1. Small- and Large-Signal Modeling for Submicron InP/InGaAs DHBT’s‘
Tom K. Johansen*, Virginie Nodjiadjim**, Jean-Yves Dupuy**, Agnieszka konczykowska**
*DTU Electrical Engineering,
Electromagnetic Systems Group,
Technical University of Denmark
DK-2800 Kgs. Lyngby
Denmark
**III-V Lab,
F Marcoussis
France

2. Outline The ”InP/InGaAs DHBT” device
Specific modeling issues for III-V HBT devices:
-The integral charge control relation (ICCR) for HBT modelling
-Charge and transit-time modelling in III-V HBT devices
-Temperature effects and self-heating
Small-signal modellng: Direct parameter extraction
Scalable large-signal model verification
Summary 2

3. The ”InP/InGaAs DHBT” Device
The introduction of an wide-gap emitter and collector to form a
Double Heterojunction Bipolar Transistor (DHBT) offers several
advantages over Homojunction Bipolar Transistors:
- Higher fT and fmax characteristic
- increased breakdown voltage
- better performance under saturation operation
Indicated in red are the 1.5µm and
0.7µm InP/InGaAs DHBT technologies
developed at the III-V Lab.

4. The ”InP/InGaAs DHBT” Device
InP/InGaAs DHBT allows simultaneously high output power and
high frequency:
- mm-Wave power amplifiers
- VCOs for PLLs
- Electronic laser drivers and transimpedance amplifiers for
ultra-high bit rate optoelectronics (>100Gbit/s operation)
III-V Lab’s 0.7µm InP/InGaAs DHBT:
Emitter
Base plug
Collector

5. InP DHBT Frequency Performance
Geometrical parameters:
Frequency characteristic:
Device
Lein [um]
Ae [um2]
Ac [um2]
T5B3H7
5.0
2.7
8.6
T7B3H7
7.0
3.9
10.9
T10B3H7
10.0
5.7
14.3
An InP DHBT large-signal model must
predict the frequency characteristic
dependence on bias and on geometry

6. HBT large-signal model topology
Circuit diagram of HBT model:
Agilent ADS SDD implementation:
The large-signal topology is nearly identical for the various HBT models
(UCSD HBT model, Agilent HBT model, FBH HBT model)

7. The integral charge control relation
DC model of bipolar transistor:
1D BJT cross-section:
Base Current
Reverse
Operation
Base Current
Forward
Operation
Net Transport
Current
Hole
concentraction
The transport current in a npn transistor
depends directly on the hole charge!

8. The Gummel-Poon model for BJTs
Gummel-Poon model formulation:
Normalized base charge:

9. Extended GP model for HBTs
Energy band diagram for abrupt DHBT:
HBT modeling approach:
≈1 in HBTs
In an abrupt DHBT additional transport mechanisms such as
thermionic emission over the barrier and tunneling through it
tend to drag the ideality factor away from unity (NF>1).
The collector blocking leads to earlier saturation at high collector
voltages (the so-called ”soft knee” effect)

10. Forward Gummel-plot for InP DHBT device
Nf=1.14
Base current in UCSD HBT model:

11. Forward Gummel-plot for InP DHBT device
Nf=1.14
Base current in Agilent HBT model:

12. Charge modeling in III-V HBT
In any transistor a change in bias requires charge movement which
takes time:
- built up depletion layers in the device
- redistribution of minority carriers
AC model of bipolar transistor:
Total emitter-collector delay:
Diffusion charge partitionen with Fex

13. Transit time formulation
Analytical transit-times:
Velocity-field diagram for InP:
Base thickness
(assumed constant)
(varies with bias)
Collector thickness
Velocity modulation effects in collector:
Collector transit-time c increase with electrical field
Collector transit-time c decrease with current due to modulation of
the electrical field with the electron charge (velocity profile modulation)
Intrinsic base-collector capacitance Cbci decrease with current

14. Transit time formulation: Full depletion
Collector transit-time model:
Slowness of electrons in InP:
Base-collector capacitance model:
Formulation used in UCSD HBT model

15. Inclusion of self-heating
Self-Heating formulation:
Thermal network
The thermal network provides an 1.order estimate of the temperture
rise (delT) in the device with dissipated power (Ith).

16. InP HBT self-heating characteristic
Self-heating in HBT devices manifests itself with the downward sloping
Ic-Vce characteristic for fixed Ib levels.

17. Small-signal modeling

18. Resistance Extraction: Standard method
Open-Collector Method:
HBT base current flow:
Rbx underestimated due to shunting
effect from forward biased external
base-collector diode!
Saturated HBT device:
Re overestimated due to the intrinsic
collector resistance!
Standard method only good for Rcx extraction

19. Emitter resistance extraction
Forward biased HBT device:
Notice: Rbi extracted assuming
uncorrected Re value.
Re can be accurately determined if correction is employed

20. Extrinsic base resistance extraction (I)
Circuit diagram of HBT model:
Distributed base lumped into a few elements
The bias dependent intrinsic base resistance Rbi describes the active region under the emitter
The extrinsic base resistance Rbx describes the accumulative resistance going from the base contact to the active region
Correct extraction of the extrinsic base resistance is important as it
influence the distribution of the base-collector capacitance
fmax modeling!

21. Extrinsic base resistance extraction (II)
Base-collector capacitance model:
Linearization of capacitance:
K1=0.35ps/V
Ae=4.7m2
Wc=0.13m
Low current linear approximation:
Physical model
Characteristic
current
Linear approx.
Linear approximation only valid at very low collector currents.

22. Extrinsic base resistance extraction (III)
Base-collector splitting factor:
Linearization of splitting factor:
K1=0.35ps/V
Ae=4.7m2
Wc=0.13m
X0=0.41
Physical model
Zero-bias splitting factor:
Linear approx.
Base collector splitting factor follows linear trend to higher currents.

23. Extrinsic base resistance extraction (IV)
Improved extraction method:
Effective base resistance model:
Rbx extraction method:
Extrinsic base resistance estimated from extrapolation in full depletion.

24. Intrinsic base resistance extraction
Improved Semi-impedance circle method:
(Rbx, Re, Rcx de-embedded)
Rbi in InP DHBT devices is fairly
constant versus base current

25. Base-collector capacitance extraction
Base-collector capacitance modelling:
Model parameters:
Base-collector capacitance extraction

26. Intrinsic element extraction
Intrinsic hybrid-pi equivalent circuit
The influence from the elements Rbx, Rbi, Re, Rcx, Cbcx, and Cceo are
removed from the device data by de-embedding to get to the intrinsic data.

27. Direct parameter extraction verification
Small-signal equivalent circuit
S-Parameters
Model Parameter
Value
Rbx []
8.0
Cbcx [fF]
10.1
Rbi []
11.1
Cbci [fF]
3.0
Rcx []
2.6
Rbci [k]
56.0
Re []
2.7
gmo [mS]
773
Cbe [fF]
340.8
d [pS] ≈0
Rbe []
34.6
Cceo [fF]
6.8

28. Scalable UCSD HBT model verification

29. Scalable Agilent HBT model verification

30. Large-signal characterization setup
Single-finger device
Load pull measurements not
possible. Load and source
fixed at 50Ω.
Lowest measurement loss at
74.4GHz

31. Large-signal single-tone verification
Measurements versus UCSD HBT model:
The large-signal performance at 74.4GHz of the individual single-finger devices is well predicted with the developed UCSD HBT model except for low collector bias voltage (Vce=1.2V).
mm-wave verification!

32. Large-signal single-tone verification
Measurements versus Agilent HBT model:
The large-signal performance at 74.4GHz of the individual single-finger devices is well predicted with the developed Agilent HBT model. The agreement at lower collector bias voltage is better.
mm-wave verification!

33. Summary The InP/InGaAs DHBT can be modeled accurately by an extended
Gummel-Poon formulation
- thermionic emission and tunneling
- collector blocking effect
- collector transit-time physical modeling
Small-signal InP/InGaAs HBT modeling
-unique direct parameter extraction approach
Scalable large-signal HBT model verfication
-RF figure-of-merits and DC characteristics
-mm-wave large-signal verification