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A novel fabrication technique of T-shaped gates using an EGMEA and PMIPK multilayer resist system and a single-step electron-beam exposure
(1998-03-01)
Lai, YL
;
Lai, YK
;
Chang, CY
;
Chang, EY
;
材料科學與工程學系
A novel fabrication process of submicron T-shaped gates using an EGMEA and PMIPK multi-layer resist system and e-beam lithography has been developed. Due to the different sensitivities of the EGMEA and PMIPK resists, narrow/wide/narrow resist opening was obtained. The status of the electron scattering and the incident primary electron beams statistically construct the absorbed energy density distribution contours. The absorbed energy density distribution contours in association with the sensitivity feature of the resists and the appropriate development conditions determine the final resist profile. Only a single exposure step and a single development step are required. The simplified fabrication process of T-shaped gates significantly reduces not only the process time but also the production costs. The simple submicron T-shaped gate fabrication process studied provides a suitable technique for the mass manufacture of the advanced InP-based and GaAs-based microwave devices and circuits.
Power PHEMT with compact device layout for low voltage CDMA application
(2000-03-16)
Chang, EY
;
Lee, DH
;
Chen, SH
;
Chang, HC
;
材料科學與工程學系
A high efficiency low voltage operation dual delta-doped AlGaAs/ InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) for low voltage code division multiple access (CDMA) application has been developed. When tested at 2.4V and 1.9GHz under IS-95 CDMA modulation, the 20.16mm PHEMT device was found to have a linear output power of 28dBm with a power added efficiency of 30.2%. The device also has a saturation power of 30.0dBm with a power added efficiency of 61.5%. The high efficiency and linearity of the PHEMT at low bias voltage is attributed to the use of the dual delta-doped PHEMT structure and to the reduction of the size of the device layout. The device is suitable for low voltage CDMA applications.
Highly selective GaAs/Al0.2Ga0.8As wet etch process for the gate recess of low-voltage-power pseudomorphic high-electron-mobility transistor
(2000-08-01)
Chang, HC
;
Chang, EY
;
Chung, CC
;
Kuo, CT
;
材料科學與工程學系
A selective wet etch process for the gate recess of the GaAs power pseudomorphic high-electron-mobility transistors (pHEMT's) was developed. The power pHEMT's used in this study were epitaxially grown power Al0.2Ga0.8As/In0.2Ga0.8As pHEMT's with a 250 Angstrom GaAs cap layer and a 300 Angstrom Al0.2Ga0.8As electron-donating layer. The electron-donating layer was used as the etch-stop layer for the gate recess. A selectivity of 3400 : 1 was achieved for GaAs/Al0.2Ga0.8As layers using citric acid/tripotassium citrate/hydrogen peroxide etching solutions in this study. This is the highest selectivity for GaAs/AlxGa1-xAs selective etching reported so far. The pHEMT's processed using this selective etching demonstrated good device power performance, and the wet recess process did not cause any contamination or damage to the device. The test data indicates that this selective etch process can be of practical use for forming the gate recess of the power pHEMT's with good device performance and excellent electrical uniformity.
A 1.2-V operation power pseudomorphic high electron mobility transistor for personal handy phone handset application
(2000-10-15)
Chang, EY
;
Lee, DH
;
Chen, SH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A 1.2 V GaAs power pseudomorphic high electron mobility transistors (PHEMT's) for personal handy phone system (PHS) handset application was developed. The power PHEMT has a dual delta doped AlGaAs/InGaAs/GaAs based structure with compact device layout. The 6.72 mm device exhibits maximum power added efficiency (PAE) of 43.62% at 1.2V drain bias with an output power of 22.18 dBm. Under 1.9 GHz pi /4-shifted quadrature phase shift keying (QPSK) modulated PHS signal, the device shows an adjacent channel leakage power (P-adj) Of -56.86 dBc at 600 kHz apart from the center frequency and a linear efficiency of 41.31%. This is the first report on the 1.2-V operation power PHEMT for PHS handset application so far.
Thermal stability of Cu/Ta/GaAs multilayers
(2000-11-20)
Chen, CY
;
Chang, L
;
Chang, EY
;
Chen, SH
;
Chang, DF
Copper metallization for GaAs was evaluated by using Cu/Ta/GaAs multilayers for its thermal stability. A thin Ta layer of 40 nm was sputtered on the GaAs substrate as the diffusion barrier before copper film metallization. As judged from sheet resistance, x-ray diffraction, Auger electron spectroscopy and transmission electron microscopy, the Cu/Ta films with GaAs were very stable up to 500 degreesC without migration into GaAs. After 550 degreesC annealing, the interfacial mixing of Ta with GaAs substrate occurred, resulting in the formation of TaAs2. At 600 degreesC annealing, the reaction GaAs with Ta and Cu formed TaAs, TaAs2, and Cu3Ga, resulting from Cu migration and interfacial instability. (C) 2000 American Institute of Physics. [S0003-6951(00)03047-3].
A GaAs/AlAs wet selective etch process for the gate recess of GaAs power metal-semiconductor field-effect transistors
(2001-01-01)
Chang, EY
;
Lai, YL
;
Lee, YS
;
Chen, SH
;
材料科學與工程學系
A highly selective wet chemical etch process for gate recess of the GaAs power metal-semiconductor field effect transistors (MES FETs) was developed. The power MESFETs used in this study were epitaxially grown devices with a 20 Angstrom A1As etch-stop layer for gate recess. The selective etch process using citric acid/potassium citrate/hydrogen peroxide solution was studied. A selectivity better than 3800:1 was achieved for GaAs/A1As layers. This selective etch was applied both to high-power, high-voltage power MESFETs and low-voltage large-periphery power MESFETs. For high-power applications, the 14.7 mm device had a breakdown voltage of 22 V. When tested at 1.88 GHz with a drain bias of 10 V, it provided a maximum output power of 38.8 dBm and a maximum power-added efficiency of 52.5%. For low-voltage applications, the 19.8 mm device was tested under IS-95 code-division multiple access (CDMA) modulation at 1.88 GHz with a drain bias of 3.5 V. Under CDMA modulation, the device showed an output power of 28.03 dBm with an adjacent channel power rejection of -29.6 dBc at 1.25 MHz offset frequency. Both devices also showed excellent uniformity in pinch-off voltages. (C) 2000 The Electrochemical Society. S0013-4651 (00)03-053-6. All rights reserved.
Backside copper metallization of GaAs MESFETs using TaN as the diffusion barrier
(2001-06-01)
Chen, CY
;
Chang, EY
;
Chang, L
;
Chen, SH
;
材料科學與工程學系
Backside copper metallization of GaAs MESFETs using TaN as the diffusion barrier was studied. A thin TaN layer of 40 nm was sputtered on the GaAs substrate before copper firm metallization. As judged from the data of X-ray diffraction (XRD), Anger electron spectroscopy (AES), and cross-sectional transmission electron microscopy (TEM), the Cu/TaN films with GaAs were very stable without interfacial interaction up to 550 OC annealing, The copper metallized MESFETs were thermally stressed at 300 degreesC, The devices showed very little change in the device characteristics (<3 %) after thermal stress, and the changes of the electrical parameters and RF characteristics of the devices after thermal stress were of the same order as those devices without Cu metallization, These results show that TaN is a good diffusion barrier for Cu in GaAs devices and the Cu/TaN films can be used for the backside copper metallization of GaAs MESFETs.
Low-voltage-operation high-power-density AlGaAs/InGaAs enhancement-mode pseudomorphic high-electron-mobility transistor for personal handy-phone handset application
(2002-01-15)
Chen, SH
;
Chang, L
;
Chang, EY
;
Chang, CY
;
材料科學與工程學系
A high-power-density enhancement-mode AlGaAs/InGaAs pseudomorphic high-electron-mobility transistor (E-PHEMT) is developed for the Japanese personal handy-phone system (PHS). The E-PHEMT has a total gate width of 3.36 mm with a gate length of 0.5 mum. The E-PHEMT shows a high power density of 247 mW/mm at 3.6 V, 196 mW/mm at 3 V, 152 mW/mm at 2.4 V and 63 mW/mm at 1.2 V, this is the highest power density reported so far for E-PHEMT with similar device size and bias conditions. When the E-PHEMT was qualified by 1.9 GHz pi/4-shifted quadrature phase shift keying (QPSK) modulated signal for PHS at 2,4 V with idle current of 30 mA. the device shows a linear PAE of 35.1% with associated power gain of 15.5 dB at output power of 22.4 dBm. The adjacent channel leakage power (P(adj)) of the de ice is -56.6 dBc at 600 kHz apart from the center frequency. The E-PHEMT meets PHS specifications and demonstrates high power density, excellent power efficiency and linearity at low bias voltage.
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.
Novel I-line phase shift mask technique for submicron T-shaped gate formation
(2002-07-01)
Chen, SH
;
Chang, HC
;
Fu, DK
;
Chang, EY
;
Lai, YL
A novel submicron (<0.2 mum) T-shaped gate technology using a phase shift mask (PSM) technique is developed. The 8% half-tone PSM was selected for the definition of the isolated narrow space. Before lithography, a 2000 Angstrom SiN film was deposited on the wafer. After i-line PSM exposure and reactive ion etching (RIE) of the silicon nitride film, openings less than 0.2 mum wide were formed on the SiN film. To further reduce the dimensions of the openings, an additional 566 Angstrom nitride was then deposited on the wafer and etched back using RIE without any mask. An opening of 0.167 mum was formed on the wafer after the dry etching process. The wafer was then coated with another layer of photoresist to form a lift-off structure. The T-shaped gate with a length of 0.167 mum was obtained using this technique. The novel T-shaped gate technology is a high-throughput process for both silicon and compound semiconductor devices.

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