mvsg model for rf applications: thermal, scalability and...
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MVSG Model for RF Applications: Thermal,
Scalability and Parasitic Modeling
Xuesong Chen1, Ujwal R Krishna2 and Lan Wei1
1. University of Waterloo (CA)
2. Texas Instruments Inc. (USA)
RF-Electronic Design Using III-V Semiconductors
2
Vehicular Communication Using GaN-Electronics
IEEE802.11P for real time traffic management
V2V wireless communication with 9000 intelligent vehicles, U-M Transportation research institute and U.S. DoT, 2012
▪ Wireless access in vehicular environments (WAVE)
▪ Licensed ITS band (5.85-5.925 GHz) and range of up to 300 m
▪ Smaller and efficient systems: Integration in mobile phones (V2V, V2H)
3
Communication Using Cellphones
GaN: Form factor, efficiency and output power
From ‘iFixit iPhone 7 teardown’ Bottleneck of
form-factor & power
consumption
Better power density and
efficiency than CMOS
4
From Physics-Modeling to Industry Standard
MVSG model chosen as GaN industry standard model
Phase-I
▪ 8 candidates
▪ Accuracy
▪ Convergence
▪ Physical nature
Phase-II
▪ 4 candidates
▪ Sponsors:
▪ ADI, TI, Toshiba
▪ Data: Triquint, Toshiba
Phase-III
▪ 2 candidates
▪ Model evaluation
▪ Feedback
Phase-IV
▪ Model support
▪ Version release
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GaN HEMT: Carrier Transport
Intrinsic
transistorDrain access
region
Source access
region
Al0.26Ga0.74N (18 nm)
G
GaN 1.2μm
GaN (3 nm)S D
RF-GaN HEMT HV-GaN HEMT
DD transport DD transportDD transport 6
MVSG Model: Device Currents
( )Vsat
dinvsinv
satD FQQ
vWI2
/,, +
=
VS point
xxo0 Lg
Source and drain
end chargeSaturation velocity
vDi
2DEG2DEG
LeffvSi
Qinv,dQinv,s
Function for transition from
short to long gate lengths
▪ Charge-based model
▪ Source/Drain symmetry ensured
▪ DD-to-ballistic transport covered
7
MVSG Model: Gate-Length Scaling
▪ 40nm RF-devices
▪ Device physics: SCE, DIBL, Access regions
▪ Quasi-ballistic transport
▪ 1 mm HV-devices
▪ Full region of operation
8
MVSG Model: Width Scaling
Model captures width-scalability for large devices
0.75 mm 1 mm 2 mm▪ Wide devices
:RF-PAs and HV-FETs
▪ Simple scaling
: Rth scaling
: Cof scaling
: Qinv scaling
▪ W/Ngf effects similar
9
MVSG Model: High-Frequency Modeling
Large signal estimations do not require any fitting
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MVSG Model: S-parameter Scaling
Model captures width-scalability for large devices
0.75 mm 1 mm 2 mm▪ High-frequency behavior
against large-W devices
▪ Simple scaling
: Rth scaling
: Cof scaing
: Qinv scaling
▪ W/Ngf effects similar
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▪ Thermal and shot noise sources added to the model
▪ Compared with on-wafer RF noise measurements at 6 GHz
- IEDM 2014
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MVSG Model: RF Noise Model
▪ Thermal and shot noise sources added to the model
▪ Compared with on-wafer RF noise measurements at 6 GHz
- IEDM 2014
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MVSG Model: RF Noise Model
IEEE802.11P: First Fully Integrated GaN RF-front-end
PA SW LNA
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MVSG Model: RF-Circuit Level Validation
PA: Psat=28.8 dBm, PAE=50% LNA: NF=3 dB, OIP3= 22 dBm
Transmitter PA Receiver LNA
Enabling RF-circuit design through dedicated physics-modeling
MIT virtual source GaNFET-RF compact model for GaN HEMTs: From device physics to RF frontend circuit design and validation- U. Radhakrishna, P. Choi, S. Goswami, LS. Peh, T. Palacios, D. Antoniadis, 2014 IEEE IEDM.
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▪ Additional parameters:
Thermal effect
Carrier velocity
Effective mobility
Thermal effect
Electrostatic parameters
Thermal effect
MVSG Model: Thermal modeling
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▪ Model calibrated against two T
▪ Temp-cos extracted
▪ Captures 2 other T
▪ Self-heating removed: pulsed IV
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MVSG Model: Thermal modeling
Self-heating: Bias Dependence
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Channel temp. using
electrical methods
Raman spectroscopy
at same power dissipation
G D
• Channel temperature (Teq) by electrical methods
show little bias dependence.
• Thermal measurements show bias
dependence (Same Pdiss, different Vg, Vd,
→ different T profile).
J. Joh, et al “Measurement of channel temperature in GaN high-electron mobility transistors,” IEEE Trans. Electron Devices, vol. 56, no. 12, pp. 2895–2901, 2009.S. Choi, et al, “The Impact of Bias Conditions on Self-Heating in AlGaN/GaN HEMTs,” IEEE Trans. Electron Devices, vol. 60, no. 1, pp. 159–162, Jan. 2013.
GaN HEMT Self-heating: Which Temperature?
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Electrostatic Potential (V)
Heat Density (W/cm-3) Lateral Electric Field (V/cm)
Lattice Temperature (K)
GS D
Lattice Temperature
Vg = 0 V, Vd = 10 V
Channel Voltage
Heat Density Electric Field
H EJ=
Vg are from 2 V to -2 V,
with an interval of 1V.
Heat generation in the channel is highly
non-uniform. Which temperature
determines the current degradation?
Self-heating: Equivalent Channel Temperature
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Equivalent Channel
Temperature
Dashed lines: Id w/o self-heating
at 300, 350, 400, 450 K
Blue line: Id with
self-heating
Vg = 0 V
eqT
Channel Temp.
Profile
G
8 W/mmP =
Equivalent channel temperature Teq:
interpolation of electro-thermal current
from single-T currents
For short-gate RF HEMTs,
Teq lies in the source access region.
X. Chen, S. Boumaiza and L. Wei, "Self-Heating and Equivalent Channel Temperature in Short Gate Length GaN HEMTs," in IEEE Transactions on Electron Devices, vol. 66, no. 9, pp. 3748-3755, Sept. 2019.
Self-heating: Equivalent Channel Temperature
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(a) Lateral Electric Field
(b) Electron Mobility
(c) Electron Velocity
G
Vg = 0 V, Vd = 10 V
G
G
Low-field region High-field region
Ids vs. Vgs_extrinsic
Ids vs. Vgs_intrinsic
Vds = 10 V
Temperature affects the low-field region (through mobility)
much more than the high-field region (through saturation velocity)
Vg - Vsi Vg - Vs
300 ~ 500 K
Self-heating: Teq in HV HEMTs
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G
G
G
(a) Lateral Electric Field
(b) Electron Mobility
(c) Electron Velocity
Low-field region High-field region
10 W/mmP =
eqT
Channel Temp.
Profile
G
For HV FETs with longer Lg: bigger part of
the gated channel is also low-field.
For long-gate HV HEMTs,
Teq lies around the source-side gate edge.
Summary
▪ MVSG model as a design tool for both device and circuit design
▪ MVSG model captures: DC, small and large-signal AC, noise, thermal
▪ Verified against various fabricated device data
▪ RF-circuit design validation using commercial foundry process
▪ Studied GaN HEMT self-heating mechanisms
▪ Explained difference between “electrical” temperature and “physical” temperature
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