High breakdown voltage (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P/InGaAs quasi-enhancement-mode pHEMT with field-plate technology

A high breakdown voltage and a high turn-on voltage (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P/InGaAs quasi-enhancement-mode (E-mode) pseudomorphic HEMT (pHEMTs) with field-plate (FP) process is reported for the first time. Between gate and drain terminal, the transistor has a FP metal of 1 /spl mu/m, which is connected to a source terminal. The fabricated 0.5/spl times/150 /spl mu/m/sup 2/ device can be operated with gate voltage up to 1.6 V owing to its high Schottky turn-on voltage (V/sub ON/=0.85 V), which corresponds to a high drain-to-source current (I/sub ds/) of 420 mA/mm when drain-to-source voltage (V/sub ds/) is 3.5 V. By adopting the FP technology and large barrier height (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P layer design, the device achieved a high breakdown voltage of -47 V. The measured maximum transconductance, current gain cutoff frequency and maximum oscillation frequency are 370 mS/mm, 22 GHz , and 85 GHz, respectively. Under 5.2-GHz operation, a 15.2 dBm (220 mW/mm) and a 17.8 dBm (405 mW/mm) saturated output power can be achieved when drain voltage are 3.5 and 20 V. These characteristics demonstrate that the field-plated (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P E-mode pHEMTs have great potential for microwave power device applications.     

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.     

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-temperature thermal stability performance in /spl delta/-doped In/sub 0.425/Al/sub 0.575/As--In/sub 0.65/Ga/sub 0.35/As metamorphic HEMT

We report, to our knowledge, the best high-temperature characteristics and thermal stability of a novel /spl delta/-doped In/sub 0.425/Al/sub 0.575/As--In/sub 0.65/Ga/sub 0.35/As--GaAs metamorphic high-electron mobility transistor. High-temperature device characteristics, including extrinsic transconductance (g/sub m/), drain saturation current density (I/sub DSS/), on/off-state breakdown voltages (BV/sub on//BV/sub GD/), turn-on voltage (V/sub on/), and the gate-voltage swing have been extensively investigated for the gate dimensions of 0.65/spl times/200 /spl mu/m/sup 2/. The cutoff frequency (f/sub T/) and maximum oscillation frequency (f/sub max/), at 300 K, are 55.4 and 77.5 GHz at V/sub DS/=2 V, respectively. Moreover, the distinguished positive thermal threshold coefficient (/spl part/V/sub th///spl part/T) is superiorly as low as to 0.45 mV/K.     

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.     

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 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.     

Diamond FET using high-quality polycrystalline diamond with f/sub T/ of 45 GHz and f/sub max/ of 120 GHz

Using high-quality polycrystalline chemical-vapor-deposited diamond films with large grains (/spl sim/100 /spl mu/m), field effect transistors (FETs) with gate lengths of 0.1 /spl mu/m were fabricated. From the RF characteristics, the maximum transition frequency f/sub T/ and the maximum frequency of oscillation f/sub max/ were /spl sim/ 45 and /spl sim/ 120 GHz, respectively. The f/sub T/ and f/sub max/ values are much higher than the highest values for single-crystalline diamond FETs. The dc characteristics of the FET showed a drain-current density I/sub DS/ of 550 mA/mm at gate-source voltage V/sub GS/ of -3.5 V and a maximum transconductance g/sub m/ of 143 mS/mm at drain voltage V/sub DS/ of -8 V. These results indicate that the high-quality polycrystalline diamond film, whose maximum size is 4 in at present, is a most promising substrate for diamond electronic devices.     

AlGaN/GaN MIS-HFETs with f/sub T/ of 163 GHz using cat-CVD SiN gate-insulating and passivation Layers

Al/sub 0.4/Ga/sub 0.6/N/GaN heterostructure field-effect transistors (HFETs) with an AlGaN barrier thickness of 8 nm and a gate length (L/sub G/) of 0.06-0.2 /spl mu/m were fabricated on a sapphire substrate. We employed two novel techniques, which were thin, high-Al-composition AlGaN barrier layers and SiN gate-insulating, passivation layers formed by catalytic chemical vapor deposition, to enhance high-frequency device characteristics by suppressing the short channel effect. The HFETs with L/sub G/=0.06-0.2 /spl mu/m had a maximum drain current density of 1.17-1.24 A/mm at a gate bias of +1.0 V and a peak extrinsic transconductance of 305-417 mS/mm. The current-gain cutoff frequency (f/sub T/) was 163 GHz, which is the highest value to have been reported for GaN HFETs. The maximum oscillation frequency (f/sub max/) was also high, and its value derived from the maximum stable gain or unilateral gain was 192 or 163 GHz, respectively.     

Influences of sulfur passivation on temperature-dependent characteristics of an AlGaAs/InGaAs/GaAs PHEMT

The influences of (NH/sub 4/)/sub 2/S/sub x/ treatment on an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) are studied and demonstrated. Upon the sulfur passivation, the studied device exhibits better temperature-dependent dc and microwave characteristics. Experimentally, for a 1/spl times/100 /spl mu/m/sup 2/ gate/dimension PHEMT with sulfur passivation, the higher gate/drain breakdown voltage of 36.4 (21.5) V, higher turn-on voltage of 0.994 (0.69) V, lower gate leakage current of 0.6 (571) /spl mu/A/mm at V/sub GD/=-22 V, improved threshold voltage of -1.62 (-1.71) V, higher maximum transconductance of 240 (211) mS/mm with 348 (242) mA/mm broad operating regime (>0.9g/sub m,max/), and lower output conductance of 0.51 (0.53) mS/mm are obtained, respectively, at 300 (510) K. The corresponding unity current gain cutoff frequency f/sub T/ (maximum oscillation frequency f/sub max/) are 22.2 (87.9) and 19.5 (59.3) GHz at 250 and 400 K, respectively, with considerably broad operating regimes (>0.8f/sub T/,f/sub max/) larger than 455 mA/mm. Moreover, the relatively lower variations of device performances over wide temperature range (300/spl sim/510 K) are observed.     

A novel InGaP/Al/sub x/Ga/sub 1-x/As/GaAs CEHBT

A new and interesting InGaP/Al/sub x/Ga/sub 1-x/As/GaAs composite-emitter heterojunction bipolar transistor (CEHBT) is fabricated and studied. Based on the insertion of a compositionally linear graded Al/sub x/Ga/sub 1-x/As layer, a near-continuous conduction band structure between the InGaP emitter and the GaAs base is developed. Simulation results reveal that a potential spike at the emitter/base heterointerface is completely eliminated. Experimental results show that the CEHBT exhibits good dc performances with dc current gain of 280 and greater than unity at collector current densities of J/sub C/=21kA/cm/sup 2/ and 2.70/spl times/10/sup -5/ A/cm/sup 2/, respectively. A small collector/emitter offset voltage /spl Delta/V/sub CE/ of 80 meV is also obtained. The studied CEHBT exhibits transistor action under an extremely low collector current density (2.7/spl times/10/sup -5/ A/cm/sup 2/) and useful current gains over nine decades of magnitude of collector current density. In microwave characteristics, the unity current gain cutoff frequency f/sub T/=43.2GHz and the maximum oscillation frequency f/sub max/=35.1GHz are achieved for a 3/spl times/20 /spl mu/m/sup 2/ device. Consequently, the studied device shows promise for low supply voltage and low-power circuit applications.     

547-GHz f/sub t/ In/sub 0.7/Ga/sub 0.3/As-In/sub 0.52/Al/sub 0.48/As HEMTs with reduced source and drain resistance

We fabricated 30-nm gate pseudomorphic channel In/sub 0.7/Ga/sub 0.3/As-In/sub 0.52/Al/sub 0.48/As high electron mobility transistors (HEMTs) with reduced source and drain parasitic resistances. A multilayer cap structure consisting of Si highly doped n/sup +/-InGaAs and n/sup +/-InP layers was used to reduce these resistances while enabling reproducible 30-nm gate process. The HEMTs also had a laterally scaled gate-recess that effectively enhanced electron velocity, and an adequately long gate-channel distance of 12nm to suppress gate leakage current. The transconductance (g/sub m/) reached 1.5 S/mm, and the off-state breakdown voltage (BV/sub gd/) defined at a gate current of -1 mA/mm was -3.0 V. An extremely high current gain cutoff frequency (f/sub t/) of 547 GHz and a simultaneous maximum oscillation frequency (f/sub max/) of 400 GHz were achieved: the best performance yet reported for any transistor.     

60-GHz high power performance In/sub 0.35/Al/sub 0.65/As-In/sub 0-35/Ga/sub 0.65/As metamorphic HEMTs on GaAs

We report on a double-pulse doped, double recess In/sub 0.35/Al/sub 0.65/As-In/sub 0.35/Ga/sub 0.65/As metamorphic high electron mobility transistor (MHEMT) on GaAs substrate. This 0.15-/spl mu/m gate MHEMT exhibits excellent de characteristics, high current density of 750 mA/mm, extrinsic transconductance of 700 mS/mm. The on and off state breakdown are respectively of 5 and 13 V and defined It gate current density of 1 mA/mm. Power measurements at 60 GHz were performed on these devices. Biased between 2 and 5 V, they demonstrated a maximum output power of 390 mW/mm at 3.1 V of drain voltage with 2.8 dB power gain and a power added efficiency (PAE) of 18%. The output power at 1 dB gain compression is still of 300 mW/mm. Moreover, the linear power gain is of 5.2 dB. This is to our knowledge the best output power density of any MHEMT reported at this frequency.     

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.     

Highly linear Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMTs

We report an Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMT with enhanced linearity. By engineering the channel region, i.e., inserting a 6-nm-thick AlGaN layer with 5% Al composition in the channel region, a composite-channel HEMT was demonstrated. Transconductance and cutoff frequencies of a 1 /spl times/100 /spl mu/m HEMT are kept near their peak values throughout the low- and high-current operating levels, a desirable feature for linear power amplifiers. The composite-channel HEMT exhibits a peak transconductance of 150 mS/mm, a peak current gain cutoff frequency (f/sub T/) of 12 GHz and a peak power gain cutoff frequency (f/sub max/) of 30 GHz. For devices grown on sapphire substrate, maximum power density of 3.38 W/mm, power-added efficiency of 45% are obtained at 2 GHz. The output third-order intercept point (OIP3) is 33.2 dBm from two-tone measurement at 2 GHz.     

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.     

Al/sub 0.25/Ga/sub 0.75/As/In/sub 0.25/Ga/sub 0.75/As pseudomorphic MODFET with high DC and RF performance

AlGaAs/InGaAs MODFETs having 25% indium in the channel and L/sub G/=0.35 mu m have been fabricated. From DC device characterisation, a maximum saturation current of 670 mA/mm and an extrinsic transconductance of 500 mS/mm have been measured. A maximum unilateral gain cutoff frequency of f/sub c/=205 GHz and a maximum current gain cutoff frequency of f/sub T/=86 GHz have been achieved. Bias dependence of f/sub c/ and f/sub T/ has been measured. At 12 GHz a minimum noise figure of NF=0.8 dB and an associated gain of 11 dB have been measured.<>     

10-W/mm AlGaN-GaN HFET with a field modulating plate

AlGaN-GaN heterojunction field-effect transistors (HFETs) with a field modulating plate (FP) were fabricated on an SiC substrate. The gate-drain breakdown voltage (BV/sub gd/) was significantly improved by employing an FP electrode, and the highest BV/sub gd/ of 160 V was obtained with an FP length (L/sub FP/) of 1 /spl mu/m. The maximum drain current achieved was 750 mA/mm, together with negligibly small current collapse. A 1-mm-wide FP-FET (L/sub FP/=1 /spl mu/m) biased at a drain voltage of 65 V demonstrated a continuous wave saturated output power of 10.3 W with a linear gain of 18.0 dB and a power-added efficiency of 47.3% at 2 GHz. To our knowledge, the power density of 10.3 W/mm is the highest ever achieved for any FET of the same gate size.     

InGaAs/InP DHBTs with 120-nm collector having simultaneously high f/sub /spl tau//, f/sub max//spl ges/450 GHz

InP/In/sub 0.53/Ga/sub 0.47/As/InP double heterojunction bipolar transistors (DHBT) have been designed for increased bandwidth digital and analog circuits, and fabricated using a conventional mesa structure. These devices exhibit a maximum 450 GHz f/sub /spl tau// and 490 GHz f/sub max/, which is the highest simultaneous f/sub /spl tau// and f/sub max/ for any HBT. The devices have been scaled vertically for reduced electron collector transit time and aggressively scaled laterally to minimize the base-collector capacitance associated with thinner collectors. The dc current gain /spl beta/ is /spl ap/ 40 and V/sub BR,CEO/=3.9 V. The devices operate up to 25 mW//spl mu/m/sup 2/ dissipation (failing at J/sub e/=10 mA//spl mu/m/sup 2/, V/sub ce/=2.5 V, /spl Delta/T/sub failure/=301 K) and there is no evidence of current blocking up to J/sub e//spl ges/12 mA//spl mu/m/sup 2/ at V/sub ce/=2.0 V from the base-collector grade. The devices reported here employ a 30-nm highly doped InGaAs base, and a 120-nm collector containing an InGaAs/InAlAs superlattice grade at the base-collector junction.     

A technique to improve the drive current of high-voltage I/O transistors in digital CMOS technologies

By combining a 0.12-/spl mu/m-long 1.2-V thin-oxide transistor with a 0.22-/spl mu/m-long 3.3-V thick-oxide transistor in a 0.13-/spl mu/m CMOS process, a composite MOS transistor structure with a drawn gate length of 0.34 /spl mu/m is realized. Measurements show that at V/sub GS/=1.2 V and V/sub DS/=3.3 V, the composite transistor has more than two times the drain current of the minimum channel length (0.34 /spl mu/m) 3.3-V thick-oxide transistor, while having the same breakdown voltage (V/sub BK/) as the thick-oxide transistor. Exploiting these, it should be possible to implement 3.3-V I/O transistors with better combination of drive current, threshold voltage (V/sub T/) and breakdown voltage in conventional CMOS technologies without adding any process modifications.