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We have developed 0.1- $\mu \text{m}$ gate-length InAlN/GaN high electron-mobility transistors (HEMTs) for millimeter-wave (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- $\mu \text{m}$ depletion-mode devices has demonstrated an output power of 1.63 W with a 15% power-added efficiency at 86 GHz.

A new device-first low-temperature bonded gallium nitride (GaN)-on-diamond high-electronic mobility transistor (HEMT) technology with state-of-the-art, radio frequency (RF) power performance is described. In this process, the devices were first fabricated on a GaN-on-silicon carbide (SiC) epitaxial wafer and were subsequently separated from the SiC and bonded onto a high-thermal-conductivity diamond substrate. Thermal measurements showed that the GaN-on-diamond devices maintained equivalent or lower junction temperatures than their GaN-on-SiC counterparts while delivering more than three-times higher RF power within the same active area. Such results demonstrate that the GaN device transfer process is capable of preserving intrinsic transistor electrical performance while taking advantage of the excellent thermal properties of diamond substrates. Preliminary step-stress and room-temperature, steady-state life testing shows that the low-temperature bonded GaN-on-diamond device has no inherently reliability limiting factor. GaN-on-diamond is ideally suited to wideband electronic warfare (EW) power amplifiers as they are the most thermally challenging due to continuous wave (CW) operation and the reduced power-added efficiency obtained with ultra-wide bandwidth circuit implementations.

High-performance 0.1- $\mu \text{m}$ 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 $\sim 25$ 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- $\mu \text{m}$ 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.

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.

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.

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.

This paper reports a successful improvement of the low breakdown voltages in short gate-length metamorphic high electron-mobility transistors. The technical approach includes both the optimization of the epitaxial layer design and the selection of the proper gate recess scheme. By employing a novel epitaxial design (including a high indium composite channel and the double-sided doping) and an asymmetric gate recess, both the off-state and on-state breakdown voltages have been improved for 50-nm high-performance metamorphic high electron-mobility transistors. The results reported herein demonstrate that these devices are excellent candidates for ultra-high-frequency power applications.

BAE Systems has developed a high power, high yield 70nm 6" 2-mil PHEMT MMIC process for frequencies up to 100GHz. Utilizing T -gate technology and 2-mil substrates, we have created a millimeter wave technology that produces excellent performance from Ka -band through W -bands. The device DC and RF characteristics have excellent uniformity across the wafer. In this paper, we report the 70nm device fabrication on 6-inch wafers and compare the DC and RF characteristics with its mature 0.1µm counterpart.

A compact analytical model of short-channel AlGaN/GaN HEMTs in the presence of a current collapse is presented. The model is based on an experimentally established trapping mechanism at the gate edges and relies on significant differences between the characteristic carrier capture-escape times and typical RF signal periods. For the first time, we implement the theory describing electric field distributions in the HEMT gate-to-drain spacing region, with and without trapped charge distributions. By consequently accounting for velocity saturation effects in gated and trapped regions of the device, the presented model shows good agreement with the experimental data. The model uses a minimal number of fitting parameters, most of which are physical parameters describing velocity-field dependence of the carriers.

We report the design, fabrication and characterization of ultrahigh gain metamorphic high electron-mobility transistors. In this letter, a high-yield 50-nm T-gate process was successfully developed and applied to epitaxial layers containing high indium mole fraction InGaAs channels grown on GaAs substrates. A unique gate recess process was adopted to significantly increase device gain by effectively suppressing output conductance and feedback capacitance. Coupled with extremely small 10 mum times 25 mum via holes on substrates thinned to 1 mil, we achieved a 13.5 dB maximum stable gain (MSG) at 110 GHz for a 30-mum gate-width device. To our knowledge, this is the highest gain performance reported for microwave high electron-mobility transistor devices of similar gate periphery at this frequency, and equivalent circuit modeling indicates that this device will operate at frequencies beyond 300 GHz.

High power AlGaN/GaN HEMTs on free-standing GaN substrates with excellent stability have been demonstrated for the first time. When operated at a drain bias of 50V, devices without a field plate showed a record CW output power density of 10.0W/mm at 10GHz with an associated power-added efficiency of 45%. The efficiency reaches a maximum of 58% with an output power density of 5.5W/mm under a drain bias of 25V at 10GHz. Long-term stability of device RF operation was also examined. Under ambient conditions, devices biased at 25V and driven at 3dB gain compression remained stable at least up to 1,000 hours, degrading only by 0.35dB in output power. Such results clearly demonstrate the feasibility of GaN - on - GaN HEMT as an alternative device technology to the GaN - on - SiC HEMT in supporting reliable, high performance microwave power applications.

In this work, we report on an innovative approach which integrates GaN-on-Diamond microstrip MMICs with a state-of-the-art microchannel cooler and provides a significant thermal advantage for high power GaN applications. Specifically, we describe efforts to develop a wide bandwidth, GaN-on-Diamond MMIC power amplifier that achieves greater than 3x RF power density compared to GaN on SiC while operating at a MMIC heat flux of >1kW/cm2 and maintaining junction temperatures below the estimated targets to achieve 106 hrs lifetime by employing a high performance, liquid phase, microchannel cooler capable of a volumetric heat dissipation rate of >10kW/cm3. To date, no prior work has been reported for GaN-on-Diamond microstrip MMICs.

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

This paper describes the design, fabrication, and measurement of a wideband 60 GHz monolithic microwave integrated circuit (MMIC) power amplifier that has demonstrated via on-wafer continuous wave (CW) measurement a record 43% power-added efficiency (PAE) at an associated output power of 224 mW and 7.5 dB of power gain. At a higher drain bias of 3.5 V, the CW output power increased to 250 mW with 38.5% PAE. Additional performance improvement is expected when the MMICs are tested on-carrier with proper heat sinking. These state-of-the-art first-pass design results can be attributed to: 1) the use of a fully selective gate recess etch 0.12-/spl mu/m InP HEMT process fabricated on 2-mm-thick 3-in diameter InP substrates with slot via holes; 2) a design based on a novel on-wafer load-pull measurement technique; and 3) an accurate large-signal nonlinear model for InP HEMTs. In order to reach the low cost required for mass production, the same MMIC design was fabricated on an InP metamorphic HEMT (MHEMT) process. The MHEMT version of the MMIC demonstrated 41.5% PAE, with an associated output power of 183 mW (305 mW/mm) and 6.9 dB of power at 60 GHz when measured CW on-wafer. These InP HEMT and MHEMT results are, to our knowledge, the highest PAE and power bandwidth ever reported at V-band.

We have developed a methodology to diagnose the physical mechanisms limiting the manufacturing uniformity of millimeter-wave power InAlAs/InGaAs HEMT's on InP. A statistical analysis was carried out on dc figures of merit obtained from a large number of actual devices on an experimental wafer. correlation studies and principal component analysis of the results indicated that variations in Si delta-doping concentration introduced during molecular-beam epitaxy accounted for more than half of the manufacturing variance. Variations in the gate-source distance that is determined by the electron-beam alignment in the gate formation process were found to be the second leading source of manufacturing variance. The statistical methodology used in this work is suitable for continuous process yield diagnostics and improvement in a manufacturing environment.

We report the design, fabrication, and characterization of ultrahigh-gain metamorphic high-electron-mobility transistors (MHEMTs) with significantly enhanced breakdown performance. In this letter, an asymmetrically recessed 50-nm Gamma-gate process has been successfully applied to epitaxial designs with double-sided-doped InAs-layer-inserted channels grown on GaAs substrates. The critical gate recess width has been optimized for device performance, including transconductance, breakdown voltage, and gain. The employment of a device passivation process greatly minimizes the adverse impacts that the aggressive vertical and lateral scaling would have introduced for pursuing enhanced performance. As a result, we have achieved 1.9-S/mm transconductance and 800-mA/mm maximum drain current at a drain bias of 1 V, 9-V off-state breakdown voltage, approximately 3.5-V on-state breakdown voltage, and 14.2-dB maximum stable gain at 110 GHz. To our knowledge, this is a record combination of gain and breakdown performance reported for microwave and millimeter-wave HEMTs, making these devices excellent candidates for ultrahigh-frequency power applications.

We have carried out a systematic study of on-state breakdown in a sample set of InAlAs/InGaAs HEMT's using a new gate current extraction technique in conjunction with sidegate and temperature-dependent measurements. We find that as the device is turned on, the breakdown voltage limiting mechanism changes from a TFE-dominated process to a multiplication-dominated process. This physical understanding allows the creation of a phenomenological physical model for breakdown which agrees well with all our experimental results, and explains the relationship between BV/sub on/ and the sheet carrier concentration. Our results suggest that depending on device design, either on-state or off-state breakdown can limit maximum power.

This paper reviews recent progress in the development of GaAs Metamorphic HEMT (MHEMT) technology for microwave, millimeter-wave, and submillimeter-wave applications. Short gate-length (50-100 nm) Metamorphic High Electron Mobility Transistors have been optimized for high gain and low noise performance. Efforts to further improve performance, manufacturability, and verify reliability will be reported. We also describe the design and performance of low noise MMIC amplifiers based on this technology.

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.

InGaAs and InP exposed to N 2 or Ar ECR plasmas show reduced photoluminescence intensity. The extent of the degradation depends on both the microwave power level and any additional r.f. power applied to increase the energy of ions in the discharge. Annealing at 200°C restores approx. one-third of the initial luminescence efficiency in both materials, but HF removal of the native oxide increases the PL intensity to ∼80% in InGaAs and ∼40% in InP. The mechanism for the degraded optical output from these materials is creation of both interface and bulk states. The latter are present to depths of ≥200 A and are more prevalent in InP. Passivation of the surfaces using (NH 4 ) 2 S treatment completely restores the PL intensity in InGaAs, but not in InP. ECR deposition of SiN x shows excellent conformity around the gate contact of submicron high electron mobility transistors, and an absence of the rabbit-ears typically present with conventional PECVD.

We report a new passivation technology based on atomic layer deposition (ALD) aluminum oxide for the GaN high electron-mobility transistor (HEMT). This new process markedly enhances GaN device's electrical performance including DC, and in particular the pulsed-IV characteristics. The achieved improvement is attributed to the outstanding interface between III-N and the ALD aluminum oxide resulting from the unique process of the ALD growth, featuring a wet-chemical-based wafer preparation as well as the self-cleaning at the very beginning of the whole growth process.

High electron mobility transistors (HEMTs) with single-quantum-well active layers composed of pseudomorphic InGaAs on GaAs and InP substrates have yielded substantial performance enhancements relative to their lattice-matched equivalents. The higher cut-off frequencies possessed by these devices have enabled new applications to be realized in the millimeter wave spectrum which are not feasible with lattice-matched HEMTs. Also, the devices are beginning to displace GaAs field effect transistors in the microwave spectrum as a result of higher gain and power-added efficiency inherent to the pseudomorphic devices. These developments in transistors and parallel developments in other strained layer material systems and devices have been paced by a resurgence in research and development in the materials science and engineering of strained epitaxial layers.

Magneto-transport and cyclotron resonance measurements were made to determine directly the density, mobility, and the effective mass of the charge carriers in a high-performance 0.15- mu m gate In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As high-electron-mobility transistor (HEMT) at low temperatures. At the gate voltage V/sub G/=0 V, the carrier density n/sub g/ under the gate is 9*10/sup 11/ cm/sup -2/, while outside of the gate region n/sub g/=2.1*10/sup 12/ cm/sup -2/. The mobility under the gate at 4.2 K is as low as 400 cm/sup 2//V-s when V/sub G/ 0.1 V. The existence of this high mobility threshold is crucial to the operation of the device and sets its high-performance region in V/sub G/>0.1 V. >

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 HEMT's.

We present the design of several wideband, millimeter-wave, MMIC, medium power amplifiers using a newly developed high-power, high-yield, 70 nm gate-length GaAs MMIC pHEMT process. These amplifiers cover a range of about 65–125 GHz, and were designed for the purpose of driving sub-millimeter wave multipliers in the local oscillator subsystem of the Atacama Large Millimeter Array (ALMA) radio telescope. The highest-frequency amplifiers in this chipset have average output power density over wide bandwidth of 200 mW/mm, representing the best performance to date for GaAs pHEMTs above W-Band.

This paper reports the scaling behaviors of 25-nm asymmetrically recessed metamorphic high electron-mobility transistors. By employing an optimized epitaxial design and an asymmetric gate recess, excellent off-state and on-state breakdown voltages have been have been demonstrated for 25-nm high-performance metamorphic high electronmobility transistors. The results reported herein demonstrate that these devices are excellent candidates for ultra-high-frequency power applications.

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.

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 MHEMT's.

With the DARPA Wide Bandgap Semiconductor Technology RF Thrust Contract, TriQuint Semiconductor and its partners, BAE Systems, Lockheed Martin, IQE-RF, II-VI, Nitronex, M.I.T., and R.P.I. are achieving great progress towards the overall goal of making Gallium Nitride a revolutionary RF technology ready to be inserted in defense and commercial applications. Performance and reliability are two critical components of success (along with cost and manufacturability). In this paper we will discuss these two aspects. Our emphasis is now operation at 40 V bias voltage (we had been working at 28 V). 1250 µ m devices have power densities in the 6 to 9 W/mm with associated efficiencies in the low- to mid 60 % and associated gain in the 12 to 12.5 dB at 10 GHz. We are usin g a dual field-plate structure to optimize these performances. Very good performances have also been achieved at 18 GHz with 400 µ m devices. Excellent progress has been made in reliability. Our preliminary DC and RF reliability tests at 40 V indicate a MTTF of 1E6hrs with1.3 eV activation energy at 150

Very low-noise 0.15- mu m gate-length W-band In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As/In/sub 0.52/Al/sub 0.48/As/InP lattice-matched HEMTs are discussed. A maximum extrinsic transconductance of 1300 mS/mm has been measured for the device. At 18 GHz, a noise figure of 0.3 dB with an associated gain of 17.2 dB was measured. The device also exhibited a minimum noise figure of 1.4 dB with 6.6-dB associated gain at 93 GHz. A maximum available gain of 12.6 dB at 95 GHz, corresponding to a maximum frequency of oscillation, f/sub max/, of 405 GHz (-6-dB/octave extrapolation) in the device was measured. These are the best device results yet reported. These results clearly demonstrate the potential of the InP-based HEMTs for low-noise applications, at least up to 100 GHz. >

With the DARPA Wide Bandgap Semiconductor Technology RF Thrust Contract, TriQuint Semiconductor and its partners, BAE Systems, Lockheed Martin, IQE-RF, II-VI, Nitronex, M.I.T., and R.P.I, are achieving great progress towards the overall goal of making gallium nitride a revolutionary RF technology ready to be inserted in defense and commercial applications. Performance and reliability are two critical components of success (along with cost and manufacturability). In this paper we will discuss these two aspects.

We present a new simple three-terminal technique for measuring the on-state breakdown voltage in HEMTs. The gate current extraction technique involves grounding the source, and extracting a constant current from the gate. The drain current is then ramped from the off-state to the on-state, and the locus of drain voltage is measured. This locus of drain current versus drain voltage provides a simple, unambiguous definition of the on-state breakdown voltage which is consistent with the accepted definition of off-state breakdown. The technique is relatively safe and repeatable so that temperature dependent measurements of on-state breakdown can be carried out. This helps illuminate the physics of both off-state and on-state breakdown.

Through accelerated life test in hydrogen, we have found, for the first time, that in addition to Pt metal, Ti metal in a Ti/Pt/Au-gate PHEMT can also induce a significant hydrogen effect by reacting with a small amount of hydrogen gas in the ambient. The hydrogen sensitivity of a PHEMT device caused by Ti gate metal is significantly less than that due to Pt. Since Ti is not a hydrogen catalyst, the resulting hydrogen sensitivity indicates that a catalytic reaction between the gate metal and hydrogen gas is not required to have a detrimental hydrogen effect. The data also show that the degradation evident in the PHEMT devices due to the Ti-H/sub 2/ interaction is similar to that from the Pt-H/sub 2/ interaction. It is clear from this work that attempting to solve the hydrogen degradation problem by eliminating the Pt gate metal in a PHEMT is ineffective.

Degradation of PHEMTs by hydrogen was verified by DC life tests in the hermetic packages and in the forming gases containing different hydrogen concentrations. We have found that a hydrogen partial pressure in the order of 2 torr will cause Ids change by 20% in about 800 hours at 125/spl deg/C and about 300 hours at 150/spl deg/C. The signature of hydrogen degradation is a sudden and significant drain current degradation followed by some recovery. It appeared that the degradation is both temperature and H/sub 2/ partial pressure dependent. Failure analysis indicates that the degradation is localized under the gate and that the major failure mechanism is due to the effective gate voltage being modified negatively by the atomic hydrogen.

High power AlGaN/GaN HEMTs on free-standing GaN substrates with excellent stability have been demonstrated for the first time. When operated at a drain bias of 50V, devices without a field plate showed a record CW output power density of 10.0W/mm at 10GHz with an associated power-added efficiency of 45%. The efficiency reaches a maximum of 58% with an output power density of 5.5W/mm under a drain bias of 25V at 10GHz. Long-term stability of device RF operation was also examined. Under ambient conditions, devices biased at 25V and driven at 3dB gain compression remained stable at least up to 1,000 hours, degrading only by 0.35dB in output power. Such results clearly demonstrate the feasibility of GaN-on-GaN HEMT as an alternative device technology to the GaN-on-SiC HEMT in supporting reliable, high performance microwave power applications.

We have developed 0.1-/spl mu/m gate-length InAlAs-InGaAs-InP power HEMT's with record efficiency and power gain at 94 GHz. A 200 /spl mu/m gate-width device has produced 58 mW output power with 6.4 dB power gain and 33% power-added efficiency. The extrapolated f/sub max/ of 600 GHz is the highest reported to date for any transistor, and smaller, 30-/spl mu/m devices fabricated on the same wafer exhibit excellent noise figure (1.4 dB at 94 GHz), demonstrating the applicability of this technology to multifunction MMICs. >

This paper reports our development of a monolithic InP HEMT based power amplifier showing state-of-the-art V-band performance. A single-stage amplifier with a 600 um cell periphery demonstrated 224 mW of output power at the peak power-added efficiency of 43% with 7.5 dB power gain at 60 GHz. To the best of our knowledge, this is the best combination of output power and efficiency reported to date at this frequency for a solid state 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.

The microwave characterization of 0.25- mu m gate-length MODFETs at 300 and 77 K is reported. Microwave S-parameter measurements of MODFETs from 0.45 to 20 GHz were used to extract their HF equivalent network parameters. After allowing for the parasitic gate and drain-to-gate feedback capacitances, the intrinsic unity-current gain frequency was determined. Using a theoretical model, the effective carrier saturation velocity and average velocity ( nu /sub av/) were obtained for the conventional AlGaAs/GaAs, the pseudomorphic AlGaAs/InGaAs/GaAs, and lattice-matched InAlAs/InGaAs/InAlAs on InP samples at 300 K and 77 K. The extracted values of nu /sub a/ range from 0.82*10/sup 7/ cm/s to 3.84*10/sup 7/ cm/s, respectively, depending on the type of MODFET and operating temperature. These high values of nu /sub av/ indicate that the velocity overshoot effect is present in the devices tested. >

Quarter-micron InAlAs/InGaAs planar-doped HEMTs (high-electron-mobility transistors) lattice-matched to InP have exhibited state-of-the-art noise and gain performance at frequencies up to 94 GHz. Minimum noise figures of 0.5, 1.2, and 2.1 dB have been measured at 18, 60, and 94 GHz, respectively. Small signal gains as high as 15.4 and 12.0 dB have been obtained at 63 and 95 GHz, respectively. Using 0.25 mu m InP-based HEMTs, a V-band three-stage amplifier yields an average noise figure of 3.0 dB with a gain of 22.0 +or-0.2 dB from 60 to 65 GHz at W-band, a two-stage amplifier exhibits a noise figure of 4.5 dB with a gain of 10.2 dB at 90.4 GHz, and a three-stage amplifier shows a noise figure of 4.8 dB with a gain of 15.0 dB at 90.4 GHz. It is concluded that these results clearly show the great potential of InP-based HEMTs for high-performance millimeter-wave low-noise receiver applications. >

Doped-channel, 0.25- mu m-gate-length, InGaAs pseudomorphic HEMTs (high electron mobility transistors) have been developed which exhibit state-of-the-art power performance at millimeter-wave frequencies, with output power density of 0.93 W/mm and power-added efficiency of 41% at 44 GHz. Using these devices, two Q-band hybrid power amplifiers have been developed. A two-stage design has produced 108 mW output power gain with 9.5 dB and 26.5% power-added efficiency. A three-stage design produced 251 mW output power with 13.6 dB of gain and 26.8% power-added efficiency. The peak efficiency of the three-state amplifier was 31.3% when biased differently. The linear gain of these amplifiers was 12 and 20 dB respectively. It is concluded that these amplifiers are an attractive alternative for designers of future millimeter-wave transmitters. >

A 0.15- mu m-gate-length double-heterojunction pseudomorphic HEMT (high electron mobility transistor) that exhibits state-of-the-art power and noise performance is reported. Power results include record power-added efficiencies of 51%, 41% and 23% at 35, 60 and 94 GHz, respectively, and output powers of 139 mW at 60 GHz and 57 mW at 94 GHz. Measured minimum noise figures of 0.55 dB at 18 GHz and 1.8 dB at 60 GHz are reported. It is suggested that because of its demonstrated performance and continued rapid rate of improvement, the pseudomorphic HEMT should be the preferred transistor for a number of millimeter-wave applications, used either as a discrete device in high-performance hybrid amplifiers or integrated into GaAs-based MMICs (monolithic microwave integrated circuits). >

The authors report the development of short gate-length (0.15-0.25- mu m) HEMTs (high-electron-mobility transistors) with state-of-the-art noise and power performance. The three families of HEMTs-conventional GaAs/AlGaAs, pseudomorphic, and InP-based-are described and compared. The InP HEMTs offer the lowest noise figure: device noise figures of 0.3 dB at 18 GHz and 1.4 dB at 94 GHz have been measured, and multistage amplifiers with 1.7-dB noise figure at 62 GHz and 3.3 dB at 92 GHz are reported. Pseudomorphic HEMTs that exhibit the best power performance of any millimeter-wave transistor have been developed, with record output powers of 658, 125, and 57 mW at 35, 60, and 94 GHz, respectively, and power-added efficiency as high as 41% at 60 GHz. A 44-GHz pseudomorphic HEMT power amplifier has generated 0.25-W output power with 27% power-added efficiency and 14-dB power gain. Finally, the reliability of the various HEMT types is discussed. >

State-of-the-art high-electron-mobility-transistor (HEMT) devices have been fabricated on InAlAs/InGaAs/InP. Devices with 30- mu m and 50- mu m gate widths and 0.15- mu m gate length were fabricated using an all-electron-beam lithography process. After mesa formation, ohmic contacts were formed using a standard NiAuGe metallization. The contacts were annealed using a rapid thermal annealer. Typical ohmic contact resistance was approximately 0.13 Omega -mm. This is the same as the typical contact for the GaAs-based pseudomorphic HEMT result. Gates were defined using a trilayer resist scheme and recessed using a wet chemical etch to reach the desired channel current. A TiPtAu metallization forms the gate. The devices exhibited performance superior to most other low noise HEMT devices. It is found that the gate leakage current increases as recess depth increases. This current increase seems to degrade noise performance. >

A VLSI architecture is presented for generating ray-tracing images of bicubic surface in Bezier form by using the subdivision algorithm. It uses a set of tree transverse operators to find the nearest intersection between a surface patch and a ray by traversing the entire subdivision tree in preorder. This scheme retains the advantage of subdivision and substantially reduces the circuit area by eliminating the need for a stack to store control points of intermediate bicubic patches. It also eliminates the multiplications needed in the subdivision iteration. The time to traverse additional nodes is offset by the removal of the stack memory access time. The performance of the architecture is analyzed and compared with the alternative approaches. >

Short-gate-length high-electron-mobility transistors (HEMTs) are reported that have exhibited state-of-the-art low-noise performance at millimeter-wave frequencies; minimum noise figure of 1.2 dB at 32 GHz and 1.8 dB at 60 GHz from 0.25- mu m HEMTs. At Ka-band, a two-stage low-noise amplifier has demonstrated an average noise figure of 2 dB from 26.5 GHz to 37 GHz with a gain of 17 dB at 32 GHz. At V-band, a two-stage amplifier yielded a noise figure of 3.2 dB at 61 GHz with flat gain 12.7*0.5 dB from 59 GHz to 65 GHz. These devices are described and the potential for their future improvement is discussed. >

The relative importance of f/sub t/ and f/sub max/ in millimeter-wave evaluation is discussed. Also presented is a study of the variation of C/sub gs/ (input capacitance), C/sub gd/ (gate-drain feedback capacitance), g/sub m/ (peak transconductance), and g/sub o/ (output conductance) with the distance, L/sub gd/, between the metal edge and the n/sup +/ cap layer on the drain side of the device in ultrashort-gate-length HEMT (high-electron-mobility transistors). For this study, a 0.15- mu m-gate-length, double-recess pseudomorphic HEMT was fabricated that exhibits a maximum frequency of oscillation, f/sub max/, of 350 GHz. This value is the highest f/sub max/ reported for any transistor. A very high C/sub gs//C/sub gd/ of 76 and a large voltage gain, g/sub m//g/sub o/ of 75 are observed in the device. These exceptional results are attained primarily by increasing L/sub gd/ to 2.3 times the gate length. >

High-performance InAlAs/InGaAs planar-doped HEMTs (high-electron-mobility transistors) lattice-matched to InP have been fabricated with a 0.25- mu m T-gate. A maximum extrinsic transconductance g/sub m/ of 900 mS/mm, corresponding to an intrinsic g/sub m/ of 1640 mS/mm, was obtained at room temperature. RF measurements at 18 GHz yielded a minimum noise figure of 0.5 dB with an associated gain of 15.2 dB and a maximum stable gain of 20.9 dB. At 58 GHz, the devices exhibited a 1.2-dB minimum noise figure with an 8.5-dB associated gain. At 63 GHz, a maximum available gain of 15.4 dB was measured for a single-stage amplifier. This value, extrapolated to -6 dB/octave, yielded a maximum frequency of oscillation f/sub max/ of 380 GHz, which is the highest f/sub max/ ever reported for any transistor. A three-stage HEMT amplifier exhibited an average noise figure of 3.0 dB with a gain of 22.0+or-0.2 dB from 60-65 GHz. >

The development of InGaAs pseudomorphic high-electron mobility transistors (HEMTs) with state-of-the-art power performance at millimeter-wave frequencies is reported. Results given include maximum power-added efficiencies of 44% at 35 GHz and 36% at 44 GHz, output power of 100 mW with 22% efficiency and 3-dB gain at 60 GHz, and output power of 9 mW at 94 GHz. Preliminary reliability data are presented, and prospects for further improvement in performance-the realization of multifinger HEMTs capable of higher output power and reduction of gate length to 0.1 mu m-are discussed. >

The authors report the first successful passivation of an InAlAs/InGaAs/InP high electron mobility transistor (HEMT) with an InAlAs layer grown at low temperature (LT) by molecular beam epitaxy (MBE). After passivation, extrinsic transconductance, gate-drain breakdown voltage, and channel breakdown voltage are increased, while the gate leakage is reduced. RF measurement of the devices shows no degradation of the noise figure measured at 58 GHz. The authors report the result of a thermal storage test performed on the device at 230 degrees C with DC parameters monitored as a function of time. The results demonstrate that the LT passivation by MBE under ultra-high vacuum ambient is an effective novel approach to solve the problem inherent to surface-sensitive III-V devices, such as the HEMT devices reported here. >