Browsing by Author "Chen, C. W."

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Density-dependent energy relaxation of hot electrons in InN epilayers
(2009-01-01)
Yang, M. D.
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Liu, Y. W.
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Shen, J. L.
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Chen, C. W.
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Chi, G. C.
This work investigates the dependence of the hot-electron energy relaxation in InN epilayers on electron density. From the high-energy tail of photoluminescence, the electron temperature of the hot electrons was determined. Acoustic phonons have an important role in the energy relaxation of the hot electrons. The density-dependent electron energy loss rate in InN can be explained by a combination of longitudinal optical and acoustic phonon emissions. A slowing of energy loss rate at high electron densities was observed and attributed to piezoelectric coupling to acoustic phonons. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3056383]
Determination of the microstructure of Eu-treated ZnO nanowires by x-ray absorption
(2010-02-08)
Huang, W. L.
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Labis, J.
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Ray, S. C.
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Liang, Y. R.
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Pao, C. W.
X-ray absorption near-edge structure (XANES), extended x-ray absorption fine structures (EXAFS), and photoluminescence measurements were used to elucidate the microstructural and photoluminescence properties of ZnO nanowires (ZnO-NWs) that had been treated with Eu by thermal diffusion. The O K- and Eu L(3)-edge XANES and EXAFS spectra at the Zn K- and Eu L(3)-edge verified the formation of Eu(2)O(3)-like layer on the surface of ZnO-NWs. X-ray diffraction, XANES and EXAFS measurements consistently suggest the lack of substitutional doping of Eu ions at the Zn ion sites in the interior of ZnO-NWs. The clear sharp and intense emission bands in the range 610-630 nm of Eu-treated ZnO-NWs originated from the intra-4f transition of Eu ions in the Eu(2)O(3)-like surface layer.
Enhanced planar poly-Si TFT EEPROM cell for system on panel applications
(2007)
Liu, Po-Tsun
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Huang, C. S.
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Chen, C. W.
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光電工程學系
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顯示科技研究所
In this work an enhanced electrically erasable programmable read-only memory (EEPROM) device comprised of twin low-temperature poly-Si thin-film transistors (TFTs) was fabricated for potential application to system-on-panel technology. Also, two kinds of memory devices with different overlap areas were developed to investigate the gate-coupling effect. The memory window of 4.8 and 4 V can be obtained at a programming voltage of 18 V, separately, for the fully overlapped EEPROM and the one with a 1 mu m length overlap between the gate and source/drain. The excellent memory characteristics of the fully overlapped TFT EEPROM cell are attributed to the enhanced gate-coupling ratio by maximizing the overlap coverage between the gate electrode and the source/drain regions. (c) 2007 The Electrochemical Society.
FLASH-TW experiment status report
(2005)
Liu, T. C.
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Chang, F. Y.
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Chen, C. C.
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Chen, C. W.
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Huang, M. A.
FLASH-TW is an experiment to measure the shower lateral and longitudinal profiles. We perform the shower profile measurement by shooting the 1.5 GeV electron beams in NSRRC on targets made of 15 aluminum blocks, each with a thickness of 2.9 cm. A scintillator (Al2O3: Cr)) is placed behind the targets, converting the secondary shower particles into light. The light from the central region of the shower is recorded by a CCD camera while the light from the outer region is monitored by PMTs. The CCD system is successfully implemented in the run 2 and run 3 of experiment FLASH at SLAC. A test run of the current experiment has been conducted in NSRRC in the past June to study the scintillator spectrum. Two more runs are planned from now to the year 2006 to measure the shower lateral and longitudinal profiles.
GROWTH OF AZO FILMS ON BUFFER LAYERS BY RF MAGNETRON SPUTTERING
(2010-12-20)
Chen, C. W.
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Tseng, C. H.
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Hsu, C. Y.
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Chou, C. P.
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Hou, K. H.
Al(2)O(3)-doped zinc oxide (in AZO, the Al(2)O(3) contents are approximately 2 wt.%) films have been grown by radio frequency (RF) magnetron sputtering at room temperature under varied sputtering pressures ranging from 3.5-15 mTorr. The electrical resistivity of AZO films is about 2.22 x 10(-3) Omega cm (sheet resistance similar to 89 Omega/square for a thickness similar to 250 nm), and the visible range transmittance is a bout 80% at the argon sputtering pressure of 15 mTorr and a RF power of 100 W. This study analyzes the structural, morphological, electrical and optical properties of AZO thin films grown on soda-lime glass substrate with 2, 5, and 10 nm thick Al buffer layers (and SiO(2) buffer). For the films deposited on the 2 nm thick Al buffer layer, we obtained ac-axis-oriented AZO/Al thin film on glass with the XRD full-width at half maximum (FWHM) of 0.31 and root mean square (RMS) surface roughness of about 3.22 nm. The lowest resistivity of 9.46 x 10(-4) Omega cm (sheet resistance similar to 37.87 Omega/square for a thickness similar to 250 nm) and a high transmittance (80%) were obtained by applying a 2 nm thick Al buffer layer. In contrast, the resistivity was slightly increased by applying the SiO(2) buffer layer.
High sensitivity carbon monoxide sensors made by zinc oxide modified gated GaN/AlGaN high electron mobility transistors under room temperature
(2011-05-30)
Hung, S. C.
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Chen, C. W.
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Shieh, C. Y.
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Chi, G. C.
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Fan, R.
AlGaN/GaN high electron mobility transistors (HEMTs) with zinc oxide (ZnO) nanowires modified gate exhibit significant changes in channel conductance upon expose to different concentration of carbon monoxide (CO) at room temperature. The ZnO nanowires, grown by chemical vapor deposition (CVD) with perfect crystal quality will attach CO molecules and release electrons, which will lead to a change in surface charge in the gate region of the HEMTs, inducing a higher positive charge on the AlGaN surface, and increasing the piezoinduced charge density in the HEMTs channel. These electrons create an image positive charge on the gate region for the required neutrality, thus increasing the drain current of the HEMTs. The HEMTs source-drain current was highly dependent on the CO concentration. The limit of detection achieved was 400 ppm in the open cavity with continuous gas flow using a 50 x 50 mu m(2) gate sensing area. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3596440]
Highly Scalable Hafnium Oxide Memory with Improvements of Resistive Distribution and Read Disturb Immunity
(2009)
Chen, Y. S.
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Lee, H. Y.
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Chen, P. S.
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Gu, P. Y.
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Chen, C. W.
A 30x30 nm(2) HfOx resistance random access memory (RRAM) with excellent electrical performances is demonstrated for the scaling feasibility in this work. A 1 Kb one transistor and one resistor (1T1R) array with robust characteristics was also fabricated successfully. The device yield of the 1 Kb array is 100%, and the endurance for these devices can exceed 10(6) cycles by a pulse width of 40 ns. Two effective verification methods, which make a tight distribution of high resistance (R-HIGH) and low resistance (R-LOW) are proposed for the array to ensure a good operation window. A thin A1O(x) buffer layer under the HfOx layer was adopted to enhance the read disturb immunity. Without large parasitic capacitance, the 1T1R RRAM devices exhibit excellent program(PGM)/erase(ERS) disturb immunity.
Influence of ZnO buffer layer deposition parameters on the structure and properties of Ga-doped ZnO thin films
(2011-04-01)
Chu, C. Y.
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Hsu, C. Y.
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Hong, J. H.
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Chou, C. P.
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Chen, C. W.
A series of transparent conductive films of gallium-doped zinc oxide (GZO) were deposited on glass substrates with various zinc oxide (ZnO) buffer layers by radio frequency (rf) magnetron sputtering. To investigate the influence of the ZnO buffer layer deposition parameters on the structure and properties of GZO films, the various ZnO buffer layers were prepared with varying annealing temperatures, sputtering pressures, thicknesses, and different if powers. The crystallinity and grain sizes of the GZO films were investigated by the x-ray diffraction (XRD). Only the (002) diffraction peak located at 2 theta similar to 34.2 degrees appears in XRD spectrums indicating a hexagonal wurtzite structure with its strongly preferred orientation along the c-axis. It was found that the GZO film quality (low resistivity and high transmittance) could be improved by varying the ZnO buffer layer deposition parameters. The resistivity of the GZO films decreases from 5.01x10(-3) to 9.45x10(-4) Omega cm and the visible range transmittance increases from 81.12 to 84.42%, when the GZO films were deposited on a 50 nm ZnO buffer layer annealed at 400 degrees C.
Nonpolar light emitting diode made by m-plane n-ZnO/p-GaN heterostructure
(2011-12-01)
Chen, C. W.
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Hung, S. C.
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Lee, C. H.
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Tun, C. J.
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Kuo, C. H.
Nonpolar (100) m-plane n-ZnO/p-GaN light-emitting-diodes (LEDs) were grown by chemical vapor deposition on p-GaN templates which was grown by metalorganic chemical vapor deposition on LiAlO(2)(100) substrate. Direct current (DC) electroluminescence (EL) measurements yielded a peak at 458nm. The EL peak position was independent of drive current and a full width of half maximum (FWHM) of 21.8 nm was realized at 20mA. The current-voltage characteristics of these diodes showed a forward voltage (V(f)) of 6V with a series resistance of 2.2 x 10(5) Omega. (C) 2011 Optical Society of America
Nonvolatile low-temperature polycrystalline silicon thin-film-transistor memory devices with oxide-nitride-oxide stacks
(2007-04-30)
Liu, Po-Tsun
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Huang, C. S.
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Chen, C. W.
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光電工程學系
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顯示科技研究所
Nonvolatile memory devices with oxide-nitride-oxide stack structures were fabricated on glass substrates using low-temperature polycrystalline silicon technology. The Fowler-Nordheim tunneling scheme is more suitable than channel hot carrier injection for the programming of the polycrystalline silicon nonvolatile memory device. A memory window of 1.5 V can be obtained at a programming voltage of 20 V. After 10(4) programming/erasing cycles, a threshold voltage shift of 1.5 V is maintained. Furthermore, the proposed memory device exhibits good retention for 50 h at 60 degrees C without a significant decline in the memory window. (C) 2007 American Institute of Physics.
Oxygen sensors made by monolayer graphene
(2012-01-01)
Hung, S. C.
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Chen, C. W.
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Yang, M. D.
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Yeh, C. W.
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Wu, C. H.
The electrical resistivity of monolayer graphene exhibit significant changes upon expose to different concentration of oxygen (O-2) at room temperature. The monolayer graphene, grown by chemical vapor deposition (CVD) with perfect uniformity within 1cmx1cm will attach O-2 molecules which will act as a p-type dopant and enhance the hole conductivity, make a change of resistivity of graphene thin film. We quantified the change of resistivity of graphene versus different O-2 concentration and the detection limit of the simple O-2 sensor was 1.25% in volume ratio.
Oxygen sensors made by monolayer graphene under room temperature
(2011-12-12)
Chen, C. W.
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Hung, S. C.
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Yang, M. D.
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Yeh, C. W.
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Wu, C. H.
The electrical resistivity of monolayer graphene exhibit significant changes upon expose to different concentration of oxygen (O(2)) at room temperature. The monolayer graphene, grown by chemical vapor deposition with perfect uniformity within 1 cm x 1 cm will attach O(2) molecules and enhance the hole conductivity, which will lead to a change of resistivity of graphene thin film. We quantified the change of resistivity of graphene versus different O(2) concentration and the detection limit of the simple O(2) sensor was 1.25% in volume ratio. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3668105]
Performance Comparison of OFDM Signal and CAP Signal Over High Capacity RGB-LED-Based WDM Visible Light Communication
(2013-08-01)
Wu, F. M.
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Lin, C. T.
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Wei, C. C.
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Chen, C. W.
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Chen, Z. Y.
We experimentally demonstrate a visible light communication (VLC) system based on a single commercially available RGB-type LED. High spectrally efficient carrier-less amplitude and phase (CAP) modulation and orthogonal frequency-division multiplexing (OFDM) are adopted in the intensity-modulation and direct-detection VLC system of limited bandwidth. In order to achieve higher capacity of the uneven-frequency-response LED-based VLC system, OFDM signals are combined with the bit-and power-loading techniques, and CAP signals of various modulation are pre-emphasized to modulate one of the RGB chips. To reach the BER of less than 10(-3), CAP and OFDM signals demonstrate the maximum data rates of 1.32 and 1.08 Gb/s, respectively, employing the blue chip. In addition to spectrally efficient formats, the wavelength-division-multiplexing (WDM) scheme is applied to further increase the capacity. After individually optimizing RGB chips, the maximum aggregate data rates of CAP and OFDM are 3.22 and 2.93 Gb/s, respectively, in our RGB-LED-based WDM VLC system. Hence, compared with OFDM, the CAP scheme shows competitive performance and provides an alternative spectrally efficient modulation for next generation optical wireless networks.
Structure and properties of GZO thin films grown on ZnO buffer layers
(2011-02-01)
Chu, C. Y.
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Huang, C. H.
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Kao, L. M.
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Chou, C. P.
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Hsu, C. Y.
Thin gallium-doped zinc oxide (in GZO the Ga(2)O(3) contents are approximately 3 wt%) films having different ZnO buffer layers were deposited using radio frequency (rf) magnetron sputtering. The use of a grey-based Taguchi method to determine the processing parameters of ZnO buffer layer deposition has been studied by considering multiple performance characteristics. A Taguchi method with an L(9) orthogonal array, signal-to-noise (S/N) ratio, and analysis of variance (ANOVA) is employed to investigate the performance characteristics in the deposition operations. The effect and optimization of ZnO buffer deposition parameters (rf power, sputtering pressure, thickness, and annealing) on the structure, morphology, electrical resistivity, and optical transmittance of the GZO films are studied. Annealing treatment and reduction in thickness resulted in a decrease in root-mean-square (RMS) surface roughness of the ZnO buffer layer. Using the optimal ZnO buffer layer obtained by the application of the grey-based Taguchi method, the electrical resistivity of GZO films was decreased from 2.94 x 10(-3) to 9.44 x 10(-4) Omega cm and the optical transmittance in the visible region was slightly increased from 84.81% to 85.82%. (C) 2010 Elsevier Ltd. All rights reserved.
Thermal analysis on the degradation of poly-silicon TFTs under AC stress
(2009-08-15)
Weng, C. F.
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Chang, T. C.
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Tai, Y. H.
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Huang, S. T.
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Wu, K. T.
In this work, the degradation mechanism of N-channel poly-silicon thin-film transistor (poly-Si TFT) has been investigated under dynamic voltage stress at room temperature. The ON-current of TFT is degraded to as low as 0.3 times of the initial value after 1000 s stress. On the other hand, both the sub-threshold swing and threshold voltage kept well during the AC stress. The current crowding effect was rapidly increased with increasing of stress duration. However, comparing the initial and degraded characteristics at rising temperature, namely, 150 degrees C, the ON-current of TFT only decrease to 75% of the initial value after 1000 s AC stress. It depicts that creation of effective trap density in tail-states of poly-Si film is responsible for the electrical degradation of poly-Si TFT. At high temperature, electron has enough energy to pass the energy barrier created by ac stress and the degradation is less obvious. (C) 2009 Published by Elsevier B.V.