-- 2.0

l , , , , .

:

l , , .

l .

.

(Legal Code) .

Disclaimer

. .

. .

. , .

http://creativecommons.org/licenses/by-nc-nd/2.0/kr/legalcodehttp://creativecommons.org/licenses/by-nc-nd/2.0/kr/

W-band RF AlGaN/GaN HEMTs on Si

fmax

High fmax AlGaN/GaN HEMTs on Si-substrate for W-band Power

Applications

2013 8

W-band RF AlGaN/GaN HEMTs on Si

fmax

High fmax AlGaN/GaN HEMTs on Si-substrate for W-band Power

Applications

2013 8

2013 8

: ()

: ()

: ()

i

RF power application AlGaN/GaN HEMTs W-

band current collapse

fmax .

GaN electron mobility, saturation velocity, thermal conductivity

, bandgap breakdown voltage ,

Si GaAs transistor power density module size

. Si GaAs RF power

, high-resistivity Si(111)

AlGaN/GaN HEMTs millimeter-wave

.

sub-micrometer AlGaN/GaN HEMTs current collapse

RF power .

RF T-gate current

collapse field plate ,

field plate bias

. fmax

, fmax .

fmax , Si- GaN

HEMTs W-band RF power .

: AlGaN/GaN HEMTs, millimeter-wave, , current collapse,

: 2011-23356

ii

1 1

1.1 1

1.2 6

2 Conventional AlGaN/GaN W-band Power HEMT 8

2.1 Sub-micrometer AlGaN/GaN HEMT 8

2.2 DC & Pulsed I-V Measurements 13

2.3 RF Measurement 16

3 AlGaN/GaN HEMT with Gate Field-plate Structure 18

3.1 Overhang gate length split 18

3.2 Current collapse gate leakage current 20

3.3 RF Measurement & Optimization 23

iii

4 Decrease of Gate Resistance by Double-head Gate 26

4.1 PR Planarization & Double-head gate 26

4.2 Pulsed I-V & RF Measurements 30

4.3 W-band GaN MMICs(Monolithic Microwave Integrated Circuits) 33

4.3.1 33

4.3.2 MMIC 35

5 40

5.1 40

5.2 40

42

Abstract 45

1

1

1.1

, 4G LTE

. radar RF power

, .

Si FET ,

Si FET

GaAs pHEMTs(High Electron Mobility Transistor), mHEMTs ,

GaN RF power ,

. [1]

1.1 RF .

GaN band gap breakdown mobility saturation

velocity application

. band gap power density(GaAs 10 )

device size , power capacitance

. GaN polarization effect GaAs

HEMT channel charge density , thermal conductivity

RF loss . [2]

GaN on , input, output matching , power supply

efficiency . [2]

1.3 GaN device

0.25 , 0.1 .

GaN HEMTs SiC, Sapphire, Si , thermal

conductivity , RF loss semi-insulating SiC GaN

epitaxial layer . , , GaN RF

, self-heating , cooling

module design compact . [3]

2

1.1 RF Power

Parameter GaAs GaN

Maximum Operating Voltage [V] 20 48

Maximum Current [mA] 500 ~1000

Maximum Breakdown Voltage [V] 40 >100

Maximum Power Density [W/mm] 1.5 >8

1.2 GaAs GaN RF power

3

1.3 GaN

High-resistivity Si SiC

, yield millimeter-

wave . current gain cutoff frequency fT

100GHz , device scaling epi design 100GHz

. [4] [5]

1.1 AlGaN/GaN HEMT on SiC

Higher thermal

conductivity

Lower self heating

Better reliability

But, High Cost!

4

RF power maximum

oscillation frequency fmax , output

power current collapse . [6]

Current collapse epitaxial layer

GaN , . Current collapse

, 1.2

, GaN epi dislocation density( 109 -2)

. dislocation trap

, surface trapping buffer trapping drain bias

dynamic on , output current . bias

RF output power .

1.2 GaN current collapse

(Fujitsu, Nov., 2010)

(Y. Koh, MDCL, SNU, 2012)

5

dielectric passivation , , epi design, field-plate

current collapse ,

. gate length ,

parasitic capacitance current collapse

field-plate current collapse

.

GaN RF power , GaN-on-SiC [7] (source-

drain 1.1 , gate length 60 ) 300GHz fmax , GaN-on-Si [8]

(source-drain 2.3 , gate length 100 ) 190GHz fmax . SiC

GaN-on-Si current collapse, buffer leakage, gate

leakage loss epitaxial layer design

.

1.3 GaN-on-Si(High-resistivity) epi

RF gate leakage current, ohmic

contact . Gate leakage current RF loss , metal

bandgap adhesion metal contact .

Short gate adhesion Ni bottom metal ,

. gate recess

leakage current . sheet ohmic contact

on , Rs, Rd . Epi

(F. Medjdoub, IEMN, 2012)

6

ohmic metal stack , ohmic recess ohmic

.

1.4 GaN-on-Si RF

1.2

millimeter-wave current collapse

gate fmax , gate resistance

fmax .

77GHz MMIC PA output power 1.3W/mm

.

Issues

Current collapse

Gate leakage current

Ohmic contact

Scaling down

& Process stability

7

5 . 2 parasitic capacitance

T-gate 0.11um AlGaN/GaN HEMT ,

3 sub-micrometer AlGaN/GaN HEMTs power current

collapse gate , .

4 parasitic effect gate resistance

fmax double-head gate .

5

.

8

2 Conventional AlGaN/GaN W-band Power HEMT

2.1 Sub-micrometer AlGaN/GaN HEMT

2.1 high-resistivity Si(111)

AlGaN/GaN epitaxial layer . Transconductance

gate channel 10 AlGaN barrier layer ,

polarization effect sheet carrier density

30% Al contents . 2.5 GaN cap layer 1.3 GaN buffer

layer , sheet resistance 290/sq .

2.5 nm GaN cap

10 nm AlGaN (30%)

1 m i-GaN

300 nm Buffer layer

HR - Si(111) substrate

2.1 AlGaN/GaN HEMT Epitaxial layer

2.2 . cleaning ,

SPM diluted HF NH3/SiH4 SiNx 30nm 350 ICP-CVD

chamber . SiNx pre-passivation [9] nitrogen

vacancy . cleaning

//IPA solvent cleaning 10 ,

: (4:1) SPM 120 5 . SiNx

oxide D.I water:HF (10:1) 5

.

9

2.2 Multi-finger AlGaN/GaN HEMT

source-drain 2 ohmic patterning SF6 gas 30

SiNx etching BCl3/Cl2 low damage GaN etching capping layer recess .

diluted HCl(3:1) wet , Si/Ti/Al/Mo/Au (5/20/80/35/50 ) ohmic metal [10]

, N2 780 1 RTA ohmic contact .

ohmic epi device isolation BCl3/Cl2

ICP-Etcher MESA etching . MESA etching ohmic process

ohmic etching

10

. source-drain ohmic contact 0.37mm , 2

source-drain 1200mA/mm .

Gate passivation layer

SiNx passivation layer dry etching passivation layer 30 .

SiNx dielectric N2/SiH4/Ar , dry etching

gas SF6. SF6 plasma treatment [11] fluorine leakage , [12]

gate leakage current . SiNx passivation layer

ICP-CVD , in-situ N2 plasma treatment [13] [14]

current collapse .

gate [15] 2.3 .

passivation layer 30nm ZEP:thinner / PMGI / ZEP:thinner (270/500/200 ) PR 3

coating 190 hard baking , e-beam lithography T-gate

patterning . Source-gate 0.6 , 2.4 patterning gate

SEM . layout 0.3 gate head

patterning e-beam dose selectivity MIBK:MEK(3:2) developer

top PR patterning , AZ300 PMGI layer develop .

0.07 gate foot patterning dose selectivity MIBK:IPA(1:1)

developer develop .

2.3 0.11 T-gate

ZEP:thinner(1:1)

PMGI

ZEP:thinner(1:1) SiNx

SiNx 30nm

Lift-off

Ni/Au

(40/360nm)

Air( = 1)

11

Patterning , 140 PR reflow gate neck head

ZEP PR SiNx dry etching selectivity dry etching gate

stem . [16]

2.4 0.11 T-gate pattern SEM view 2.5 PR reflow hard baking SEM view

SF6 100sccm 20W 0.1Torr plasma dry etching 115 gate length

, profile 2.6 . oxide B.O.E

1:30 , Ni/Au(40/360 ) gate metal lift-off . M1 metal

(Ni/Au 40/460 ) 250 SiNx 30 2nd passivation Air bridge, M2 metal

(Ti/Au 50/1500 ) .

2.6 Etching 0.11 gate foot SEM view

Under etching

1.6um 490nm

395nm

12

2.7 SF6 dry etching PR SiNx selectivity

0

50

100

150

200

250

300

350

400

0.1Torr, 20W 0.07Torr, 20W 0.1Torr, 40W

ZEP Etch rate(/min)

SiNx Etch rate(/min)

0

50

100

150

200

250

300

350

400

0.1Torr, 20W 0.07Torr, 20W 0.1Torr, 40W

ZEP Etch rate(/min)

SiNx Etch rate(/min)

After 140 5min bake

13

2.8 0.11 AlGaN/GaN HEMTs multi-finger (), 4x37

2.2 DC & Pulsed I-V Measurements

DC 4155A . 2.9

gate schottky reverse leakage current . Gate forward turn-on

1.1V , off-state gate reverse breakdown 1mA/mm

20V . 0.11 target 15V

, bias

RF loss . gate leakage

short length gate , epi barrier layer

, Al mole fraction , buffer leakage current

[17]. gate field

, gate

.

14

2.9 Gate schottky () reverse leakage current()

transfer curve output 2.10 . Transconductance

VDS = 5V , threshold IDS = 1mA/mm -2.8V .

Gm.max VGS = -2.3V 420mS/mm , output VDS 3V

knee VGS = 0V 900mA/mm drain .

-6 -5 -4 -3 -2 -1 0 1 21E-12

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

I G[A

/mm

]

VG[V]

-100 -80 -60 -40 -20 0-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

I G[m

A/m

m]

VG[V]

15

2.10 Transfer curve() output ()

power pulsed I-V 2.11

passivation layer gate current

collapse . bias point Vgs = 0V , gate lag Vgs = -5V,

drain lag Vds = 10V, 20V , drain pulse 10V on 50%

drain . drain output

output power .

Gate gate head air(=1) bias electric

field , current collapse . RF

passivation layer 30 current collapse

[18].

-7 -6 -5 -4 -3 -2 -1 00

200

400

600

800

1000

1200

VGS[V]

I DS[m

A/m

m]

0

100

200

300

400

500

Gm[m

S/m

m]

0 2 4 6 8 10 12 14 16 18 200

200

400

600

800

1000

VGS = -4V to 0V

I DS

[mA

/mm

]

VDS[V]

VDS

= 5V

16

2.11 2x50 Pulsed I-V

2.3 RF Measurement

0.11 RF Network Analyzer S-parameter

. S-parameter ,

, RF/microwave

.

2.12 S-parameter Smith chart

freq (1.000GHz to 50.00GHz)

S(1

,1)

S(1

,2)

S(2

,1)

S(2

,2)

0 2 4 6 8 10 12 14 16 18 200.0

0.2

0.4

0.6

0.8

1.0

Vgs = 0V, Vds = 0V (bias)

Vgs =-5V, Vds = 0V

Vgs =-5V, Vds = 10V

Vgs =-5V, Vds = 20V

I ds[A

/mm

]

Vds

[V]

Pulse width = 500ns, Separation = 1ms

17

2.13 T-gate AlGaN/GaN HEMT gain (2x50 )

Small-signal parameters gain plot

2.13 . MAG, U small-signal parameters

small-signal , large-signal RF power

FOM(Figure of Merit) .

Gm.max Vgs fmax Vds bias point , -

20dB/decade extrapolation 135GHz fmax .

de-embedding probe .

Vgs

= -2.3V, Vds

= 15V

2x50um

FT = 67GHz

Fmax(MAG)

= 135GHz

Fmax

x BV = 3.4THz-V

Pre-de-embedded

18

3 AlGaN/GaN HEMT with Gate Field-plate Structure

3.1 Overhang gate length split

0.11 T-gate , gate leakage current current collapse

RF loss , output power MMICs

PA . gate

. current collapse gate

parasitic capacitance

, parasitic current collapse

gate leakage current .

3.1 overhang gate .

3.1 Overhang gate

19

T-gate , SiNx

passivation layer 60 . SiNx parasitic

field plate [18]. Passivation layer

gate ZEP coating dose selectivity

MIBK:IPA(1:1) developer 40 patterning . 60 SiNx

dry etching 30 gate length

. one step etching 30W 10W two step etching

. 3.2 patterning two step etching .

3.2 Gate foot patterning etching profile SEM view

SF6 100sccm 0.1Torr 30W vertical etching , SiNx

10W etching overetching damage etching profile slope .

Gate foot patterning PMGI/ZEP:thinner 2 coating lift-off

Under etching

110nm

140nm

20

. etching SiNx top opening length , gate

head length source 0.05, drain 0.05/0.1/0.15/0.2/0.25

split. parasitic gate drain field

, gate metal T-gate Ni/Au(40/360) .

3.2 Current collapse gate leakage current

4155A pulse .

3.3 gate schottky reverse leakage current .

3.3 Gate schottky () reverse leakage current()

21

Forward turn-on T-gate 1.1V , reverse breakdown

1mA/mm 60V . 0.11

, 20V leakage current T-gate 1/4 .

Overhang gate head length bias 40V

bias overhang gate head length leakage current

. gate leakage current MS contact

T-gate field-plate gate leakage current

[19].

transfer curve output 3.4 .

transconductance VDS = 5V , threshold -3V. Gm.max

VGS = -2.8V 435mS/mm T-gate channel control . Output

3V knee , VGS = 0V 900mA/mm drain

. T-gate kink [20]

. drain bias off-state current

. off-state current gate

.

VDS

= 5V

22

3.4 Transfer curve() output ()

Output power current collapse field-plate

gate , 3.5 pulsed I-V .

3.5 Gate head length pulsed I-V (2x50 )

bias point Vgs = 0V, gate lag Vgs = -5V, drain lag Vds = 10V, 20V , gate

head length drain 0.05/0.1/0.2 plot . T-gate

gate-drain field drain pulse 20V

Pulse width = 500ns, Separation = 1ms

23

30% drain . gate head length

current collapse , length

. current collapse bias RF

output power [21].

3.3 RF Measurement & Optimization

RF S-parameter .

3.6 S-parameter Smith chart

Small-signal parameters gain plot

3.17 .

Gate head length 0.05 , Gm.max Vgs

fmax Vds bias point , -20dB/decade extrapolation

151GHz fmax . RF power

cut-off breakdown voltage T-gate 3

9THz-V .

24

3.7 Overhang gate gain (2x50 )

T-gate parasitic

fmax . gate resistance 3.4 3.2

, RF transconduuctance 588mS/mm 683mS/mm

, finger parasitic

. current collapse

gate leakage current bias point

fmax

.

parasitic capacitance current gain cut-off

fT . drain bias Gm.max point 5V

.

gate head length current collapse

fmax, fT, Cgs, Cgd length

3.8 .

Vgs

= -2.5V, Vds

= 15V

2x50um

FT= 61GHz

Fmax(MAG)

= 151GHz

LF.GD = 0.05um Fmax

x BV = 9THz-V

Pre-de-embedded

25

3.8 Gate head length RF parameter (2x50 )

Gate head length current collapse

gate head drain 0.05 0.25 fmax

30GHz, fT 20GHz . Cgs

Cgd length parasitic capacitance .

current collapse trade-off

T-gate ,

current collapse gate leakage current output power

gate .

Cgs

= 120fF @ T-gate Cgd

= 9.9fF @ T-gate

fmax

= 135GHz @ T-gate f

T = 67GHz @ T-gate

26

4 Decrease of Gate Resistance by Double-head Gate

4.1 PR Planarization & Double-head gate

0.11 AlGaN/GaN HEMT RF power

T-gate parasitic

. gate

fmax .

Gate gate metal , gate length, gate width,

gate pad . scale layout gate

width, gate-pad gate metal top gate length

. 4.1 double-head gate .

27

4.1 Double-head gate

gate PR planar

coating . PR coating

[22] planar coating . PR

planar coating O2 plasma ashing etch back gate metal

. Planar coating gate PR etch back

metal , parasitic

.

PMGI/ZEP:thinner 2 coating e-beam dose selectivity

MIBK:MEK(3:2) developer patterning . Pattern

gate metal e-beam scattering pattern gate

head . Ni/Au(40/360 ) metal lift-off .

planar coating PR . PR

PR

PR copolymer(MMA) 2000rpm 8000 . PR

coating rpm 1500rpm rpm coating

coating uniformity etch back .

2000rpm coating

PR . 4.2 PR

rpm coating . Coating planar

uniformity .

28

4.2 Non-planarized coating SEM view

PR baking .

coating PR 3 thermal budget

. PMGI ZEP baking 190 baking

PR . Baking ZEP patterning develop

4.3 pattern edge crack .

copolymer .

4.3 Baking pattern crack (ZEP layer)

PMGI develop stop layer PR

. PMGI develop AZ300 bottom PR

4.4 etch back planar PR develop

29

. copolymer AZ300

planar .

4.4 Without etch stop layer (), with etch stop layer () SEM view

4.5 4.6 double-head gate SEM

. 230 stem 380 gate head length .

4.5 Double-head gate SEM view

PMGI

Copolymer

ZEP:thinner

30

4.6 Double-head gate SEM view

4.2 Pulsed I-V & RF Measurements

DC double-head gate

, current collapse .

4.7 Double-head gate I-V

385nm

230nm

31

Vturn-on Breakdown voltage (@1mA/mm) Hard breakdown voltage Gm.max

1.1V 40V ~90V 410mS/mm

4.1 Double-head gate DC

4.8 double-head gate pulsed I-V . bias

point Vgs = 0V, gate lag drain lag . Single-head gate field-

plate current collapse , air(=1) gap 2nd head

T-gate electric field

, .

4.8 Double-head gate pulsed I-V (2x50 )

4.9 4.10 fmax . MAG

-20dB/decade extrapolation single-head 20GHz

. bias point Gm.max Vgs = -2V, Vds fmax

15V. 4.2 gate resistance .

Pulse width = 500ns, Separation = 1ms

32

4.9 Single-head gate gain (4x37 )

4.10 Double-head gate gain (4x37 )

Single-head gate Double-head gate

Gate resistance 3.2 0.8

4.2 Double-head gate gate resistance

Vgs

= -2V, Vds

= 15V

4x37um

Fmax(MAG)

= 141GHz

Pre-de-embedded

Fmax

x BV = 5.6THz-V

Vgs

= -2V, Vds

= 15V

4x37um

Fmax(MAG)

= 160GHz

Pre-de-embedded

Fmax

x BV = 6.4THz-V

33

4.3 W-band GaN MMICs

4.3.1

0.11 AlGaN/GaN HEMT on Si fmax W-

band MMICs . MMICs

pinch-off current, threshold ,

Gm, output current

.

transfer curve .

2x2 AlGaN/GaN epi MMICs

layout 4.11 .

4.11 W-band MMICs 2x2 layout

, transfer curve

4.12 . Double-head gate metal 2nd

2cm

2cm

34

passivation layer SiNx 15 final passivation gate width

100 DC (1 finger) 35 .

4.12 35 double-head gate final passivation (), () transfer curve

final passivation 90% double-

head gate 0.11 AlGaN/GaN HEMT on Si

.

final passivation parasitic capacitance

trade-off . MMICs

Gm.max

= 410 mS/mm

(average)

Vth

= -3V (250mV)

VDS

= 5V

35

uniformity final passivation

.

4.3.2 MMIC

MMICs

. 4.13 MMICs .

2. SiNx Pre-passivation

3. Ohmic contact

5. Ohmic alloy &MESA Etching

6. SiNx Removal

1. Surface cleaning

Source Drain Source

7. SiNx Passivation

8. Gate process (foot, 1st

head, 2nd

head)

4. E-beam marker

36

4.13 AlGaN/GaN HEMT MMICs

, M1

metal layer . MMICs M1 metal M1

metal layer. inactive , inactive

SiNx passivation layer . buffer leakage path

. Buffer leakage path , RF loss , MIM

10. SiNx 2nd

passivation

11. NiCr TFR

12. Passive & Circuit M1 metal

13. MIM dielectric deposition & etching

14. Air bridge & M2 metal

9. Active M1 metal

37

capacitor NiCr TFR . MIM capacitor SRF

. 4.14 M1 metal buffer leakage current

. inactive carbon

doping epi buffer leakage path . GaN

epi SiNx layer M1 metal , MESA etching ion

implant buffer carrier . SiNx layer insulating

pad-to-pad leakage current .

SiNx layer , ion implant

buffer carrier pad-to-pad leakage current .

epi buffer , high-

resistivity Si GaN-on-Si .

4.14 Buffer leakage path metal pad-to-pad leakage current

M1 metal M1 layer MMICs signal line MIM

capacitors bottom metal roughness cleanliness .

post-gate annealing 400

annealing metal .

MIM capacitor breakdown voltage .

M1 metal MIM dielectric M1

38

metal cleanliness MIM

capacitor breakdown .

Au metal source splitting M1 metal

rough , MIM capacitor breakdown metal

source cleaning [23]. 4.15 Au metal roughness

.

4.15 Au metal roughness AFM (), SEM view()

NiCr TFR . MMICs

TFR 20/sq , NiCr 1000 .

M1 metal (Ni/Au 40/460) , N2/NH3 SiNx 1000 MIM

dielectric 250 ICP-CVD chamber .

MIM capacitor NiCr TFR B.O.E

1:7 wet etching . passivation layer SiNx MIM

dielectric SiNx wet etch rate MIM dielectric wet etching

passivation layer SiNx etch stop .

air-bridge M2 metal (Ti/Au 50/1500)

.

Roughness Average = 1.6 nm

39

4.15 W-band MMICs Micro-depth Image

40

5

5.1

RF power AlGaN/GaN HEMT

current collapse MMICs

. GaN-on-Si , gate

length current collapse RF power

output power .

current collapse gate-drain

electric field field-plate .

parasitic

. current collapse RF

power output power , field-

plate parasitic 0.11 gate .

gate double-head gate parasitic

maximum oscillation frequency . 90%

, W-band MMICs .

5.2

0.11 AlGaN/GaN HEMT on Si current collapse ,

fmax , millimeter-wave power .

GaN-on-Si epitaxial

layer design. SiC RF epi

growth design dislocation , buffer loss

current collapse, leakage current .

41

current collapse

passivation layer .

PEALD passivation , .

gate leakage current SF6 plasma

fluorine trap current collapse , kink [24]

.

double-head gate 1st gate metal , 2nd gate metal

. 2nd gate head stem double-head

parasitic capacitance , gate resistance

.

42

[1] U. K. Mishra, L. Shen, T. E. Kazior, Y. F. Wu, GaN-Based RF Power Devices and Amplifiers,

Proceedings of the IEEE, Vol. 96(2), pp. 287-305, Feb. 2008.

[2] S. Azam, Q. Wahab, The present and future trends in High Power Microwave and Millimeter

Wave Technologies, InTechOpen, Mar, 2010.

[3] T. Kikkawa, K. Joshin, M. Kanamura, GaN Device for Highly Efficient Power Amplifiers,

FUJITSU Sci. Tech. J., Vol. 48, No. 1, pp. 40-46, Jan. 2012.

[4] H. Sun, D. Marti, S, Tirelli, A. R. Alt, H. Benedickter, C. R. Bolognesi, Millimeter-wave GaN-

based HEMT development at ETH-Zurich, International Journal of Microwave and Wireless

Technologies, 2(1), 33-38, Apr. 2010.

[5] S, Tirelli, D. Marti, H. Sun, A. R. Alt, H. Benedickter, E. L. Piner, C. R. Bolognesi, 107-GHz

(Al,Ga)N/GaN HEMTs in Silicon With Improved Maximum Oscillation Frequencies, IEEE

Electron Device Letters, Vol. 31, No. 4, Apr. 2010.

[6] R. Vetury, N. Q. Zhang, U. K. Mishra, The Impact of Surface States on the DC and RF

Characteristics of AlGaN/GaN HFETs, IEEE Transactions on Electron Devices, Vol. 48, No. 3,

Mar. 2001.

[7] J. W. Chung, W. E. Hoke, E. M. Chumbes, T. Palacios AlGaN/GaN HEMT With 300-GHz fmax,

IEEE Electron Device Letters, Vol. 31, No. 3, Mar. 2010.

[8] F. Medjdoub, M. Zegaoui, B. Grimbert, D. Ducatteau, N. Rolland, and P. A. Rolland, First

Demonstration of High-Power GaN-on-Silicon Transistors at 40 GHz, IEEE Electron Device

Letters, Vol. 33, No. 8, Aug. 2012.

43

[9] J. C. Her, H. J. Cho, C. S. Yoo, H. Y. Cha, J. E. Oh. K. S. Seo, " SiNx prepassivation of

AlGaN/GaN high-electron-mobility transistors using remote-mode plasma-enhanced chemical

vapor deposition, Japanese Journal of Applied Physics, Vol. 49, pp. 041002, Apr. 2010.

[10] L. Wang, F. M. Mohammed, & I. Adesida, Differences in the reaction kinetics and contact

formation mechanisms of annealed Ti/Al/Mo/Au Ohmic contacts on n-GaN and AlGaN/GaN

epilayers, Journal of Applied Physics, 101, 013702, Jan. 2007.

[11] G. Vanko, T. Lalinsky, S. Hascik, I. Ryger, Z. Mozolova, J. Skriniarova, M. Tomaska, I. Kostic,

A. Vincze, Impact of SF6 plasma treatment on performance of AlGaN/GaN HEMT, Vacuum 84,

235-237, 2010.

[12] M. Wang & K. J. Chen, Improvement of the Off-State Breakdown Voltage With Flourine Ion

Implantation in AlGaN/GaN HEMTs, IEEE Transactions on Electron Devices, Vol. 58, No. 2,

Feb. 2011.

[13] J. H. Kim, H. G. Choi, M. W. Ha, H. J. Song, C. H. Roh, J. H. Lee, J. H. Park & C. K. Hahn,

Effects of nitride-based pretreatment prior to SiNx passivation in AlGaN/GaN high-electron

mobility transistors on silicon substrates, Japanese Journal of Applied Physics, Vol. 49, No. 4,

pp. 04DF05-1, Apr. 2010.

[14] S. Han, Y. H. Oh, M. S. Lee, D. H. Kim, K. S. Seo Influence of in situ N2 Plasma Pretreatment

on the SiN Prepassivation of AlGaN/GaN HEMT, International Conference on Solid State

Devices and Materials, pp. 212-213. 2012.

[15] A. S. Wakita., et al., Novel high yield tri-layer resist process for 0.1 T-gate fabrication,

Journal of Vacuum Science & Technology B, Vol. 13, (6), pp. 2725-2728, Nov. 1995.

[16] D. J. Meyer, B. P. Downey, R. Bass, D. S. Katzer, S. C. Binari, 40nm T-Gate Process

Development using ZEP Reflow, CS MANTECH Conference, Apr. 2012.

[17] S. Sudharsanan & Shreepad Karmalkar, Modeling of reverse gate leakage in AlGaN/GaN high

44

electron mobility transistors, Journal of Applied Physics, 107, 064501, Mar. 2010.

[18] Yi Pei, S. Rajan, M. Higashiwaki, Z. Chen, S. P. DenBaars, U. K. Mishra, Effect of Dielectric

Thickness on Power Performance of AlGaN/GaN HEMTs, IEEE Electron Device Letters, Vol.

30, No. 4, Apr. 2009.

[19] W. Saito, M. Kuraguchi, Y. Takada, K. Tsuda, I. Omura, T. Ogura, Influence of Surface Defect

at AlGaN/GaN HEMT Upon Schottky Gate Leakage Current and Breakdown Voltage, IEEE

Transactions on Electron Devices, Vol. 52, No. 2, Feb. 2005.

[20] M. Wang & K. J. Chen, Kink Effect in AlGaN/GaN HEMTs Induced by Drain and Gate

Pumping, IEEE Electron Device Letters, Vol. 32, No. 4, Apr. 2011.

[21] S. C. Binari, K. Ikossi, J. A. Roussos, W. Kruppa, D. Park, H. B. Dietrich, D. D. Koleske, A. E.

Wickenden, R. L. Henry, Trapping Effects and Microwave Power Performance in AlGaN/GaN

HEMTs, IEEE Transaction on Electron Devices, Vol. 48, No. 3, Mar. 2001.

[22] G. J. Burek, M. A. Wistey, U. Singnisetti, A. Nelson, B.J. Thibeault, S. R. Bank, M. J. W.

Rodwell, A. C. Gossard, Height-selective etching for regrowth of self-aligned contacts using

MBE, Journal of Crystal Growth, 311, Nov. 2008.

[23] J. Maeng, Development of Embedded Capacitor in a Thin-film Multichip Module-Deposited

Architecture, Seoul National University, Master Thesis, Feb. 2008.

[24] R. Cuerdo, Y. Pei, Z. Chen, S. Keller, S. P. DenBarrs, F. Calle, and U. K. Mishra, The Kink

Effect at Cryogenic Temperatures in Deep Submicron AlGaN/GaN HEMTs, IEEE Electron

Device Letters, Vol. 30, No. 3, Mar. 2009.

45

Abstract

In this thesis, improvement of fmax on AlGaN/GaN HEMTs by reducing current collapse effects

and gate leakage current was studied for W-band power applications.

In general, the advantages of GaN are the higher electron mobility, saturation velocity, and

thermal conductivity than other semiconductor materials such as Si and GaAs. And one of the most

superior characteristic is high breakdown voltage because of high energy band gap, so high power

density makes possible that size of GaN module can be small. Through these features, GaN based

HEMT has investigated for substituting Si, GaAs RF power device, and AlGaN/GaN on high

resistivity Si(111)- substrate is a low cost solution for the lower microwave frequency bands.

On the other hand, the problems of these sub-micrometer AlGaN/GaN HEMTs that have not

been cleared yet are current collapse effects and gate leakage currents. To reduce these drawbacks,

gate with field plate structure was adopted instead of T-gate structure which was used generally to

reduce parasitic effects, and the applied gate structure was optimized by splitting the length of field

plate. As a result, the degradation by parasitic effects was minimized, and possible bias range was

increased. The gate resistance of optimized device was additionally required to be small to improve

fmax. From this reason, double-head gate process was challenged and high fmax was obtained.

The results in this research showed capacities of AlGaN/GaN HEMTs on Si-substrate that can be

applied for power device at W-band.

keywords : AlGaN/GaN HEMTs, millimeter-wave, gate structure, current collapse,

gate resistance

Student Number : 2011-23356

1 1.1 1.2

2 Conventional AlGaN/GaN W-band Power HEMT2.1 Sub-micrometer AlGaN/GaN HEMT 2.2 DC & Pulsed I-V Measurements2.3 RF Measurement

3 AlGaN/GaN HEMT with Gate Field-plate Structure3.1 Overhang gate length split3.2 Current collapse gate leakage current 3.3 RF Measurement & Optimization

4 Decrease of Gate Resistance by Double-head Gate4.1 PR Planarization & Double-head gate 4.2 Pulsed I-V & RF Measurements4.3 W-band GaN MMICs(Monolithic Microwave Integrated Circuits) 4.3.1 4.3.2 MMIC

5 5.1 5.2

Abstract