Browsing by Author "Fang, CY"

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A novel I-line phase shift mask (PSM) technique for submicron T-Gate formation
(2001)
Fu, DK
;
Chang, HC
;
Fang, CY
;
Lee, CS
;
Chang, EY
Submicron T-gate formation using I-line stepper with phase shift mask (PSM) technique [1,2,3] has become very attractive for GaAs MMIC technology due to its low capital investment and high throughput. In this paper a novel submicron (<0.2mum) T-gate technology using phase shift mask technique is reported. The 8% half-tone PSM was selected for the definition of the isolated narrow space. Before lithography, 2500Angstrom SiN film was deposited on the wafer. After I-line PSM exposure and RIE etch of the silicon nitride film, openings with less than 0.25mum wide were formed on the SiN film. To further reduce the dimension of the openings, the wafer was then deposited addition 500Angstrom nitride and etched back using RIE without any mask. Less than 0.2mum openings were formed on the wafer after the dry etch. The wafer was then coated with another layer of photoresist to form lift-off structure. Gate length of 0.185mum was obtained using this technique. This novel process is a high throughput T-gate process compared to conventional E-beam lithography technology for GaAs MMIC production.
A study of subbands in AlGaN/GaN high-electron-mobility transistor structures using low-temperature photoluminescence spectroscopy
(2002-06-17)
Fang, CY
;
Lin, CF
;
Chang, EY
;
Feng, MS
;
材料科學與工程學系
Al0.15Ga0.85N/GaN high-electron-mobility transistor (HEMT) structures with various delta-doping concentrations and spacer thicknesses grown on sapphire by metalorganic chemical-vapor deposition are investigated. The Hall mobility is as high as 1333 cm(2)/V s at room temperature and 6330 cm(2)/V s at 77 K. Two-dimensional electron gas (2DEG) phenomena, which have not been clearly resolved in the literature, are observed by photoluminescence (PL) spectra at low temperature in this study. The PL spectra peaks of the interband transitions from 2DEG subbands to the valence band are in the range from 3.486 to 3.312 eV. The effects of the strain caused by different Al fractions of the top layer, and that of the spacer thickness on the 2DEG phenomena are discussed. Redshifts due to temperature variations for various HEMT structures are observed in 2DEG subbands and in the band-edge emission, which is believed to be evidence of interband transitions from 2DEG subbands to valence bands. (C) 2002 American Institute of Physics.
AIGaN Schottky characteristics after hybrid photo-enhanced wet and inductively coupled plasma etch
(2001)
Huang, WJ
;
Fang, CY
;
Wong, JS
;
Lee, CS
;
Chang, EY
AlGaN Schottky contact characteristics after hybrid photo-enhanced wet etch and Inductively coupled plasma etch (ICP) is studied. AlGaN was grown by MOCVD on sapphire substrate. KOH solution and 100mW/cm(2) UV illumination by Hg are lamp was used for photo-enhanced wet etch. Gas mixture of Cl-2 and N-2 was used for ICP etch. The Schottky metal used in this study is Ni/Au (100nm/100nm) and the Ohmic metal used is Al (100nm). Typical etch rates are 0.28nm/min and 265nm/min with a roughness of 0.6nm and 1.17nm for wet and dry etch respectively. The ICP process etches more rapidly but the etched surfaces are rougher when compared to the wet-etch process. After ICP etch at 600 watt for 60sec, the schottky diode has an ideality factor n=2.6, and the barrier height phi(B)=0.65 eV However, for the ICP etched sample followed by photo-enhanced wet chemical etch for 30mins, the sample has an ideality factor n=0.99, and the barrier height phi(B)=0.86 eV, and the breakdown voltage is recovered from 4V to 7.5V The study indicates that the wet chemical etch can remove the damage caused by ICP etching. Overall, the hybrid dry/wet etch process is a high etch rate process and cause very low damages on the etched surface.
AIGaN/GaN HEMT sub-bands study using low-temperature photoluminescence
(2001)
Fang, CY
;
Lin, CF
;
Lee, CS
;
Chang, EY
;
Feng, MS
Al0.1Ga0.9N/GaN HEMTs (High Electron Mobility Transistor) structures with different delta-doping concentration and spacer thickness grown on sapphire by MOCVD are studied. The hall mobility is as high as 1333 cm(2)/V s. at room temperature and 6330 cm(2)/V s at 77 K. Obvious 2-DEG phenomena not clearly resolved in literatures before are observed by PL spectra measured at low temperature. The influences of delta-doping concentration and spacer thickness on the 2-DEG phenomena are discussed. Peaks red-shift of different HEMT structures due to temperature variation are observed in 2-DEG sub-bands as well as at the band-edge emission that is believed as a strong evidence of 2DEG sub-bands to valence bands transmission.
Etching damages on AlGaN, GaN and InGaN caused by hybrid inductively coupled plasma etch and photoenhanced chemical wet etch by Schottky contact characterizations
(2003-07-01)
Fang, CY
;
Huang, WJ
;
Chang, EY
;
Lin, CF
;
Feng, MS
The surface damaging effects of the inductively coupled plasma (ICP) etch and the photoenhanced chemical (PEC) wet etch on AlGaN, GaN and InGaN were systematically investigated. The surface morphologies and the etch rates after ICP etch and PEC wet etch were explored to achieve optimum conditions for a hybrid etch technique. The etch rates increased with the ICP power or concentration of KOH(aq) and the surface roughness was less after PEC wet etch than it was after ICP etch. Schottky characterizations of GaN and AlGaN diodes after pure ICP etch, pure PEC etch and hybrid ICP/PEC etch were investigated to elucidate the damaging effects on the surfaces. It shows that the PEC etch is an effective way to achieve a damage-free surface for GaN-based materials, and the hybrid ICP/PEC etch can be used for applications which require high etch rate and damage-free surfaces.
Graphical method for the determination of the complex NMR shift and equilibrium constant for a hetero-association accompanying self-associations
(1997-08-01)
Lin, CC
;
Fang, CY
;
Kao, DY
;
Chen, JS
;
應用化學系
We describe a novel graphical method which, in conjunction with the previously proposed graphical determination of mono;ner shift, dimer shift, and dimerization constant for self-association, allows us to determine the complex shift and equilibrium constant for a hetero-association, A + B reversible arrow AB, accompanying self-associations, A + A reversible arrow A(2), and B + B reversible arrow B-2. The merit of the new method includes the removal of the restrictions imposed on the conventional Benesi-Hildebrand (B-H) plot: (1) that the concentration of one component must be much less than that of the other; (2) that there be no accompanying self-association, The simultaneous equilibrium of the self-association of 2-pyrrolidone (A) and that of 4-methyl-alpha-pyrrolidone (B) and the hetero-association between A and B in acetonitrile-d(3) at 25 degrees C is studied. The inappropriateness of the B-H plot in dealing with this case is also pointed out.
Graphical method for the determination of the complex NMR shift and equilibrium constant for a hetero-association accompanying self-associations
(1997-08-01)
Lin, CC
;
Fang, CY
;
Kao, DY
;
Chen, JS
;
交大名義發表
We describe a novel graphical method which, in conjunction with the previously proposed graphical determination of mono;ner shift, dimer shift, and dimerization constant for self-association, allows us to determine the complex shift and equilibrium constant for a hetero-association, A + B reversible arrow AB, accompanying self-associations, A + A reversible arrow A(2), and B + B reversible arrow B-2. The merit of the new method includes the removal of the restrictions imposed on the conventional Benesi-Hildebrand (B-H) plot: (1) that the concentration of one component must be much less than that of the other; (2) that there be no accompanying self-association, The simultaneous equilibrium of the self-association of 2-pyrrolidone (A) and that of 4-methyl-alpha-pyrrolidone (B) and the hetero-association between A and B in acetonitrile-d(3) at 25 degrees C is studied. The inappropriateness of the B-H plot in dealing with this case is also pointed out.
Monomer shift, dimer shift and dimerization constant for self-association determined graphically from the NMR dilution shift: Pyrrolidone in CDCl3 as an example
(1997-01-01)
Chen, JS
;
Fang, CY
;
Baird, JK
;
應用化學系
;
Department of Applied Chemistry
We describe a graphical method for analysis of dilution NMR shift data, which permits the self-consistent determination of the monomer shift, dimer shift, and dimerization constant for systems involving a monomer-dimer equilibrium. The new method specifically avoids the manual extrapolation to zero concentration conventionally used to obtain the monomer shift. In addition, it provides quantitative measures for both the consistency and error of the determination. Measurements of the dilution shift for pyrrolidone in CDCl3 over a series of temperatures are used to demonstrate the applicability of the graphical method. The enthalpy and entropy of the dimerization reaction are determined via a van't Hoff plot of the temperature dependence of the dimerization constant.
Monomer shift, dimer shift and dimerization constant for self-association determined graphically from the NMR dilution shift: Pyrrolidone in CDCl3 as an example
(1997-01-01)
Chen, JS
;
Fang, CY
;
Baird, JK
;
應用化學系
;
Department of Applied Chemistry
We describe a graphical method for analysis of dilution NMR shift data, which permits the self-consistent determination of the monomer shift, dimer shift, and dimerization constant for systems involving a monomer-dimer equilibrium. The new method specifically avoids the manual extrapolation to zero concentration conventionally used to obtain the monomer shift. In addition, it provides quantitative measures for both the consistency and error of the determination. Measurements of the dilution shift for pyrrolidone in CDCl3 over a series of temperatures are used to demonstrate the applicability of the graphical method. The enthalpy and entropy of the dimerization reaction are determined via a van't Hoff plot of the temperature dependence of the dimerization constant.
Study of titanium tungsten nitride and tungsten nitride Schottky contacts on n-GaN
(2003-07-01)
Lee, CS
;
Chang, EY
;
Chang, L
;
Fang, CY
;
Huang, YL
The Schottky diode behaviors of the TiWNx and the WNx Schottky contacts to n-GaN were investigated at different annealing temperatures. Both TiWNx and WNx films were deposited by the reactive DC sputtering method. The WNx/n-GaN contact exhibited excellent electrical characteristics even after rapid-thermal annealing up to 850degreesC for 10s. The ideality factor and barrier height remained 1.09 and 0.8OeV, respectively, after 850degreesC annealing. However, the TiWNx/n-GaN contact was thermally stable only up to 650degreesC annealing; the values of the ideality factor and the barrier height were 1.14 and 0.76 eV, respectively, after 650degreesC annealing and started to degrade when annealed at higher temperatures. The deterioration of the TiWNx/n-GaN contact at higher temperatures was due to the inter-diffusion of the TiWN film and the GaN material.