study on reducing thermal properties of m-dhbt

Metamorphic HBT MDCL EE SNU

Study on Reducing Thermal Study on Reducing Thermal Properties of M-DHBT Properties of M-DHBT

2005. 6. 16 설경선


INDEX

Introduction– Trend– Overview of HBT– Overview of Double HBT– Overview of Metamorphic HBT

Key issues of M-HBT (Self-Heating) Thermal resistance comparison

– M-HBT vs InP L-HBT– M-HBT with graded InAlP buffer vs InP buffer– Thermal resistance of InP-Based MHBT on GaAs subs using grade Inx

Ga1-xP Conclusion Reference


Introduction (Trend)

Trend for GaAs Semiconductors in Handsets– Demand on GaAs is driven by handset industry– Power amp / switch / small signal amp– GaAs covers 90% of Power amp market

Fig. PA market share estimate by semiconductortechnology for 2004 (source: RFMD)

WHY?

– Demand for high efficiency / output power at low(3V) supply voltage HBT / MESFET amp

– HBT : require single polarity power supply• Better amplifier linearity


Introduction (Overview of HBT)

Merits– Wide bandgap emitter high base dopping base resistance↓, devic

e speed↑

– Low emitter-base turn on voltage reduce in power consumption

– Electron transit time (factor of epitaxial growth, not lithography)

– Entire emitter area conducts current flow high current handling per unit area

– Low 1/f noise


Introduction (Double HBT)

Double Heterojunction (increased collector bandgap)– Suppress in hole injection into base from collector (when B-C junction for

ward biased)– Diminish in charge storage in saturation– Speed up device turn-off from saturation region– Symmetrical (circuit flexibility)

Fig. Energy-bandgap diagram of DHBT

– Increase in BV– Reduction in leakage

current


Overview of Metamorphic HBT

InP based HBT– Superior material transport properties (>SiGe, GaAs)– ft / fmax / Je

– Higher Thermal conductivity : GaAs(0.55W/cm-℃), InP(0.68W/cm-℃)– Problem : Cost, mechanical property (fragile)

Metamorphic HBT grown on GaAs substrate– GaAs substrate + InP HBT Epitaxy– Use of Buffer – ( ex) InAlAs / InAlP / InP / AlGaAsSb)

Metamorphic

low cost Good performance


Key issues of HBT (Self-Heating).

Self-Heating effect– Negative slope : due to self heating increase in IB & IC(Δ IB > Δ IC)– Negative resistance effect becomes significant when power dissipatio

n is large

Fig. IC vs VCE


Thermal resistance comparison 1.

Comparison of M-HBT & InP L-HBT

Layer structure of MHBT on GaAs

InGaAs 200nm n-type 2E19InAlAs 250nm n-type 5E18

InAlAs 100nm n-type 4E17

InGaAs 50nm p-type 4E19

InGaAs 40nm n-type 1E16


InP 7nm n-type 1E18InP 390nm n-type 1E16

InP 550nm n-type 8E18


Metamorphic Buffer InxAl1-xAsGaAs S.I Substrate

Layer structure of InP LHBT

InGaAs 200nm n-type 2E19InAlAs 250nm n-type 5E18

InAlAs 100nm n-type 4E17




InP 7nm n-type 1E18InP 390nm n-type 1E16

InP Substrate




Common emitter I-V

VBE vs VCE at 50℃

MHBT show

-Slightly lower offset voltage

-Relatively lower current gain

-Higher thermal resistanceRth at range of 30~150℃



Comparison of M-DHBT with graded InAlP buffer & InP– High speed DHBT must operate at Emitter power density exceeding 2

50 kW/cm2

– Thermal resistance is critically dependent of subcollector / buffer / substrate

– Why InAlP : Thermally advantageous relative to InAlAs buffer

– Why InP : comparable thermal conductivity to InP-LHBT



Comparison of M-HBT with graded InAlP buffer & InP

upper buffer thermal conductivity is more important (heat flux spread)

InxAl1-xP(x=1 at upper buffer, x=0.5 at lower buffer)advantageous relative to AlGaAsSb & InAlAs buffer (InAs-AlAs & AlGaAs-AlGaSb : upper buffer has low thermal conductivity)



Layer structure of MDHBT

DC parameter of InP & InAlP buffer layer

Temperature rise at 7.5mW disspation bias



Thermal resistance of InP-Based MHBT on GaAs subs using grade InxGa1-xP– Problem of direct growth of InP on GaAs subs :

• high surface roughness / defect density of buffer layer

Graded InxGa1-xP buffer• Upper buffer(x=1, InP) (0.68W/cm-K)• In0.5Ga0.5P(~0.16W/cm-K) > In0.53Ga0.47As(0.044W/cm-K)



Layer structure of MDHBT

DC parameter of InP & InAlP buffer layer



Common emitter I-V

VBE vs VCE at 50℃

Rth at range of 30~150℃


Conclusion

A: LHBT

B: MHBT with InGaP buffer

C: MHBT with InAlAs buffer

– InP buffer : advantageous reduction on thermal resistance

– InGaP buffer : improve in material quality


Reference

On the Thermal Resistance of Metamorphic and Lattice-Matched InP HBTs: A Comparative Study Hong Wang, Hong Yang, K. Radhakrishnan and Chee Leong Tan

Thermal Properties of Metamorphic Buffer Materials for Growth of InP Double Heterojunction Bipolar Transistors on GaAs Substrates Y. M. Kim, M. Dahlstrom, M. J. W. Rodwell, and A. C. Gossard 2003

Thermal stability of current gain in InGaP/GaAsSb/GaAs double-heterojunction bipolar ransistors B. P. Yan, C. C. Hsu, X. Q. Wang, and E. S. Yang 2004

Thermal Resistance of Metamorphic InP-Based HBTs on GaAs Substrates Using a Linearly Graded InxGa1 xP Metamorphic Buffer Hong Yang, Hong Wang, Member, IEEE, K. Radhakrishnan, Member, IEEE, and Chee Leong Tan 2004

Trends and Opportunities for Gallium Arsenide Semiconductors in Handsets Paul J. Augustine

Low Leakage and High Speed InP/In0.53Ga0.47As/InP Metamorphic HBT on GaAs substrate Y.M.Kim, M.J.W. Rodwell, A.C. Gossard

InGaAs-InP Metamorphic DHBTs Grown on GaAs With Lattice-Matched Device Performance and ft, fmax >268Ghz Zach Griffith, YoungMin Kim, Mattias Dahlstrom 2004

study on reducing thermal properties of m-dhbt

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