Low Leakage and High Speed InPIn0.53Ga0.47AsInP Metamorphic Double Heterojunction Bipolar Transistor

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Low Leakage and High Speed InP/In0.53Ga0.47As/InP
Metamorphic Double Heterojunction Bipolar
Transistors on GaAs Substrates

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

ymkim_at_sandia.gov 505-284-1625, 309-401-9210 fax
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• Introduction
• Morphology
• Thermal property
• DC rf performance
• Leakage current
• Summary

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Introduction
 
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Technical Objective
Develop InP-based HBTs for Naval Radar/Comms ICs
better device bandwidth breakdown than GaAs or
Si bipolar transistors microwave ADCs, DACs,
digital frequency synthesis
Develop InP HBTs on GaAs substrates for better
cost yield
low cost, high volume processing wafer size is
critical compatibility with Silicon process
tools compatibility with process tools in
existing GaAs HBT process lines 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
Requirements for metamorphic HBTs Low
substrate leakage, low junction leakage, low
material roughness high reliability, high
performance, IC demonstration
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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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UCSB
What are the potential problems ?
Young-Min Kim
Leakage current through threading dislocation
Reliability (?)
High speed ft , fmax
Thick buffer layerpoor thermal conductivity
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Morphology
 
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Morphology of metamorphic layer
UCSB
Young-Min Kim
AlGaAsSb
InAlAs
5 ?m
5 ?m
rms 11.7 nm
rms 4.0 nm
InP
InAlP
rms 5 nm
rms 5.2 nm
5 ?m
5 ?m
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RHEED of metamorphic layer
UCSB
Young-Min Kim
AlGaAsSb
InAlAs
InP
InAlP
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Vertical TEM image of InP metamorphic buffer HBT
DHBT structure
AlAs current blocking layer
InP metamorphic buffer
1?m
defect density drops after 1mm buffer layer
thickness Threading dislocation density of
m-buffer 107/cm2
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Thermal Property
 
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Device Junction Temperature Calculation
UCSB
Young-Min Kim
1000 µm
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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DC rf performance
 
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Structure of metamorphic M-DHBT
UCSB
Young-Min Kim

• 300 ? base with carbon doping grading
• 200 ? setback layer between base and
• collector grade
• 2170 ? 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, 8e19/cm3 5e19/cm3
carbon graded doping 2170 Å collector
200 Å setback GaAs substrate InP
metamorphic buffer layer (high thermal
conductivity) Processing conventional mesa
HBT 2.7 µm base mesa, 0.7 µm emitter
Base ohmic change Ti/Pt/Au ?
Pd/Ti/Pd/Au Results 216 GHz ft, 284 GHz
fmax, 5 Volt BVCEO, b21
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f?,fmax vs. current density at different VCE
UCSB
Young-Min Kim
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Leakage Current
 
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Gummel characteristics and leakage
 
UCSB
Large area LMHBT 100??m x 130 ?m B-C junction
Large area MHBT 100??m x 130 ?m B-C junction
IC
IC
VCB 0.3 V
VCB 0.3 V
IB
IB

• , MHBT ? 20 x , LMHBT
• Leakage current ? bulk

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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
IC
IC
VCB 0.3 V
VCB 0.3 V
IB
IB

• , MHBT ? , LMHBT
• metal pad on SiNx

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Summary
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 Leakage
current (1 nA) comparable to LMHBT
Record metamorphic HBT bandwidth 216 GHz f?, 284
GHz fmax Low operating junction temperature
with InP metamorphic buffer Future Work
Reliability test is needed IC demonstration