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2-V-operation delta-doped power HEMT's for personal handy-phone systems
(1997-08-01)
Lai, YL
;
Chang, EY
;
Chang, CY
;
Liu, TH
;
Wang, SP
A high-efficiency and high-power-density delta-doped AIGaAs/InGaAs HEMT with low adjacent channel leakage has been developed for the digital wireless personal handy-phone system (PHS). When qualified by 1.9-GHz pi/4-shifted quadrature phase shift keying (QPSK) modulated PHS standard signals, the 2.0-V-operation HEMT with a 1-mm gate width demonstrated a power-added efficiency of 45.3% and an output power density of 105 mW/mm. This is the highest power density ever reported by the power transistors for the PHS. The state-of-the-art results for the PHS operating at 2.0 V were achieved by the delta-doped power HEMT for the first time.
5 mm high-power-density dual-delta-doped power HEMT's for 3 V L-band applications
(1996-05-01)
Lai, YL
;
Chang, EY
;
Chang, CY
;
Chen, TK
;
Liu, TH
A high-power-density dual-delta-doped AlGaAs/InGaAs/GaAs high electron mobility transistor (HEMT) for personal communication applications has been developed. A 5.0 mm gate-width device operating at a drain bias of 3.0 V gave an output power over 1 W, The 1 mu m gate-length HEMT exhibited a current density of 425 mA/mm at V-gs = 0.5 V, The maximum transconductance of the device was 270 mS/mm, The effective knee voltage was as low as 0.3 V, At the class AB operation, the HEMT demonstrated an output power density of 200 mW/mm, 64% power-added efficiency and 18.2 dB linear gain at 900 MHz, This is the highest power density of a dual-delta-doped AlGaAs/InGaAs/GaAs HEMT reported to date for low voltage (3 V) wireless applications.
Reactive ion etching of GaN with BCl3/SF6 plasmas
(1996-07-01)
Feng, MS
;
Guo, JD
;
Lu, YM
;
Chang, EY
;
材料科學與工程學系
Reactive ion etching (RIE) with BCl3/SF6 plasmas of high quality GaN films grown by low pressure metallorganic chemical vapor deposition (LP-MOCVD) is reported. A high etch rate of 2100 Angstrom min(-1) was achieved with BCl3/SF6 plasmas at gas pressure 40 mtorr, total gas flow rate 40 seem, and radio-frequency (RF) power 300 W. The parameters affecting the etch rates such as BCl3/SF6 flow ratio, total gas pressure, RF power and self-bias voltage have been studied. Results indicate that under high RF power (300 W) the radical concentration is an etch rate-limiting factor at lower BCl3/SF6 pressure (lower than 40 mtorr), while self-bias voltage (ion bombardment) is a rate-limiting factor at higher pressure (more than 40 mtorr). Under lower RF power (150 W), self-bias voltage becomes the dominant factor of etch rate. Scanning electron microscopy (SEM) shows that the etched profile is highly anisotropic, and the etched area has some columnar residues due to Al compound contamination from the Al cathode during RIE.
Highly selective etch process for the manufacture of GaAs power MESFET's
(1999)
Chang, EY
;
Lai, YL
;
Lee, YS
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In this paper, a highly selective etch process for the manufacture of GaAs power metal-semiconductor field-effect transistor (MESFET's) has been developed. The selective etch process using citric acid/potassium citrate/hydrogen peroxide solutions were studied. The experimental results were utilized to the gate recess process of the GaAs MESFET's for advanced wireless communication applications. When operating at a drain bias of 10 V and a frequency of 1.88 GHz, the 14.7-mm-wide MESFET's provided a maximum output power (Pout) of 38.8 dBm with a power-added efficiency (PAE) of 49.5% and a gain of 8.42 dB. The linear gain was 12.2 dB and the Pout at l-dB compression was 37.7 dBm with a PAE of 50.7%. The maximum PAE was 52.5%.
Backside copper metallization of GaAs MESFET's using Ta and TaN as diffusion barrier
(2000)
Chang, EY
;
Chen, CY
;
Chang, L
;
Chen, SH
;
材料科學與工程學系
Backside copper metallization of GaAs MESFET's ( Metal Semiconductor Field Effect Transistor) using Ta and TaN as the diffusion barrier layers was studied. A thin diffusion barrier Ta(40nm) or TaN(40nm) was sputtered on the GaAs substrate as the diffusion barrier for copper metallization. Material reactions of these films with GaAs substrate at different annealing temperatures were characterized by X-ray diffraction, Auger electron spectroscopy and transmission electron microscopy. Copper and diffusion barrier layer films were very stable up to 500 degrees C. At higher temperatures, Ta atoms started to react with GaAs substrate to form TaAs and TaAs, and Cu atoms started to penetrate into the GaAs substrate. The backside of the GaAs MESFET's was metallized using these Cu/Ta and Cu/TaN films. After 300 degrees C 2 hr annealing, the MESFET's showed very little change in the device characteristics. The experimental results show that both Ta and TaN are good diffusion barriers for backside copper metallization in GaAs devices.
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.
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.
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.
2.4 V-operated enhancement-mode power PHEMTs for personal handy-phone system application
(2001)
Chen, SH
;
Chang, EY
;
Lin, YC
;
Lee, CS
;
友訊交大聯合研發中心
Enhacement-mode pseudomorphic high electron mobility transistors (E-PHEMTs) were developed for low voltage wireless communication applications. Under drain bias of 3.6 V, the device delivered a high output power density of 265.25 mW/mm (29.5dBm) with a power-added-efficiency (PAE) of 50.54 %. Under 1.9GHz pi/4-shifted quadrature phase shift keying(QPSK) modulation signal, the 3.36 mm devices meet personal handy-phone system (PHS) specification at an output power level of 22.42 dB with PAE of 35.12% under 2.4 V drain bias. The E-PHEMTs developed are adequate for low-voltage-operated PHS application.
2.4 V-operated enhancement mode PHEMT with 32 dBm output power and 61 % power efficenciecy
(2001)
Chen, SH
;
Chang, EY
;
Lin, YC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A 2.4 V operated enhancement-mode pseudormorphic high electron mobility transistors (E-PHEMTs) with high output power and power-added-efficiency (PAE) have been developed. With optimally designed epitaxial structure and gate recess process, the E-PHEMT shows high power performance and high power gain. Under 2.4 V bias at 1.9 GHz, the E-PHEMT shows maximum output power of 32.25 dBm and maximum power-added efficiency of 61.45% with linear power gain of 13.93 dB when the device was tuned for maximum output power match. When tuned for maximum output power added efficiency, the E-PHEMT can achieve a maximum PAE of 78.51%. The developed E-PHEMT with superior power performance is one of the candidates for power amplifiers used for 2.4 V-operated 3G wireless communication system.

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