Browsing by Author "Wu, YS"

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A new yellow fluorescent dopant for high-efficiency organic light-emitting devices
(2006-02-21)
Wu, YS
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Liu, TH
;
Chen, HH
;
Chen, CH
;
應用化學系
We describe the design and synthesis of a sterically hindered yellow dopant, tetra(l-butyl)rubrene (TBRb) which, when doped in either 1,4-bis[N-(1-naphthyl)-N'-phenylamino]-biphenyl or aluminum tris(8-hydroxyquinoline) (Alq(3)) as emitter, shows nearly 25% increase in luminance efficiency over that of the state-of-the-art rubrene (Rb) device without significantly effecting its corresponding color. At 5% doping in Alq3 and 20 mA/cm(2) current drive condition, the electroluminescence efficiency of TBRb reaches 8.5 cd/A and 2.8 1m/W with a yellow color of Commission Internationale de l'Eclairage chromaticity coordinates (CIEx,y)=[0.52,0.48], which is among the best ever reported for yellow electrofluorescence in organic light-emitting devices. (c) 2005 Elsevier B.V. All rights reserved.
Characterization of electronic structure of aluminum (III) bis(2-methyl-8-quninolinato)-4-phenylphenolate (BAlq) for phosphorescent organic light emitting devices
(2005-03-07)
Chu, TY
;
Wu, YS
;
Chen, JF
;
Chen, CH
;
電子物理學系
The structure of the triplet host material, aluminum (111) bis(2-metliyl-8-quninotinato)-4-phenylphenolate (BAlq), has been optimized by density functional theory (DFT) with B3LYP methods to study the electronic distribution of its HOMO and LUMO energy states. Calculated triplet bandgap energy of BAlq is shown to be consistent with the experimental data. By analyzing the partial density states (PDOS) of these ligands contributing to the total density of states (TDOS), it is concluded that the HOMO and LUMO orbitals of BAlq are mainly localized on the 4-phenylphenol and 2-methyl-8-hydroxyquin oline ligands, respectively. (C) 2005 Elsevier B.V. All rights reserved.
Comparison of TFTs made by IMPRINT and IMPRINT-ELA methods
(2006)
Hou, CY
;
Wu, YS
;
材料科學與工程學系
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Department of Materials Science and Engineering
Comparison of low-temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs) fabricated by both IMPRINT and IMPRINT-excimer loser annealing (ELA) methods was investigated. IMPRINT poly-Si was fabricated by pressing imprint mold (coated with Ni film) together with amorphous Si film and then annealing at 550 degrees C. After the sample stack was separated, IMPRINT poly-Si film was irradiated by an excimer laser to form IMPRINT-ELA poly-Si. Upon increasing the laser energy to 345 mJ/cm(2), the performance of IMPRINT-ELA-TFT was found to be far superior to that of IMPRINT-TFT due to larger grains and fewer intragrain defects of the IMPRINT-ELA poly-Si film than that of the IMPRINT poly-Si film. The mobility of the IMPRINT-ELA-TFT was 413 cm(2)/Vs, which was 31.7 times higher than that of the IMPRINT-TFT. The on/off current ratio of the IMPRINT-ELA-TFT was 4.24 x 10(6), which was two orders magnitude higher than that of the IMPRINT-TFT. (c) 2006 The Electrochemical Society.
Effect of surface passivation removal on planarization efficiency in Cu abrasive-free polishing
(2006)
Fang, JY
;
Tsai, MS
;
Dai, BT
;
Wu, YS
;
Feng, MS
Selective removal of surface passivation on protruded Cu film is a critical factor of Cu planarization. For a stress-free Cu abrasive-free polishing (Cu AFP) process, due to the lack of mechanical abrasion by abrasives, a polishing pad is used instead of abrasives to remove surface passivation during Cu planarization. Thus, the planarization efficiency in Cu AFP relates to the efficiency of surface passivation removed by a pad. Comparing Cu oxides with a non-native Cu-BTA (Cu-Benzotriazole) monolayer used as surface passivation, this study found that an oxide-free Cu surface should be required in Cu AFP. When Cu oxides function as surface passivation in Cu AFP, they are removed with greater difficulty by a pad resulting in low planarization efficiency. Contrary to Cu oxides, high planarization efficiency can be obtained with non-native Cu-BTA as surface passivation in Cu AFP. (c) 2005 The Electrochemical Society.
Effect of thermal annealing of Ni/Au ohmic contact on the leakage current of GaN based light emitting diodes
(2003-09-22)
Hsu, CY
;
Lan, WH
;
Wu, YS
;
材料科學與工程學系
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Department of Materials Science and Engineering
The effect of thermal annealing on current-voltage properties of GaN light emitting diodes (LEDs) has been studied. At annealing temperatures above 700 degreesC, the p-n junction of the diodes became very leaky and Ga-contained metallic bubbles were observed on the surface of Ni/Au p-ohmic contact. Transmission electron microscopy and energy dispersive x-ray spectrometer studies revealed that these metallic bubbles resided directly on top of the threading dislocations in GaN and both Ni and Au were indiffused into the LED structure along the cores of the TDs. The conducting paths formed by the metal containing dislocation cores are believed to be the cause for the observed short circuit behavior of p-n junctions at high annealing temperatures. (C) 2003 American Institute of Physics.
Effects of oxygen on the growth of Ni induced lateral crystallization of amorphous silicon films
(2003-06-26)
Lin, YD
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Wu, YS
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Chao, CW
;
Hu, GR
;
材料科學與工程學系
Effects of oxygen on the growth of metal (Ni) induced lateral crystallization (MILC) of amorphous silicon have been investigated. It is found that the oxygen in the annealing ambient did not degrade the MILC length or growth rate. The oxygen existence in Ni film does not degrade the MILC growth rate either. However, it retards the nucleation of poly-Si for about 4 h. This is because that NiO needed an incubation period to be reduced to nickel metal for the subsequent mediated crystallization of a-Si process. (C) 2003 Elsevier Science B.V. All rights reserved.
Effects of tertiary butyl substitution on the charge transporting properties of rubrene-based films
(2004-03-08)
Fong, HH
;
So, SK
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Sham, WY
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Lo, CF
;
Wu, YS
The charge transporting properties of rubrene (5,6,11,12-tetraphenylnaphthacene or RB), and a new rubrene-based complex, tetra(t-butyl)-rubrene [2,8-di(t-butyl)-5,11-di[4-(t-butyl)phenyl]-6,12-diphenylnaphthacene or TBRB], were examined in the form of amorphous films as functions of electric field and temperature by means of time-of-flight technique. At room temperature, the hole mobility mu for RB is 7-9 x 10(-3) cm(2) V-1 s(-1) whereas mu for the more bulky TBRB is about 2 x 10(-3) cm(2) V-1 s(-1). The microscopic conduction mechanism in both materials can be modeled by the Gaussian disorder model in which hopping conduction occurs through a manifold of sites with energetic and positional disorder. The energetic disorder in RB and TBRB is almost identical and is about 78 meV in each case, and is mainly controlled by van der Waals interaction. The t-butyl groups in TBRB induce large fluctuations in the spatial separation among TBRB molecules and result in an increase in the positional disorder, and hence a reduction in the hole mobility. (C) 2003 Elsevier B.V. All rights reserved.
Efficient white organic light emitting devices with dual emitting layers
(2005-09-22)
Wu, YS
;
Hwang, SW
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Chen, HH
;
Lee, MT
;
Shen, WJ
In this paper, a new white organic light-emitting device (OLED) with the structure of indium tin oxide/CFx/1,4-bis[N-(1-naphthyl)-N'-phenylamino]-biphenyl (NPB) (30 mn)NPB: 2,8-di(t-butyl)-5,11-di[4-(t-butyl)phenyl]-6,12-diphenylnaphthacene (20 nm; 1.6 %)/2-methyl-9,10-di(2-naphthyl) anthracene: p-bis(p-NN-di-phenyl-aminostyryl)benzene (40 nm, 3%)/aluminum tris(8-hydroxyquinoline) (20 nm)/LiF (1 nm)/Al (200 mn) has been investigated. The device showed white emission with a high-luminous yield of 9.75 cd/A at 20 mA/cm(2), but its Commission Internationale de l'Eclairage chromaticity coordinates appeared to change from (0.34, 0.42) at 6 mA/cm(2) to (0.27, 0.37) at 200 mA/cm(2) due to the shift of recombination zone. The change of color with drive current was suppressed by introduction of an electron-blocking layer of NPB along with a hole-blocking layer of aluminum (III) bis(2-methyl-8-quinolinato)4-phenylphenolato to the white OLED which successfully confined the recombination site and achieved a luminous yield of 9.9 cd/A at 20 mA/cm(2). (c) 2005 Elsevier B.V All rights reserved.
Electrochemically deposited Pd-induced crystallization of parallel needlelike polycrystalline silicon from prepatterned amorphous silicon thin films
(2002-02-01)
Chao, CW
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Hu, GR
;
Wu, YS
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Chen, YC
;
Feng, MS
Electrochemically deposited Pd-induced crystallization of prepatterned amorphous silicon (a-Si) thin films was proposed for the first time in this study. Most of palladium clusters were found to deposit on the sidewall of the amorphous-silicon islands. After samples were annealed at 530degreesC, parallel needlelike polycrystalline silicon grains were observed on the a-Si film with a constant angle of similar to55degrees from the edge. The direction of the primary grain growth was along [211] and the secondary growth occurred along [011] direction. (C) 2001 The Electrochemical Society.
Enhanced performance of an InGaN-GaN light-emitting diode by roughening the undoped-GaN surface and applying a mirror coating to the sapphire substrate
(2006-05-01)
Peng, WC
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Wu, YS
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材料科學與工程學系
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Department of Materials Science and Engineering
An InGaN-GaN light-emitting diode (LED) with a roughened undoped-GaN surface and a silver mirror on the sapphire substrate was fabricated through a double transfer method. It was found that, at an injection current of 20 mA, its luminance intensity was 100% larger than conventional LEDs. Its output power was 49% larger than conventional LEDs. (c) 2006 American Institute of Physics.
Formation of phase grating in planar aligned cholesteric liquid crystal film
(2002-11-15)
Wu, JJ
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Wu, YS
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Chen, FC
;
Chen, SH
;
光電工程學系
Electric-field-induced cholesteric liquid crystal phase gratings were investigated by means of changing the film thickness-to-natural-pitch ratio d/p(0) and the applied voltage. Planar parallel (180degrees)-, antiparallel (0degrees)- and twist (90degrees)-aligned films were fabricated. By varying the d/p(0) value, we found that the stripes of the gratings could only be in two directions. It was interesting that the directions were mutually perpendicular. This device could be used as a grating switch.
Growth mechanism of laser annealing of nickel-induced lateral crystallized silicon films
(2006-01-01)
Hu, GR
;
Wu, YS
;
Chao, CW
;
Shih, HC
;
材料科學與工程學系
The growth mechanism of a hybrid process to crystallize amorphous silicon (a-Si) film was studied. In the process, a-Si was first converted to polycrystalline silicon (poly-Si) using Ni-metal-induced lateral crystallization (NILC), and then annealed with an excimer laser (ELA). Two regions based on different crystallization mechanisms were found on these NILC-ELA films: (A) a-Si melting region, and (13) a-Si/poly-Si melting region. In the a-Si melting region, the sizes and shapes of the needle Si grains were similar to those of NILC poly-Si. In the a-Si/poly-Si melting region, the shapes and sizes of poly-Si grains were quite different from those of NILC needlelike grains. Two crystallization regimes were found in the a-Si/poly-Si melting region: (1) geometrical coalescence regime and (2) complete melting regime. In the geometrical coalescence regime, the width of grains dramatically increased to 600 nm due to the geometrical coalescence of Si needle grains. However, in the complete melting regime, the NILC Si films melted completely. Small poly-Si grains were formed by homogeneous nucleation and growth.
High-power AlGaInP light-emitting diodes with metal substrates fabricated by wafer bonding
(2004-03-15)
Peng, YCS
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Wu, YS
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材料科學與工程學系
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Department of Materials Science and Engineering
High-power light-emitting diodes (LEDs) fabricated on Cu substrates were investigated in this study. The AlGaInP LED structure was bonded to a Cu substrate by using indium-tin-oxide as the diffusion barrier layer. It was found that Cu-substrate-bonded LED devices could be operated in a much higher injection forward current, 800 mA, which was eight times higher than that used in traditional GaAs-substrate LEDs. The luminous intensity of the Cu-substrate LEDs could reach as high as 1230 mcd, which was three times higher than that of the GaAs-substrate LEDs. (C) 2004 American Institute of Physics.
Highly efficient yellow and white organic electroluminescent devices doped with 2,8-di(t-butyl)-5,11-di[4-(t-butyl)phenyl]-6,12-diphenylnaphthacene
(2004-11-08)
Liu, TH
;
Wu, YS
;
Lee, MT
;
Chen, HH
;
Liao, CH
We describe the applications of a sterically-hindered yellow dopant, 2,8-di(t-butyl)-5,11-di[4-(t-butyl)phenyl]-6,12-diphenylnaphthacene (TBRb) which, when compared to 5,6,11,12-tetraphenylnaphthacene (Rb) in either tris(8-hydroxyquinolinato)aluminum or 1,4-bis[N-(1-naphthyl)-N-'-phenylamino]-4,4(') diamine (NPB) as host emitter, shows a 50%-34% increase in luminance efficiency over that of Rb device without significantly affecting its color. In addition, we have incorporated the TBRb doped yellow NPB emitter into the two-element white organic light-emitting diodes based on p-bis(p-N,N-di-phenyl-aminostyryl)benzene doped 2-methyl-9,10-di(2-naphthyl) anthracene sky-blue emitter which improved the luminance efficiency by 44% over that of Rb to 12.8 cd/A and 4.3 lm/W at 20 mA/cm(2) with CIEx,y=[0.31,0.38]. (C) 2004 American Institute of Physics.
Improved annealing process for electroless Pd plating induced crystallization of amorphous silicon
(2003-08-01)
Hu, GR
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Huang, TJ
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Wu, YS
;
材料科學與工程學系
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Department of Materials Science and Engineering
Electroless Pd plating induced crystallization of amorphous silicon (a-Si) thin films has been proposed for fabricating low-temperature polycrystalline silicon thin film transistors (LTPS TFTs). However, the current crystallization process often leads to poor device performance due to the large amount of I'd-silicide residues in the poly-Si thin films. It was found that the amount of I'd silicide increased with annealing time and temperature. In this study, a two-step annealing process was developed to obtain the appropriate amount of Pd silicide for inducing the crystallization of a-Si. The device characteristics were significantly improved by this two-step process.
Optical properties of a novel yellow fluorescent dopant for use in organic LEDs
(2005-08-01)
Choy, WCH
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Wu, YS
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Chen, CH
;
Cheah, KW
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電子與資訊研究中心
In this paper, the optical properties of a novel organic, 2,8-di(t-butyl)-5,11-di[4(t-butyl)phenyl]-6,12-diphenylnaphthacene (tetra(t-butyl)rubrene) have been investigated. Our results show that there are two peaks in the photoluminescence (PL) spectra of tetra(t-butyl) rubrene (TBRb) which are also confirmed in the electroluminescence (EL) spectra. Photo-quenching of the PL intensity is observed when the irradiation time increases. It is shown that oxidation is the dominant reason for photo-quenching. The absolute refractive index and absorption coefficient have also been determined and the results correlate well with the PL results. The results show that TBRb can be a good dopant to achieve the Forster energy transfer and to assist light emission. The optical properties of TBRb are similar to those of rubrene; however, the PL of TBRb is much stronger than that of rubrene. Finally, although crystalline organics have been commonly reported by heating the sample, we report crystallization of TBRb at low temperature < 230 K when the TBRb film is in an amorphous form before cooling.
Optically heterodyne diagnosis of a high-saturation-power undoped InP sandwiched InGaAs p-i-n photodiode grown on GaAs
(2006-06-12)
Liao, YS
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Shi, JW
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Wu, YS
;
Kuo, HC
;
Feng, M
We demonstrate the optical heterodyne diagnostics and high saturation power characteristics of a novel undoped InP sandwiched In0.53Ga0.47As p-i-n photodiode with a partially p-doped photoabsorption layer, which is grown on a linearly graded metamorphic InxGa1-xP buffered GaAs substrate layer and exhibits an excellent low dark current density of 3.6 x 10(-7) A/cm(2). Such a top-illuminated optical receiver exhibits an illuminating window of 60-mu m diameter, which performs ultra-linear power handling capability up to 18 dBm at 1550 nm, providing a maximum photocurrent of 35 mA under a reverse bias of 9 volts. These result in extremely high current bandwidth and bandwidth-responsivity products of 350 mA center dot GHz and 4.8 GHz center dot A/W, respectively, at receiving frequency of up to 10 GHz. (c) 2006 Optical Society of America.
Pattern effect optimized with non-native surface passivation in copper abrasive-free polishing
(2005)
Fang, JY
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Tsai, MS
;
Dai, BT
;
Wu, YS
;
Feng, MS
Pattern effects, resulting from different metal removal rates on various feature designs in copper chemical mechanical polishing (Cu CMP), can be reduced in an abrasive-free slurry formulated with HNO3 and benzotriazole (BTA). In the slurry, non-native Cu-BTA adlayer is formed instead of native metal oxide as surface passivation layer on a Cu surface, and it benefits nonlinear Cu removal rate as function of down force. Moreover, by controlling the down force, the Cu removal rate can be independent of down force resulting in the reduction of pattern effect. (C) 2005 The Electrochemical Society.
Performance of InGaN-GaN LEDs fabricated using glue bonding on 50-mm Si substrate
(2006-01-01)
Peng, WC
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Wu, YS
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材料科學與工程學系
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Department of Materials Science and Engineering
Vertical InGaN-GaN light-emitting diodes (LEDs) epitaxial films were successfully fabricated on a 50-mm Si substrate using glue bonding and laser liftoff technology. A high-temperature stable organic film, rather than a solder metal, was used as the bonding agent. It was found that the light output of the vertical InGaN LED chip exceeded that of the conventional sapphire-substrate LEDs by about 20% at an injection current of 20 mA. The vertical InGaN LEDs operated at a much higher injection forward current (280 mA) than sapphire-substrate LEDs (180 mA). The radiation pattern of the vertical InGaN LEDs is more symmetrical than that of the sapphire-substrate LEDs. Furthermore, the vertical InGaN LEDs remain highly reliable after 1000 h of testing.
Phase gratings in pretilted homeotropic cholesteric liquid crystal films
(2002-10-01)
Wu, JJ
;
Chen, FC
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Wu, YS
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Chen, SH
;
光電工程學系
We studied the fingerprint texture of homeotropic cholesteric liquid crystal (CLC) films. Parallel (360) and antiparallel (180) alignment treatments were adopted for these films such that the molecules at the boundaries had an approximately I pretilt angle to the substrate normal. The experimental results showed that the homeotropic film may be more suitable than the planar-parallel film for use in an electrically controlled phase grating.