Ray Pengelly,

Cree RF and Microwave Products,

Research Triangle Park, NC 27709

October 21, 2010

Agenda

GaN HEMT Transistor Structures

High Power Densities – Blessing or Curse?

Thermal Management

CW, Pulsed and Linear Operation

Wideband General Purpose Amplifiers

Linear and Efficient Telecommunication Amplifiers

Doherty and Envelope Tracking Approaches

GaN HEMT MMICs

Packaging

Improvements to device structures and package materials

Device Reliability

Trends – Applications and Higher Frequencies

Strengths of GaN HEMTs High breakdown voltage VDD large; RL high – easier to match; lower losses

High sheet charge density; ns = 1 x 1013

Current density is large

Device area can be reduced

Large Watts/mm of gate periphery

High saturated drift velocity High saturation current density and W/mm

Small device area per watt – lower capacitances

Low drain-source capacitance Easier to match

More suitable for switch-mode amplifiers

Attributes of GaN HEMTs

High Voltage Operation

High power densities – 4 to 8 watts/mm at 28 and

50 volt operation respectively – both a blessing and a curse!

High Frequency Performance – present Cree process has fT of 27 GHz

High Efficiency

Low Quiescent Current

High Native Linearity

Low capacitance per peak watt (12% of LDMOS and 21% of GaAs MESFET) – supports broad bandwidths

Enable new amplifier architectures

Highly correctable under DPD (digital pre-distortion)

Almost constant CDS as a function of VDS – great for Drain Modulation

Si GaAs 4H-SiC GaN

Band Gap (eV)

1.12 1.43 3.26 3.4

Thermal Conductivity

(W/Kcm)

1.5 0.46 4.9 1.5

Breakdown Field

(106V/cm)

0.25 0.3 2.2 3

SaturatedElectron Velocity

(peak) (107

cm/s)

1(1)

1(2.1)

2(2)

1.5(2.7)

Relative Permittivity

11.9 13.1 10 8.9

5

GaN versus Si, GaAs and SiCConcept Si GaN on SiC

DPD High thermal time constant

Moderate bandwidth

Low thermal time constant

Large bandwidth

Doherty Low off-state impedanceHigh output capacitance

High off-state impedanceLow output capacitance

LINC Large non-linear output

capacitance

Small non-linear output

capacitance

EER Poor amplitude to phase modulation

conversionModerate bandwidth

Good amplitude to phase modulation

conversionLarge bandwidth

Class F/E/J Low fT

Moderate breakdown

High fT

High breakdown

Impact of GaN on power amplifier conceptsMaterial properties of major semiconductors

GaN HEMT Structures

Field plate is connected to gate

Increases breakdown voltage

Reduces dispersion, depletion of channel by surface traps

Without field plate With field plate

Field Plate Operation

Improved I-V with Field Plated Devices

Typical Power Performance of Field Plated HEMTs

Blessings and Curses of High Power Density

At 28 volts, Cree GaN HEMTs have an RF power density of 4 watts per millimeter of gate periphery

At 48 volts, the same transistors have an RF power density of 8 watts per millimeter

At 65 volts, the same transistors have an RF power density of 11 watts per millimeter

With high operating voltages and power densities the design engineer has to be very aware of thermal management e.g. A CGH21120F transistor operating at 48 volts will generate 220 watts of

CW RF power and at PSAT have a drain efficiency of 65%

Dissipated heat is 118 watts – TRISE is 177OC – Needs de-rating The same device can operate at 35 volts producing 150 watts of CW power

with 70% drain efficiency

Dissipated heat is 64 watts – TRISE is 90OC – TCASE can be >100OC

Blessings and Curses of High Power Density

Pulsed Operation Pulses need to be shorter than 100’s of microseconds to make

substantial reductions in channel temperature

Good news is that the effective “pulse widths” for modern digital modulation schemes such as W-CDMA and WiMAX with 5 to 20 MHz channel bandwidths are < 100 nsec

Linear Operation Operating GaN HEMTs at high drain voltages impacts

backed-off (linear region) operating temperatures e.g. At 28 volts a CGH27120 delivers 16 watts average power under

WiMAX at a drain efficiency of 25% Dissipated heat is 48 watts with a TRISE of 82OC – NO derating

At 48 volts a CGH27120 delivers > 30 watts average power under WiMAX at a drain efficiency of 25% Dissipated heat is >90 watts with a TRISE of 153OC – Needs derating to

TCASE of 72OC

General Purpose Application Insertions for GaN HEMTs

Emphasis usually on P1dB or saturated power, wide bandwidth and best efficiency

Applications include

Wideband, noisy, jammers

Software defined radios

Tactical communications

Phased array systems

Test instrumentation

Medical applications – e.g. ablation

Exciter applications – e.g. lighting

0.5 to 2.5 GHz Reference High Power Amplifier Performance using Cree CGH40045F

pg. 13

CGH40045F Gain and Input Return Loss versus Frequency

0

6

12

18

24

30

0 500 1000 1500 2000 2500

Frequency (MHz)

Gain

(d

B)

-15

-12

-9

-6

-3

0

Inp

ut

Retu

rn L

oss (

dB

)

S21 S11

CGH40045F - Output Power and Drain Efficiency versus Frequency

10

15

20

25

30

35

40

45

50

55

60

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Frequency (GHz)

Po

we

r O

ut

(dB

m)

0

10

20

30

40

50

60

70

80

90

100

Dra

in E

ffic

ien

cy

(%

)

Power Out (dBm)

Drain Efficiency (%)

• > 50 watts CW power over 5:1

frequency range

• 55 to 65% drain efficiency

Performance of Push-Pull Power Amplifier for 0.5 to 2.5 GHz using Cree CGH40090PP

CGH40090PP -Output Power and Drain Efficiency versus Frequency

10

15

20

25

30

35

40

45

50

55

60

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Frequency (GHz)

Po

we

r O

ut

(dB

m)

0

10

20

30

40

50

60

70

80

90

100

Dra

in E

ffic

ien

cy (

%)

Power Out (dBm)

Drain Efficiency (%)

CGH40090PP Gain and Drain Efficiency vs Output Power

0

10

20

30

40

50

60

20 25 30 35 40 45 50

Power Out (dBm)

Gain

(d

B)

0

10

20

30

40

50

60

Dra

in E

ffic

ien

cy (

%)

0.5 GHz Gain 1.0 GHz Gain 1.5 GHz Gain 2.0 GHz Gain 2.5 GHz Gain

0.5 GHz DE 1.0 GHz DE 1.5 GHz DE 2.0 GHz DE 2.5 GHz DE

Drain Efficiency is 50%

CGH40045F under Pulsed Stimulus at 50V drain voltage

pg. 15

CGH40045 Pulse Transfer

Vds=50V, 40uS Pulse 10% Duty Cycle, F=2.5GHz

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0

Input Power (dBm)

Ou

tpu

t P

ow

er

(dB

m)

Dra

in E

ffic

ien

cy

(%

)

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

Gain

(d

B)

Pout

Drain Efficiency

Gain

100 watt

The CGH40045F GaN HEMT was originally designed for 28 volt

operation - Works well at 50 volts within thermal constraints

Performance of CGH40180PP in Demonstration Amplifier

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

100

120

140

160

180

200

220

240

260

1050 1100 1150 1200 1250 1300 1350

Dra

in E

ffic

ien

cy

CW

Ou

tpu

t P

ow

er

(W)

Frequency (MHz)

Power and Efficiency vs Frequency

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

6

8

10

12

14

16

18

20

22

30 32 34 36 38 40 42 44 46 48 50 52 54

Dra

in E

ffic

ien

cy

Ga

in (

dB

)

Output Power (dBm)

Gain and Drain Efficiency vs Output Power

GaN HEMT MMICs and Foundry Services

Range of custom MMICs completed successfully for top tier DoD contractors

Power Amplifiers

Low noise amplifiers

Switches

Limiters

Complete transceivers

First COTS GaN MMICs released in June 2008

Both SiC MESFET and GaN HEMT Foundry services are available

DC to 18 GHz

CMPA0060002F Typical Performance

pg. 18

CMPA0060005F -S21, S11 & S22 versus Frequency

0

2

4

6

8

10

12

14

16

18

20

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Frequency (GHz)

Ga

in (

dB

)

-30

-27

-24

-21

-18

-15

-12

-9

-6

-3

0

Inp

ut/

Ou

tpu

t R

etu

rn L

os

s (

dB

)

S21_48V S11_48V S22_48V

CMPA0060005F -Output Power and

Power Added Efficiency versus Frequency

30

31

32

33

34

35

36

37

38

39

40

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Frequency (GHz)

Po

we

r O

utp

ut

(dB

m)

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

Po

we

r A

dd

ed

Eff

icie

nc

y (

%)

PSat_48V

PAE_48V

0.5” x 0.5” Package

• Wide bandwidth: 20 MHz to 6 GHz

• 3 watts typical Power Output

• 20% efficiency

• 17 dB Small Signal Gain

• 28 volt operation

• Small 0.25 sq. inch footprint

CMPA2560025F Typical Performance

pg. 19

Saturated Power Output and Power Added Efficiency versus Frequency

40

41

42

43

44

45

46

47

48

49

50

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5

Frequency (GHz)

Sa

tura

ted

Po

we

r O

utp

ut

(dB

m)

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

Po

we

r A

dd

ed

Eff

icie

nc

y (

%)

Typical Psat (dBm)

PAE at 44 dBm (%)

CMPA2560025F -S21, S11 & S22 versus Frequency

0

3

6

9

12

15

18

21

24

27

30

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Frequency (GHz)

Gain

(d

B)

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Inp

ut/

Ou

tpu

t R

etu

rn

Lo

ss (

dB

)

(S21) (S11) (S22)

0.5” x 0.5” Package

• Wide bandwidth: 2.5 to 6 GHz

• 25 watts typical Power Output

• 30% efficiency

• 24 dB Small Signal Gain

• 28 volt operation

• Small 0.25 sq. inch footprint

Telecommunication Insertions for GaN HEMTs

Emphasis usually on linearity and efficiency under relatively high peak to average ratio signals

Applications include

WiBro and WiMAX at 2.3, 2.6, 3.5 and 5.5 GHz

W-CDMA

LTE (Long Term Evolution)

DVB (Digital Video Broadcast)

Multi-Carrier GSM

Secure COFDM Links

Efficiencies for Doherty and ET Power Amplifiers in 2.11 to 2.17 GHz UMTS Band (meeting 3GPP SEM)

DC to RF Efficiency, %

W-CDMA @ PAR of 7.6 dB (unless otherwise stated)

90 watts DohertyW-CDMA 53% CREE GaN HEMT

100

75

50

25

25 50 75 100

50 watts DohertyW-CDMA43% NXP Si LDMOSFET

20 watts DohertyW-CDMA57% Delft/Cree GaN

37 watts ETW-CDMA50% UCSD/Nitronex GaN

40 watts ETW-CDMA43% Cree GaN

70 watts DohertyW-CDMA40% Freescale Si LDMOSFET

8 watts DohertyWiMAX52% @ PAR=11.2dBDelft/Cree GaN

Average Power, Watts

2 watts HEERWiMAX @ PAR=8.5dB50% Postech/Cree GaN

16 watts DohertyW-CDMA49% Postech/Cree GaN

42 watts ETW-CDMA58% UCSD/Triquint GaAs HVHBT

Basic Doherty Amplifier Configuration

pg. 22

RF

InputClass AB Bias

Class C-like Bias

Peaking Amp

Main Amp

Quarter-Wave Line

(~ 50 Ohms, Z TBD)

Quarter-Wave

Output Transformer

(~35 Ohms)

RF

Output

0o

90o

• The Doherty amplifier configuration is becoming more and more popular

as a means of improving overall DC to RF conversion efficiency

• Up to certain input power levels the carrier amplifier saturates earlier

than a conventional Class A/B Amplifier because of the load impedance

it sees – the peaking amplifier is still OFF

• Above a certain input power level the peaking amplifier turns ON and

contributes power as well as altering the load line to the carrier amplifier

CDPA21480 UMTS Band Doherty Amplifier

pg. 23

Energy Storage Capacitors

90O Line

90O Line

Wilkinson Splitter

RF Input

RF Output

2.5 x 3.5 inches

Measured Single-Channel W-CDMA ACLR & Efficiency vs. RF Average Output Power

CGH21240DD WCDMA Transfer with & without DPDSingle Channel WCDMA, 6.8 dB PAR with CFR

Vds=50V, Idsq=600 mA, Frequency=2.14 GHz

-70

-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

28 30 32 34 36 38 40 42 44 46 48 50

WCDMA Average Output Power (dBm)

AC

LR

(d

Bc)

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

55%

Dra

in E

ffic

ien

cy

ACLR-5 ACLR+5

ALT-10 ALT+10

ACLR-5 (PD) ACLR+5 (PD)

ALT-10 (PD) ALT+10 (PD)

Drain Effic (PD)

How Envelope Tracking (ET) Works

pg. 25

Switch Mode GaN HEMT ET HPA Summary

Single Carrier W - CDMA

Peak to Average Ratio 7.6 dB

Average Output Power> 14 watts

Gain > 15 dB

EVM < 2%

Overall Efficiency > 50%

pg. 26

DSP

Signal

generation,

Decresting/

detroughing,

pre-distortion,

time alignment

LPF

Up-

converterBPF

Driver RF HPA

Envelope

amplifier

Envelope

Down-

converterLPF

RF

ADC

DAC

Application of GaN Class E Amplifers in

EER/ET Amplifier Systems

D. Kimball1, J. Jeong1, C. Hsia1, P. Draxler1,2,

P. Asbeck1, D. Choi3, W. Pribble4

and R. Pengelly4

1 ECE Department, UCSD, La Jolla CA 9209

2 Qualcomm, San Diego, CA

3 Nokia Research, San Diego, CA

4 Cree, Durham, NC 27703

pg. 27

CGH21120F under compressed Class A/B

under Envelope Tracking (multi-carrier WCDMA)

GaN HEMT Class F Amplifier provides 86% PAE at 17 watts at 2 GHz

805B_N1, Vdd = 42.5 V

0

2

4

6

8

10

12

14

16

18

20

14 16 18 20 22 24 26 28 30 32

Pin (dBm)

Gain

(d

B),

Po

ut

(W)

0

10

20

30

40

50

60

70

80

90

100

PA

E,

N

Pout(W)

Gain(dB)

PAE

N

Performance vs. Drain Voltage

805B_N1, 2 GHz

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

0.0 10.0 20.0 30.0 40.0 50.0

Vdd (v)

Po

ut

(W),

Ga

in (

dB

)

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

PA

E,

N

Gain (dB)

Pout (W)

M axPAE

Drain Efficiency

Lbw Lbw

Cds RL

22 ,Z

4, 11

Z

3Z

63

Zdrain

VD bias

Lbw55 ,Z66 ,Z

C1

R1

C2

R2

4, 44

Z

86% PAE 17 W

Data provided by S. Long and D. Schmelzer, UCSB

Effect of Efficiency on Transistor Operating Temperature

Packaging of High Power Density Transistors

TiPtAu

80%Au20%Sn

?

• Package flange material needs to have high thermal conductivity

but also have a coefficient of expansion that is close to SiC

• Unfortunately there a limited number of choices to get both right

simultaneously!

Properties of Relevant MaterialsMaterial Structure Thermal

ConductivityW/mK

Coefficient of Thermal

Expansionppm/K

Cu Pure 393 17

Diamond 1500 1.4

Silicon 136 4.1

SiC 4H-SI 430 4

AlSiC 63%SiC >175 7.9

W90Cu 90% W 185 6.5

W75Cu 75% W 225 9

Mo70Cu 70% Mo 185 9.1

Mo50Cu 50% Mo 250 11.5

CuMoCu 1:4:1 220 6

CuMoCu 1:1:1 310 8.8

Cu/Mo70Cu/Cu 1:4:1 laminate 340 8

Thermal ImprovementsAt the transistor level

New power transistor layouts to reduce junction temperature at constant power density

At the package level

• New flange materials with

higher thermal conductivityand CTE match to SiC

• Present CuW is ~200 W/mK• New SuperCMC is 350 W/mK

• Aluminum diamond

is 550 W/mK

Presentlayout

NewLayoutprovides20% reduction in operatingtemperatures

TJ decreases by 10%

TJ decreases by further 15%

Combined lowers 175 C junction temperature to123 C

Robustness

Robustness falls into several categories

Voltage and Current overload

Voltage and Current withstand due to output load mis-match

Pulsed energy withstand at transistor input

Electro-static discharge withstand

Radiation (total dose) withstand

Self-generated heating

• For many military applications, the output load mis-match withstand is

critical. Normally specified to a minimum of 10:1 VSWR – simulates disconnected

antenna!

• If in a Class A/B amplifier peak drain voltage is 96 volts (assuming 48 volt rail)

then at worst case phase with 80% of power being reflected back the peak drain

voltage will be 134 volts

• Hence the need for Vbd’s of at least 150 volts for GaN HEMTs

when operating at 48 volts!

Shockley, Brattain and Bardeen, 1947

Reliability - Cree GaN vs. other GaN Suppliers

101

102

103

104

105

106

10

150

175

200

225

250

275

300

325

350

375

400425

Te

mp

era

ture

(deg

. C

)

MTTF (hours)

710

810

9

Cree GaN on SiC

Cree GaN

GaN on Si under DC

operation

E a = 2.0 eV

GaN on SiC

Ea = 1.3 eV

Supplier T GaN

GaN on Si

Ea

= 1.6 eV

Cree GaN devices are the most reliable in the industry

580 million Cree device hours in the field

Higher Frequencies

Switches, LNA’s etc.

MMIC Switches Separate RF and Control

Ports

No need for Chokes

Takes no control current

PIN diode replacement

High Power Operation

Wideband Operation

Low Noise Amplifiers – X-Band

Two-Stage X-Band MMIC Low Noise Amplifier

Measured and Modeled Two-Stage LNA s-parameters

Measured Two-Stage noise figure parameters

D. Krause et al, 2004

“A maximum input power level of

23 dBm is reached at a 7 dB

compression level without any

sign of short term degradation”

Other Wide Bandgap Device Applications

Other circuits using Wide Bandgap devices include Mixers (both FET and

diode)

Multipliers

Limiters

DC/DC Converters

Phase Shifters

Attenuators – analog and digital

Oscillators

90 nm GaN HEMT Technology for mm-waves

Performance of GaN HEMTs at mm-waves

(passivated – higher capacitance)

Acknowledgements I would like to acknowledge the assistance

of my Cree colleagues in preparing this presentation

Ulf Andre

Don Farrell

Don Gajewski

Chris Harris

Jim Milligan

Brad Millon

Carl Platis

Art Prejs

Bill Pribble

Scott Shephard

Simon Wood