Yi-Chung Lien

Low-noise metamorphic HEMTs with reflowed 0.1-/spl mu/m T-gate

A 0.1-/spl mu/m T-gate fabricated using e-beam lithography and thermally reflow process was developed and applied to the manufacture of the low-noise metamorphic high electron-mobility transistors (MHEMTs). The T-gate developed using the thermally reflowed e-beam resist technique had a gate length of 0.1 /spl mu/m and compatible with the MHEMT fabrication process. The MHEMT manufactured demonstrates a cutoff frequency f/sub T/ of 154 GHz and a maximum frequency f/sub max/ of 300 GHz. The noise figure for the 160 /spl mu/m gate-width device is less than 1 dB and the associated gain is up to 14 dB at 18 GHz. This is the first report of a 0.1 /spl mu/m MHEMT device manufactured using the reflowed e-beam resist process for T-gate formation.

Effect of Gate Sinking on the Device Performance of the InGaP/AlGaAs/InGaAs Enhancement-Mode PHEMT

An enhancement-mode InGaP/AlGaAs/InGaAs pseudomorphic high-electron mobility transistor using platinum (Pt) as the Schottky contact metal was investigated for the first time. Following the Pt/Ti/Pt/Au gate metal deposition, the devices were thermally annealed at 325 degC for gate sinking. After the annealing, the device showed a positive threshold voltage (Vth) shift from 0.17 to 0.41 V and a very low drain leakage current from 1.56 to 0.16 muA/mm. These improvements are attributed to the Schottky barrier height increase and the decrease of the gate-to-channel distance as Pt sinks into the InGaP Schottky layer during gate-sinking process. The shift in the Vth was very uniform across a 4-in wafer and was reproducible from wafer to wafer. The device also showed excellent RF power performance after the gate-sinking process

2 V-operated InGaP-AlGaAs-InGaAs enhancement-mode pseudomorphic HEMT

A low-voltage single power supply enhancement-mode InGaP-AlGaAs-InGaAs pseudomorphic high-electron mobility transistor (PHEMT) is reported for the first time. The fabricated 0.5/spl times/160 /spl mu/m/sup 2/ device shows low knee voltage of 0.3 V, drain-source current (I/sub DS/) of 375 mA/mm and maximum transconductance of 550 mS/mm when drain-source voltage (V/sub DS/) was 2.5 V. High-frequency performance was also achieved; the cut-off frequency(F/sub t/) is 60 GHz and maximum oscillation frequency(F/sub max/) is 128 GHz. The noise figure of the 160-/spl mu/m gate width device at 17 GHz was measured to be 1.02 dB with 10.12 dB associated gain. The E-mode InGaP-AlGaAs-InGaAs PHEMT exhibits a high output power density of 453 mW/mm with a high linear gain of 30.5 dB at 2.4 GHz. The E-mode PHEMT can also achieve a high maximum power added efficiency (PAE) of 70%, when tuned for maximum PAE.

Copper-Airbridged Low-Noise GaAs PHEMT With

A GaAs pseudomorphic HEMT (PHEMT) with Cu-metallized interconnects was successfully developed. Sputtered WN_x was used as the diffusion barrier and Ti was used as the adhesion layer to improve the adhesion between WN_x/Cu interface in the thin-metal structure. After copper metallization, the PHEMTs were passivated with silicon nitride to avoid copper oxidation. The Cu-airbridged PHEMT showed the saturation I_DS was 250 mA/mm and the g_m was 456 mS/mm. The Ti adhesion layer plays a significant role on the g _m and V_p uniformity of the Cu-metallized PHEMTs. The GaAs PHEMTs with Ti/WN_x/Ti/Cu multilayer have better noise figure and associated gain than those of the devices without the Ti adhesion layer. The fabricated Cu-metallized GaAs PHEMT with Ti/WN _x/Ti/Cu multilayer has a noise figure of 0.76 dB and an associated gain of 8.8 dB at 16 GHz. The cutoff frequency (f_T) is 70 GHz when biased at V_DS=1.5V. These results show that the Ti/WN_x/Ti multilayer can serve as a good diffusion barrier for Cu metallization process of airbridge interconnects on GaAs lownoise PHEMTs

hboxTi/hboxWN_x/hboxTi

Electrical characteristics and thermal stability of the Ti∕Pt∕Cu Schottky contact on InAlAs were investigated. The Ti∕Pt∕Cu Schottky contact had comparable electrical properties compared to the conventional Ti∕Pt∕Au contact after annealing. As judged from the material analysis, the Ti∕Pt∕Cu on InAlAs after 350°C annealing showed no diffusion sign into the InAlAs. After 400°C annealing, the interfacial mixing of Cu and the underlying layers occurred and resulted in the formation of Cu4Ti. The results show that Ti∕Pt∕Cu Schottky contact using platinum as the diffusion barrier is very stable up to 350°C annealing and can be used for InAlAs∕InGaAs high-electron mobility transistors and monolithic microwave integrated circuits.

Diffusion Barrier for High-Frequency Applications

A high linearity and high efficiency enhancement-mode InGaP/AlGaAs/InGaAs pseudomorphic high electron mobility transistor (PHEMT) for single supply operation has been developed. The low voltage operation is achieved by the very low knee voltage of the device and the linearity is improved by the optimizing concentrations of the two δ-doped layers. Biased at drain-to-source voltage VDS = 2 V, the fabricated 0.5 ×200 µm2 device exhibited a maximum transconductance of 448 mS/mm. The measured minimum noise figure (NFmin) was 0.86 dB with 12.21 dB associated gain at 10 GHz. The device shows a high output third-order intercept point (OIP3)-P1 dB of 13.2 dB and a high power efficiency of 35% when under wideband code-division multiple-access (W-CDMA) modulation signal.

Thermal stability of Ti∕Pt∕Cu Schottky contact on InAlAs layer

A 70 nm In0.52Al0.48As/In0.6Ga0.4As power metamorphic high electron mobility transistor (MHEMT) with a double δ-doping structure was fabricated and evaluated. The device has a high transconductance of 827 mS/mm. The saturated drain-source current of the device is 890 mA/mm. A current gain cutoff frequency ( fT) of 200 GHz and a maximum oscillation frequency ( fmax) of 300 GHz were achieved owing to the nanometer gate length and high indium content in the channel. When measured at 32 GHz, the 0.07×160 µm2 device demonstrates a maximum output power of 14.5 dBm (176 mW/mm) and a P1 dB of 11.1 dBm (80 mW/mm) with a 9.5 dB power gain. The excellent DC and RF performance of the 70 nm MHEMT are comparable to those of InP-based HEMTs and show the great potential for Ka-band power applications.

Double δ-Doped Enhancement-Mode InGaP/AlGaAs/InGaAs Pseudomorphic High Electron Mobility Transistor for Linearity Application

An In_0.52Al_0.48As/In_0.6Ga_0.4As metamorphic high-electron mobility transistor (MHEMT) with 0.15-mum Gamma-shaped gate using deep ultraviolet lithography and tilt dry-etching technique is demonstrated. The developed submicrometer gate technology is simple and of low cost as compared to the conventional E-beam lithography or other hybrid techniques. The gate length is controllable by adjusting the tilt angle during the dry-etching process. The fabricated 0.15-mum In_0.52Al_0.48As/In_0.6Ga_0.4As MHEMT using this novel technique shows a saturated drain-source current of 680 mA/mm and a transconductance of 728 mS/mm. The f_T and f_max of the MHEMT are 130 and 180 GHz, respectively. The developed technique is a promising low-cost alternative to the conventional submicrometer E-beam gate technology used for the fabrication for GaAs MHEMTs and monolithic microwave integrated circuits

High-Performance In0.52Al0.48As/In0.6Ga0.4As Power Metamorphic High Electron Mobility Transistor for Ka-Band Applications

A 70-nm In0.52Al0.48As/In0.6Ga0.4 power MHEMT with double delta-doping was fabricated and evaluated. The device has a high transconductance of 827 mS/mni. The saturated drain-source current of the device is 890 niA/mm. A current gain cutoff frequency (fT) of 200 GHz and a maximum oscillation frequency (fmax ) of 300 GHz were achieved due to the nanometer gate length and the high Indium content in the channel. When measured at 32 GHz, the 4 times 40 mum device demonstrates a maximum output power of 14.5 dBm with PldB of 11.1 dBm and the power gain is 9.5 dB. The excellent DC and RF performance of the 70-nm MHEMT shows a great potential for Ka-band power applications.

Fabrication of 0.15-

A metamorphic high electron-mobility transistor (HEMT) manufactured with reflowed submicron T-gate using e-beam lithography for high-speed optoelectronics applications is developed. The In/sub 0.53/Al/sub 0.47/As/InGaAs HEMT uses In/sub x/Al/sub 1-x/As as the buffer layer between GaAs substrate and the InP lattice-matched HEMT structure. The T-gate developed has a gate length of 160 /spl mu/m. The fabricated metamorphic HEMT has a saturation drain current of 280 mA/mm and a transconductance of 840 mS/mm at V/sub DS/ = 1.2 V. Noise figure for 160 /spl mu/m gate-width device is less than 1 dB and the associated gain is up to 14 dB at 18 GHz. The device demonstrates a cut-off frequency f/sub T/ of 150 GHz and a maximum frequency f/sub MAX/ up to 350 GHz. The metamorphic HEMT developed has the potential for high-speed optoelectronics applications.