Browsing by Issue Date, starting with "2013-07-24"

Now showing 1 - 20 of 31125

Controllable Disorder in a Hybrid Nanoelectronic System: Realization of a Superconducting Diode
(2013-07-24)
Lo, Shun-Tsung
;
Chen, Kuang Yao
;
Lin, Sheng-Di
;
Wu, J-Y.
;
Lin, T. L.
We have studied a hybrid nanoelectronic system which consists of an AlGaAs/GaAs two-dimensional electron gas (2DEG) in close proximity (similar to 70 nm) to an Al superconducting nanofilm. By tuning the current through the Al film, we can change the conductance of the 2DEG and furthermore vary the effective disorder in the Al superconducting film in a controllable way. When a high current is injected into the film, screening which couples the Al film and the 2DEG results in a collapse of anti-symmetric behavior in the current-voltage characteristics, V(I) similar to - V(-I), which holds true in a conventional superconductor. Our results may open a new avenue of experimentally realizing a superconducting diode.
Plastic response of dislocation glide in solid helium under dc strain-rate loading
(2013-07-24)
Zhou, Caizhi
;
Su, Jung-Jung
;
Graf, Matthias J.
;
Reichhardt, Charles
;
Balatsky, Alexander V.
We develop a model for the gliding of dislocations and plasticity in solid He-4. This model takes into account the Peierls barrier, multiplication and interaction of dislocations, as well as classical thermally and mechanically activated processes leading to dislocation glide. We specifically examine the dc stress-strain curve and how it is affected by temperature, strain rate, and dislocation density. As a function of temperature and shear strain, we observe plastic deformation and discuss how this may be related to the experimental observation of elastic anomalies in solid hcp He-4 that have been discussed in connection with the possibility of supersolidity or giant plasticity. Our theory gives several predictions for the dc stress strain curves, for example, the yield point and the change in the work-hardening rate and plastic dissipation peak, that can be compared directly to constant strain-rate experiments and thus provide bounds on model parameters.
BAND-NOTCHED ULTRA-WIDEBAND ANTENNA
(2013-07-25)
Chung Shyh-Jong
;
Chuang Chao-Tang
A band-notched ultra-wideband antenna comprises a top layer non-uniform short-circuit metal patch, a middle layer metal radiation patch, and a bottom layer metal patch. The bottom layer metal patch includes a coupled open/short circuit stub which is set close to the middle layer metal radiation patch. The equivalent circuit of the top layer non-uniform short-circuit metal patch is a parallel LC resonator, and the equivalent circuit of the coupled open/short circuit stub is a series LC resonator. The resonant frequency of the top layer non-uniform short-circuit metal patch is equivalent to the resonant frequency of the coupled open/short circuit stub, so as to function as a second-order bandstop filter to yield high notch-band-edge selectivity without increasing total circuit area of the band-notched ultra-wideband antenna.
INTELLIGENT ANALYSIS METHOD OF LEAKAGE CURRENT DATA FOR CHIP CLASSIFICATION
(2013-07-25)
WEN Charles Hung-Pin
;
CHANG Chia-Ling
An intelligent analysis method of leakage current data for chip classification is provided. The analysis method includes steps of: providing a plurality of given patterns to a chip and measuring a plurality of leakage currents of the chip corresponding to the given patterns; finding a minimum value of the leakage currents and deriving an uninfected process parameter according to the minimum value; calculating a plurality of σ-Iddq values based on the uninfected process parameter and the given patterns; and applying a clustering algorithm to the σ-Iddq values to classify whether the chip is a defect-free one. By employing the novel method, it is advantageous of high efficiency and precision without involving any threshold-value determination, visual inspection and/or pattern modification.
An endoscopic system adopting a liquid crystal lens with an electrically tunable depth-of-field
(2013-07-29)
Chen, Hung-Shan
;
Lin, Yi-Hsin
;
光電工程學系
;
Department of Photonics
Conventional endoscopic systems consisting of several solid lenses suffer from a fixed and limited depth-of-field (DOF). For practical applications, conventional endoscopes mechanically change the distance between the solid lenses of a lens module in order to change the focusing plane and DOF to see clearly in a scene. In this paper, we demonstrate an electrically tunable endoscopic system adopting a liquid crystal lens. By means of tunable focusing properties of the LC lens as a positive lens and a negative lens, the object at different objective distances can be imaged to the image sensor clearly and the corresponding depth-of-field can also help to enlarge the total spatial depth perception in a scene. The optical mechanism is discussed. In the experiments, under adjustment of three discrete lens powers of the LC lens, the viewing range or total spatial depth perception of the endoscopic system is from 76.4 mm to 12.4 mm which is 2x improved compared to the conventional one without LC lens. We believe this study can be extended to the applications of industrial and medical endoscopes. (C) 2013 Optical Society of America
Effects of crystallization mechanism on the electrical characteristics of green continuous-wave-laser-crystallized polycrystalline silicon thin film transistors
(2013-07-29)
Chou, Chia-Hsin
;
Lee, I-Che
;
Yang, Po-Yu
;
Hu, Ming-Jhe
;
Wang, Chao-Lung
Thin film transistors (TFTs) with amorphous silicon films crystallized via continuous-wave green laser at a wavelength of 532 nm exhibit very different electrical characteristics in various crystallization regions, corresponding to the Gaussian energy density distribution of the laser beam. In the center region subjected to the highest energy density, the full melting scheme led to the best crystallinity of the polycrystalline silicon film, resulting in the highest field-effect mobility of 500 cm(2) V-1 s(-1). In contrast, the edge region that resulted in solid phase crystallization exhibited the worst mobility of 48 cm 2 V-1 s(-1) for the polycrystalline silicon TFTs. (C) 2013 AIP Publishing LLC.
Effects of ZnO-nanostructure antireflection coatings on sulfurization-free Cu2ZnSnS4 absorber deposited by single-step co-sputtering process
(2013-07-29)
Jheng, Bao-Tang
;
Liu, Po-Tsun
;
Wang, Min-Chuan
;
Wu, Meng-Chyi
;
電子工程學系及電子研究所
ZnO nanostructures as anti-reflective coatings were synthesized by using hydrothermal technique for a sulfurization-free Cu2ZnSnS4 absorber prepared by co-sputtering deposition. By controlling the morphology of solution-grown ZnO nanostructures, the average reflectance of the Cu2ZnSnS4 solar cell with branched ZnO nanorods decreased from 7.6% to 1.12%, and the energy conversion efficiency promoted by 10.4% from the initial value of 4.8% to 5.3%. The efficiency improvement was well studied with the effects of the gradually increased refractive index between the air and the top electrode of Cu2ZnSnS4 solar device, due to the presence of the ZnO nanostructure. (C) 2013 AIP Publishing LLC.
Single-shot detection of mid-infrared spectra by chirped-pulse upconversion with four-wave difference frequency generation in gases
(2013-07-29)
Nomura, Y.
;
Wang, Y. -T.
;
Kozai, T.
;
Shirai, H.
;
Yabushita, A.
Single-shot detection of ultrabroadband mid-infrared spectra was demonstrated by using chirped-pulse upconversion technique with four-wave difference frequency generation in gases. Thanks to the low dispersion of the gas media, the bandwidth of the phase matching condition of the upconversion process becomes very broad and the entire mid-infrared spectrum spanning from 200 to 5500 cm(-1) was upconverted by using a 10 ps chirped pulse to visible wavelength radiation, which was detected with a conventional visible dispersive spectrometer. This method was demonstrated by the successful measurement of infrared absorption spectra of organic polymer films. (C) 2013 Optical Society of America
Dual-port subthreshold SRAM cell
(2013-07-30)
Chiu Yi-Te
;
Chang Ming-Hung
;
Yang Hao-I
;
Hwang Wei
An innovative dual-port subthreshold static random access memory (SRAM) cell for sub-threshold voltage operation is disclosed. During write mode, the dual-port subthreshold SRAM cell would cut off the positive feedback loop of the inverters and utilize the reverse short-channel effect to enhance write capability. The single-ended read/write port structure further reduces power consumption of the lengthy bit line. Therefore, the dual-port subthreshold SRAM cell is a suitable for long operation in a first-in first-out memory system. Although the lower voltage reduces the stability of the memory cell, the dual-port subthreshold SRAM cell of the present invention can still stably operate.
Vibrational and electronic relaxation in MEH-PPV using few cycle pulses
(2013-07-30)
Kobayashi, Takayoshi
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Yamashita, Munenori
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Du, Juan
;
Zhang, Jun
;
Iwakura, Izumi
The electronic population decay time is determined to be about 500 fs in (poly-[2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylenevinylenel (MEH-PPV) using 5.7 fs pulses. The ultrafast electronic dephasing time and the self-trapping time of free exciton to form an exciton polaron is determined as 25 +/- 2 fs and 50 +/- 23 fs, respectively. Real-time spectrogram analysis reveals dynamic mode coupling among the high-frequency and low-frequency modes. The energy-ladder descent vibrational process is clarified using the first moment of the difference absorption spectrum. The phase relaxation time is calculated from the widths of the Fourier spectra of several strongly coupled modes. (C) 2013 Elsevier B.V. All rights reserved.
Strain enhanced ferroelectric properties of multiferroic BiFeO3/SrTiO3 superlattice structure prepared by radio frequency magnetron sputtering
(2013-07-31)
Chiu, Shang-Jui
;
Liu, Yen-Ting
;
Lee, Hsin-Yi
;
Yu, Ge-Ping
;
Huang, Jia-Hong
Asymmetric superlattice structures consisting of SrTiO3 (STO) and multiferroic BiFeO3 (BFO) sublayers were deposited on a Nb-doped STO (001) substrate with a radio frequency magnetron sputtering system. For an investigation of the effect of strain on the microstructures, ferroelectric properties and piezoelectric properties resulting from a difference of lattice parameters of the BFO sublayer, varying the thickness of the STO sublayer in a range 1-2.5 nm introduced interfacial strain into the superlattice. The epitaxial relation and strain state of films were clearly observed with a synchrotron as a source of radiation. The results of X-ray diffraction measurements clearly showed that the decrease of strain was related to the thickness of the STO substrate. A separate diffraction signal of the superlattice structure with thickness >= 1.75 nm of the STO sublayer was found, indicating a large strain relaxation in these superlattice films. The remnant polarization values P-r, piezoelectric coefficient d(33) and leakage properties of the BFO/STO superlattice thin films that improved with increasing in-plane strain provide strong evidence of a strain-enhancement effect. The BFO/STO superlattice with a well defined crystal structure and a large strain state showed a large P-r, greater than a BFO single layer of the same thickness. (C) 2013 Elsevier B.V. All rights reserved.
A novel approach to collaborative testing in a crowdsourcing environment
(2013-08-01)
Tung, Yuan-Hsin
;
Tseng, Shian-Shyong
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資訊工程學系
;
Department of Computer Science
Software testing processes are generally labor-intensive and often involve substantial collaboration among testers, developers, and even users. However, considerable human resource capacity exists on the Internet in social networks, expert communities, or internet forums-referred to as crowds. Effectively using crowd resources to support collaborative testing is an interesting and challenging topic. This paper defines the collaborative testing problem in a crowd environment as an NP-Complete job assignment problem and formulates it as an integer linear programming (ILP) problem. Although package tools can be used to obtain the optimal solution to an ILP problem, computational complexity makes these tools unsuitable for solving large-scale problems. This study uses a greedy approach with four heuristic strategies to solve the problem. This is called the crowdsourcing-based collaborative testing approach. This approach includes two phases, training phase and testing phase. The training phase transforms the original problem into an ILP problem. The testing phase solves the ILP using heuristic strategies. A prototype system, called the Collaborative Testing System (COTS), is also implemented. The experiment results show that the proposed heuristic algorithms produce good quality approximate solutions in an acceptable timeframe. (c) 2013 Elsevier Inc. All rights reserved.
Probing Local Ionic Dynamics in Functional Oxides at the Nanoscale
(2013-08-01)
Strelcov, Evgheni
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Kim, Yunseok
;
Jesse, Stephen
;
Cao, Ye
;
Ivanov, Ilia N.
A scanning probe microscopy technique for probing local ionic dynamics in electrochemically active materials based on the first-order reversal curve current-voltage (FORC-IV) method is presented. FORC-IV imaging mode is applied to a Ca-substituted bismuth ferrite (Ca-BFO) system to separate the electronic and ionic phenomena in this material and visualize the spatial variability of these behaviors. The variable-temperature measurements further demonstrate the interplay between the thermally and electric-field-driven resistance changes in Ca-BFO. The FORC-IV is shown to be a simple, powerful, and flexible method for studying electrochemical activity of materials at the nanoscale and, in conjunction with the electrochemical strain microscopy, it can be used for differentiating ferroelectric and ionic behaviors.
Robust MIMO Detection Under Imperfect CSI Based on Bayesian Model Selection
(2013-08)
Cheng, Chien-Chun
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Sezginer, Serdar
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Sari, Hikmet
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Su, Yu T.
;
電子工程學系及電子研究所
A robust receiver for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems is proposed. We are interested in the scenario when only a limited number of observations in both time and frequency domains are available. For this scenario, perfect channel state information is impossible to obtain and the receiver suffers from statistical information mismatch. To overcome this limitation, we first propose the optimum receiver by performing jointly channel and data estimation. For statistical information mismatch, we construct a finite set of covariance matrices and derive a model-selection scheme based on Bayesian Model Selection. Finally, the sliding-window scheme is used in order to enhance the model selection accuracy. Simulation results are presented, showing that the proposed scheme outperforms the conventional scheme under imperfect channel knowledge.
Au Nanostructure-Decorated TiO2 Nanowires Exhibiting Photoactivity Across Entire UV-visible Region for Photoelectrochemical Water Splitting
(2013-08-01)
Pu, Ying-Chih
;
Wang, Gongming
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Chang, Kao-Der
;
Ling, Yichuan
;
Lin, Yin-Kai
Here we demonstrate that the photoactivity of Au-decorated TiO2 electrodes for photoelectrochemical water oxidation can be effectively enhanced in the entire UV-visible region from 300 to 800 nm by manipulating the shape of the decorated Au nanostructures. The samples were prepared by carefully depositing Au nanoparticles (NPs), Au nanorods (NRs), and a mixture of Au NPs and NRs on the surface of TiO2 nanowire arrays. As compared with bare TiO2, Au NP-decorated TiO2 nanowire electrodes exhibited significantly enhanced photoactivity in both the UV and visible regions. For Au NR-decorated TiO2 electrodes, the photoactivity enhancement was, however, observed in the visible region only, with the largest photocurrent generation achieved at 710 nm. Significantly, TiO2 nanowires deposited with a mixture of Au NPs and NRs showed enhanced photoactivity in the entire UV visible region. Monochromatic incident photon-to-electron conversion efficiency measurements indicated that excitation of surface plasmon resonance of Au is responsible for the enhanced photoactivity of Au nanostructure-decorated TiO2 nanowires. Photovoltage experiment showed that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was attributable to the effective surface passivation of Au NPs. Furthermore, 3D finite-difference time domain simulation was performed to investigate the electrical field amplification at the interface between Au nanostructures and TiO2 upon SPR excitation. The results suggested that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was partially due to the increased optical absorption of TiO2 associated with SPR electrical field amplification. The current study could provide a new paradigm for designing plasmonic metal/semiconductor composite systems to effectively harvest the entire UV visible light for solar fuel production.
Channel Thickness Effect on High-Frequency Performance of Poly-Si Thin-Film Transistors
(2013-08-01)
Chen, Kun-Ming
;
Tsai, Tzu-I
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Lin, Ting-Yao
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Lin, Horng-Chih
;
Chao, Tien-Sheng
In this letter, we present the high-frequency performances of polycrystalline silicon (poly-Si) thin-film transistors (TFTs) with a nominal gate length of 0.22 mu m. Owing to the short gate length and adoption of salicide process, cutoff frequency (f (T)) of 17 GHz and maximum oscillation frequency of similar to 21 GHz are obtained. The result suggests that the poly-Si TFT technology is applicable to RF integrated circuits up to 2 GHz. In addition, we also investigate the effects of channel thickness on the high-frequency characteristics of poly-Si TFTs. We find that the variation of f (T) with channel thickness is mainly due to the change in transconductance.
Crystallized Ohmic Contact Effect in AlGaN/GaN High Electron Mobility Transistor
(2013-08-01)
Liao, Sheng Yu
;
Chang, Tsu
;
Hsu, Hsiao-Hsuan
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Cheng, Chun-Hu
;
Chang, Liann-Be
In this study, we investigate the grain size effect of high electron mobility transistor devices with ohmic contact metals of stacked Ti/Al/Ni/Au and Ti/Al/Mo/Au. In addition to a comparison of electrical characteristics, the ohmic contacts were also examined by a scratch test for the observation of adhesion behavior. The experimental results demonstrate that the metal grain size is strongly dependent on metal adhesion, which may lead to bonding issues. Moreover, the grain-induced lateral stress lowers the drive current and increases the off-state current owing to the degraded gate swing and transconductance of transistor switching characteristics. (C) 2013 The Japan Society of Applied Physics
Holographic photon production with magnetic field in anisotropic plasmas
(2013-08-01)
Wu, Shang-Yu
;
Yang, Di-Lun
;
物理研究所
;
Institute of Physics
We investigate the thermal photon production from constant magnetic field in a strongly coupled and anisotropic plasma via the gauge/gravity duality. The dual geometry with pressure anisotropy is generated from the axion-dilaton gravity action introduced by Mateos and Trancancelli and the magnetic field is coupled to fundamental matters(quarks) through the D3/D7 embeddings. We find that the photon spectra with different quark mass are enhanced at large frequency when the photons are emitted parallel to the anisotropic direction with larger pressure or perpendicular to the magnetic field. However, in the opposite conditions for the emitted directions, the spectra approximately saturate isotropic results in the absence of magnetic field. On the other hand, a resonance emerges at moderate frequency for the photon spectrum with heavy quarks when the photons move perpendicular to the magnetic field. The resonance is more robust when the photons are polarized along the magnetic field. On the contrary, in the presence of pressure anisotropy, the resonance will be suppressed. There exist competing effects of magnetic field and pressure anisotropy on meson melting in the strongly coupled super Yang-Mills plasma, while we argue that the suppression led by anisotropy may not be applied to the quark gluon plasma.
Ambient temperature SNAD process treating anaerobic digester liquor of swine wastewater
(2013-08-01)
Daverey, Achlesh
;
Hung, Nien-Tzu
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Dutta, Kasturi
;
Lin, Jih-Gaw
;
環境工程研究所
In present study, effluent from anaerobic digestion of swine wastewater was treated by the simultaneous partial nitrification, anaerobic ammonium oxidation and denitrification (SNAD) process using a lab scale 5 L sequencing batch reactor (SBR) under ambient temperature. The fluctuation of anaerobic digester liquor quality (COD, 387 +/- 145 mg/L; TKN, 662 +/- 190 mg/L; NH4+-N, 519 +/- 134 mg/L) and temperature created difficulties to develop a stable SNAD process in the SBR (days 1-285). Fed batch feeding strategy was adopted to have a stable condition in the reactor and overcome the negative effects of organic nitrogen. The average total nitrogen, NH4+-N and COD removal efficiencies in the SBR under steady state conditions (days 485-523) were 80%, 96% and 76%, respectively. The results showed that presence of organic nitrogen, mode of feeding and reactor temperature affects the SNAD process. (C) 2013 Elsevier Ltd. All rights reserved.
Data mining-based hierarchical cooperative coevolutionary algorithm for TSK-type neuro-fuzzy networks design
(2013-08-01)
Hsu, Chi-Yao
;
Lin, Sheng-Fuu
;
Chang, Jyun-Wei
;
電機工程學系
;
Department of Electrical and Computer Engineering
This study proposes a data mining-based hierarchical cooperative coevolutionary algorithm (DMHCCA) for TSK-type neuro-fuzzy networks design. The proposed DMHCCA consists of two-level evolutions: the neuro-level evolution (NULE) and the network-level evolution (NWLE). In NULE, a data mining-based evolutionary learning algorithm is utilized to evolve neurons. The good combinations of neurons evolved in NULE are reserved for being the initial populations of NWLE. In NWLE, the initial population are mated and mutated to produce new structure of networks. Similar to NULE, the good neurons of evolved network in NWLE are inserted into the NULE. Thus, by interactive two-level evolutions, the neurons and structure of network can be evolved locally and globally, respectively. Simulation results using DMHCCA are reported and compared with other existing models. Application of DMHCCA to a three-dimensional (3D) surface alignment task is also described, and experimental results are presented better performance than other alignment systems.