Microwave noise performance of AlGaN-GaN HEMTs with small DC power dissipation

We report low microwave noise performance of discrete AlGaN-GaN HEMTs at DC power dissipation comparable to that of GaAs-based low-noise FETs. At 1-V source-drain (SD) bias and DC power dissipation of 97 mW/mm, minimum noise figures (NF/sub min/) of 0.75 dB at 10 GHz and 1.5 dB at 20 GHz were achieved, respectively. A device breakdown voltage of 40 V was observed. Both the low microwave noise performance at small DC power level and high breakdown voltage was obtained with a shorter SD spacing of 1.5 /spl mu/m in 0.15-/spl mu/m gate length GaN HEMTs. By comparison, NF/sub min/ with 2 /spl mu/m SD spacing was 0.2 dB greater at 10 GHz.     

Output power density of 5.1/mm at 18 GHz with an AlGaN/GaN HEMT on Si substrate

Microwave frequency capabilities of AlGaN/GaN high electron mobility transistors (HEMTs) on high resistive silicon (111) substrate for power applications are demonstrated in this letter. A maximum dc current density of 1 A/mm and an extrinsic current gain cutoff frequency (F/sub T/) of 50 GHz are achieved for a 0.25 /spl mu/m gate length device. Pulsed and large signal measurements show the good quality of the epilayer and the device processing. The trapping phenomena are minimized and consequently an output power density of 5.1 W/mm is reached at 18 GHz on a 2/spl times/50/spl times/0.25 /spl mu/m/sup 2/ HEMT with a power gain of 9.1dB.     

DC, RF, and microwave noise performances of AlGaN/GaN HEMTs on sapphire substrates

High-performance AlGaN/GaN high electron-mobility transistors with 0.18-/spl mu/m gate length have been fabricated on a sapphire substrate. The devices exhibited an extrinsic transconductance of 212 mS/mm, a unity current gain cutoff frequency (f/sub T/) of 101 GHz, and a maximum oscillation frequency (f/sub MAX/) of 140 GHz. At V/sub ds/=4 V and I/sub ds/=39.4 mA/mm, the devices exhibited a minimum noise figure (NF/sub min/) of 0.48 dB and an associated gain (Ga) of 11.16 dB at 12 GHz. Also, at a fixed drain bias of 4 V with the drain current swept, the lowest NFmin of 0.48 dB at 12 GHz was obtained at I/sub ds/=40 mA/mm, and a peak G/sub a/ of 11.71 dB at 12 GHz was obtained at I/sub ds/=60 mA/mm. With the drain current held at 40 mA/mm and drain bias swept, the NF/sub min/,, increased almost linearly with the increase of drain bias. Meanwhile, the Ga values decreased linearly with the increase of drain bias. At a fixed bias condition (V/sub ds/=4 V and I/sub ds/=40 mA/mm), the NF/sub min/ values at 12 GHz increased from 0.32 dB at -55/spl deg/C to 2.78 dB at 200/spl deg/C. To our knowledge, these data represent the highest f/sub T/ and f/sub MAX/, and the best microwave noise performance of any GaN-based FETs on sapphire substrates ever reported.     

AlGaN/GaN HEMTs on SiC with f/sub T/ of over 120 GHz

AlGaN/GaN high electron mobility transistors (HEMTs) grown on semi-insulating SiC substrates with a 0.12 /spl mu/m gate length have been fabricated. These 0.12-/spl mu/m gate-length devices exhibited maximum drain current density as high as 1.23 A/mm and peak extrinsic transconductance of 314 mS/mm. The threshold voltage was -5.2 V. A unity current gain cutoff frequency (f/sub T/) of 121 GHz and maximum frequency of oscillation (f/sub max/) of 162 GHz were measured on these devices. These f/sub T/ and f/sub max/ values are the highest ever reported values for GaN-based HEMTs.     

High microwave and noise performance of 0.17-/spl mu/m AlGaN-GaN HEMTs on high-resistivity silicon substrates

AlGaN-GaN high-electron mobility transistors (HEMTs) based on high-resistivity silicon substrate with a 0.17-/spl mu/m T-shape gate length are fabricated. The device exhibits a high drain current density of 550 mA/mm at V/sub GS/=1 V and V/sub DS/=10 V with an intrinsic transconductance (g/sub m/) of 215 mS/mm. A unity current gain cutoff frequency (f/sub t/) of 46 GHz and a maximum oscillation frequency (f/sub max/) of 92 GHz are measured at V/sub DS/=10 V and I/sub DS/=171 mA/mm. The radio-frequency microwave noise performance of the device is obtained at 10 GHz for different drain currents. At V/sub DS/=10 V and I/sub DS/=92 mA/mm, the device exhibits a minimum-noise figure (NF/sub min/) of 1.1 dB and an associated gain (G/sub ass/) of 12 dB. To our knowledge, these results are the best f/sub t/, f/sub max/ and microwave noise performance ever reported on GaN HEMT grown on Silicon substrate.     

High-performance enhancement-mode AlGaN/GaN HEMTs using fluoride-based plasma treatment

We report a novel approach in fabricating high-performance enhancement mode (E-mode) AlGaN/GaN HEMTs. The fabrication technique is based on fluoride-based plasma treatment of the gate region in AlGaN/GaN HEMTs and post-gate rapid thermal annealing with an annealing temperature lower than 500/spl deg/C. Starting with a conventional depletion-mode HEMT sample, we found that fluoride-based plasma treatment can effectively shift the threshold voltage from -4.0 to 0.9 V. Most importantly, a zero transconductance (g/sub m/) was obtained at V/sub gs/=0 V, demonstrating for the first time true E-mode operation in an AlGaN/GaN HEMT. At V/sub gs/=0 V, the off-state drain leakage current is 28 /spl mu/A/mm at a drain-source bias of 6 V. The fabricated E-mode AlGaN/GaN HEMTs with 1 /spl mu/m-long gate exhibit a maximum drain current density of 310 mA/mm, a peak g/sub m/ of 148 mS/mm, a current gain cutoff frequency f/sub T/ of 10.1 GHz and a maximum oscillation frequency f/sub max/ of 34.3 GHz.     

Broadband microwave noise characteristics of high-linearity composite-channel Al/sub 0.3/Ga/sub 0.7/N/Al/sub 0.05/Ga/sub 0.95/N/GaN HEMTs

We report broadband microwave noise characteristics of a high-linearity composite-channel HEMT (CC-HEMT). Owing to the novel composite-channel design, the CC-HEMT exhibits high gain and high linearity such as an output third-order intercept point (OIP3) of 33.2 dBm at 2 GHz. The CC-HEMT also exhibits excellent microwave noise performance. For 1-/spl mu/m gate-length devices, a minimum noise figure (NF/sub min/) of 0.7 dB and an associated gain (G/sub a/) of 19 dB were observed at 1 GHz, and an (NF/sub mi/) of 3.3 dB and a G/sub a/ of 10.8 dB were observed at 10 GHz. The dependence of the noise characteristics on the physical design parameters, such as the gate-source and gate-drain spacing, is also presented.     

Low damage, Cl/sub 2/-based gate recess etching for 0.3-/spl mu/m gate-length AlGaN/GaN HEMT fabrication

The traditional dry etching for GaN using the Ar/Cl/sub 2/ mixture gas in the reactive ion etching system has been developed. In order to reduce the surface damage, the additional CH/sub 4/ gas is introduced. However, this approach still has the problems of the residual surface damage and low etching selectivity between the AlGaN and GaN materials. Therefore, the following rapid thermal annealing (RTA) at 700/spl deg/C is necessary to recover the surface properties. In this study, we proposed the Ar/Cl/sub 2//CH/sub 4//O/sub 2/ for the GaN gate-recess etching in AlGaN/GaN HEMTs fabrication, which achieves a low surface damage and a high etching selectivity simultaneously. The 0.3 /spl mu/m gate-length AlGaN/GaN HEMTs present a transconductance of 230 mS/mm, an f/sub T/ of 48 GHz, and f/sub max/ of 60 GHz, respectively.     

Millimeter-wave high-power 0.25-/spl mu/m gate-length AlGaN/GaN HEMTs on SiC substrates

Reports on the CW power performance at 20 and 30 GHz of 0.25 /spl mu/m /spl times/ 100 /spl mu/m AlGaN/GaN high electron mobility transistors (HEMTs) grown by MOCVD on semi-insulating SiC substrates. The devices exhibited current density of 1300 mA/mm, peak dc extrinsic transconductance of 275 mS/mm, unity current gain cutoff (f/sub T/) of 65 GHz, and maximum frequency of oscillation (f/sub max/) of 110 GHz. Saturated output power at 20 GHz was 6.4 W/mm with 16% power added efficiency (PAE), and output power at 1-dB compression at 30 GHz was 4.0 W/mm with 20% PAE. This is the highest power reported for 0.25-/spl mu/m gate-length devices at 20 GHz, and the 30 GHz results represent the highest frequency power data published to date on GaN-based devices.     

Low noise RF MOSFETs on flexible plastic substrates

We report a low minimum noise figure (NF/sub min/) of 1.1 dB and high associated gain (12 dB at 10 GHz) for 16 gate-finger 0.18-/spl mu/m RF MOSFETs, after thinning down the Si substrate to 30 /spl mu/m and mounting it on plastic. The device performance was improved by flexing the substrate to create stress, which produced a 25% enhancement of the saturation drain current and lowered NF/sub min/ to 0.92 dB at 10 GHz. These excellent results for mechanically strained RF MOSFETs on plastic compare well with 0.13-/spl mu/m node (L/sub g/=80 nm) devices.     

A GaN differential oscillator with improved harmonic performance

The first AlGaN/GaN HEMT based differential oscillator is reported. The MMIC oscillates at a frequency of 4.16 GHz and provides 22.9 dBm of power from one side at a biasing of V/sub gs/-1 V and V/sub ds/20 V. The HEMTs each have a 0.7 /spl mu/m/spl times/200 /spl mu/m gate. The second harmonic is 45 dB below the carrier and the third harmonic is more than 70 dB below the carrier. To our knowledge, this is the best reported harmonic performance for a GaN oscillator. The oscillator efficiency is between 4% and 9.4% depending on bias. The measured phase noise is -86.3 dBc and -115.7 dBc at offsets of 100 kHz and 1 MHz respectively. The phase noise at a 1 MHz offset is similar to the noise performance of FET based differential oscillators in other technologies.     

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.     

AlGaN/GaN/InGaN/GaN DH-HEMTs with an InGaN notch for enhanced carrier confinement

We report an AlGaN/GaN/InGaN/GaN double heterojunction high electron mobility transistors (DH-HEMTs) with high-mobility two-dimensional electron gas (2-DEG) and reduced buffer leakage. The device features a 3-nm thin In/sub x/Ga/sub 1-x/N(x=0.1) layer inserted into the conventional AlGaN/GaN HEMT structure. Assisted by the InGaN layers polarization field that is opposite to that in the AlGaN layer, an additional potential barrier is introduced between the 2-DEG channel and buffer, leading to enhanced carrier confinement and improved buffer isolation. For a sample grown on sapphire substrate with MOCVD-grown GaN buffer, a 2-DEG mobility of around 1300 cm/sup 2//V/spl middot/s and a sheet resistance of 420 /spl Omega//sq were obtained on this new DH-HEMT structure at room temperature. A peak transconductance of 230 mS/mm, a peak current gain cutoff frequency (f/sub T/) of 14.5 GHz, and a peak power gain cutoff frequency (f/sub max/) of 45.4 GHz were achieved on a 1/spl times/100 /spl mu/m device. The off-state source-drain leakage current is as low as /spl sim/5 /spl mu/ A/mm at V/sub DS/=10 V. For the devices on sapphire substrate, maximum power density of 3.4 W/mm and PAE of 41% were obtained at 2 GHz.     

Very low noise RF nMOSFETs on plastic by substrate thinning and wafer transfer

A very low minimum noise figure (NF/sub min/) of 1.2 dB and a high associated gain of 12.8 dB at 10 GHz were measured for six-finger, 0.18-/spl mu/m radio frequency (RF) metal-oxide semiconductor field-effect transistors mounted on insulating plastic following substrate-thinning (/spl sim/30 /spl mu/m) and wafer transfer. Before this process, the devices had a slightly better RF performance of 1.1-dB NF/sub min/ and a 13.7-dB associated gain. The small RF performance degradation of the active transistors transferred to plastic shows the potential of integrating electronics onto plastic.     

30-GHz Low-Noise Performance of 100-nm-Gate-Recessed n-GaN/AlGaN/GaN HEMTs

We demonstrate a 100-nm-gate-recessed n-GaN/AlGaN/GaN high-electron mobility transistor (HEMT) with low-noise properties at 30 GHz. The recessed GaN HEMT exhibits a low ohmic-contact resistance of 0.28 $Omega cdot hbox{mm}$ and a low gate leakage current of 0.9 $muhbox{A/mm}$ when biased at $V_{rm GS} = -hbox{3} hbox{V}$ and $V_{rm DS} = hbox{10} hbox{V}$. At the same bias point, a minimum noise figure of 1.6 dB at 30 GHz and an associated gain of 5 dB were achieved. To the best of our knowledge, this is the best noise performance reported at 30 GHz for gate-recessed AlGaN/GaN HEMTs.      

An ultralow-loss and broadband micromachined RF inductor for RFIC input-matching applications

In this brief, we demonstrate that ultralow-loss and broadband inductors can be obtained by using the CMOS process compatible backside inductively coupled-plasma (ICP) deep-trench technology to selectively remove the silicon underneath the inductors. The results show that a 378.5% increase in maximum Q-factor (Q/sub max/) (from 10.7 at 4.7 GHz to 51.2 at 14.9 GHz), a 22.1% increase in self-resonant frequency (f/sub SR/) (from 16.5 to 20.15 GHz), a 16.3% increase (from 0.86 to 0.9999) in maximum available power gain (G/sub Amax/) at 5 GHz, and a 0.654-dB reduction (from 0.654 dB to 4.08/spl times/10/sup -4/ dB) in minimum noise figure (NF/sub min/) at 5 GHz were achieved for a 2-nH inductor after the backside ICP dry etching. In addition, state-of-the-art ultralow-loss G/sub Amax//spl les/0.99 (i.e., NF/sub min//spl les/0.045 dB) for frequencies lower than 12.5 GHz was achieved for this 2-nH inductor after the backside inductively coupled-plasma dry etching. This means this on-chip inductor-on-air can be used to realize an ultralow-noise 3.1-10.6 GHz ultrawide-band RFIC. These results show that the CMOS process compatible backside ICP etching technique is very promising for system-on-a-chip applications.     

Implementation of perfect-magnetic-coupling ultralow-loss transformer in RFCMOS technology

In this letter, we propose a single-turn multiple-layer interlaced stacked transformer structure with nearly perfect magnetic-coupling factor (k/sub IM//spl sim/1) using standard mixed-signal/RF CMOS (or BiCMOS) technology. A single-turn six-layer interlaced stacked transformer was implemented to demonstrate the proposed structure. Temperature dependence (from -25/spl deg/C to 175/spl deg/C) of the quality-factor (Q-factor), k/sub Im/, resistive-coupling factor (k/sub Re/), maximum available power gain (G/sub Amax/), and minimum noise figure (NF/sub min/) performances of the transformer are reported. State-of-the-art G/sub Amax/ of 0.762 and 0.904 (i.e., NF/sub min/ of 1.181 dB and 0.437 dB) have been achieved at 5.2 and 8 GHz, respectively, at room temperature, mainly due to the perfect magnetic-coupling factor and the high resistive-coupling factor. The present analysis is helpful for RF engineers to design ultralow-voltage high-performance transformer-feedback low-noise amplifiers and voltage-controlled oscillators, and other radio frequency integrated circuits which include transformers.     

Very low-noise Al/sub 0.3/Ga/sub 0.7/As/Ga/sub 0.65/In/sub 0.35/As/GaAs single quantum-well pseudomorphic HEMTs

AlGaAs/GaInAs/GaAs pseudomorphic HEMTs with an InAs mole fraction as high as 35% in the channel has been successfully fabricated. The device exhibits a maximum extrinsic transconductance of 700 mS/mm. At 18 GHz, a minimum noise figure of 0.55 dB with 15.0 dB associated gain was measured. At 60 GHz, a minimum noise figure as low as 1.6 dB with 7.6 dB associated gain was also obtained. This is the best noise performance yet reported for GaAs-based HEMTs.<>     

AlGaN-GaN HEMTs on Si with power density performance of 1.9 W/mm at 10 GHz

AlGaN-GaN high electron mobility transistors (HEMTs) on silicon substrate are fabricated. The device with a gate length of 0.3-/spl mu/m and a total gate periphery of 300 /spl mu/m, exhibits a maximum drain current density of 925 mA/mm at V/sub GS/=0 V and V/sub DS/=5 V with an extrinsic transconductance (g/sub m/) of about 250 mS/mm. At 10 GHz, an output power density of 1.9 W/mm associated to a power-added efficiency of 18% and a linear gain of 16 dB are achieved at a drain bias of 30 V. To our knowledge, these power results represent the highest output power density ever reported at this frequency on GaN HEMT grown on silicon substrates.     

Planar integration of E/D-mode AlGaN/GaN HEMTs using fluoride-based plasma treatment

A planar-fabrication technology for integrating enhancement/depletion (E/D)-mode AlGaN/GaN high-electron mobility transistors (HEMTs) has been developed. The technology relies heavily on CF/sub 4/ plasma treatment, which is used in two separate steps to achieve two objectives: 1) active device isolation and 2) threshold-voltage control for the enhancement-mode HEMT formation. Using the planar process, depletion- and enhancement-mode AlGaN/GaN HEMTs are integrated on the same chip, and a direct-coupled FET logic inverter is demonstrated. Compared with the devices fabricated by a standard mesa-etching technique, the HEMTs by a planar process have comparable dc and RF characteristics with no obvious difference in the device isolation. The device isolation by a plasma treatment remains the same after 400 /spl deg/C annealing, indicating a good thermal stability. At a supply voltage (V/sub DD/) of 3.3 V, the E/D-mode inverters show an output swing of 2.85 V, with the logic-low and logic-high noise margins at 0.34 and 1.47 V, respectively.