200 GHz fmax, ft InP/In0.53Ga0.47As/InP Metamorphic Double Heterojunction Bipolar Transistors on GaAs Substrates

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200 GHz fmax, ft InP/In0.53Ga0.47As/InP
Metamorphic Double Heterojunction Bipolar
Transistors on GaAs Substrates
2003 Indium Phosphide and Related Materials, May
13, Santa Barbara

• Y.M. Kim, M. Urteaga, M. Dahlström, M.J.W.
  Rodwell, A.C. Gossard
• Department of Electrical Engineering, Materials
  Department,
• University of California, Santa Barbara

kymdow_at_ece.ucsb.edu 805-893-3543, 413-208-9864
fax
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Why InP-based HBTs ?
better device bandwidth than GaAs or Si bipolar
transistors microwave ADCs, DACs, digital
frequency synthesis better Emaxvsat than GaAs
millimeter-wave power
Why metamorphic HBTs ?--economic argument
low cost, high volume processing wafer size is
critical compatibility with Silicon process
tools GaAs substrates, processes 6" diameter
now large InP substrates high cost, high
breakage, only 4" available today breakage much
worse with 6" wafers grow InP-based HBTs on
GaAs substrates for cost and manufacturability
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UCSB
Metamorphic HBTs
Young-Min Kim
InGaAs/InP or InGaAs/InAlAs HBT on a GaAs
substrate Lattice mismatch between substrate and
epitaxial device layersThick intervening buffer
layer to capture most defects
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What are the potential problems ?
Leakage current through threading dislocation
Reliability (?)
High speed ft , fmax
Thick buffer layerpoor thermal conductivity
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Morphology RHEED of metamorphic layer
UCSB
Young-Min Kim
AlGaAsSb
InAlAs
InAlP (nomarski)
InP (nomarski)
5 ?m
5 ?m
InAlP (RHEED)
InP (RHEED)
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Morphology RHEED of metamorphic layer
UCSB
Young-Min Kim
InAlAs (nomarski)
AlGaAsSb (nomarski)
5 ?m
5 ?m
AlGaAsSb (RHEED)
InAlAs (RHEED)
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Device Junction Temperature Calculation
UCSB
Young-Min Kim
1000 µm
Metamorphic buffer Thermal conductivity (W/mK)
InAlAs 10.5
AlGaAsSb 8.4
InAlP 8
InP 35
LM GaAs 44
LM InP 69
1000 µm
HBT 7.5 µm x 0.4 µm
Metamorphic layer 1.5 µm
GaAs 350 µm

• Assume temperature independent thermal
  conductivity
• Assume no flow through emitter
• Power density 250 kW/cm2
• Handbook of III-V HBT by W.Liu

• InP buffer
• Good thermal conductivity
• Smaller than LM value

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Simulation of HBT Junction Temperature vs.
Buffer Layer Thermal Conductivity
UCSB
Young-Min Kim

• Power density 250 kW/cm2
• 0.4 ?m x 7.5 ?m emitter device
• 1.2 ?m x 8 ?m base-collector
• junction device

InAlP
InP
Without metamorphic
AlGaAsSb
InAlAs
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Simulated HBT Temp vs. Power Density
UCSB
Young-Min Kim
HBTs for fast logic High speed high power
density40 GHz clock 100 kW/cm287 GHz clock
260 kW/cm2 (UCSB results)
High junction temperature degaded reliability
Need high thermal conductivity buffer layer
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Experimental Measurement of Temperature Rise
UCSB
Young-Min Kim
Temperature rise can be calculated by measuring
and
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Results of Temperature Rise Measurement
UCSB
Young-Min Kim

• Metamorphic InP buffer MHBT Lattice Matched HBT
  
• Similar temperature rise
• Metamorphic InAlP buffer MHBT
• Large temp rise

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Structure of metamorphic M-DHBT
UCSB
Young-Min Kim
Layer Material Doping (cm-3) Thickness (Å)
Emitter Cap In0.53Ga0.47As 2 ? 1019 Si 300
Grade In0.53Ga0.47As/In0.52Al0.48As 2 ? 1019 Si 200
N Emitter InP 1 ? 1019 Si 700
N- Emitter InP 8 ? 1017 Si 500
Grade In0.53Ga0.47As/In0.52Al0.48As 4 ? 1017 Si 280
Base In0.53Ga0.47As 4 ? 1019 Be 300
Set back In0.53Ga0.47As 2 ? 1016 Si 300
Grade In0.53Ga0.47As/In0.52Al0.48As 2 ? 1016 Si 240
Delta Doping InP 3.6 ? 1018 Si 30
Collector InP 2? 1016 Si 1430
Sub collector In0.53Ga0.47As 1? 1019 Si 250
Sub collector InP 1? 1019 Si 1250
Buffer InP undoped 15000
GaAs (100) semi-insulating substrate GaAs (100) semi-insulating substrate GaAs (100) semi-insulating substrate GaAs (100) semi-insulating substrate

• 300 ? base with 50 meV bandgap grading
• 300 ? setback layer between base and
  collector grade
• 2000 ? collector
• 1.5 µm InP metamorphic layer grown at 470oC

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InP/InGaAs/InP Metamorphic DHBTon GaAs substrate
UCSB
Young-Min Kim
Growth 300 Å base, 2000 Å collector
GaAs substrate InP metamorphic buffer
layer (high thermal conductivity) Processing
conventional mesa HBT narrow 1.2 um base
mesa, 0.4 um emitter Results 200 GHz ft, 200
GHz fmax, 6 Volt BVCEO, b27
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UCSB
Gummel characteristics and leakage
Young-Min Kim
Small area MHBT 1.2??m x 8 ?m B-C junction
Small area LMHBT 1.2??m x 8 ?m B-C junction

• , MHBT gt , LMHBT
• However, acceptable level for most circuit
  applications

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f?,fmax vs. current density at different VCE
UCSB
Young-Min Kim
450 kA/cm2 Kirk threshhold at VCE1.5 V
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Metamorphic InP/InGaAs/InP DHBTs grown on GaAs
Substrates
Motivation breakage, available diameters,
cost of InP substrates InP HBT processes
1.51 more expensive than GaAs
mostly due to material cost M-HBT will
facilitate industry transition from GaAs to InP
HBT Buffer Layers Several investigated
InAlAs, AlGaAsSb, InAlP, InP only InP shows
acceptable thermal conductivity ( high speed
high power density) Present Results
Acceptable level of leakage current (54 nA)
Record metamorphic HBT bandwidth 200 GHz f?,
200 GHz fmax Low operating junction
temperature with InP metamorphic buffer
Reliability test is needed