Large-Signal Modeling of GaN HEMTs for Linear Power Amplifier

151 Pages·2008·4.23 MB·English

Endalkachew Shewarega Mengistu

Large-Signal Modeling of GaN HEMTs for
Linear Power Amplifier Design
This work has been accepted by the faculty of electrical engineering / computer science of the University of
Kassel as a thesis for acquiring the academic degree of Doktor der Ingenieurwissenschaften (Dr.-Ing.).

Supervisor: Prof. Dr.-Ing. G. Kompa
Co-Supervisor: Prof. Dr. H. Hillmer

Defense day: 25th January 2008

Bibliographic information published by Deutsche Nationalbibliothek
The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie;
detailed bibliographic data is available in the Internet at http://dnb.d-nb.de.

Zugl.: Kassel, Univ., Diss. 2008
ISBN: 978-3-89958-381-6
URN: urn:nbn:de:0002-3816

© 2008, kassel university press GmbH, Kassel
www.upress.uni-kassel.de

Printed by: Unidruckerei, University of Kassel
Printed in Germany
Dedicated to the memory of my father

Acknowledgments

I wish to express my special gratitude to my research advisor Prof. Dr.-Ing.
G. Kompa, head of the Department of High Frequency Engineering, Kassel
University, for giving me the chance to work in different research projects
in the past four years. I am very grateful for his continuous support and
encouragement in the course of this work. My thanks also goes to our
industry research partners for their cooperation by providing devices and
some of the measurement data.
I am very grateful to Prof. Dr. H. Hillmer for his time in accepting the task
of second examiner of this dissertation. In addition, I would also like to
thank the members of the examination committee Prof. Dr.-Ing. J. Börcsök
and Prof. Dr. K.-J. Langenberg for accepting to sit in the commission at a
short notice.
I am thankful to all members of the Department of High Frequency
Engineering for their support and teamwork spirit. My gratitude goes to
Dr.-Ing. B. Bunz, Dipl.-Ing. J. Weide, Mrs. H. Nauditt, Mr. A. Zena
Markos, Mr. S. Embar, Mr. B. Wittwer, and all others who I did not
mention by name. I want to thank them all for their encouragement and
comforting help.

Endalkachew Shewarega Mengistu
Dec. 2007
Contents

Chapter 1: Introduction 1
1.1 State-of-the-Art Power HEMTs ……………………………….… 2
1.2 Need for Large-Signal Model ……………………………….… 3
Chapter 2: AlGaN/GaN HEMTs 7
2.1 HEMT Structure and Processing ………………………………..… 10
2.1.1 Substrates ………………………………..… 11
2.1.2 Piezoelectric and Spontaneous Polarizations ………..… 11
2.1.3 Epitaxy and Device Fabrication …………………….….… 12
2.1.3.1 Epitaxy ………………………………..… 13
2.1.3.2 Device Fabrication ……………………………….… 15
2.1.3.3 Technology Related Problems .……………….… 17
2.2 Key Power FET Parameters ………………………………..… 18
Chapter 3: Bias-Dependent Linear AlGaN/GaN HEMTs Model 25
3.1 S-Parameter Measurements ………………………… 26
3.2 Electrical Equivalent Circuit Model ……………………………… 28
3.3 Extraction of Extrinsic Parameters …………………………….… 29
3.3.1 Optimizer Based Data Fitting Techniques ………………… 30
3.3.2 Analytical Method ………………………………… 30
3.4 Standard Equivalent Circuit Model
3.4.1 Extrinsic Parameters ………………………………..… 31
3.4.2 Intrinsic Parameters ……………………………..…… 39
3.5 Modified Procedure for Extraction of Extrinsic Elements ………… 42
3.5.1 Improved Parasitic Network ……………………….…. 44
3.6 Small-Signal Model Verification ……………………….…. 50
3.7 Nonlinear Voltage Referencing ………………………..… 52
Chapter 4: Large-Signal Modeling of Power FETs 53
4.1 Data Bases for Large-Signal Model …………………………… 53
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4.2 Large-Signal Models for IMD Prediction …………………………… 55
4.3 Top-Down Modeling …………………………… 60
4.4 Device Characterization …………………………… 66
4.4.1 Pulsed DC Measurement …………………………… 69
4.4.1.1 System Requirements …………………………… 70
4.4.1.2 External Temperature Controller …………………… 71
4.4.1.3 Characterization of Dispersion Effects …………… 72
4.4.1.4 Trapping Effects …………………………… 73
4.4.1.5 Thermal Effects …………………………… 77
4.4.2 Transients …………………………… 78
4.4.3 Characterization of High Power HEMTs …………………… 83
Chapter 5: AlGaN/GaN HEMTs Large-Signal Modeling 85
5.1 Nonlinear Charge Modeling …………………………… 86
5.2 Drain Current Models Based on DC I(V) and S-Parameters …… 88
5.3 Data Bases for Dispersive Large-Signal Models …………………… 89
5.3.1 Drain Current Models Based on Pulsed I(V) Measurements …. 92
5.3.2 Diode Current Models …………………………… 98
5.3.3 Thermal Modeling of AlGaN/GaN HEMT Structures …… 100
5.3.3.1 Thermal Resistance …………………………… 104
5.4 Large-Signal Model Equivalent Circuit …………………………… 107
5.4.1 Model Implementation …………………………… 108
5.4.2 Model Verification …………………………… 110
5.4.2.1 Static and Pulsed I(V) Characteristics ..………...….. 111
5.4.2.2 S-Parameters ……………………..…….… 113
5.4.2.3 Large-Signal Waveforms ……………………… … 113
5.4.2.4 Intermodulation Distortion …………………. 115
Chapter 6: Conclusion and Future Work 119
6.1 Key Research Results …………………………… 119
6.2 Future Characterization and Modeling of Power FETs ……………… 122
A. Pulsed DC System Test ………………………………………….… 125
B. Device Stability in Pulsed I(V) Measurements ..…………………… 129
References 131
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List of Symbols

BV Gate-drain breakdown voltage V
gd
C Drain-source capacitance F
ds
C Gate-drain capacitance F
gd
C , C Gate-source and gate-drain capacitance of a ‘cold- F
gs0 gd0
FET’ biased below pinchoff
C Gate-source capacitance F
gs
C Parasitic drain-source pad capacitance F
pda
C Drain-source inter-electrode capacitance F
pdi
C Parasitic gate-source pad capacitance F
pga
C Gate-source inter-electrode capacitance F
pgi
C Thermal capacitance s·W/K
th
e Electron charge (1.602x10-19C) C
E Electric field V/cm
E Fermi level eV
F
E Bottom edge of conduction band eV
C
f Current gain cutoff frequency Hz
T
f Power gain cutoff frequency Hz
max
f Function modeling traps associated with deep-level A/V
D
f Function modeling traps associated with surface state A/V
G
f Function modeling thermal effects A/K
θ
G , G Differential gate-source diode conductance S
fs gs
G , G Differential gate-drain diode conductance S
fd gd
G Channel transconductance S
m
G Drain-to-source conductance S
ds
i , i Pulsed DC gate-source and drain-source current A
GS DS
I , I Static DC gate-source and drain-source current A
GS DS
I Maximum drain-source current (gate-forward bias) A
max
I Saturated drain-source current (zero gate bias voltage) A
dss
iISO Isothermal drain source DC current A
DS
IISO Static DC drain-source current A
DS
L Gate length µm
G
L Drain-source spacing µm
DS
L Gate-source spacing µm
GS
L Gate-drain spacing µm
GD
L , L , L Gate, drain, and source inductance Η
g d s
n Sheet charge concentration (σ/e) cm-2
S
P Output power at Fundamental frequency W
out
P RF input power W
in
P DC input power W
DC
PAE Power Added Efficiency, %
P Instantaneous dissipated power W
diss
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P , P Average dissipated power W
diss0 0
P Spontaneous polarization induced charge density C/cm2
SP
P Piezoelectric polarization induced charge density C/cm2
PE
Q Gate-source charge C
gs
Q Gate-drain charge C
gd
R Thermal resistance K/W
th
R , R , R Gate, drain, and source resistance Ω
g d s
R Gate-source charging resistance Ω
i
R Channel resistance Ω
c
R Gate-drain charging resistance Ω
gd
s Gate-pitch (gate-to-gate spacing) µm
S Scattering parameters
ij
T Ambient temperature K
0
T Chuck (back-plate) temperature K
c
T Channel temperature K
ch
Te Estimated channel temperature K
ch
v Saturation velocity cm/s
s
v , v Pulsed DC gate-source and drain-source voltage V
GS DS
V , V Bias gate-source and drain-source voltage V
GS0 DS0
V , V Terminal gate-source and drain-source voltage V
GS DS
V , V Intrinsic gate-source and drain-source voltage V
gs ds
V Pinchoff gate-source voltage V
P
W Gate width µm
G
Y Small-signal admittance parameters S
ij
Z , Z , Z Intrinsic gate, drain, and source branch impedance Ω
g d s
Z Small-signal impedance parameters Ω
ij

∆T Change in channel temperature K
ch
∆Te Change in channel temperature, estimated K
ch
ε Relative dielectric permittivity
r
η Drain Efficiency %
d
κ Thermal conductivity W/cm·K
µ Electron mobility cm2/V·s
σ Sheet charge density C/cm2
τ Transit delay time s
φ Barrier height V
B

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List of Abbreviations and Acronyms

2-DEG Two-Dimensional Electron Gas
3G Third Generation
ACPR Adjacent Channel Power Ratio
ADC Analog-to-Digital Converter
ADS® Advanced Design System
BTS Base Transceiver Station
CAD Computer Aided Design
CCDF Complementary Cumulative Distribution Function
CW Continuous Wave
DAC Data Access Component
DC Direct Current
DiVA Dynamic I(V) Analyzer
DPD Digital Predistortion
EEC Electrical Equivalent Circuit
EER Envelope Elimination and Restoration
EVM Error Vector Magnitude
FET Field Effect Transistor
HPA High Power Amplifier
HEMT High Electron Mobility Transistor
HFET Heterojunction FET
HBT Heterojunction Bipolar Transistor
IMD Intermodulation Distortion
LDMOS Laterally Diffused MOS
LUT Look-up Table
MBE Molecular Beam Epitaxy
MESFET MEtal-Semiconductor FET
MOCVD Metal-Organic Chemical Vapor Deposition
MOS Metal-Oxide-Semiconductor
MSG Maximum Stable Gain
PAE Power Added Efficiency
PAR Peak-to-Average Ratio
RF Radio Frequency
SDD Symbolically Defined Device
SFP Source Filed Plate
TEC Thermal Expansion Coefficient
UMTS Universal Mobile Telecommunications System
VNA Vector Signal Analyzer
W-CDMA Wideband Code Division Multiple Access
WiMAX Worldwide Interoperability for Microwave Access
(Based on IEEE 802.16 Standard)
WirelessMAN Wireless Metropolitan Area Network
(Official Name for IEEE 802.16)

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