Power Gain Cutoff Frequency Research Articles

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.

Enhanced-performance of AlGaN-GaN HEMTs grown on grooved sapphire substrates

We report significantly improved dc characteristics and RF performance of AlGaN-GaN HEMTs grown on grooved sapphire substrates. Grooves 60 nm deep with 2-/spl mu/m-wide ridges and 4-/spl mu/m-wide trenches were created along the orientation of the substrate by inductively coupled-plasma reactive ion etching. Device mesas were defined over the trench regions where superior crystalline quality was observed by other characterization techniques. Compared to conventional HEMTs grown on the planar area, the devices on the grooved substrate show increased drain saturation current and peak transconductance. Their reverse gate leakage current is over three orders of magnitude lower. These devices also show increased off-state breakdown voltage with hard breakdown characteristics. For nominal 1-/spl mu/m-gate-length HEMTs, the best current gain and power gain cutoff frequencies were 15 and 54 GHz, respectively. The on-wafer output power, gain, and power-added efficiency of an unpassivated device measured at 4 GHz were 3.26 W/mm, 25.7 dB, and 55.6%. The enhanced performance is attributed to low-density mixed dislocations and high crystalline quality over the trench regions.

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 ×100 μm 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 xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) of 12 GHz and a peak power gain cutoff frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) 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.

III-nitride metal-insulator-semiconductor heterojunction field-effect transistors using sputtered AlON thin films

In this letter, a III-nitride metal-insulator-semiconductor heterostructure field-effect transistors (MISHFET) was demonstrated by incorporating a sputtered AlON layer in the AlGaN∕GaN heterostructure field-effect transistors (HFET). The AlON layer was deposited on the HFET structure by magnetron sputtering, followed by rapid thermal annealing at 850°C for 45s. A reverse gate leakage current that is four orders of magnitude lower was obtained in the MISHFET, compared to that in HFET. The MISHFET also shows 20% increase in the drain saturation current. For a MISHFET with 1-μm-long gate, the current gain cutoff frequency, ft and the power gain cutoff frequency, fmax are measured to be 13 and 37GHz, respectively.

0.13-&amp;lt;tex&amp;gt;$muhbox m$&amp;lt;/tex&amp;gt;RF CMOS and Varactors Performance Optimization by Multiple Gate Layouts

0.13-/spl mu/m radio frequency (RF) CMOS devices with multifinger gate structure have been fabricated by the standard logic process, and the measured effective gate-length is 80 nm. Extensive RF characterization has been done to obtain cutoff frequency (f/sub T/), associated power gain cutoff frequency (f/sub max/), minimum noise figure (NF/sub min/), output power (P/sub out/), and power added efficiency (PAE) for RF circuit design and to explore the optimized gate layout in terms of the extracted RF device parameters. Our important finding to be reported in this paper is that an optimized unit finger width (W/sub F/) exists by trade-off among f/sub T/, f/sub max/, NF/sub min/, P/sub out/, and PAE. Under fixed total width to achieve the same current drivability (I/sub ds/), the smaller W/sub F/ and the larger finger number (N/sub F/) leads to higher f/sub max/ but lower f/sub T/ due to trade-off between gate resistance (R/sub g/) and parasitic gate capacitance. As for NF/sub min/ complicated by f/sub T/ and R/sub g/, counter-balance between parasitic gate capacitance and R/sub g/ leads to nearly constant NF/sub min/ w.r.t. various splits of (W/sub F/,N/sub F/). Regarding P/sub out/ and PAE, W/sub F/ of 4 /spl mu/m and N/sub F/ of 18 is the optimized layout parameter, which offers the maximum P/sub out/ of around 11 dBm and PAE of 30.5% at 5.8 GHz. The performances of accumulation-mode MOS varactors with different gate layout structures are also investigated in this report. Since the same area varactors with different gate layout may result in different parasitic resistance and fringing capacitance, which will affect the capacitance tuning range and the associated Q-factor. The maximum Q-factor is about 59 of the 120 /spl mu/m/sup 2/ gate area varactor, and its tuning range is from 210 fF to 1.64 pF, where the maximum C/sub max//C/sub min/ ratio is about 7.8.

Device characteristics of GaAs-based heterojunction bipolar transistors using an InGaAs/GaAsP strain-compensated layer as a base material

An InGaAs/GaAsP strain-compensated layer has been proposed as a base material for GaAs-based double heterojunction bipolar transistors (DHBTs). As known, decreasing bandgap energy of the base layer in heterojunction bipolar transistors (HBTs) can result in a smaller turn-on voltage. Using InGaAs as a base material is one possible approach to achieve the aim. However, compressive strain induced by InGaAs diminishes the influence of indium-adding-induced bandgap energy reduction, and thus abates the advantage of turn-on voltage reduction. In this study, a 280 Å GaAs0.81P0.19 layer has been inserted below the In0.054Ga0.946As base layer to compensate the compressive strain induced by the InGaAs base layer. The result shows that the utilization of an InGaAs/GaAsP strain-compensated layer results in a reduction of the turn-on voltage by 20 mV. A turn-on voltage reduction of 190 mV over a conventional HBT with a GaAs base layer is achieved by utilizing the In0.054Ga0.946As/GaAs0.81P0.19 strain-compensated base layer. This particular DHBT has a small offset voltage of 55 mV and a knee voltage of 0.6 V. A peak current gain of 58.98, a unity-current-gain cut-off frequency fT of 22 GHz and a unilateral power gain cut-off frequency fMAX of 25 GHz are also achieved for this particular DHBT.

High Bandwidth and Low-Leakage Current InP–&amp;lt;tex&amp;gt;$hbox In_0.53hbox Ga_0.47hbox As$&amp;lt;/tex&amp;gt;–InP DBHTs on GaAs Substrates

InP-In/sub 0.53/Ga/sub 0.47/As-InP double heterojunction bipolar transistors (DHBTs) were grown on GaAs substrates. A 284-GHz power-gain cutoff frequency f/sub max/ and a 216-GHz current-gain cutoff frequency f/sub /spl tau// were obtained, presently the highest reported values for metamorphic HBTs. The breakdown voltage BV/sub CEO/ was >5 V while the dc current gain /spl beta/ was 21. High thermal conductivity InP metamorphic buffer layers were employed in order to minimize the device thermal resistance.

Submicron InP-InGaAs single heterojunction bipolar transistors with f/sub T/ of 377 GHz

Submicron InP-InGaAs-based single heterojunction bipolar transistors (SHBTs) are fabricated to achieve record-breaking speed performance using an aggressively scaled epitaxial structure coupled with a submicron emitter process. SHBTs with dimensions of 0.35 ×16 μm have demonstrated a maximum current gain cutoff frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> of 377 GHz with a simultaneous maximum power gain cutoff frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 230 GHz at the current density Jc of 650 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Typical BV/sub CEO/ values exceed 3.7 V.

Impact of metal/oxide interface on DC and RF performance of depletion-mode GaAs MOSFET employing MBE grown Ga 2O 3(Gd 2O 3) as gate dielectric

Employing Ga 2O 3(Gd 2O 3) as gate dielectric and Si-doped GaAs as conducting channel, depletion-mode GaAs MOSFETs were fabricated. DC I– V and transfer curves show no pinch-off and drain current hysteresis. Etching a thin layer from the top of Ga 2O 3(Gd 2O 3) in the gate region before gate metal deposition leads to full pinch-off and significantly reduces the drain current hysteresis. This process may remove the contaminated Ga 2O 3(Gd 2O 3) due to exposure to chemicals and prior processes, and thus results in a clean gate metal to oxide interface. The clean gate metal to Ga 2O 3(Gd 2O 3) interface also leads to higher DC transconductance, higher unity current gain cut-off frequency as well as higher unity power gain cut-off frequency as compared with GaAs MOSFET devices with a contaminated metal/oxide interface at the gate.

High-performance InP/In/sub 0.53/Ga/sub 0.47/As/InP double HBTs on GaAs substrates

InP/In/sub 0.53/Ga/sub 0.47/As/InP double heterojunction bipolar transistors (HBTs) were grown on GaAs substrates. A 140 GHz power-gain cutoff frequency f/sub max/ and a 207 GHz current-gain cutoff frequency f/sub /spl tau// were obtained, presently the highest reported values for metamorphic HBTs. The breakdown voltage BV/sub CEO/ was 5.5 V, while the dc current gain /spl beta/ was 76. High-thermal-conductivity InP metamorphic buffer layers were employed in order to minimize the device-thermal resistance.

InP/In 0.53Ga 0.47As/InP double heterojunction bipolar transistors on GaAs substrates using InP metamorphic buffer layer

InP/In 0.53Ga 0.47As/InP double heterojunction bipolar transistors were grown on GaAs substrates. A 92 GHz power-gain cutoff frequency f max and a 165 GHz current-gain cutoff frequency f τ were obtained, presently the highest reported values for metamorphic HBTs. The breakdown voltage BV CEO was 5 V while the DC current-gain β was 27. In order to minimize the transistor operating junction temperature, high-thermal-conductivity InP metamorphic buffer layers were employed.

SCALING OF InGaAs/InAlAsHBTs FOR HIGH SPEED MIXED-SIGNAL AND mm-WAVE ICs

High bandwidths are obtained with heterojunction bipolar transistors by thinning the base and collector layers, increasing emitter current density, decreasing emitter contact resistivity, and reducing the emitter and collector junction widths. In mesa HBTs, minimum dimensions required for the base contact impose a minimum width for the collector junction, frustrating device scaling. Narrow collector junctions can be obtained by using substrate transfer processes, or -if contact resistivity is greatly reduced -by reducing the width of the base Ohmic contacts in a mesa structure. HBTs with submicron collector junctions exhibit extremely high f max and high gains in mm-wave ICs. Logic gate delays are primarily set by depletion-layer charging times, and neither fτ nor f max is indicative of logic speed. For high speed logic, epitaxial layers must be thinned, emitter and collector junction widths reduced, current density increased, and emitter parasitic resistance decreased. Transferred-substrate HBTs have obtained 21 dB unilateral power gain at 100 GHz. If extrapolated at -20 dB/decade, the power gain cutoff frequency f max is 1.1 THz. Transferred-substrate HBTs have obtained 295 GHz f τ . Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz, 66 GHz master-slave flip-flops, and 18 GHz clock rate Δ-Σ ADCs.

SiGe pMODFETs on silicon-on-sapphire substrates with 116 GHz f/sub max/

The dc and microwave results of Si/sub 0.2/Ge/sub 0.8//Si/sub 0.7/Ge/sub 0.3/ pMODFETs grown on silicon-on-sapphire (SOS) substrates by ultrahigh vacuum chemical vapor deposition are reported. Devices with L/sub g/=0.1 μm displayed high transconductance (377 mS/mm), low output conductance (25 mS/mm), and high gate-to-drain breakdown voltage (4 V). The dc current-voltage (I-V) characteristics were also nearly identical to those of control devices grown on bulk Si substrates. Microwave characterization of 0.1×50 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> devices yielded unity current gain (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) and unilateral power gain (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) cutoff frequencies as high as 50 GHz and 116 GHz, respectively. Noise parameter characterization of 0.1×90 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> devices revealed minimum noise figure (F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> ) of 0.6 dB at 3 GHz and 2.5 dB at 20 GHz.

Submicron scaling of HBTs

The variation of heterojunction bipolar transistor (HBT) bandwidth with scaling is reviewed. High bandwidths are obtained by thinning the base and collector layers, increasing emitter current density, decreasing emitter contact resistivity, and reducing the emitter and collector junction widths. In mesa HBTs, minimum dimensions required for the base contact impose a minimum width for the collector junction, frustrating device scaling. Narrow collector junctions can be obtained by using substrate transfer or collector-undercut processes or, if contact resistivity is greatly reduced, by reducing the width of the base ohmic contacts in a mesa structure. HBTs with submicron collector junctions exhibit extremely high f/sub max/ and high gains in mm-wave ICs. Transferred-substrate HBTs have obtained 21 dB unilateral power gain at 100 GHz. If extrapolated at -20 dB/decade, the power gain cutoff frequency f/sub max/ is 1.1 THz. f/sub max/ will be less than 1 THz if unmodeled electron transport physics produce a >20 dB/decade variation in power gain at frequencies above 110 GHz. Transferred-substrate HBTs have obtained 295 GHz f/sub T/. The substrate transfer process provides microstrip interconnects on a low-/spl epsiv//sub r/ polymer dielectric with a electroplated gold ground plane. Important wiring parasitics, including wiring capacitance, and ground via inductance are substantially reduced. Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz and per-stage gain-bandwidth products over 400 GHz, and master-slave latches operating at 75 GHz.

A 30-nm-gate field-effect transistor

The fabrication technology is developed for and characteristics are investigated of a GaAs Schottky-barrier field-effect transistor (SBFET) with an effective gate length of 30 nm. The SBFET power gain cutoff frequency is 150 GHz. The noise factor at 12–37 GHz is comparable with that of two-dimensional electron gas transistors. The theoretical electron transit time under the gate is below 0.1 ps.

Submicron transferred-substrate heterojunction bipolar transistors

We report submicron transferred-substrate AlInAs/GaInAs heterojunction bipolar transistors (HBT's). Devices with 0.4-/spl mu/m emitter and 0.4-/spl mu/m collector widths have 17.5 dB unilateral gain at 110 GHz. Extrapolating at -20 dB/decade, the power gain cutoff frequency f/sub max/ is 820 GHz. The high f/sub max/, results from the scaling of HBT's junction widths, from elimination of collector series resistance through the use of a Schottky collector contact, and from partial screening of the collector-base capacitance by the collector space charge.

3 - 9-GHz GaN-based microwave power amplifiers with L-C-R broad-band matching

We present an initial demonstration of GaN-based broad-band power amplifiers in the form of a flip-chip integrated circuit (FC-IC) with AlN as the circuit substrates. The input matching consists of a high-to-low impedance transformer and an L-C-R broad-band network. Using 0.7-μm gate-length GaN high-electron-mobility transistors (HEMT's) with current-gain and power-gain cutoff frequencies of 18 and 35 GHz, excellent transducer gain up to 11.5 dB at 8 GHz, along with a bandwidth of 3-9 GHz, was achieved. The saturation power levels were about 32 and 35 dBm, respectively, for these two amplifiers using 1- and 2 mm-wide devices, which are about twice as high as achievable with GaAs-based counterparts of the same sizes.

Transferred-substrate HBTs with 254 GHz f τ

The authors report the simultaneous achievement of record current gain cutoff frequency f/sub /spl tau// and high power gain cutoff frequency f/sub max/ in a transferred-substrate HBT. The device parasitics are examined, and inferences made about the relative value of various approaches toward further improvements in f/sub /spl tau// and f/sub max/. Transferred-substrate HBTs with record f/sub /spl tau// of 254 GHz are reported.

A GaAs HEMT MMIC chip set for automotive radar systems fabricated by optical stepper lithography

A 77 GHz automotive radar system for collision avoidance and intelligent cruise control has recently gained interest because of its huge market potential. The questions of the optimum technological and system approaches leading to both low cost and high performance have not yet been finally answered. The approach to this problem reported here differs mainly in two aspects from the GaAs monolithic microwave integrated circuit (MMIC) solutions described earlier: (1) 0.12 /spl mu/m gatelength pseudomorphic high electron mobility transistors (PHEMTs) are fabricated by optical stepper lithography, (2) a coplanar design is used. A fully passivated PHEMT MMIC fabrication process is reported with current-gain and power-gain cutoff frequencies exceeding 115 and 220 GHz, respectively. The design and performance of a chip set consisting of four different MMICs [voltage controlled oscillator (VCO), harmonic mixer, transmitter, receiver] are described. The great potential of this MMIC approach to meet all system requirements of an automotive radar sensor in a cost-effective and production-oriented way is shown. To our knowledge, this is the first demonstration of W-band coplanar multifunctional MMICs fabricated by optical stepper lithography.

Microwave performance of AlGaN/GaN inverted MODFET's

A continuous wave output power of 1.5 W/mm with a power added efficiency of 17.5% has been achieved at 4 GHz in inverted AlGaN/GaN MODFET's (IMODFET's) with 2 μm gate lengths and 78 μm gate widths. The current gain and available power gain cutoff frequencies were 6 and 11 GHz, respectively. We suggest that the input characteristics of GaN-based FET's play an important role in the output power that can be obtained. In the present devices, high transconductance, 100 mS/mm, retained over a 5 V input swing is thought to alleviate the limitations imposed by the input characteristics. Moreover, the buried AlGaN buffer layer is suggested as having assisted in the reduction of the output conductance which aids the power gain.