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

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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)

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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

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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

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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

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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

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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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