K. Nichols

Fully monolithic 4 watt high efficiency Ka-band power amplifier

Design and performance of a power amplifier that has established a new benchmark for Ka-band power is reported. The amplifier achieved >4 Watts at 25 to 31% PAE with 14 dB of power gain from 29 to 31 GHz. This output power, bandwidth, and efficiency is superior to the best previously reported results. The amplifier is implemented in an improved fully selective 0.15 um power PHEMT process.

9.4-W/mm power density AlGaN-GaN HEMTs on free-standing GaN substrates

High power microwave AlGaN-GaN high electron-mobility transistors (HEMTs) on free-standing GaN substrates are demonstrated for the first time. Measured gate leakage was -2.2 /spl mu/A/mm at -20 V and -10 /spl mu/A/mm at -45 V gate bias. When operated at a drain bias of 50 V, devices showed a record continuous-wave output power density of 9.4 W/mm at 10 GHz with an associated power-added efficiency of 40%. Long-term stability of device RF operation was also examined. Under room conditions, devices driven at 25 V and 3-dB gain compression remained stable in 200 h, degrading only by 0.18 dB in output power. Such results illustrate the potential of GaN substrate technology in supporting reliable, high performance AlGaN-GaN HEMTs for microwave power applications.

Very high gain millimeter-wave InAlAs/InGaAs/GaAs metamorphic HEMT's

We report the first demonstration of W-band metamorphic HEMTs/LNA MMICs using an AlGaAsSb lattice strain relief buffer layer on a GaAs substrate. 0.1/spl times/50 /spl mu/m low-noise devices have shown typical extrinsic transconductance of 850 mS/mm with high maximum drain current of 700 mA/mm and gate-drain breakdown voltage of 4.5 V. Small-signal S-parameter measurements performed on the 0.1-/spl mu/m devices exhibited an excellent f/sub T/ of 225 GHz and maximum stable gain (MSG) of 12.9 dB at 60 GHz and 10.4 dB at 110 GHz. The three-stage W-band LNA MMIC exhibits 4.2 dB noise figure with 18 dB gain at 82 GHz and 4.8 dB noise figure with 14 dB gain at 89 GHz, The gain and noise performance of the metamorphic HEMT technology is very close to that of the InP-based HEMT.

High-performance double-recessed InAlAs/InGaAs power metamorphic HEMT on GaAs substrate

Double-recess power metamorphic high electron mobility transistors (MHEMTs) on GaAs substrates were successfully demonstrated. The In/sub 0.53/Al/sub 0.47/As/In/sub 0.65/Al/sub 0.35/As structures exhibited extrinsic transconductance of 1050 mS/mm and breakdown of 8.3 V, which are comparable to that of the InP power HEMT. Excellent maximum power added efficiency (PAE) of 60.2% with output power of 0.45 W/mm and record associated power gain of 17.1 dB were realized at 20 GHz. A maximum output power of 0.51 W/mm has also been demonstrated with the device. This is the first demonstration of high-efficiency K-band power MHEMTs.

0.2-

We report a successful application of atomic layer deposition (ALD) aluminum oxide as a passivation layer to gallium nitride high electron-mobility transistors (HEMTs). This new passivation process results in 8%-10% higher dc maximum drain current and maximum extrinsic transconductance, about one order of magnitude lower drain current in the sub-threshold region, 10%-20% higher pulsed- IV drain current, and 27%-30% higher RF power with simultaneously 5-8 percentage point higher power-added efficiency. The achieved improvement in device performance is attributed to the outstanding quality of the interface between III-N and the ALD aluminum oxide resulting from the uniqueness of the adopted ALD process, featuring a wet-chemical-based wafer preparation as well as a pregrowth self-cleaning procedure in the growth chamber. This technology can be readily integrated into the HEMT-based integrated circuit fabrication process, making the ALD aluminum oxide-passivated GaN HEMTs excellent candidates for multiple microwave and millimeter-wave power applications.

\mu{\rm m}

This paper reviews recent progress in the development of GaAs metamorphic HEMT (MHEMT) technology for microwave applications. Commercialization has begun, while efforts to further improve performance, manufacturability and reliability continue. We also report the first multi-watt MHEMT MMIC power amplifiers, demonstrating up to 3.2W output power and record power-added efficiency (PAE) at Ka-band.

AlGaN/GaN High Electron-Mobility Transistors With Atomic Layer Deposition

Design and performance of a power amplifier that has established new benchmarks for 6 to 18 GHz power is reported. The amplifier achieved 7.5 Watts max, 5.4 Watts average, 4 Watts min with 36 % max, 22 % average PAE and 12 dB of power gain from 6 to 18 GHz. This output power, bandwidth, and efficiency is superior to the best previously reported results. The amplifier is implemented in a fully selective 0.15 um double recess power PHEMT process.

{\rm Al}_{2}{\rm O}_{3}

InP HEMTs with a double recess 0.12 /spl mu/m gate have been developed. The material structure was designed to be fully selective etched at both recess steps for improved uniformity and yield across the whole wafer. Devices demonstrated DC characteristics of extrinsic transconductances of 1000 mS/mm, maximum current density of 800 mA/mm and gate-drain reverse breakdown voltages of -7.8 V. Power measurements were performed at both 20 GHz and 60 GHz. At 20 GHz, the 6/spl times/75 /spl mu/m devices yielded 65% maximum power added efficiency (PAE) with associated gain of 13.5 dB and output power of 185 mW/mm. When tuned for maximum output power it gave an output power density of 670 mW/mm with 15.6 dB gain and 49% PAE. At 60 GHz, maximum PAE of 30% has been measured with associated output power density of 290 mW/mm and gain of 7.4 dB. This represents the best power performance reported for InP-based double recess HEMTs.

Passivation

High-performance 0.1-μm InAlN/GaN high electron-mobility transistors (HEMTs) have been successfully developed for power amplifiers operating at E-band (targeting 71-76 and 81-86-GHz bands). High maximum drain current of 1.75 A/mm and maximum extrinsic transconductance of 0.8 S/mm have been achieved for depletion-mode devices. Enhancement-mode HEMTs have also shown maximum drain current of 1.5 A/mm and maximum extrinsic transconductance of 1 S/mm. The selection of atomic layer deposition aluminum oxide (Al2O3) for device passivation enables a two-terminal breakdown voltage of ~25 V, excellent subthreshold characteristics as well as the pulsed-IV featuring little current collapse for both types of HEMTs. When biased at a drain voltage of 10 V, a first-pass two-stage power amplifier design based on 0.1-μm depletion-mode devices has demonstrated an output power of 1.43 W with 12.7% power-added efficiency at 86 GHz, a level of performance that has been attained previously only by state-of-the-art counterparts based on AlGaN/GaN HEMTs at a much higher drain bias and compression level.

Progress in GaAs metamorphic HEMT technology for microwave applications

State-of-the-art power performance of a V-band InP HEMT MMIC is reported using a slot via process for reducing source inductance and a fully selective gate recess process for uniformity and high yield. The 0.1 /spl mu/m gate length, high performance InGaAs/InAlAs/InP HEMTs that were utilized in the circuit exhibited a maximum power density of 530 mW/mm, power added efficiency of 39%, and a gain of 7.1 dB. At 60 GHz, a single-stage monolithic power amplifier achieved an output power of 224 mW with a PAE of 43%. The associated gain was 7.5 dB. These results are the best combination of output power and efficiency reported for an InP device and a MMIC at V-band, and clearly demonstrates the potential of the InP HEMT technology for very high efficiency, millimeter wave power applications.