for two-step growth, including obtaining three-dimensional (3D) GaN islands in the nucleation layer and coalescing with a further two-dimensional (2D) growth mode. The result shows that the nucleation layer grown under high temperature (1150 °C) leads to large islands with few grain boundaries. Under the same temperature, the effect of the V/III ratio on the growth of the overlaying GaN layer to obtain a flat and void free a-plane GaN layer is also studied. The result indicates one can directly grow a smooth epitaxial layer on an r-plane sapphire by changing the V/III ratio. The rms roughness decreases from 13.61 to 2.02 nm. The GaN crystal quality is verified using a mixed acid to etch the film surface. The etch pit density (EPD) is 3.16 ×107 cm-2.
Grazing Incidence X-ray Diffraction Measurements of Columnar InAs/GaAs Quantum Dot Structures
Authors: Mukai Kohki , Watanabe Keita , Kimura Yuuta
Published: April 2010

The lattice constant distribution inside a columnar InAs/GaAs quantum dot (QD) and its crystal orientation dependence were evaluated by grazing incidence X-ray diffraction (GIXD) measurement. The QDs were grown by stacking Stranski–Krastanow (SK)-type InAs QDs directly in the growth direction with very thin GaAs interval layers. We evaluated the dependence of the in-plane lattice constant on QD height by GIXD measurement using equipment available for laboratories. We found that the lattice constants at the top and bottom of the QDs were almost the same when the height and diameter of the QDs were almost equal. As the number of stacks was increased to grow high QDs, the lattice constant at the QD top became larger in the [110] direction than in the [110] direction, but this relationship was reversed at the bottom. We consider that GIXD measurement with compact equipment will contribute to the swift and efficient development of QD devices.
Growth and Characterization of InGaAs Nanowires Formed on GaAs(111)B by Selective-Area Metal Organic Vapor Phase Epitaxy
Authors: Yoshimura Masatoshi , Tomioka Katsuhiro , Hiruma Kenji , Hara Shinjiro , Motohisa Junichi , Fukui Takashi
Published: April 2010

We fabricated InGaAs nanowires (NWs) in SiO2mask openings on a GaAs(111)B substrate at growth temperatures of 600–700 °C using catalyst-free selective-area metal organic vapor phase epitaxy. At a growth temperature of 600 °C, particle-like depositions occurred, but they decreased in number and density when the growth temperature was increased to 650 °C and disappeared above 675 °C. The heights and growth rates of the NWs increased when the growth temperature was increased and the mask opening diameter was decreased from 300 to 50 nm. Photoluminescence (PL) spectra measured for the NWs indicated a blue shift in the peak from 0.95 to 1.3 eV as the growth temperature was increased from 600 to 700 °C, indicating an increase in the Ga composition from 62 to 88% in the InGaAs NWs.
Low Temperature Metal-Induced Lateral Crystallization of Si1-xGex Using Silicide/Germanide-Forming-Metals
Authors: Phung Thanh Hoa , Xie Ruilong , Tripathy Sudhiranjan , Yu Mingbin , Zhu Chunxiang
Published: April 2010

Metal-induced lateral crystallization (MILC) of Si1-x
Ge
x
(0≤x≤1) using Ni, Co, and Pd is carried out at 375 °C. It is found that the MILC rates increase with increasing Ge fraction when Ni and Co are used; however, the rate reaches a maximum at Ge mole fraction of 0.7 for Pd induced lateral crystallization of SiGe. The difference in these two trends is due to different contributions of the three processes involved during the metal-induced crystallization. Using Ni and Co, the MILC rates of Si1-x
Ge
x
are limited by the silicon germanide formation and diffusion process for all Ge mole fractions. While the MILC rate of Si1-x
Ge
x
using Pd is also controlled by these two processes when x is smaller than 0.7, the rate is dominantly limited by the lattice mismatch between silicon germanide and SiGe when the Ge mole fraction is larger than 0.7. Comparing the quality of MIC Ge films induced by the three metals, crystalline Ge film induced by Co has the largest grain size and the smoothest surface. Regarding the MILC rate, Pd has a similar rate as Ni in MILC of Ge, and a much higher rate than those of Ni and Co in MILC of Si0.3Ge0.7.
Properties of SiGe Films Fabricated by Reactive Thermal Chemical Vapor Deposition Using Lamp Heating
Authors: Wakagi Masatoshi , Suzumura Isao , Kagatsume Akiko , Asanuma Haruhiko , Nishimura Etsuko , Matsumura Mieko , Hosoi Tsutomu , Hanna Jun-ichi
Published: April 2010

The structural and electrical properties of SiGe films deposited by reactive thermal chemical vapor deposition using a lamp heating system with a source gas mixture of GeF4 and Si2H6 were investigated. In the SiGe film depositions with respective GeF4 and Si2H6 flow rates of 0.06 and 3 sccm, the film structure changed from crystalline to amorphous during the film growth. The results of secondary ion mass spectroscopy analysis and high-temperature deposition suggest that the gas phase reactions cause the structural change. To suppress the gas phase reactions, low-pressure depositions are investigated. The SiGe film deposited at a relatively low pressure of 400 Pa shows good crystallinity. The thin-film transistor with this SiGe film also reveals a high p-channel mobility of about 10 cm2·V-1·s-1.
Thin Graphitic Structure Formation on Various Substrates by Gas-Source Molecular Beam Epitaxy Using Cracked Ethanol
Authors: Maeda Fumihiko , Hibino Hiroki
Published: April 2010

We have studied the growth of graphene by gas-source molecular beam epitaxy, with a cracked-ethanol source. Three substrates – Si substrate with thin oxide layer, c-surface of sapphire, and graphene layers formed on SiC – were used to draw out clues to the optimum conditions for graphene growth. Raman spectroscopy and X-ray photoelectron spectroscopy analyses indicate that hardly any or fairly small amounts of graphene are formed on the Si and sapphire, although thin films of graphitic material can be formed. We estimated nominal growth rates on the three substrates and found that the growth rate on the graphene was much smaller than those on the other two substrates. We studied the growth process of graphene on graphene by reflection high-energy electron diffraction and found that two-dimensional graphene islands grew laterally but their lateral orientations were not aligned.
Dual-Gate Single-Electron Transistor with Silicon Nano Wire Channel and Surrounding Side Gates
Authors: Lee Dong Seup , Kang Kwon-Chil , Lee Joung-Eob , Yang Hong-Seon , Lee Jung Han , Park Byung-Gook
Published: April 2010

In this paper, we propose a novel self-aligned dual-gate single-electron transistor having nano wire channel and surrounding side gates. By restricting the control gate effect to the top surface of the channel and intensifying the depletion effect through the surrounding side gates, the parasitic metal–oxide–silicon field-effect transistor (MOSFET) current and the quantum dot size are expected to be decreased. These advantages of the proposed structure are investigated through three-dimensional (3D) device simulation. In addition, the devices are fabricated by utilizing the silicon process and their electrical characteristics are analyzed at both room temperature and low temperature. Also, diverse device parameters are extracted from the measurement results, and they are systematically compared.
Light-Induced Carrier Transfer in NiSi-Nanodots/Si-Quantum-Dots Hybrid Floating Gate in Metal–Oxide–Semiconductor Structures
Authors: Morisawa Naoya , Ikeda Mitsuhisa , Nakanishi Sho , Kawanami Akira , Makihara Katsunori , Miyazaki Seiichi
Published: April 2010

We have fabricated a metal–oxide–semiconductor (MOS) capacitor with a hybrid floating gate stack consisting of silicon quantum dots (Si-QDs) and NiSi Nanodots (NiSi-NDs) with a 3-nm-thick interlayer SiO2, and studied the effect of 1310 nm light irradiation on charge distribution in a hybrid floating gate. The light irradiation resulted in a reduced flat-band voltage shift due to the charging of the hybrid floating gate under the application of gate biases in comparison to the shift in the dark. This result can be interpreted in terms of the shift of the charge centroid toward the gate side in the hybrid floating gate caused by the photoexcitation of electrons in NiSi-NDs and the subsequent electron tunneling to Si-QDs. When the light irradiation was turned off, the transferred charges moved back from the Si-QDs to the NiSi-NDs without being emitted to the Si substrate.
Thin-Film Transistor Type Flash Memory with Biomineralized Co Nanodots on Silicon-on-Insulator
Authors: Ohara Kosuke , Yamashita Ichiro , Uraoka Yukiharu
Published: April 2010

We proposed the fabrication of nanodot-type floating gate memory with biomineralized nanodots on silicon-on-insulator. High-density Co bionanodots (Co-BNDs) were adsorbed on SiO2. The current–voltage curve with a large hysteresis caused by electron injection into Co-BNDs and the emission of Co-BNDs were observed. A good retention characteristic due to charge confinement in the potential well of a Co-BND was observed. Good writing and erasing characteristics were observed. We confirmed that the memory has high reliability with good endurance. This proposed flash memory is promising for memory devices in system-on-panel displays owing to its fast writing/erasing speed and high reliability.
Characterization of Nonvolatile Memory Behaviors of Al/Poly(vinylidene fluoride–trifluoroethylene)/Al2O3/ZnO Thin-Film Transistors
Authors: Yoon Sung-Min , Yang Shin-Hyuk , Byun Chun-Won , Park Sang-Hee Ko , Jung Soon-Won , Cho Doo-Hee , Kang Seung-Youl , Hwang Chi-Sun , Ishiwara Hiroshi
Published: April 2010

The combination of a ferroelectric polymer and an oxide semiconductor is a very promising solution to realize embeddable nonvolatile memory thin-film transistors (TFTs) for novel electronic devices. Memory TFTs with a gate structure of Al/80 nm-poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)]/4 nm Al2O3/5 nm ZnO were fabricated and their programming characteristics were investigated. Good performances in memory and transistor behaviors were successfully confirmed. When the voltage pulses of ± 15 V and 990 ms were employed, a memory on/off ratio of 4400 was obtained. It was found that the initial memory on/off ratio was closely related to the applied programming conditions such as pulse amplitude and width of programming voltage signals. Retention behaviors were also sensitively affected by the programming conditions. The initial memory on/off ratio of approximately 300 decreased to 3.4 after a lapse of 104 s when the programming voltage, pulse duration, and gate bias during the retention period were set to be ± 18 V, 500 ms, and open, respectively.
Enhancement of Current Drivability of Nanograting Polycrystalline Silicon Thin-Film Transistors
Authors: Kuroki Shin-Ichiro , Zhu Xiaoli , Kotani Koji , Ito Takashi
Published: April 2010

The nanograting channel structure was introduced to a polycrystalline silicon thin-film transistor (poly-Si TFT) to enhance the current drivability. With the formation of the nanograting in the channel region, the effective width was enhanced without the increase in the planar area. At the same overdrive voltage, the drain current of the nanograting TFTs was larger than that of the conventional planar ones at the same planar dimension. In addition to the increase in the effective channel width, the drivability enhancement was further caused by the increase in electron mobility. The increase in the electron field-effect mobility by the nanograting structure was 42% at the maximum.
Quantum Chemistry Study of Surface Structure Effects on Secondary Electron Emission in MgO Protecting Layers for Plasma Displays
Authors: Serizawa Kazumi , Onuma Hiroaki , Kikuchi Hiromi , Suesada Kazuma , Kitagaki Masaki , Yamashita Itaru , Miura Ryuji , Suzuki Ai , Tsuboi Hideyuki , Hatakeyama Nozomu , Endou Akira , Takaba Hiromitsu , Kubo Momoji , Kajiyama Hiroshi , Miyamoto Akira
Published: April 2010

MgO protecting layers, which have high ion induced secondary electron emission coefficient (γ), are required in order to decrease the firing voltage of plasma displays. Theoretical estimation of ideal γ value is needed for a design of better protecting layers. In this study, we report our developed γ calculation method based on a tight-binding quantum calculation and application to an estimation of γ values of MgO protecting layers. From our calculation results, it was revealed that electron trap sites arising from surface roughness would work as an effective emission sites and increase γ value. Especially for Xe+ species as induced ion, the γ value changed drastically by the presence of the trapped electron. It is also suggested that a presence of chemisorbed water on the MgO surface decreases the γ values because of the contribution of the electrons at the low energy levels originated from surface OH groups.
Transient Current Study on Pt/TiO2-x/Pt Capacitor
Authors: Zhong Ni , Shima Hisashi , Akinaga Hiro
Published: April 2010

Transient transport characteristic has been studied in the Pt/TiO2-x
/Pt devices. A peak in the current density–time (J–t) curve was observed under direct-current (dc) electric field stress. The peak position (τ) was investigated as a function of various dc field stress and measurement temperature (T). With increase of field stress and T, τ exhibits a decrease. After analyzing the present result according to space-charge-limited current (SCLC) theory and electron/hole conduction influenced mode, we concluded that the transient current of Pt/TiO2-x
/Pt device does not come from the oxygen vacancy (VO) migration directly, but the electron/hole transport. The peak in the J–t curve is attributed to the change of electron/hole conduction caused by VO redistribution under dc field stress.
Current Reduction Mechanism in Organic Thin Film Transistors
Authors: Ishikawa Yoshinori , Wada Yasuo , Tsutsui Ken , Toyabe Toru
Published: April 2010

Hidden origin of current reduction mechanism in organic thin film transistor (OTFT) structure is investigated based on a device simulation, which makes it possible to derive current–voltage (I–V) characteristics, potential distribution and carrier concentration inside a device by solving Poisson's equation and continuity equation. It is made clear that the device performances improve more than twice to three hundred times only by inserting high impurity concentration layer under the source/drain contact region. The cause of the inferior characteristics of conventional OTFT devices is attributed to the deficiency of carriers in the channel region, resulting to a very high potential drop at the source–channel interface, thus leading to an apparent decrease of carrier mobility. These results clearly indicate the direction of OTFT technology development, i.e., development of high carrier concentration, or heavily doped organic semiconductor materials.
Temperature Dependence of Electrical Properties of Ambipolar Organic Transistors Based on F16CuPc/α-Sexithiophene p–n Heterojunction
Authors: Ye Rongbin , Baba Mamoru , Ohta Koji , Suzuki Takanori , Mori Kunio
Published: April 2010

Ambipolar organic thin-film transistors based on a F16CuPc/α-sexithiophene p–n heterojunction have been fabricated and analyzed to investigate the temperature dependence of ambipolar mobilities. At high temperatures (>50 K), the ambipolar mobilities follow a thermally activated hopping process. Thermal activation energy (E
a) is 79.3 meV for n-channel and 60.9 meV for p-channel, larger than those of single-layer devices when the temperature exceeds 140 K. The increase in E
a appears to originate from the small ambipolar mobilities. At temperatures ranging from 50 to 140 K, we have a second regime with much lower E
a of 5.7 meV for n-channel and 4.6 meV for p-channel, where the charge transport is dominated by shallow traps. On the other hand, the ambipolar mobilities become practically temperature independent at temperatures lower than 50 K, which is described as bandlike transport.
High-Speed Operation of Step-Edge Vertical-Channel Organic Transistors with Pentacene and 6,13-Bis(triisopropyl-silylethynyl) Pentacene
Authors: Kudo Kazuhiro , Takano Tomoki , Yamauchi Hiroshi , Iizuka Masaaki , Nakamura Masakazu
Published: April 2010

Organic field-effect transistors (OFETs) with a novel structure, step-edge vertical-channel OFETs (SVC-OFETs), have been developed to obtain a short channel by a self-aligned process. SVC-OFETs enable the fabrication of a submicron channel by forming the channel region around the step-edge structure. Carriers flow in the vertical direction in the short channel of the step-edge structure. SVC-OFETs show excellent device performance characteristics with a high current and a high cutoff frequency of approximately 1.5 MHz, which is a very high value for organic transistors.
Tuning of Threshold Voltage in Organic Field-Effect Transistor by Dipole Monolayer
Authors: Ou-Yang Wei , Chen Xiangyu , Weis Martin , Manaka Takaaki , Iwamoto Mitsumasa
Published: April 2010

We have studied the threshold voltage shift of top-contact organic field-effect transistors (OFETs) with a dipole monolayer between pentacene active layer and SiO2 gate insulator. Since dipole moment projection in normal of the monolayer can be regulated by changing the ordering, the relationship between threshold voltage shift and spontaneous polarization of the monolayer has been gained. Experimental results show the dipole monolayer causes a large negative threshold voltage shift and the shift is linearly proportional to the polarization of the monolayer. We propose a dipole layer model to interpret the observed phenomena with an assumption that the threshold voltage shift is due to compensation of electric field in organic semiconductor layer induced by the dipole monolayer, which is uncommon for the general consideration. Excitingly, a good agreement between the experiment and the analysis shows validity of our modeling and provides the capability of tuning threshold voltage for OFET devices.
Study of Organic Field-Effect Transistors Using Charge Modulation Spectroscopy: Behavior of Injected Carriers
Authors: Miyazawa Ryo , Taguchi Dai , Weis Martin , Manaka Takaaki , Iwamoto Mitsumasa
Published: April 2010

We have studied poly(3-hexylthiophene) (P3HT) and the injected charge behavior in metal–insulator–semiconductor (MIS) diodes. Charge modulation spectroscopy (CMS) and impedance measurements were conducted to study the energy states and location of injected carriers in the MIS diodes with the P3HT. CMS spectra clearly showed polaron state formation in the P3HT by injected holes. We also observed threshold voltage shifts in capacitance–voltage (C–V) characteristics due to photoillumination and application of voltage. The results showed the trapping of injected holes and electrons generated by illumination, suggesting the presence of electron and hole trapping states in the P3HT MIS diodes.
Color-Tunable Polymer Light-Emitting Diodes with Conjugated Polymer Homojunctions
Authors: Huang Chun-Yuan , Su Yan-Kuin , Cheng Chiao-Yang , Rao M. V. Madhava , Chen Ying-Chih , Huang Tsung-Syun , Wen Ten-Chin , Guo Tzung-Fang
Published: April 2010

Color-tunable light-emitting diodes with a polymer homojunction structure have been demonstrated. The homojunction structure consisted of two emissive layers, and poly(9,9-dioctylfluorene) (PFO) was used as the host material in both emissive layers. One emissive layer was composed of a blend of blue-emitting PFO and its green-emitting copolymer, and the other one was composed of a blend of green-emitting PFO copolymer and red-emitting poly[2-methoxy-5(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEHPPV). In device characterization, when the injection current was increased, partial electrons could easily pass through the second emissive layer and flow into the first emissive layer near the anode, because there was no potential barrier existing in the homojunction. Therefore, the emission color of our devices could be tuned as orange, yellow, white, and cyan by adjusting the injection current or bias voltage.
Enhancing Efficiency of Organic Light-Emitting Diodes Using a Carbon-Nanotube-Doped Hole Injection Layer
Authors: Su Shui-Hsiang , Chiang Wang-Ta , Hou Cheng-Chieh , Kao Lien-Cheng , Yokoyama Meiso
Published: April 2010

A nanocomposite layer consisting of multiwalled carbon nanotube (MWCNT)-doped poly(3,4,-ethylene dioxythiphene):poly(styrene sulfonic acid) (PEDOT:PSS) was employed as a hole injection layer (HIL) in an organic light-emitting diode (OLED). The structure of the OLED is glass/indium-tin oxide (ITO)/MWCNT-doped PEDOT:PSS/PEDOT:PSS/tris(8-hydroxyquinolinato)aluminum (Alq3)/LiF/Al. The luminous efficiency of the OLED is as high as 2.1 cd/A, which is 70% higher than that of a conventional device without an MWCNTs-doped HIL. The MWCNTs in the PEDOT:PSS act as a hole-blocking material that results in a reduction in holes transport ability, and therefore, in a balance between electron and hole mobilities, leading to enhanced luminescent performance. The mechanism was well demonstrated by through investigations by atomic force microscopy (AFM) of the film surface morphology and carrier injection properties of hole-only devices.
Development of Computational Method for Analysis of Carrier Transfer in Light-Emitting Polymers
Authors: Yamashita Itaru , Serizawa Kazumi , Onuma Hiroaki , Suzuki Ai , Miura Ryuji , Tsuboi Hideyuki , Hatakeyama Nozomu , Endou Akira , Takaba Hiromitsu , Kubo Momoji , Williams Mark C. , Miyamoto Akira
Published: April 2010

For the analysis of the relationship between carrier transfer properties and morphologies of light-emitting polymers, it is important to investigate carrier transfer pathways. We developed a novel computational method for analysis of carrier transfer pathways by the combination of tight-binding quantum chemistry calculation with Monte Carlo method. This novel method was applied to the prediction of electron transfer in poly(9,9'-dioctylfluorene)(PDOF), which is known as a blue light-emitting polymer. We successfully investigated the electron transfer pathways in PDOF films. We found that the electron transfer mainly occurs in an intra chain, but the inter chain electron transfer was also observed between aromatic rings whose distance was less than 4.0 Å.
Fabrication of Electrophoretic Display Driven by Membrane Switch Array
Authors: Senda Kazuo , Usui Hiroaki
Published: April 2010

Electrophoretic devices (EPDs) and organic light-emitting diodes (OLEDs) have potential application in a large-area flexible displays, such as digital signage. For this purpose, a new backplane is capable of driving a large unit is required instead of thin-film transistors. In this paper we describe the fabrication of a membrane switch array suitable for driving large-scale flat-panel displays. An array of membrane switches was prepared using flexible printed circuit (FPC) technology of polyimide films, by combining low-temperature processes of lamination and copper electroplating methods. An array of 256 matrix switches with a pixel size of 7 mm2 was prepared to drive the EPD front panel. The switches were driven at a voltage of about 40 V and a frequency of 10 Hz. The operation characteristics agreed well with the result of the theoretical calculation. The calculation also suggested that driving voltage can be lowered by increasing pixel size. The contact resistance of the membrane switch was as low as 0.2 Ω, which implies the wide applicability of this device for driving a variety of elements.
Gas Adsorption Properties of Fluorocarbon Thin Films Prepared Using Three Different Types of RF Magnetron Sputtering Systems
Authors: Iwamori Satoru , Hasegawa Norihiko , Yano Satoshi , Noda Kazutoshi
Published: April 2010

Fluorocarbon thin films were deposited onto a quartz crystal with a poly(tetrafluoroethylene) target using three different types of RF magnetron sputtering systems with strong, weak, and unbalanced magnetic fields. The adsorption properties of these thin films for water, ethanol, acetone, acetaldehyde, toluene, and methyl salicylate were evaluated using the quartz crystal microbalance (QCM) method in order to characterize the surface properties of these thin films. These thin films have low sensitivities to non-polar solvents that contain methyl and aromatic groups, and high sensitivities to polar solvents that contain carbonyl and hydroxyl groups. Chemical structures, especially, polar moieties in these fluorocarbon thin films would affect the gas adsorption properties.
Adsorption Properties of Thin Films Prepared by RF Sputtering with a Poly(biphenyltetracarboxylic dianhydride–paraphenylene diamine) Polyimide Target
Authors: Iwamori Satoru , Yano Satoshi , Sugimoto Ryousuke , Uemura Akihiro , Matsumoto Hiroyuki , Noda Kazutoshi
Published: April 2010

Thin films were deposited onto a quartz crystal with a poly(biphenyltetracarboxylic dianhydride–paraphenylene diamine) (BPDA–PDA) polyimide target by RF sputtering, and the adsorption properties of these thin films for water, ethanol, acetone, acetaldehyde, toluene, and methyl salicylate were evaluated by the quartz crystal microbalance (QCM) method to characterize the surface properties of these thin films. Chemical structures, especially surface free energies of these thin films would affect the gas adsorption properties. In addition, the number of adsorbed gas molecules increased with decreasing molecular weight on each sputtered thin film. Furthermore, these gas molecules would be adsorbed inside the sputtered thin films as well as on the top surface. The number of adsorbed gas molecules increased with decreasing molecular size on each sputtered thin film.
Single-Crystal Growth and Charge Transport Properties of an Alternating Co-Oligomer Composed of Thiophene and Phenylene Rings
Authors: Yamao Takeshi , Nishimoto Yoshihiro , Terasaki Kohei , Akagami Hiroshi , Katagiri Toshifumi , Hotta Shu , Goto Midori , Azumi Reiko , Inoue Masamitsu , Ichikawa Musubu , Taniguchi Yoshio
Published: April 2010

We grow single crystals of a thiophene/phenylene co-oligomer (TPCO) composed of seven alternating thiophene and phenylene rings (AC'7). These crystals are grown in a liquid phase directly onto silicon substrates covered with a silicon dioxide layer. The grown crystals are well-defined hexagons and are composed of a molecular layered structure along the molecular length. Top-contact field-effect transistors are fabricated by depositing metal electrodes on the AC'7 crystals grown on the substrates. We estimate the field effect mobilities in the transistor device configurations. The mobility data are associated with the crystallographic results of the material. The devices produce a maximum mobility of ∼0.1 cm2·V-1·s-1. This value is higher than that obtained for another TPCO composed of five alternating rings (AC5). The present results indicate that AC'7 crystals are potentially useful for electrical device applications.
Effect of Self-Assembled Monolayer Modification on Indium–Tin Oxide Surface for Surface-Initiated Vapor Deposition Polymerization of Carbazole Thin Films
Authors: Umemoto Yuya , Kim Seong-Ho , Advincula Rigoberto C. , Tanaka Kuniaki , Usui Hiroaki
Published: April 2010

With the aim of controlling the interface between an inorganic electrode and an organic layer, a surface-initiated vapor deposition polymerization method was employed to prepare carbazole polymer thin films that are chemically bound to an indium–tin oxide (ITO) surface. A self-assembled monolayer (SAM) that has an azo initiator as a terminal group was prepared on an ITO surface, on which carbazole acrylate monomers were evaporated under ultraviolet (UV) irradiation. The surface morphological characteristics of the films prepared with/without UV irradiation and with/without the SAM were compared. It was found that the UV irradiation leads to the polymerization of carbazole monomers irrespective of the type of substrate used. On the other hand, the surface morphological characteristics were largely dependent on the existence of the SAM. Uniform and smooth polymer thin films were obtained only when the monomers were evaporated on the SAM-modified surface under UV irradiation. A comparison of film growth characteristics on a UV–ozone-treated ITO surface suggested that the formation of uniform films was made possible not by the modification of surface energy but by the growth of the polymers chemically bound to the substrate surface.
Molecular Orientation of Poly(3-hexylthiophene)/Fullerene Composite Thin Films
Authors: Mohamad Khairul Anuar , Komatsu Natsuki , Uesugi Katsuhiro , Fukuda Hisashi
Published: April 2010

Focused on the relationship between the molecular orientation and the electrical performance of poly(3-hexylthiophene)/[6,6]-phenyl C61-butyric acid methyl ester (P3HT/PCBM) composite thin films to elucidate the effect of changing amount of PCBM in P3HT:PCBM by weight ratio in organic solution has been studies. The P3HT/PCBM composite thin films were investigated by an electron spin resonance (ESR) and X-ray diffraction (XRD) to reveal the film molecular and structure orientation. It was observed that the composite films with a small amount of PCBM were capable of altering the molecular structure of P3HT. It was also observed that the presence of a small amount of PCBM molecules improved the device performance of P3HT thin film transistors (TFTs), which provide the mobility on the order of 10-3 cm2 V-1 s-1 with an on/off current ratio of 10-4. The threshold voltage was also higher than of pure P3HT TFTs.
Integrated Bio-Imaging Sensor Array with Complementary Metal–Oxide–Semiconductor Cascode Source–Drain Follower
Authors: Matsumoto Hirokazu , Tsukada Junichi , Ozawa Hiroaki , Uno Shigeyasu , Nakazato Kazuo , Terasaki Nao , Yamamoto Noritaka , Hiraga Takashi , Iwai Masako , Konno Masae , Ito Kohsuke , Inoue Yasunori
Published: April 2010

A new bio-imaging sensor with photosystem I (PSI) of Thermosynechococcus elongatus and complementary metal–oxide–semiconductor (CMOS) circuits is demonstrated. Photons are converted into electrons by PSI, and electrons are detected as an electric signal by a CMOS integrated circuit. For a sensor circuit, a 4 ×4 sensor array with a CMOS source–drain follower is designed and fabricated by a standard CMOS process. An extended-gate electrode and an SU-8 passivation layer are formed on a CMOS chip by a post-CMOS process, and PSI is electrostatically fixed on the electrode. A 3×4 image of the pattern of light illuminated on a chip is taken with the sensor array, where four cells are used as reference cells.
Implantable Image Sensor with Light Guide Array Plate for Bioimaging
Authors: Sasagawa Kiyotaka , Mitani Masahiro , Sugiyama Tetsuya , Noda Toshihiko , Tokuda Takashi , Ohta Jun
Published: April 2010

We propose and demonstrate the fabrication of a light guide array (LGA) structure to improve the spatial resolution of an implantable image sensor. An LGA structure is composed of an array of holes with a high aspect ratio. By restricting the incident angle into image sensor pixels, unwanted incident light is eliminated and degradation of the spatial resolution owing to the gap from the image sensor is reduced. An LGA plate is fabricated by etching holes on a silicon wafer. The LGA plate is embedded on an image sensor and the improvement of spatial resolution is verified. As an example, images of fluorescent beads were obtained using the image sensor with the LGA plate. The imaging contrast and resolution were successfully enhanced.
Progressive-Type Fused pH and Optical Image Sensor
Authors: Nakazawa Hirokazu , Ishida Makoto , Sawada Kazuaki
Published: April 2010

A fused pH and optical image sensor is proposed and fabricated using a complimentary metal–oxide–semiconductor (CMOS) integrated circuit technology. In the proposed image sensor, a pH sensor and an optical sensor are fused in the same pixel, enabling the pH and the optical signal to be detected simultaneously in the same sensing area. Moreover, the proposed image sensor enables us to measure each piece of information without any signal cross-talk. Therefore, the relationship between pH and light distributions can be clarified by using the proposed image sensor. The proposed image sensor is expected to have applications in various fields, such as biochemical, environmental, and medical fields.