a 2-32 ghz coplanar waveguide inalas-ingaas-inp hbt cascode distributed amplifier

8/7/2019 A 2-32 GHz coplanar waveguide InAlAs-InGaAs-InP HBT cascode distributed amplifier

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A 2-32 GHz Coplanar Waveguide InAIAs/lnGaAs-lnP HBTCascode Distributed AmplifierKevin W. Kobayashi, John Cowles, Liem Tran, Tom Block,

Aaron K. Oki, and Dwight C. StreitTRW Electronics Systems and Technology DivisionOne Space ParkRedondo Beach, CA 90278

2x2 oA, 2x3 Matrix DA , .capacitive couple. J~~~~!Tl~AlGaAs HBT 131L.- Ir

4-section,Conventional, AThls W o r k fAlGaAs HETI11

AbstractA 2-32 GHz InAIAs/lnGaAs-lnP HBT CPW distributed

amplifier (DA) has been demonstrated which benchmarks thehighest bandwidth reported for an HBT DA. The DA combines a100 GHz fmax and 60 GHz f-r HBT technology with a cascodecoplanar waveguide DA topology to achieve this recordbandwidth. The cascode CPW DA demonstrates both designtechniques and technology capability which can be applied tomore complex circuit functions such as active baluns formixers, active combiners/dividers, and low dc power-broadband amplification at millimeter-wave frequencies.

1. IntroductionPreviously reported HBT distributed amplifier gain

and bandwidth performance are summarized in Fig. 1[1],[2],[3],[4]. The 2-32 GHz response of the present workis believed to be the highest bandwidth reported for an HBTdistributed amplifier, and is also the first CPW DA designimplemented in InAIAsllnGaAs-lnP HBT technology. A 33 GHzInAIAs/lnGaAs-based HBT cascode direct-coupled amplifierhas also been previously reported[5]. However, due to the useof an unmatched analog design topology, the return-loss was 16 GHz which, unfortunately, limits thepractical bandwidth to less than half of the amplifiers 3-dBbandwidth. The present work achieves good broadband return-loss which is typically > 13 dB across the full band using adistributively matched topology.

II. InAlAsllnGaAs HBT TechnologyA similar 1 pm fully self-aligned InAIAs/lnGaAs HBT

process has previously been described in detail[6] along withseveral MMlC demonstr ations [7],[8],[9],[10],[11]. TheInAlAsllnGaAs HBT device structures are grown using solidsource Molecular Beam Epitaxy. Be and Si are used as p- andn-type dopants for the base and emitterlcollector,

HBT Distributed Amplifier Performance4-section.Anen. G mpe n. .

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5-secllon,CPW cascodeInGaAs HET00 1 0 20 30 4 0

3-dB Bandwidth (GHz)Fig. 1 Summary of previously reported HBT DA gain andbandwidth performance: Nominal Gain vs. 3-dB Bandwidth.respectively. The base-collector epitaxial structure consistsof a base thickness of 800 8, uniformly doped to 3x1Ol9 cm-3, a 70008, thick n-type collector lightly doped to lx lO1 6cm-3, and an N+ sub-collector doped to 2x1019 ~ m - ~ .heemitter structure incorporates an InGaAs/lnAIAs cap which isheavily doped for good emitter contact. The base-emitterjunction consists of a compositionally graded quarternarylayer of Inl -x -y Ga x AIy As. Compositional base-emittergrading is used to achieve uniformly consistent dc beta and Vbematching between devices, as well as for producingconsistently repeatable device rf performance. The HBT dcbeta across the wafers are typically 20 at a Jc=lO kA/cm2.The breakdown voltage BVceo is =11V and the BVcbo is =13 V.

A high performance fully self-aligned 1-pm emitterwidth process is used to produce HBTs with an f T a n dfmax(fr0m MAG) of = 60 and 100 GHz, respectively. Thecorresponding device fum ax (from unilateral gain) is 130GHz. These numbers were achieved from a 1x10 pm2 quad-emitter HBT biased at a current density of Jc=120 kA/cm2and a Vce= 2.0V.

95CH3577-7/95/0000-0195$01.OO 0 995 IEEE195

IEEE 1995 Microwave and Millimeter-Wave Monolithic Circuits Symposium


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HBT cascode DA. A CPW design environment was used because 90SyIt offers smaller chip size implementation, lower parasiticground inductance, and easier manufacturability because -backside vias are not required. In addition, a CPW design z 70!z:: 60-transmission lines and proximity effects which simplifies the

circuit modeling at millimeter-wave. This last advantage is s % -

environment can minimize interline coupling between EYU

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t:especially attractive for millimeter-wave HET DAs becausethe small inductive line lengths normally required to

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Fig. 6 Microphotograph of the fabricated CPW cascode HBT DA.Chip size is 1.Sxl.2 mm2.

GHz, the cascode offers as much as 7 dB more available devicegain. The amplifier supply voltage is 5V and draws 33 mA ofcurrent. The total power consumption is 165 mW. Fig. 6shows a microphotograph of the fabricated CPW cascode HBT.This photograph illustrates how compact the transmission linenetworks are about each of the 5 HBT cascode gain cells. Had amicrostrip environment been used, backside vias would havebeen required for each of the cascode cells and would have madethe input and output transmission-line networks almostphysically impossible to layout. The microstrip design wouldhave degraded the performance because of its sensitivity toproximity effects, whereas, the CPW design geometricallyconfines the fields such that the proximity effects of adjacentstructures are lessened. Recently reported experimental data

predicted while a 5.5-6 dB gain and 32 GHz bandwidth wasmeasured. The measured return-losses are better than 13 dBacross most of the 2-40 GHz band. The discrepancy betweenthe original simulation and measured data is due to a differencein performance between the HBT design model and the actualfabricated devices. Because a cascode pair is used for the gaincell, even a slight change in performance in the HBTs couldresult in a dramatic change in the amplifier's bandwidthresponse. When a new HBT design model is generated from themore recent device s-parameters (taken from the samesite/wafer as the measured circuit data) and used in thesimulation, the distributed amplifier's simulated gain matches

3 dB (S21) + dB (S11I 0 B IS111 x d B ( S 2 1 lM o d e l M o d e l M e a s M e a sI I I I I I I I

supporting this claim demonstrated that as much as a 10 dBimprovement in isolation between arms of a SPDT switch atmillimeter-wave frequencies can be achieved using a CPWenvironment[ l2]. Thus, our CPW DA approach allows thedesign to be more easily modeled and results in a compact chip

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-2 0IV . Measured ResultsThe original simulation performance of the HBT cascode I I I I I I I

0 10 20 30 40Frequency IGHz)PW DA is compared against the measured performance asshown in Fig. 7. A 5 dB gain and 40 GHz 3-dB bandwidth was Fig. 7 Original simulation versus the measured performance.

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its measured gain to within 0.5 dB up to 40 GHz, shown in Fig.8. The corresponding modeled input return-loss also closelymatches the measured data. For frequencies above 20 GHz, theinput return-loss actually becomes much better than themodeled by > 5 dB. Fig. 9 also illustrates that the modeledoutput return-loss tracks the measured data which is betterthan 15 dB across most of the band. Even the simulatedresonances in the output return-loss response match themeasured response to within a few GHz. Both Figs. 8 and 9seem to reflect the accuracy of the LIBRA(4.0) CPW modelswhen the circuit is layed-out to minimize proximity,radiation, and parasitic effects.

I I I I ' SimulationI

V. ConclusionWe have demonstrated a 2-32 GHz HBT distributed

amplifier which is believed to be the highest reportedbandwidth for an HBT DA. A 5-section cascode DA topologybased on an InAIAsllnGaAs-lnP HBT technology was used toachieve this benchmark. A CPW design environment wasimplemented in order to minimize interline coupling andproximity effects as well as to simplify the DA's fabrication.The cascode HBT CPW DA demonstrates both design techniquesand technology capability which can be applied to othermillimeter-wave MMlC circuit functions such as active balunsfor mixers, active combinerddividers, and low dc power-broadband amplification at millimeter-wave frequencies.

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0 10 20 30 40Frequency IGHz)

Fig. 8 Simulated gain and input return-loss using measuredHBT s-parameters (from same wafer-site as the measuredcircuit) vs. measured circuit performance.

0 B (S22)Mode l 0 dB 6 2 2 )

-30 I I I I I I I I0 10 M 30 40Frequency (GHz)

Fig. 9 Simulated output return-loss using measured HBT s-parameters (from same wafer-site as the measured circuit)vs . measured circuit performance.References[ 1 ] B. Nelson, et.al., "High Linearity, low dc powermonolithic GaAs HBT broadband amplifiers to 11 GHz", in

1990 / E E Microwave and Mlllimeter- Wave MonolithicCircuit Symp. Dig., Dallas, TX, pp. 15-18.[ 21 K.W. Kobayashi, et.al., "GaAs HBT wideband matrixdistributed and Darlington feedback amplifiers to 24 GHz",/E Transactions on Microwave Theory and Techniques, vol.39, no. 12, pp. 2001-2009,[ 31 K.W. Chang, et.al., "2-19-GHz Low Power and High-IP3 Monolithic HBT Matrix Amplifier", / E MicrowaveGuided Wave Lett., vol. 2, pp. 17-19, Jan. 1992.[ 4 ] K.W. Kobayashi, et.al., "A Novel HBT DistributedAmplifier Design Topology based on Attenuation CompensationTechniques", 1994 / E Microwave and Mlllimeter-WaveMonolithic Circuit Symp. Dig., San Diego, CA, pp. 179-182.[ 51 M. Rodwell, et.al., "33 GHz Monolithic CascodeAllnAs/GalnAs Heterojunction Bipolar Transistor FeedbackAmplifier," in / E 1990 BCTM Dig., pp. 252-255.[ 6 ] L.T. Tran, et.al., " lnAIAs/lnGaAs HBT withExponentially Graded Base Doping and Graded InGaAlAsEmitter-Base Junction," in 1992 /E ndium Phosphide andRelated Materials Dig., Newport, Rhode Island, 1992, pp.( 7 1 K.W. Kobayashi, et.al., "lnP based HBT Millimeter-Wave Technology and Circuit performance to 40 GHz," in1993 I MMWMC Symp. Dig., Atlanta, Georgia, pp.85-88.[ 81 K.W. Kobayashi, et.al., "A Novel Active Feedback DesignUsing InAIAs/lnGaAs Heterojunction Bipolar Transistors," in/ E Microwave and Guided-Wave Letts., vol. 4, no. 5,pp.146-148, May 1994.[ 9 ] K.W. Kobayashi and A.K. Oki, "A Novel HeterojunctionBipolar Transistor VCO using an Active Tuneable Inductance,"/ E Microwave and Guided-Wave Letts., vol. 4, no. 7, 1994.[ 1 0 ) K.W. Kobayashi, et.al., "Low Power ConsumptionInAIAs/lnGaAs-As/lnGaAs HBT X-band Double-BalancedUpconverter," in / E / E Trans. on JSSC, vol. 29, no. 10,[ 1 1 ] K.W. Kobayashi, et.al. , "Low Power ConsumptionInAIAsllnGaAs-lnP HBT X-band SPDT PIN Diode Switch," in/ E Microwave and Guided-Wave Lett., vol. 10. no. 3.[ 121 K.W. Kobayashi, et.al., "A 50 MHz-30 GHz BroadbandCo-Planar Waveguide SPDT PIN Diode Switch with 45 dBIsolaion," / E Microwave & Guided-Wave Letts., vol. 5, no.2, 1994.

Dec., 1991.

439 - 441 .

Oct., 1994, pp. 1238-1243.

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a 2-32 ghz coplanar waveguide inalas-ingaas-inp hbt cascode distributed amplifier

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