bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced p-Channel Metal–Oxide–Semiconductor Field-Effect Transistor Charge Pump for Low-Voltage Applications
Authors: Hsu Chien-Pin , Wu Hai-Ming , Lin Hongchin
Published: April 2010

In this paper, a power-efficient two-phase p-channel metal–oxide–semiconductor field-effect transistor (PMOSFET) charge pump with two auxiliary clocks to boost the gate biases of the switching transistors is proposed for low-voltage applications. It can increase overdrive voltages of the switching transistors, preserve low voltage drops within the transistors, and work well at a reduced supply voltage. Simulation results show that the proposed two-stage charge pump improves the voltage gain by more than 30% for 0.35 µm complementary metal–oxide–semiconductor (CMOS) field-effect transistor (FET) technology and improves the maximum power efficiency by 40% for 0.18 µm CMOS technology in comparison with Racape and Daga's charge pump. Measurement results show that the voltage gains of the proposed two-stage charge pump are more than 95.7 and 92% at supply voltages higher than 1.4 and 0.7 V for 0.35 and 0.18 µm CMOS technologies, respectively. A compact model of power efficiency for the proposed charge pump is derived and verified by simulations and measurements. Results show that the power efficiency can be approximately 60% at low supply voltages.
Picosecond Pulse Generators in InP-Based High Electron Mobility Transistor Technology for 10 Gbps Wireless Communication
Authors: Nakasha Yasuhiro , Kawano Yoichi , Suzuki Toshihide , Ohki Toshihiro , Takahashi Tsuyoshi , Makiyama Kozo , Hara Naoki
Published: April 2010

In this paper, we present simple digital-based pulse generators (PGs) that emit short pulses with a full width at half-maximum (FWHM) of only several picoseconds in order to realize millimeter-wave impulse radio (IR) systems that can transmit signals at 10 Gbps and above. There are distinctive advantages of using digital techniques. Scaling devices and reducing parasitic capacitances can enhance performance, which is examined by a transition analysis of the PGs. Secondly, retiming techniques enable the PGs to suppress jitter, which is essential for maintaining transmission quality. Two types of PGs are demonstrated: Type-I PG with advanced 75 nm InP-based high electron mobility transistors (HEMTs) having a cavity structure generated short pulses with a record FWHM of <4.9 ps at 20 Gbps, realizing sub-THz IR systems. Type-II PG with mature 100 nm InP-based HEMTs without the cavity retimed 6.5 ps pulses, resulting in very small jitter of 256 fs. Type-II PG was used to construct an IR transmitter of over 10 Gbps at millimeter-wave frequencies (75–110 GHz).
Effects of Nitride-Based Plasma Pretreatment Prior to SiNx Passivation in AlGaN/GaN High-Electron-Mobility Transistors on Silicon Substrates
Authors: Kim Ji Ha , Choi Hong Goo , Ha Min-Woo , Song Hong Joo , Roh Cheong Hyun , Lee Jun Ho , Park Jung Ho , Hahn Cheol-Koo
Published: April 2010

The effects of nitride-based plasma pretreatment on the output characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) on silicon substrates are investigated. N2 and NH3 plasma pre-treatment methods are studied to overcome the RF dispersion phenomenon caused by nitrogen-vacancy (VN)-related defect reduction. It is found that the nitride-based plasma pretreatment is effective to overcome the RF dispersion in AlGaN/GaN HEMTs on Si. The NH3 plasma pretreatment markedly reduced RF dispersion from 63 to 1%. This is considered to be attributable to the reduction of the effective VN-related defect density and elimination of carbon/oxide residuals on the surface of AlGaN/GaN HEMTs. A NH3 plasma pretreatment prior to SiN
x
100 nm passivation in the AlGaN/GaN HEMTs on Si markedly improves the total output power from 15 to 18.1 dBm under the operating conditions of V
DS = 15 V/V
GS = -1 V.
Excellent Stability of GaN-on-Si High Electron Mobility Transistors with 5 µm Gate–Drain Spacing Tested in Off-State at a Record Drain Voltage of 200 V and 200 °C
Authors: Marcon Denis , Hove Marleen Van , Visalli Domenica , Derluyn Joff , Das Jo , Medjdoub Farid , Degroote Stefan , Leys Maarten , Cheng Kai , Mertens Robert , Germain Marianne , Borghs Gustaaf
Published: April 2010

AlGaN/GaN high electron mobility transistors (HEMTs) were electrically stressed in pinch-off condition at a drain voltage up to 200 V for 200 h at an ambient temperature of 200 °C. The tested transistors which were grown and processed on 4-in. silicon substrate showed negligible degradation. This proves that a combination of a high quality AlGaN/GaN/AlGaN double heterostructure, the in-situ Si3N4 deposition technique and an accurately optimized gate technology result in excellent device stability under harsh conditions.
Ga-Doped ZnO/GaN Schottky Barrier UV Band-Pass Photodetector with a Low-Temperature-Grown GaN Cap Layer
Authors: Chang Kuo-Hua , Sheu Jinn-Kong , Lee Ming-Lun , Kang Kai-Shun , Huang Jing-Fong , Wang Wei-Li , Lai Wei-Chih
Published: April 2010

Ga-doped ZnO (GZO) films were deposited onto low-temperature-grown (LTG) GaN/i-GaN (PD-I) and i-GaN (PD-II) epitaxy layers to form Schottky barrier UV band-pass photodetectors (PDs). The UV PDs exhibited a narrow band-pass spectral response ranging from 330 to 380 nm. It was also found that by using an LTG GaN layer on top of conventional nitride-based UV PDs, the leakage current was significantly reduced and a much larger photocurrent-to-dark-current contrast ratio was achieved. The short-wavelength cutoff at around 330 nm can be attributed to the marked absorption of the GZO top contact layer. The zero-bias peak responsivities were estimated to be 0.13 and 0.08 A/W at 360 nm for PD-I and PD-II, respectively. When the reverse bias was below -10 V, the dark current of PD-I was considerably below 20 pA.
High Temperature Operation of Boron-Implanted Diamond Field-Effect Transistors
Authors: Ueda Kenji , Kasu Makoto
Published: April 2010

Diamond field effect transistors (FETs) with Pt or Al Schottky gate electrodes were fabricated on high-quality boron (B)-implanted layers formed by combining ion-implantation and high-pressure and high-temperature annealing. The high temperature characteristics of these FETs were examined. Pt-gate B-implanted diamond FETs showed maximum drain current (I
DS) of 0.16 mA/mm at gate voltage of -2 V and drain voltage of -20 V at 25 °C. The I
DS increased as temperature increased because of the activation of boron, and it showed maximum value of 3.9 mA/mm at ∼200 °C. Al-gate FETs showed similar temperature dependence of I
DS, though the operation temperature and I
DS were higher than those of Pt-gate FETs. High-temperature operation of the B-implanted diamond FETs was possible above 550 °C without severe drain bulk leakage, though the maximum I
DS gradually decreased as temperature increased because of drain bulk leakage above 300 °C.
Extraction of Drain Current and Effective Mobility in Epitaxial Graphene Channel Field-Effect Transistors on SiC Layer Grown on Silicon Substrates
Authors: Kang Hyun-Chul , Olac-vaw Roman , Karasawa Hiromi , Miyamoto Yu , Handa Hiroyuki , Suemitsu Tetsuya , Fukidome Hirokazu , Suemitsu Maki , Otsuji Taiichi
Published: April 2010

We have fabricated and characterized field-effect transistors (FETs) with an epitaxial graphene channel on a SiC layer grown on a Si substrate. Epitaxial graphene can be formed on SiC substrates by thermal decomposition of its surface under an ultrahigh-vacuum (UHV) condition. To incorporate the thermal decomposition of SiC on Si substrates, we used an approach of growing a thin 3C-SiC(111) layer on Si substrates and subsequently annealing them in UHV to form graphene on the surface of the 3C-SiC layer. Backgate-field-effect transistors using the SiC layer as a gate insulator were characterized. Although a large amount of gate-leakage current is observed, the drain current modulation by backgate voltage is confirmed by extracting the channel current from the total drain current. The extracted channel current characteristics also suggest that the extracted effective mobility exceeds the universal mobility of bulk silicon under similar circumstances.
AlGaN Metal–Semiconductor–Metal Photodetectors with Low-Temperature AlN Cap Layer and Recessed Electrodes
Authors: Chen Chin-Hsiang , Chang Shoou-Jinn , Wu Ming-Hsien , Tsai Sung-Yi , Chien Hsiu-Ju
Published: April 2010

Al0.16Ga0.84N 320 nm near-solar-blind ultraviolet (UV) metal–semiconductor–metal photodetectors (MSM-PDs) with a low-temperature AlN (LT-AlN) layer and inductively coupled plasma (ICP) recessed electrodes were successfully fabricated. Compared with the conventional MSM-PDs, it was found that the measured photocurrent was much larger for the MSM-PD with the LT-AlN layer and ICP recessed electrodes. The responsivity of the MSM-PD with the LT-AlN layer and ICP recessed electrodes was also found to be larger, which could be attributed to the ICP-etching-induced photoconductive gain.
Nitride-Based Metal–Semiconductor–Metal Photodetectors with InN/GaN Multiple Nucleation Layers
Authors: Chen Chin-Hsiang , Wang Kuo-Ren , Tsai Sung-Yi , Chien Hsiu-Ju , Wu San-Lein
Published: April 2010

GaN metal–semiconductor–metal (MSM) photodetectors with InN/GaN multiple nucleation layers were proposed and fabricated. We achieved a much smaller dark current and a larger photocurrent-to-dark current ratio from the proposed device with InN/GaN multiple nucleation layers than that from the GaN MSM photodetector with conventional single low-temperature GaN nucleation layer. We also achieved a much larger UV-to-visible spectral response ratio of photoresponse at 360–450 nm from the photodetector with InN/GaN multiple nucleation layers. Furthermore, we also found that we can significantly reduce noise current density using these InN/GaN multiple nucleation layers.
Enhanced Luminescence Efficiency of InGaN/GaN Multiple Quantum Wells by a Strain Relief Layer and Proper Si Doping
Authors: Tsai Ping-Chieh , Su Yan-Kuin , Chen Wen-Ray , Huang Chun-Yuan
Published: April 2010

The effects of a strain relief layer (SRL) employed in the InGaN/GaN light-emitting diodes (LEDs) was demonstrated. The wavelength shift was reduced to as small as 2.5 nm by inserting a SRL between n-GaN and InGaN/GaN multiple quantum wells (MQWs). For the improvement of optical properties, a proper Si-doped layer was simultaneously added in the last several barriers of In0.08Ga0.92N/GaN SRL. It can be found that the output power was increased more than 25% as the Si doping level was increased up to 5 times in the last three barriers of SRL at an injection current of 20 mA. Furthermore, the forward voltages at 20 mA were almost the same for all LEDs with different doping levels and positions.
A Screen-Printed Sn-Based Substrate Technology for the Fabrication of Vertical-Structured GaN-Based Light-Emitting Diodes
Authors: Wang Pei-Ren , Wang Shui-Jinn , Kuo Hon-Yi , Uang Kai-Ming , Chen Tron-Min , Wang Po-Hung , Lee Wei-Chi , Kuo Der-Ming
Published: April 2010

A dicing-free substrate technology was proposed and demonstrated to simplify the fabrication of vertical-structured metal substrate GaN-based light-emitting diodes (VM-LEDs) using a Sn-based solder screen printing technique with patterned laser lift-off technology. As compared with conventional sapphire substrate GaN-based LEDs, VM-LEDs with an effective emission area of 1000×1000 µm2 were found to have a 0.38 (0.87) V reduction in forward voltage at 350 (700) mA. In addition, their enhancement in light output power in the current range of 350–700 mA was found to successively increase from 55 to 76%. By considering these results, the power conversion efficiency of VM-LEDs was found to be 2.14 times that of regular LEDs at 700 mA.
Enhanced Light Output of Vertical-Structured GaN-Based Light-Emitting Diode with Surface Roughening Using KrF Laser and ZnO Nanorods
Authors: Lee Wei-Chi , Uang Kai-Ming , Chen Tron-Min , Kuo Der-Ming , Wang Pei-Ren , Wang Po-Hong , Wang Shui-Jinn
Published: April 2010

To further improve the performance of vertical-structured GaN-based light-emitting diodes (V-LEDs), surface roughening using a KrF laser and KOH wet chemical etching, followed by hydrothermal growth of vertically aligned ZnO nanorods on top of the n-GaN surface were investigated and discussed. Compared with that of the V-LEDs (300×300 µm2in chip size) with only surface KOH wet etching, the formation of curved protrusions and ZnO nanorods on the n-GaN surface typically enables an increase in light output power (Lop) by 29% at 20 mA and 41% at 100 mA with a decrease in forward voltage (Vf) from 3.24 to 3.06 V at 20 mA and 3.9 to 3.7 V at 100 mA, respectively. The cumulative effect of the curved protrusions, hexagonal cones, and vertically aligned ZnO nanorods formed as a result of effectively reducing the effective thickness of the n-GaN layer, improving the ohmic contact to n-GaN, increasing the surface emission area, and enhancing the escape probability of photons was responsible for these improvements.
Indium-Doped MgxZn1-xO Films for ZnO-Based Heterojunction Diodes
Authors: Tsuboi Takako , Yamamoto Kenji , Nakamura Atsushi , Temmyo Jiro
Published: April 2010

Indium-doped Mg
x
Zn1-x
O (Mg
x
Zn1-x
O:In) thin film and ZnO:In thin films were successfully grown by remote plasma-enhanced metalorganic chemical vapor deposition (RPE-MOCVD). The In supply source used is trimethylindium (TMIn). The surface morphology, structural changes, and optical band gap energy in Mg
x
Zn1-x
O:In were investigated by varying the amount of the supplied TMIn and were compared with ZnO:In systems. Our main achievement point is that we have markedly improved the surface morphology of Mg0.05Zn0.95O:In films from being pillar like to being film like with an increase in the amount of indium. The improved green electoluminescence emission (EL) characteristic the ZnO-based DH system was employing the Mg0.05Zn0.95O:In film here and in conclusions.
Enhanced Room-Temperature 1.6 µm Electroluminescence from Si-Based Double-Heterostructure Light-Emitting Diodes Using Iron Disilicide
Authors: Suzuno Mitsushi , Koizumi Tomoaki , Kawakami Hideki , Suemasu Takashi
Published: April 2010

We have fabricated Si/β-FeSi2/Si (SFS) double-heterostructure (DH) light-emitting diodes (LEDs) on Si(111) substrates with β-FeSi2 thickness ranging from 80 nm to 1 µm, and Si0.7Ge0.3/β-FeSi2/Si0.7Ge0.3(SGFSG) DH LEDs with a 200-nm-thick β-FeSi2 layer using lattice-matched Si0.7Ge0.3 layers by molecular-beam epitaxy. The electroluminescence (EL) peaked at an emission wavelength of approximately 1.6 µm at room temperature. As the thickness of the β-FeSi2 layer was increased in the SFS DH LEDs, the emission power of EL increased for a given current density J. EL with an emission power of over 0.4 mW and an external quantum efficiency of approximately 0.1% was achieved for the SFS DH LED with a 1-µm-thick β-FeSi2 layer. The smallest J value necessary for EL output, which is approximately 1 A/cm2, was achieved for the SGFSG DH LEDs.
Optical Signal Modulation of Semiconductor Soliton Device with Circular Ring Resonator
Authors: Shih Ming Chang , Sheih Wen Hsuan , Chen Cheng Seng
Published: April 2010

We demonstrated a novel optical signal modulation by the interaction of spatial solitons generated from a semiconductor ridge waveguide circular ring resonator with an input signal from the Y-junction coupling section. By controlling the optical power of the circular ring resonator with emission at 660 nm, in which a spatial soliton waveguide is formed owing to the photorefractive effect, one can manipulate the transmission of the input signal through the soliton waveguide. For an input signal of 1560 nm, the transmission through this soliton waveguide can be modulated within a 10 dB depth. The fabrication and optical properties of the fabricated devices are presented.
Reduction in Operation Voltage of Silicon Ring Optical Modulator Using High-k (Ba,Sr)TiO3 Cladding Layer
Authors: Amemiya Yoshiteru , Nishida Mizue , Ding Hao , Fukuyama Masataka , Yokoyama Shin
Published: April 2010

Electric-field drive Si ring optical modulators with a (Ba,Sr)TiO3 (BST) cladding layer have been fabricated. A lateral electric field is applied across the Si ring using the side Pt electrodes, and the optical output from the drop port is measured. It is estimated that an operation voltage of less than 10 V is possible when the relative dielectric constant of the cladding layer is larger than 150 and the quality factor is 5×104. The operation voltage of the fabricated optical modulator with a BST cladding layer is reduced to <1/8 relative to that of the SiO2 and Si3N4 cladding layers. One reason for the still high operation voltage (125 V for 75% modulation) is the low quality factor, which is limited by the light propagation loss of the BST film. It is also estimated that an operation voltage of less than 10 V is achievable when the propagation loss of the cladding layer is improved to less than 28 dB/cm.
Design of Polarization-Independent Si-Wire-Waveguide Wavelength Demultiplexer for Optical Network Unit
Authors: Okayama Hideaki , Kotani Kyoko , Maeno Yoshinori , Shimura Daisuke , Yaegashi Hiroki , Ogawa Yoh
Published: April 2010

We report the design of a compact wavelength demultiplexer using a Si wire waveguide as an optical network unit. We use a Mach–Zehnder lattice interferometeric filter structure to attain a flat-top response. The large wavelength dispersion of the Si wire waveguide requires special design considerations for widely separated wavelength channels. Preliminary experimental results obtained by the device fabricated in a silicon-on-insulator wafer showed a flat-top filter response.
Effect of Mesa Shape on Threading Dislocation Density in Ge Epitaxial Layers on Si after Post-Growth Annealing
Authors: Takada Yoichi , Osaka Jiro , Ishikawa Yasuhiko , Wada Kazumi
Published: April 2010

The effect of mesa shape on threading dislocation density in Ge epilayers on Si is studied. It is found from the etch-pit counting on the surfaces that the post-growth annealing reduces the threading dislocation densities in Ge mesa structures on Si and in the blanket Ge layers. The dry-etched mesas with vertical sidewalls show dislocation densities identical to those for the blanket layers. This indicates that the reduction in threading dislocation density in the dry-etched mesas is predominantly due to the annihilation of dislocations with opposite Burgers vectors, while the motion of dislocations to the mesa edges does not contribute. On the other hand, the selective-grown mesas with inclined (311) facet sidewalls show lower dislocation densities than those for the blanket layers, indicating that the dislocations can glide out beyond the mesa edges. Since the shear stress thermally induced in Ge is responsible for the dislocation glide motion, the present result suggests that the selective-grown mesas should be different from the dry-etched mesas in terms of the shear stress accumulated during the annealing. Strain simulations for these mesa structures show that the strength and distribution of the thermally induced shear stress are quite different near the top edges between the mesa structures. We discuss the relationship between the distribution of thermal stress and the reduction in dislocation density.
Hexagonal AlN(0001) Heteroepitaxial Growth on Cubic Diamond (001)
Authors: Hirama Kazuyuki , Taniyasu Yoshitaka , Kasu Makoto
Published: April 2010

Structural properties of a hexagonal aluminum nitride (AlN) (0001) layer grown on a cubic diamond (001) substrate by metalorganic vapor-phase epitaxy (MOVPE) are investigated to discuss its growth mechanism. It was found that the AlN layer consists of tilted and rotated domains, which are nucleated just on diamond (001) substrates at the initial growth stage. The tilted AlN domains form on the diamond {111} facets of the pits, which are created on the diamond (001) surface during the thermal cleaning in H2. The AlN[0001] direction of the tilted domains is oriented normal to the diamond {111} facets because the atomic bonding configurations of AlN(0001) and diamond (111) planes are similar. On the other hand, two kinds of rotated AlN domains form on the diamond (001) surface. The [0001] direction of the rotated AlN domains is oriented normal to diamond (001) surface, and the AlN[1010] or [1120] direction is oriented to the diamond [110] direction. The formation of the two kinds of rotated AlN domains originates from the nucleation on two different diamond (001) terraces with one atomic layer height difference.
Improvement in a-Plane GaN Crystal Quality by Investigating Different Buffer Layer
Authors: Hsu Hsiao-Chiu , Su Yan-Kuin , Huang Shyh-Jer , Wang Yu-Jen , Wu Chun-Ying , Chou Ming-Chieh
Published: April 2010

Non-polar a-plane GaN epitaxial layer was grown on r-plane sapphire substrates by metal–organic chemical vapor deposition (MOCVD). In this paper, we implanted different buffer layer, including the GaN buffer layers under different growth parameters and in situ SiN
x
layer, to improve the crystal quality. First, high growth temperature (1150 °C) of GaN buffer layer can improve the crystal quality than low temperature (540 °C) by scanning electron microscopy (SEM) images. The inverse pyramidal pits are also reduced by implanting in situ SiN
x
interlayer, behaving as a nanomask deposited on r-plane sapphire. The GaN film quality is also improved by growing GaN buffer layer under low V/III ratio and confirmed by high-resolution X-ray diffraction (HR-XRD). An improvement of crystal quality through initial surface roughening can be verified by atomic force microscopy (AFM). The rms roughness of the overlaying GaN surface can be reduced from 11.82 to 1.54 nm. The growth mechanism was discussed.
Epitaxial Overgrowth of Gallium Nitride Nano-Rods on Silicon (111) Substrates by RF-Plasma-Assisted Molecular Beam Epitaxy
Authors: Ku Jui-Tai , Yang Tsung-Hsi , Chang Jet-Rung , Wong Yuen-Yee , Chou Wu-Ching , Chang Chun-Yen , Chen Chiang-Yao
Published: April 2010

Strain-free gallium nitride (GaN) overgrowth on GaN nano-rods is realized by RF-plasma assisted molecular beam epitaxy (RF-MBE) on silicon (Si) substrate. The strain-free condition was identified by the strong free A exciton (FXA) photoluminescence (PL) peak at 3.478 eV and the E2 high phonon Raman shift of 567 cm-1. It is clearly demonstrated that the critical diameter of GaN nano-rods is around 80 nm for the overgrowth of strain-free GaN. The blue-shift of PL peak energy and phonon Raman energy with decreasing the diameter of nano-rod result from the strain relaxation of overgrowth GaN.
Fabrication of Self-Assembled InGaAs Squarelike Nanoholes on GaAs(001) by Droplet Epitaxy
Authors: Boonpeng Poonyasiri , Jevasuwan Wipakorn , Panyakeow Somsak , Ratanathammaphan Somchai
Published: April 2010

The fabrication of self-assembled InGaAs squarelike nanoholes on GaAs(001) substrates grown by droplet epitaxy using molecular beam epitaxy was reported. The formation mechanism is explained by the As4 diffusion in droplets during the supply of As4 flux. The effects of substrate temperature (300–390 °C) during the InGa droplet deposition on their dimension and density were investigated. The surface morphology of InGaAs nanoholes as well as their depth profile was examined by atomic force microscopy (AFM). The square shape is oriented along [110] and [110] crystallographic directions with slightly different profiles due to anisotropy behavior. The size uniformity of the squarelike nanoholes is well controlled with less deviation at higher substrate temperatures.
Effect of Drain Bias Stress on Stability of Nanocrystalline Silicon Thin Film Transistors with Various Channel Lengths
Authors: Kim Sun-Jae , Park Sang-Geun , Ji Seon-Beom , Han Min-Koo
Published: April 2010

We report the electrical stability of bottom-gate nanocrystalline silicon (nc-Si) thin film transistors (TFTs) with various channel lengths under drain bias stress for the first time. As the bias stress at the drain terminal increases at a fixed gate bias, the threshold voltage (V
TH) shift of the nc-Si TFTs decreases significantly. Under the drain bias stress, the V
TH shift decreases with channel length. The smaller V
TH shift was analyzed on the basis of the concentration of the channel charge. A high drain bias reduces the carrier concentration near the drain terminal. Also, the ratio of the depleted charges to total charges increases with decreasing channel length due to the drain bias. Thus, a short-channel TFT has a smaller normalized channel charge than a long-channel TFT. A low carrier concentration induces a small number of defect states; thus the V
TH shift of a short-channel TFT is smaller than that of a long-channel TFT.
Ferroelectric Properties of Lead Zirconate Titanate Thin Film on Glass Substrate Crystallized by Continuous-Wave Green Laser Annealing
Authors: Jiang Jun , Kuroki Shin-Ichiro , Kotani Koji , Ito Takashi
Published: April 2010

The ferroelectric properties of lead zirconate titanate (PZT) films crystallized by a continuous-wave (CW) green laser are discussed in this paper. After CW green laser annealing, two kinds of typical crystallization modes of the PZT thin films were observed: island crystallization and lateral crystallization. In the island crystallization region, the PZT film was crystallized uniformly over the thin films. However, poor surface roughness was found in lateral crystallization region. Significant improvements of ferroelectric characteristics have been achieved in the island crystallization region after optimizing with a low energy density. By varying energy density from 4.5 to 7.1 kW/cm2 and fixing annealing time at 42.5 ms, significant features were found at an energy density of 5.3 kW/cm2. A maximum remanent polarization of 27 µC/cm2 was obtained.
Dislocation-Based Si-Nanodevices
Authors: Reiche Manfred , Kittler Martin , Buca Dan , Hähnel Angelika , Zhao Qing-Tai , Mantl Siegfried , Gösele Ulrich
Published: April 2010

The realization of defined dislocation networks by hydrophobic wafer bonding allows the electrical characterization of individual dislocations. The present paper investigates the properties of such dislocations in samples containing high dislocations densities down to only six dislocations. The current induced by a single dislocation is determined by extrapolation of the current measured for various dislocation densities. Based on our present and previously reported analyses the electronic properties of individual dislocations can be inferred. The investigations show that dislocations in the channel of metal–oxide–semiconductor field-effect transistors (MOSFETs) result in increasing drain currents even at low drain and gate voltages. Because a maximum increase of the current is obtained if a single dislocation is present in the channel, arrays of MOSFETs each containing only one dislocation could be realized on the nanometer scale. The distance of the dislocations can be well controlled by wafer bonding techniques.
Slow and Fast Electron Channels in a Coherent Quantum Dot Mixer
Authors: Austing Guy , Payette Chris , Yu Guolin , Gupta James , Aers Geof , Nair Selva , Amaha Shinichi , Tarucha Seigo
Published: April 2010

We describe a means to realize slow and fast electron channels by coherent mixing of single-particle levels in quantum dots. The underlying physics, which gives insight into state superposition, can potentially be realized in multi-dot structures with complex gate control. However, we employ vertical double dot structures and in our scheme the mixing of single-particle levels arises because of natural perturbations in the confining potential of the high-symmetry dots. Additionally, because of the intrinsic properties of a Fock–Darwin-like spectrum, we utilize a magnetic field to bring multiple single-particle energy levels into close proximity. We determine single-electron resonant tunneling times (effectively dwell times when on resonance) that are either extended in the slow channel or shortened in the fast channel. Most dramatically, for the slow channel, slow-down factors of ∼10 and single-electron resonant tunneling times extended into the µs range are demonstrated in all systems of two, three, and four mixed single-particle states investigated here.
Voltage Switching Technique for Detecting Nuclear Spin Polarization in a Quantum Dot
Authors: Takahashi Ryo , Kono Kimitoshi , Tarucha Seigo , Ono Keiji
Published: April 2010

We have introduced a source–drain voltage switching technique for studying nuclear spins in a vertical double quantum dot. Switching the source–drain voltage between the spin-blockade state and the zero-bias Coulomb blockade state can tune the energy difference between the spin singlet and triplet, and effectively turn on/off the hyperfine interaction. Since the change in the nuclear spin state affects the source–drain current, nuclear spin properties can only be detected by transport measurement. Using this technique, we have succeeded in measuring the timescale of nuclear spin depolarization. Furthermore, combining this technique and an RF ac magnetic field, we successfully detected continuous-wave NMR signals of 75As, 69Ga, and 71Ga, which are contained in a quantum dot.
Robustness of Charge-Qubit Cluster States to Double Quantum Point Contact Measurement
Authors: Tanamoto Tetsufumi
Published: April 2010

We theoretically investigate the robustness of cluster states in charge qubit system based on quantum dot (QD) and double quantum point contact (DQPC). Trap state is modeled by an island structure in DQPC and represents a dynamical fluctuation. We found that the dynamical fluctuations affect the cluster states more than static fluctuation caused by QD size fluctuation.
Effect of Ribbon Width and Doping Concentration on Device Performance of Graphene Nanoribbon Tunneling Field-Effect Transistors
Authors: Lam Kai-Tak , Chin Sai-Kong , Seah Da Wei , Kumar S. Bala , Liang Gengchiau
Published: April 2010

The device performance of graphene nanoribbon (GNR) tunneling field-effect transistor (TFET) is studied using the self-consistent non-equilibrium Green's function (NEGF) and quasi-two dimensional Poisson solver based on the Dirac equation model. The effects of different GNR widths and doping concentrations at the source and drain on the device characteristics are investigated and the electronic property of the GNR TFET is found to be strongly dependent on its width. A comprehensive characterization of this dependence is expected to be crucial to the designs and fabrications of GNR TFETs. Furthermore, the doping concentrations at the source and drain is found to play a crucial role on the ON- and OFF-state currents (I
ON and I
OFF) respectively. Therefore, the ability to control the doping concentrations allows the tailoring of the drive current, the I
ON/I
OFF ratio and the subthreshold swing of GNR TFETs to meet different design requirements.
Comparative Study of Tunneling Field-Effect Transistors and Metal–Oxide–Semiconductor Field-Effect Transistors
Authors: Choi Woo Young
Published: April 2010

Electrical characteristics of tunneling field-effect transistors (FETs) have been compared with those of metal–oxide–semiconductor FETs (MOSFETs) in terms of subthreshold swing (SS), on/off current ratio, off current and on current. According to simulation results, tunneling FETs have advantages over MOSFETs for low-power consumption: smaller SS below 60 mV/dec at room temperature, lower off current, higher on/off current ratio and better immunity to short channel effects. However, low on current of tunneling FETs is problematic for reasonable circuit performance. In this paper, in order to boost on current, strain-induced low bandgap substrate has been considered. It is observed that on current of tunneling FETs can be comparable with that of MOSFETs as more strain is applied. The tunneling FET can be thought of as a promising alternative to the MOSFET for low-power application.
Suppression of Critical Current in Submicron Intrinsic Josephson Junction Fabricated in a Bi2Sr2Ca2Cu3O10+δ Single Crystal Whisker
Authors: Saini Shrikant , Kim Gui Shik , Kim Sang-Jae
Published: April 2010

We have fabricated intrinsic Josephson junction array stack in a Bi2Sr2Ca2Cu3O10+δ (Bi-2223) single crystal whisker using three dimensional focused ion beam milling technique. We report measurements of current density depend on junctions array at 30 K upon the junction cross-sectional area S showing a strong suppression in critical current density for junctions with S≤1 µm2. We discussed quantum fluctuations of phase in submicron junctions which is a cause for suppression of critical current density.
Electron Injection into Pentacene Field-Effect Transistor Observed by Time-Resolved Optical Second Harmonic Generation Imaging
Authors: Manaka Takaaki , Nakao Motoharu , Liu Fei , Weis Martin , Iwamoto Mitsumasa
Published: April 2010

Electron injection from a gold (Au) electrode into a pentacene field-effect transistor (FET) was investigated by time-resolved microscopic optical second harmonic generation (TRM-SHG) imaging. The evolution of the TRM-SHG images below the source electrode evidently showed the presence of electron injection. The transient electric field migration in the FET channel indicated an inhibited electron transport attributed to a high electron trap density. The theoretical approach based on the two-dimensional coupled diffusion-drift and Poisson equations with the multiple-trapping and releasing process clearly supports the trap-inhibited transport.
Development of Field-Effect Transistor-Type Photorewritable Memory Using Photochromic Interface Layer
Authors: Yoshida Manabu , Suemori Kouji , Uemura Sei , Hoshino Satoshi , Takada Noriyuki , Kodzasa Takehito , Kamata Toshihide
Published: April 2010

We developed a novel field-effect transistor (FET) type photorewritable memory using a photochromic interface layer between the active layer and the gate insulator layer. A diarylethene (DAE) derivative was employed as a photochromic material and pentacene was employed as an active layer. DAE has two types of photoisomer, i.e., the closed- and open-ring isomers. In this study, it was clarified that the highest occupied molecular orbital (HOMO) level of the closed-ring DAE worked as an interfacial deep trap level, and that the generation of the interfacial deep trap level by photoisomerization induced the photoswitching and photomemory behaviors of transistor properties.
Organic Electronics: Relaxation Time Controlled Devices
Authors: Weis Martin , Taguchi Dai , Manaka Takaaki , Iwamoto Mitsumasa
Published: April 2010

In present work the charge transport through the metal–semiconductor–metal (MIM), organic field-effect transistor (OFET) and organic static induction transistor (OSIT) is discussed on the basis of dielectric physics. The propagation of injected carriers is evaluated by the transmission line model and discussed for two- and three-electrodes systems individually. On the basis of this analysis we find different carrier transport mechanism: (i) the drift in electric field for MIM structure, (ii) interface charge propagation on the organic semiconductor–gate insulator interface for the OFET structure, and (iii) drift or interface limited charge transport in the OSIT structure. We show that the charge transport mechanism depends on the relaxation time on the interface.
Alignment Properties of Liquid Crystal Molecules under AC and DC Voltage Application Studied by Surface Plasmon Resonance and Optical Waveguide Spectroscopy
Authors: Ikarashi Aya , Baba Akira , Shinbo Kazunari , Kato Keizo , Kaneko Futao
Published: April 2010

In this study, we report the evaluation of the tilt angle of liquid crystal (LC) molecules near the surface of SiO2 alignment layers and in the whole cell when AC and/or DC voltages are applied. The LC molecule 4-cyano-4'-n-pentylbiphenyl was used. The LC cell consisted of a Au (50 nm)/SiO2 (30 nm)/LC (3 µm)/SiO2 (30 nm)/Au (100 nm) system. Surface plasmon resonance (SPR) spectroscopy and optical waveguide spectroscopy (OWS) in an attenuated total-reflection configuration were used to monitor the alignment properties of LC molecules. From the SPR/OWS angular scan properties, the profile of the tilt angle from the surface to inside the cell was obtained. Furthermore, the effect of space-charge polarization on the LC alignment properties was observed from the SPR kinetic properties. As demonstrated in this report, this technique should provide useful information for understanding the interfacial phenomena in LC displays.
Effects of an Electric Field and a Solvent during Thermal Treatment in Film Formation of Poly(vinylidene fluoride–tetrafluoroethylene)
Authors: Jeong Jong-Hyeon , Kimura Chiharu , Aoki Hidemitsu , Sugino Takashi
Published: April 2010

In order to apply a poly(vinylidene fluoride–tetrafluoroethylene) piezoelectric polymer to a micro generator as a membrane, the polymer is deposited by spin coating on a substrate. To improve the stability of the film surface, the film is annealed at a temperature higher than its melting point. In this process, the chain structure of the polymer is transmuted by O atoms, and remanent polarization also decreases. We have attempted to enforce the rearrangement of the polymer chain through an electric field in an annealing process. By applying an electric field to an annealing process, O atoms and unnecessary bonds are eliminated. As a result, the remanent polarization of the film annealed with an electric field is measured twice and compared with that of the film annealed without an electric field.
Preparation of Electrospun Polymer Fibers Using a Copper Wire Electrode in a Capillary Tube
Authors: Shinbo Kazunari , Onozuka Shintaro , Hoshino Rikiya , Mizuno Yoshinori , Ohdaira Yasuo , Baba Akira , Kato Keizo , Kaneko Futao
Published: April 2010

Polymer fibers were prepared by an electrospinning method utilizing a copper wire electrode in a capillary tube. The morphology of electrospun poly(vinyl alcohol) (PVA) fibers was observed, and was found to be dependent on the wire electrode tip position in the capillary tube, the concentration of the polymer solution, the distance between the electrodes, and the applied voltage. By using the wire electrode, the experimental setup is simple and the distance between the electrodes and the applied voltage can be easily reduced. Furthermore, the preparation of poly(3-hexylthiophene) (P3HT) fibers was carried out. P3HT fibers were successfully prepared by mixing poly(ethylene oxide) (PEO) in P3HT solution. Orientation control was also carried out by depositing the fibers on a rotating collector electrode, and the alignment of the P3HT:PEO fibers was confirmed. Anisotropy of the optical absorption spectra was also observed for the aligned fibers.
Complementary Metal Oxide Semiconductor Based Multimodal Sensor for In vivo Brain Function Imaging with a Function for Simultaneous Cell Stimulation
Authors: Tagawa Ayato , Mitani Masahiro , Minami Hiroki , Noda Toshihiko , Sasagawa Kiyotaka , Tokuda Takashi , Ohta Jun
Published: April 2010

We have developed a multimodal complementary metal oxide semiconductor (CMOS) sensor device embedded with Au electrodes for fluorescent imaging and cell stimulation in the deep brain of mice. The Au electrodes were placed on the pixel array of the image sensor. Windows over the photodiodes were opened in the electrode area for simultaneous fluorescent imaging and cell stimulation in the same area of the brain tissue. The sensor chip was shaped like a shank and was packaged by two packaging methods for high strength or minimal invasion. The experimental results showed that the 90 ×90 µm2 Au electrodes with windows were capable of injecting theta burst stimulation (TBS)-like current pulses at 0.2–1 mA in a saline solution. We successfully demonstrated that fluorescent imaging and TBS-like current injection can be simultaneously performed in the electrode area of a brain phantom.
Detection of 8 nm Diameter Superparamagnetic Beads by Magnetically-Induced Manipulation of Micrometer-Sized Magnetic Beads: A Novel Protocol for Magnetically-Labeled Biosensing
Authors: Morimoto Yoshitaka , Takamura Tsukasa , Park Sang Yoon , Sakamoto Satoshi , Kawata Shintaro , Handa Hiroshi , Sandhu Adarsh
Published: April 2010

Biosensing platforms based on functionalized superparamagnetic beads acting as “magnetic-labels” show tremendous potential for rapid and highly-sensitive point of care medical diagnosis. Recently, for greater quantification, there are increasing demands for the use of magnetic labels with diameters of 8–150 nm, which are comparable in size to actual biomolecules. However, detection of small numbers of sub-150 nm sized magnetic beads by magnetoresistive device-based platforms is extremely challenging due to the intrinsic noise of these electronic devices. Here, we describe an easy and economical detection method of low areal densities of 8-nm-diameter superparamagnetic “target beads” immobilized over millimeter-sized substrates by optically monitoring the magnetically induced “capture” of easily visible, micrometer sized superparamagnetic “columnar beads” by the targets in less than a few tens of seconds.
Selective Detection of Antigen-Antibody Reaction Using Si Ring Optical Resonators
Authors: Fukuyama Masataka , Yamatogi Shinya , Ding Hao , Nishida Mizue , Kawamoto Chika , Amemiya Yoshiteru , Ikeda Takeshi , Noda Tomohide , Kawamoto Seiji , Ono Kazuhisa , Kuroda Akio , Yokoyama Shin
Published: April 2010

Si ring optical resonators have been fabricated by the Si LSI technology using electron beam lithography and reactive ion etching. The resonator is applied for sensing receptor-analyte reaction using silicon-binding protein, Si-tag, which enables receptors immobilized on a Si dioxide surface with a controlled orientation. For the receptor, the major house-dust mite allergen called Der f 2 was used, and for the analyte anti-Der f 2 immunoglobulin type G (IgG), which is selectively bound to Der f 2, was used. Antiserum against Der f 2, which contains anti-Der f 2 IgG, was diluted to 1/100 with the pure water, and exposed to the resonator on which the Der f 2 was adsorbed with the Si-tag. Then the resonance wavelength was shifted by 0.18 nm, while exposure of the normal rabbit serum containing no Der f 2 IgG resulted in the peak shift less than half (0.07 nm). These results indicate the selective reaction between Der f 2 and anti-Der f 2 IgG.
In situ Measurement of Combustion Gas Using Terahertz Time Domain Spectroscopy Setup for Gas Phase Spectroscopy and Measurement of Solid Sample
Authors: Uno Takeshi , Tabata Hitoshi
Published: April 2010

The transmission properties of gas phase samples heavily contaminated with aerosols, particles, and water vapor generated by combustible materials as well as the feasibility of pollution detection were obtained by terahertz time domain spectroscopy (THz-TDS) in the 0.2 to 3 THz frequency region. The absorption properties of solid-state samples and their correlation with the intensity of real-time THz images were measured using a THz camera in the region of λ≥30 µm. Molecules with weaker dipole moments, such as carbon monoxide, which was detected at higher concentrations in the combustion gas by gas chromatography analysis, did not exhibit sufficient absorption owing to the resolution of THz-TDS. However, no attenuation of transmittance was observed, and we confirmed that THz spectroscopy enables direct and simultaneous measurements of gas phase samples containing contaminants without prefiltration to remove particles in contrast to infrared (IR) spectroscopy. Finally, we confirmed that the absorption properties of solid-state samples correspond to the intensities of real-time THz images.
Lead Zirconate Titanate Acoustic Energy Harvester Proposed for Microelectromechanical System/IC Integrated Systems
Authors: Shinoda Shigeki , Tai Takahiro , Itoh Hisanori , Sugou Tomohisa , Ichioka Hirohide , Kimura Shu , Nishioka Yasushiro
Published: April 2010

In this paper, we report on microelectromechanical system (MEMS) energy harvesters with a diaphragm consisting of a 1-µm-thick lead zirconate titanate (PZT) film formed by the sol–gel method. Electrical power can be generated using the piezoelectric effects of the PZT diaphragm that vibrates in acoustic fields. Harvesters with different diaphragm diameters of 1.5 and 2.0 mm were fabricated. The top electrode covered the entire PZT diaphragm. The measured first resonance frequencies of those diaphragms were 6.02 and 5.72 kHz, and the third resonance frequencies were 24.02 and 18.02 kHz, respectively. The measured frequency spectrum indicated that the induced voltages are larger and more widely distributed for the third resonance than for the first resonance. Those devices generated power of 1.1 ×10-11and 5.1 ×10-12W under the irradiation of 100 dB sound pressure at their third resonance frequencies.
Observation of Spin Relaxation in InGaAs/AlAsSb Quantum Wells
Authors: Izumi Sotaro , Gozu Shin-Ichiro , Mozume Teruo , Saeki Yu , Nukui Takao , Tackeuchi Atsushi
Published: April 2010

We have investigated the exciton spin relaxation in InGaAs/AlAsSb quantum wells using time-resolved spin-dependent pump and probe reflectance measurements. The spin relaxation time of 1.46 µm electron-heavy hole excitons at room temperature is obtained to be 27–54 ps for an excitation power of 20–100 mW. The carrier density dependence of the exciton spin relaxation time was clearly observed, suggesting that the spin relaxation mechanism is strongly related to the Bir–Aronov–Pikus process at room temperature.
Fine-Grained Power-Gating Scheme of a Metal–Oxide–Semiconductor and Magnetic-Tunnel-Junction-Hybrid Bit-Serial Ternary Content-Addressable Memory
Authors: Matsunaga Shoun , Natsui Masanori , Hiyama Kimiyuki , Endoh Tetsuo , Ohno Hideo , Hanyu Takahiro
Published: April 2010

A fine-grained power-gating scheme combining metal–oxide–semiconductor (MOS) transistors with magnetic-tunnel-junction (MTJ) devices, where storage data still remains even if the power supply is cut off, is proposed for an ultra low-power bit-serial ternary content-addressable memory (TCAM). Once a mismatched result is detected in a sequence of a bit-level equality-search operation, the power supply of all the cells in the word circuit is cut off, which greatly reduces the standby power dissipation in the word circuit. The standby power dissipation of the proposed TCAM in the standby mode is reduced to about 1.2% in comparison with that of a complementary MOS (CMOS)-only-based TCAM. Moreover, the power-delay product of the proposed TCAM is reduced to 15.5% in comparison with that of the corresponding CMOS-only-based TCAM.
The Performance of Magnetic Tunnel Junction Integrated on the Back-End Metal Line of Complimentary Metal–Oxide–Semiconductor Circuits
Authors: Endoh Tetsuo , Iga Fumitaka , Ikeda Shoji , Miura Katsuya , Hayakawa Jun , Kamiyanagi Masashi , Hasegawa Haruhiro , Hanyu Takahiro , Ohno Hideo
Published: April 2010

In this paper, we have described the complementary metal–oxide–semiconductor (CMOS)/magnetic tunnel junction (MTJ) integrated process technology; MTJs were fabricated on via metal with surface roughness of 0.3 nm with 0.14 µm CMOS process and 60 ×180 nm2 MTJ process. It is shown that by this process technology, the fabricated MTJ on CMOS logic circuit plane achieves a large change in a resistance of 3.63 kΩ (anti-parallel) with the TMR ratio of 138% at room temperature, which is large enough for a sensing scheme of standard CMOS logic. Furthermore, we have successfully demonstrated the DC and AC operation of this MTJ with write transistors. As the results, our MTJ achieves high enough write/read performance with transistors for realizing MTJ-based logic circuits.