Méthodes avancées de caractérisation et de modélisation des transistors HEMT GaN

Jean‐Christophe NALLATAMBY , Julien COUVIDAT, Sylvain LAURENT,Raphaël SOMMET, Michel PRIGENT & Raymond QUERE

XLIM, CNRS‐Université de Limoges

21‐22 mars 2018

INTRODUCTION

Potential applications for the GaN HEMTS are numerous

- For power amplifier of Radar T/R modules

- For base stations PA

- For multi-tone PA in space applications

- Pulsed, phase/frequency modulated for Radar Systems

- Highly complex signal (OFDM, QAM, ….)

All those applications involve complex modulated signals

2

Key challenges of GaN HEMT Technology

• Deep level states (Traps) in the

bandgap of the material.

• Surface traps could be formed due to

defects or impurities formed at the

surface during crystal growth or in

device fabrication process.

• AlGaN/GaN HEMTs grown on

foreign substrates results in

imperfect crystals with dislocations

or defects.

• These defects cause the formation of

deep level states within the GaN and

AlGaN material.

Consequences of Traps

Gate lag, Drain lag and drain current collapse/ DC

– RF dispersion.

DC – RF dispersion – limits the large signal

performance of the device.

Trapping effects also contributes to dynamic RON,

which affects the power switching applications.

Physical location of traps in the device

3

Different ways for characterization

Trap investigation using :Pulsed I-V characterization: Gate lag and drain lag identification but no information on the dynamics of the trapsLow frequency S-parameters measurementLow frequency noise characterizationDeep level transient spectroscopy (I-DLTS) measurement Large signal characterization (in frequency and time domain)

Parasitic effects still limit the performances of PA : Thermal effectsTrapping effects

All these characteristics should be consistently modeled

4

Gate and Drain-Lag Mechanism

Gate-Lag Drain-Lag

5

Ron & Idss measurements for thermal assessment

Based on a new and simple method proposed by J. Joh and all “Measurement of Channel Temperature in GaN High Electron Mobility Transistors”:

Ron measurement. Idss measurement.

Tools required : Pulsed I(V) Test bench measurement (PIV). (pulse width: 500 ns; duty cycle: 0.05%) Thermal chuck. (variation range: 25 °C to 175 °C)

Thermal Resistance Determination Methodology in 2 steps: Thermal chuck sweep with fixed zero dissipated output power. Dissipated output power sweep with fixed thermal chuck control.

Vds

IdsIdss

Ron=δVds/ δIds

Vgs=0V

6

Ron & Idss measurements for thermal assessmentPulsed I(V) characteristics (VGSi = 0 V) from various quiescent bias points (VGS0 = 0 V, VDS0 = 2-13.5 V) with fixed thermal chuck at 25 °C :

Pulsed I-V characteristics (VGS = 0 V) from zero power quiescent bias point(VDS0 = VGS0 = 0 V) :

Vgs0: gate bias point.

Vds0: drain bias point.

Vdsi: drain pulsed point.

7

Thermal Resistance

0( ) ( )

( ) (0)

ONON ON

ONON diss ON diss

diss

dRR T R T TdT

dRR P R PdP

/ON ON

THdiss diss

dR dRTRP dP dT

y = 0,0323x + 3,5969

y = -0,6888x + 449,79

320

340

360

380

400

420

440

0 50 100 150 200

Ta (°C)

Idss

(mA

)

4

5

6

7

8

9

10

Ron

(Ohm

)Idss

Ron

Linear (Ron)

Linear (Idss)

Baseplate temperature sweep Dissipated power sweep

|| ||

8

320

340

360

380

400

420

440

0 1 2 3 4 5Power dissipation (W)

Idss

(mA

)

44,555,566,577,588,5

Ron

(Ohm

)

Idss Ron

Trapping and Thermal Effects

• Difficult to disassociate trapping and thermal effects, especially at lower operating frequencies.

• Trapping and thermal time constants are almost of the same order.

Positive Pulse

Negative Pulse

Illustration of Trapping and Thermal Effects

Trapping +Thermal

TrappingTj = Tchuck + RTH × Pdiss

Pdiss = VDS× IDS

Power limit

Tchuck =25ºC

9

LF- Y22 Parameter setup

• Study of the output admittance (Y22) Low‐Frequency Y22 analysis at several temperatures

• Output admittance very sensitive to trapping phenomena• Easy extraction of time constant

(Low Frequency S22 measurement [10Hz to 10MHz])

10

Trapping model

The emission constants can be extracted either from peak values of Y22 imaginary part

The number of traps is defined by the number of peaks of the Y22 imaginary part

In Low Frequency Cds is equal to open then

AlGaN/GaN : 8x250 μm

Ids=50mA and Vds=40V @ 100°C

with

11

LF‐ Y22 Parameter (8×75 µm Device)

en – trap emission rate σn – Cross section of traps NC – effective density of electrons in the conduction band Vth – thermal velocity of electrons g – degeneracy factor Ea – Trap activation energy

f , f =

eT

σ Ag exp.

EKT

A . e

Traps Energy Level: Ea = 0.4 eV

FI,peak

• The frequency at the peak of Imag(Y22) gives the emission time constant

• Arrhenius law extraction of activation energy (Ea) and capture cross section (σn)

12

LF Noise Measurement (6×75 μm Device)

_ ∗ ∗

Measurement Setup

Equivalent Circuit

Voltage Amplifier:

eati – Voltage noise source

iati – Current noise source

Zati – Impedance

SV_meas – Measured voltage noise spectral density

Sir – Thermal noise spectral density

Z = Zeq || R

= .

13

LF Noise Measurement (6×75 μm Device)

Ea1 = 0.57 eV; σn = 2.13× 10-16 cm2

Ea2 = 0.51 eV; σn = 4.96× 10-15 cm2

Identified Traps Physical Properties: • Extracted physical properties of traps are inagreement with literature reported data forFe-doped GaN devices.

14

I‐DLTS Test Bench (Vg Pulse)

Bias TeeDC

RF+DCRF

DC SupplyE3641A

Bias TeeDC

RF+DC RF 50 Ω50 Ω

Pulse Generator8114A

DUT

AWGAF3252

TRIGHigh Sampling Scope DPO7054

GPIB

Thermal Chuck

Slow Sampling Scope DPO7054

Gauss Probe

Gauss Probe

• Pulse generator on the gate• DC voltage supply on the drain• Pulses qualified (dc path bandwidth = 20MHz) bias tees• One scope acquires the range 10‐7 to 10‐2 sec, the other for

10‐3 to 102 sec• Sampling first scope=100‐9 sec second scope=1‐6 sec• An AWG is used to generate pulse width and triggered start

point measurement• Probe station with thermal chuck

Example : Vgs_pulse = ‐8VVds0 = 10VId = 50mA/mmTfilling = 10µs, 1ms et 100msTempérature = 25°C, 75°C, 100°C et 125°C

0

0,2

0,4

0,6

0,8

1

1,2

1,0E‐06 1,0E‐05 1,0E‐04 1,0E‐03 1,0E‐02 1,0E‐01 1,0E+00 1,0E+01

Id normalisé

Temps (s)

25°C

50°C

75°C

100°C

125°CTfilling=1ms

AlGaN/GaN 2x100 um

15

Equation of fitting curvefor one temperature :

·

I-DLTS Test Bench (Vd Pulse)

Bias TeeDC

RF+DCRF

DC SupplyE3641A

Bias TeeDC

RF+DC RF 50 Ω50 Ω

Pulse Generator8114A

DUT

AWGAF3252

TRIG

High Sampling Scope DPO7054

GPIB

Thermal Chuck

Slow Sampling Scope DPO7054

Gauss Probe

Gauss Probe

• Pulse generator on the drain• DC voltage supply on the gate• Pulses qualified (dc path bandwidth = 20MHz)

bias tees• One scope acquires the range 10-7 to 10-2 sec, the

other for 10-3 to 102 sec• Sampling first scope=100-9 sec second scope=1-6

sec• An AWG is used to generate pulse width and

triggered start point measurement• Probe station with thermal chuck

Example :Vds_pulse = 20VVds0 = 10VId = 50mA/mmTfilling = 10μs, 1ms et 100msTempérature = 25°C, 75°C, 100°C et 125°C

AlGaN/GaN 2x100 um

0

0,2

0,4

0,6

0,8

1

1,2

1,0E‐06 1,0E‐05 1,0E‐04 1,0E‐03 1,0E‐02 1,0E‐01 1,0E+00 1,0E+01

Id normalisé

Temps (s)

25°C

75°C

100°C

125°C

Tfilling=1ms

16

Equation of fitting curve forone temperature :

·

y = 0,4806x ‐ 11,303

y = 0,2517x ‐ 0,3644

0

1

2

3

4

5

6

7

8

9

27 29 31 33 35 37 39 41

ln(τT²)

1/KT

Trap 1Trap 2Fit (Trap1)Fit (Trap2)

y = 0,4522x ‐ 11,321

0

1

2

3

4

5

6

7

27 29 31 33 35 37 39 41

ln(τT²)

1/KT

Trap 1

Fit (Trap1)

Identification of traps

Ea = 0,4522 eVσ = 1,43E-16 cm²

Ea = 0,2517 eV and 0,4806 eVσ = 2,50E-21 cm² and 1,40E-16 cm²

Vg Pulse

Vd Pulse

17

· ··

·

g = 1 ; T² = 158404 K² Nc = 3,13E18cm‐3 Vth = 2,92E7cm/s

To determine the activation energy Ea and the capture cross‐section σn by using the Arrhenius equation : ·

· ·

· 1

ln · · ln·

With and

Steps of the modeling process

freq (2.000GHz to 40.00GHz)

S(1,

1) ;

S(2,

2)

5 10 15 20 25 300 35

-60

-40

-20

0

20

40

-80

60

freq, GHz

Pha

se (S

(1,2

))

5 10 15 20 25 300 35

-5

0

5

10

15

-10

20

freq, GHz

dB (S

(2,1

))

5 10 15 20 25 300 35

-24

-22

-20

-26

-18

freq, GHz

dB (S

(1,2

))

5 10 15 20 25 300 35

0

50

100

-50

150

freq, GHzPh

ase

(S(2

,1))

10 20 300 40

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.0

0.8

Vds (V)Id

s (A

)

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-5 0 5 10 15 20 25 30 35 40 45 50

Id e

n Am

pere

s

Vds en Volts

8x75 POLAR Vgs=-4.401 V, Vds=+22.97 V, Id =+0.163 A

Vgs=+1.000 VVgs= +0.00nVVgs=-1.000 VVgs=-2.000 VVgs=-3.000 VVgs=-4.000 VVgs=-5.000 VVgs=-6.000 VVgs=-7.000 VVgs=-8.000 V

Idss

y = -0,0024x + 1,6085

1,2

1,25

1,3

1,35

1,4

1,45

1,5

1,55

1,6

0 20 40 60 80 100 120 140 160

Is_gs

0,00E+00

5,00E-15

1,00E-14

1,50E-14

2,00E-14

2,50E-14

3,00E-14

3,50E-14

0 20 40 60 80 100 120 140 160

y= 1,6E-16+1,04973E-16*EXP(T/26,3157)

Cgs_1D

0,00E+00

1,00E-13

2,00E-13

3,00E-13

4,00E-13

5,00E-13

6,00E-13

-10 -8 -6 -4 -2 0 2Vgs

Cgs

(F)

MesureModele

Cgd_1D

0,00E+00

2,00E-14

4,00E-14

6,00E-14

8,00E-14

1,00E-13

1,20E-13

1,40E-13

-60 -50 -40 -30 -20 -10 0Vgd

Cgd

(F)

MesureModele

VdsVgs_int

VgsRfill

Rempty C

k+

+

k

Vds

Vds

VdsVgs_int

VgsRfill

Rempty C

k+

+

k

Vds

Vds

5.40E-02

5.50E-02

5.60E-02

5.70E-02

5.80E-02

5.90E-02

6.00E-02

0.00E+00 2.00E-06 4.00E-06 6.00E-06 8.00E-06 1.00E-0

Modèle petit-signal Modèle I-V Capacités NL Modèle thermique Modèles de pièges

Cgs=f(Vgs)

Cgd=f(Vgd)

Ids=f(Vgs_pièges,Vds,T)

Dgs=f(Vgs)

Dgd=f(Vgd)

Rs=f(T)

Rd=f(T)

Rgd=f(T)

Étapes de modélisation

RgLgCpgLsCpdLdRsRd

RiCdsτGmGdCgsCgdRgd

Ids=f(Vgs,Vds,T)

Dgs=f(Vgs)

Dgd=f(Vgd)Ids=f(Vgs,Vds)

freq (2.000GHz to 40.00GHz)

S(1,

1) ;

S(2,

2)

5 10 15 20 25 300 35

-60

-40

-20

0

20

40

-80

60

freq, GHz

Pha

se (S

(1,2

))

5 10 15 20 25 300 35

-5

0

5

10

15

-10

20

freq, GHz

dB (S

(2,1

))

5 10 15 20 25 300 35

-24

-22

-20

-26

-18

freq, GHz

dB (S

(1,2

))

5 10 15 20 25 300 35

0

50

100

-50

150

freq, GHzPh

ase

(S(2

,1))

10 20 300 40

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.0

0.8

Vds (V)Id

s (A

)

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-5 0 5 10 15 20 25 30 35 40 45 50

Id e

n Am

pere

s

Vds en Volts

8x75 POLAR Vgs=-4.401 V, Vds=+22.97 V, Id =+0.163 A

Vgs=+1.000 VVgs= +0.00nVVgs=-1.000 VVgs=-2.000 VVgs=-3.000 VVgs=-4.000 VVgs=-5.000 VVgs=-6.000 VVgs=-7.000 VVgs=-8.000 V

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-5 0 5 10 15 20 25 30 35 40 45 50

Id e

n Am

pere

s

Vds en Volts

8x75 POLAR Vgs=-4.401 V, Vds=+22.97 V, Id =+0.163 A

Vgs=+1.000 VVgs= +0.00nVVgs=-1.000 VVgs=-2.000 VVgs=-3.000 VVgs=-4.000 VVgs=-5.000 VVgs=-6.000 VVgs=-7.000 VVgs=-8.000 V

Idss

y = -0,0024x + 1,6085

1,2

1,25

1,3

1,35

1,4

1,45

1,5

1,55

1,6

0 20 40 60 80 100 120 140 160

Is_gs

0,00E+00

5,00E-15

1,00E-14

1,50E-14

2,00E-14

2,50E-14

3,00E-14

3,50E-14

0 20 40 60 80 100 120 140 160

y= 1,6E-16+1,04973E-16*EXP(T/26,3157)

Cgs_1D

0,00E+00

1,00E-13

2,00E-13

3,00E-13

4,00E-13

5,00E-13

6,00E-13

-10 -8 -6 -4 -2 0 2Vgs

Cgs

(F)

MesureModele

Cgd_1D

0,00E+00

2,00E-14

4,00E-14

6,00E-14

8,00E-14

1,00E-13

1,20E-13

1,40E-13

-60 -50 -40 -30 -20 -10 0Vgd

Cgd

(F)

MesureModele

VdsVgs_int

VgsRfill

Rempty C

k+

+

k

Vds

Vds

VdsVgs_int

VgsRfill

Rempty C

k+

+

k

Vds

Vds

5.40E-02

5.50E-02

5.60E-02

5.70E-02

5.80E-02

5.90E-02

6.00E-02

0.00E+00 2.00E-06 4.00E-06 6.00E-06 8.00E-06 1.00E-0

VdsVgs_int

VgsRfill

Rempty C

k+

+

k

Vds

Vds

VdsVgs_int

VgsRfill

Rempty C

k+

+

k

Vds

Vds

5.40E-02

5.50E-02

5.60E-02

5.70E-02

5.80E-02

5.90E-02

6.00E-02

0.00E+00 2.00E-06 4.00E-06 6.00E-06 8.00E-06 1.00E-0

Modèle petit-signal Modèle I-V Capacités NL Modèle thermique Modèles de pièges

Cgs=f(Vgs)

Cgd=f(Vgd)

Ids=f(Vgs_pièges,Vds,T)

Dgs=f(Vgs)

Dgd=f(Vgd)

Rs=f(T)

Rd=f(T)

Rgd=f(T)

Étapes de modélisation

RgLgCpgLsCpdLdRsRd

RiCdsτGmGdCgsCgdRgd

Ids=f(Vgs,Vds,T)

Dgs=f(Vgs)

Dgd=f(Vgd)Ids=f(Vgs,Vds)

Various parasitics effects are successively added

18

We call these traps "Fast Emitting Traps". Highlighted in low frequency

[S] meas.

Knee walk-out for Vds,max > 15V Slow traps activated and not

modeled

model (fast-trap only)meas. Bias 0V/0V, VDS,max = 15Vmeas. Bias 0V/0V, VDS,max = 30V

Non linear electrothermal model with trapping effects

19

Large signal validation : DC drain current drop due to both fast and slow traps

New trap model :

Investigation of Fast and Slow Charge Trapping Mechanisms of GaN/AlGaN HEMTs through Pulsed I-V Measurements and the Associated

New Trap Model

Presentation by Julien Couvidatat IMS Philadelphie 2018

20

Linearity Measurement with Multi-Tones Signal

• PA Linearity Performances hugely depend on driven signals

• To measure linearity with Complex Modulated Signals like real signals (LTE,..) the needto demodulate signal

10.

% 10

• Emulation with an 8-ton generic signal with same statistical properties than ComplexModulated Signals (PAPR, PDF,…)

• No need to demodulate• Signal composed of 8 tones such as IM3, IM5 non overlap with themselves and 8-tones

signal • Computation of a C/I by summing all InBand (between the 1st and last signal tone)

IM3 and IM5 powers

• Definition of Figure Of Merite (by analogy with EVM)

21

38

1 . ∆ with 1≤ k ≤ n

. 1st frequency

rank of frequency

∆ . distance between tons

. offset frequency

. .

Building of the 8-tones Signal

are Unequally Spaced

Powerf1 f2

kfk ).( 1

...fk

...f8

FFT grid : 217 Frequencies separatedby

pk 0,1, 3 , 3 , 3 , 3 , 3 , 3 guaranteesnon overlapbetweenIM3, IM5and8tones

22

Example of simulated PA Output Signal

Non overlap between IM3, IM5 and 8-tones Signals

23

Unequally Spaced Multi Tons test bench up to 6 GHz

IF BW : 10 MHzDynamic range: 65~70 dB

IF 160MHz

% 10

24

Multi-tone LP measurement

• 1-tone to 8-tones characteristics

Power characteristics are obtained for each frequency in the same way as for

classical LP systems

• C/IM3 is the total power for carriers / total IM power

• FOM is an EVM like measure (can be set equal to the EVM in some particular cases)

25

• Linearity Assessment

AlGaN/GaN 8x75 m – VDS0=30V, f0= 2 GHz

Spectrum results and Linearity measurement

Pin=-33dBm

Pin=4dBm

Input Output

26

AML26P2401Bias : 15V 190mA

Power sweep : -33dBm to 4dBm8 tones around 2GHz

With >2MHz of bandwidth

“Linearity Characterization of RF Circuits through an Unequally Spaced Multi-Tone Signal” Sylvain Laurent et al.Microwave Measurement Conference (ARFTG), 2016 88th ARFTG

IF bandwidth : 38MHz

Typical dynamic: 90dB

Unequally Spaced Multi Tons test benchUnder development up to 50 GHz

“A fully calibrated NVNA set-up for linearity characterization of RF power devices using Unequally Spaced Multi-Tone signal through IM3 & IM5 measurements » Presentation by V. Gillet at

91st ARFTG Microwave Measurement Symposium June 15, 2018, Philadelphia PA

27

Conclusion

• GaN HEMTs modeling still remains a challenging task

• Impact of Low Frequency parasitic on large signal performances must be evaluated

• Dynamics of traps play a major role• A tentative model able to consistently take into

account those dynamics has been proposed • Special nonlinear measurement set-ups are

mandatory to assess all the effects

28

Acknowledgements

• Thanks to III-V lab and UMS Foundry for supplying the device wafers.

• Thanks to PhD Students of XLIM for providing measurement characteristics

• Thanks to the Agence Nationale de la Recherche (ANR) and Direction

Générale de l'Armement (DGA) France.

• This work was supported by COMPACT project under contract ANR-17-

ASTR- 0007-01 and VeGaN project, France, under Contract FUI 18

29

30