P.C. Chao

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.

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 fully selective double recess InAlAs/InGaAs/InP HEMTs

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.

0.1-

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.

\mu \text{m}

A 50nm MHEMT millimeter-wave MMIC low noise amplifier with state-of-the-art performance is reported. The 3-stage LNA exhibits on-wafer noise figure (NF) as low as 1.6dB with 25dB gain at 80GHz, and also shows unprecedented wideband performance, with 20dB minimum gain across the 30-100GHz band and NF <;2.5dB over the 43-90GHz band. An LNA packaged in a WR-12 module has flange NF of 2.0dB over 74-80GHz and NF <;2.6dB with 27 ± 2dB gain across the full 60-90GHz waveguide band.

Atomic Layer Deposition Al 2 O 3 Passivated InAlN/GaN High Electron-Mobility Transistors for E-Band Power Amplifiers

We have fabricated and characterized ultrashort gate-length metamorphic high-electron mobility transistors (HEMTs) optimized for high gain performance for millimeter- and submillimeter-wave applications. In this paper, we have systematically evaluated the impact of gate length in the range of 25-50 nm on the device performance by exploring epitaxial layer designs, gate-to-channel distances, and recess widths. The study shows the 25-nm devices underperform their 50-nm counterparts in most of the key figures of merit including output conductance, voltage gain, off-state breakdown, on-state breakdown, and, most importantly, the maximum stable gain. This observation is actually in good agreement with the state-of-the-art results published so far, which indicate that the best overall performance of HEMTs for millimeter- and submillimeter-wave applications comes from devices with gate lengths ranging from 35 to 50 nm. The 25-nm devices, on the other hand, appear to have difficulty in achieving the proper vertical scaling for optimum gain, which is limited by the minimum gate layer thickness necessary to retain good Schottky characteristics. This limitation may eventually be overcome with the adoption of new materials used as the gate layer that can be integrated into the HEMT fabrication process.

A 50nm MHEMT millimeter-wave MMIC LNA with wideband noise and gain performance

We have developed 0.1-μm gate-length InAlN/GaN high electron-mobility transistors (HEMTs) for millimeterwave (MMW) power applications, particularly at 71-76 and 81-86 GHz bands. The impacts of depth and width of the gate recess groove on electrical performance have been analyzed and compared. Competing passivation technologies, atomic layer deposition (ALD) aluminum oxide (Al2O3) and plasma-enhanced chemical vapor deposition (PECVD) SiN, have also been assessed in terms of dc, pulsed-IV, and high-frequency characteristics. It has been found that while PECVD SiN-passivated HEMTs and the monolithic microwave integrated circuits slightly underperform their ALD Al2O3-passivated counterparts, their MMW power performance can be further boosted with the gate recess due to the improved aspect ratio and scaling characteristics. When biased at a drain voltage of 10 V, a first-pass two-stage power amplifier design based on recessed PECVD SiN-passivated 0.1-μm depletion-mode devices has demonstrated an output power of 1.63 W with a 15% power-added efficiency at 86 GHz.

Gate-Length Scaling of Ultrashort Metamorphic High-Electron Mobility Transistors With Asymmetrically Recessed Gate Contacts for Millimeter- and Submillimeter-Wave Applications

We report successful development of an advanced no-field-plate AlGaN/GaN high electron mobility transistors (HEMTs) for millimeter-wave (MMW) applications. The HEMT adopts a reduced source-drain spacing of 2 μm and the 0.2-μm gate is placed 0.5 μm off the source electrode. Additionally, the devices and monolithic microwave integrated circuits (MMICs) are fabricated on the SiC substrate of 2mil, enabling the fabrication of 15 μm × 25 μm slot via holes for realizing low inductance and more compact devices to facilitate MMW MMIC design. As a result, the narrow band MMICs have achieved an output power of 10.4 W with associated power added efficiency (PAE) of 31% at 28 GHz, and 10.7W and 27% at 36 GHz, respectively. Besides, a state-of-the-art 2-stage single-ended wideband MMIC demonstrates output power of 5-7.9 W and associated PAE of 13-21% from low K-band to high Ka-band.

0.1-

Whereas gate-length reduction has served as the major driving force to enhance the performance of GaAs- and InP-based high-electron mobility transistors (HEMTs) over the past three decades, the limitation of this approach begins to emerge. In this paper, we present a systematic evaluation of the impact of greatly reduced source-drain spacing on the performance of 50-nm asymmetrically recessed metamorphic HEMTs (MHEMTs). Extremely high extrinsic transconductance has been achieved over a wide drain bias range starting from as low as 0.1 V by reducing source-drain spacing to 0.5 μm with a self-aligned (SAL) ohmic process. The measured maximum extrinsic transconductance of 3 S/mm is a new record for all HEMT devices on a GaAs substrate and is equal to the best results reported for InP-based HEMTs. With the use of an asymmetric recess, SAL MHEMTs also demonstrate remarkable improvement in other major figures of merit, including off-state breakdown, on-state breakdown, subthreshold characteristics, ION/IOFF ratio, and the voltage gain over the other SAL HEMTs reported so far. However, they still, in a few respects, under perform the conventional devices typically with 2-μm source-drain spacing. In particular, the on-state breakdown of the SAL devices has been capped at approximately 2 V, even with a very wide asymmetric recess. It appears that the uniqueness of the SAL technology would best fit applications that require low voltage and/or low DC power consumption, which can be fully tapped only when the parasitic capacitance is also properly controlled with, e.g., a high stem gate process.

\mu \text{m}

We report the design, fabrication and characterization of metamorphic high electron-mobility transistors (MHEMTs) with self-aligned ohmic electrodes. In this work, asymmetrically recessed 50-nm Γ-gates have been successfully used as the shadow mask for ohmic metal deposition. Extremely high extrinsic transconductance over a wide drain bias from 0.1 to 1.25 V can be made possible by fabricating devices with small gate-source spacing, small source-drain spacing, and the non-alloyed ohmic. Measured maximum extrinsic transconductance of 3 S/mm is a new record for all HEMT devices on GaAs and equals the best results from InP-based HEMTs. The same devices also show a voltage gain of 22, maximum stable gain of 10.8 dB at 110 GHz, and breakdown voltage of 4.3 V, which all are the highest among any self-aligned HEMTs based on InGaAs channel. The outstanding performance is the result of the seamless integration of the asymmetric gate recess and Γ-gate-based self-aligned ohmic process.