Graphene Field-Effect Transistors on Hexagonal Boron Nitride … · 2015. 6. 8. · Gate sweeps and IV curves for SP34 (hBN) 13.04.2012. Christian Benz-2,5 -2,0 -1,5 -1,0 -0,5 0,0

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association

Institute of Nanotechnology; Physikalisches Institut, Faculty of Physics, KIT

www.kit.edu

13.04.2012

Graphene Field-Effect Transistors on Hexagonal Boron Nitride Operating at Microwave Frequencies Christian Benz1,4, Emiliano Pallecchi2, Zeineb Ben Aziza1,4, Jens Mohrmann1,4, Andreas C. Betz2, Kenji Watanabe3, Takashi Taniguchi3, Hilbert v. Löhneysen1,4, Bernard Plaçais2, and Romain Danneau1,4 1Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Germany — 2Laboratoire Pierre Aigrain, Ecole Normale Supérieure, Paris, France — 3National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan — 4Physikalisches Institut, KIT, Germany

Institute of Nanotechnology, KIT 2

Outline

1. Introduction to graphene RF applications

2. Graphene FETs at microwave frequencies

2.1 GFETs on sapphire substrates 2.2 Using hexagonal boron nitride (hBN) 2.3 Using hBN & few-layer graphene gates

3. Summary & conclusions

Christian Benz 13.04.2012


Graphene RF applications

High carrier mobility & thinness

Focus on analog RF (small on/off ratio ~2 – 20)

High transit frequencies fT


14.7 GHz 100 GHz 155 GHz 300 GHz Meric et al. (2008) Lin et al. (2010) Wu et al. (2011) Liao et al. (2010) Columbia University IBM T. J.Watson R.C. IBM T. J.Watson R.C. University of California Tech. Dig. IEDM 4796738 Nano Lett. 9, 422 Nature 472, 74 Nature 467, 305

350 GHz Sung et al. (2012) IBM


Broadband RF mixer / voltage amplifier


Lin Y.-M., Valdes-Garcia A., Han S.-J., et al. Science, 332(6035):1294-1297

Han S.-J., Jenkins K.A., Valdes-Garcia A., et al. Nano letters; 2011;11(9):3690-3


Problems / our approach

Interactions with the substrate

Impurity scattering

Losses due to resistivity

Sapphire substrate

Interaction with the gate dielectric

Inertness of graphene

Oxidized Al + Al2O3 (ALD)

Later: hexagonal boron nitride


Si/SiO2

Institute of Nanotechnology, KIT 6 Christian Benz 13.04.2012

Test setup at ENS, Paris

AC AC DC DC


Microwave measurements

S-parameter measurement with vector network analyzer (VNA)

GFET + pads GFET dummy-open dummy-short

De-embedding (subtracting parasitic capacitances) Ydeemb = YGFET - Ydummy

Extraction of current gain |h21| and transit frequency fT


S S G D S S

Source Gate Drain Source


RF performance of our GFET on sapphire

1 10 100

1

10

100

1000

1 100,1

1

10

0,1

1

10

Cur

rent

gai

n Ih

21I

f (GHz)

-101

-1,0 -0,5 0,0 0,5 1,0

Vds (V) g

mRF

(mS)

U

MAG

f (GHz)


~ 1/f

fT ~ 3 GHz fT-deemb ~ 80 GHz

Pallecchi E., Benz C., et al. Appl. Phys. Lett. 99(11):113502 (2011)

gmRF max = 250 µS/µmV

Similar performance @ 300K & 77K


RF transistors on hBN


Atomically flat -> higher mobility

Gate dielectric with κ = 4

Reversed preparation cycle

Transfer of exfoliated

hBN and graphene

Graphene hBN

Wang H et al. Electron Device Lett., IEEE. 2011;32(99):1–3


Linear IV characteristics Vds -1.0 to 1.0V Ids max ~ 9 mA

Gate sweep to find maximum transconductance

Gate sweeps and IV curves for SP34 (hBN)


-2,5 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0100

110

120

130

140

150

160

170

180

190

200

210

220

230

R ds (Ω

)

Vg (V)

Vds 0.08 V 0.2 V 0.5 V 0.8 V 1.2 V

0,00 0,25 0,50 0,75 1,000,000

0,125

0,250

0,375

0,500

0,625

Vg 0.80 V 0.40 V 0 V -0.40 V -0.80 V

I ds (m

A/µm

)

Vds (V)


S-parameter measurement up to 40 GHz Gate length 100 nm, channel width ~ 16 µm fT ≈ 53 GHz gmRF ≈ 90 µS/µm

1 100

25

50

75

100

Re[Y

21] (

µS/µ

m)

Frequency (GHz)40 0,1 1 10 100

0,1

1

10

100

1000

curre

nt g

ain

|h21

|

Frequency (GHz)

h21 h21 (de-embeded)

RF results from SP34 (hBN)


fT = 6.4 GHz

fT ~ 53 GHz


Ripples in Graphene on hBN



RF transistors on hBN with graphene gates


Few-layer graphene gate

Improved flatness

Total device thickness: < 10 nm

Only one metal evaporation step


Preparation steps – ML graphene gate device


Exfoilation of (multilayer) graphene




Oxygen plasma etch




Transfer of hBN flake (highlighted)




Transfer of mono-layer graphene flake




Electron beam lithography: PMMA mask




Metal evaporation Ti (10nm) / Al (100 nm)

Gate Drain

Source

Source


AFM – less ripples / bubbles due to dry transfer


Source


Gate sweeps and IV curves for SP38

0,0 0,2 0,4 0,6 0,80,00

0,04

0,08

0,12

0,16

0,20

0,24

0,28

I ds (m

A/µm

)

Vds (V)

Gate voltage Vg 0.2 V 0.3 V 0.4 V 0.5 V 0.6 V 0.7 V 0.8 V


-1,2 -1,0 -0,8 -0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2

40

60

80

100

R ds (Ω

)

Vg (V)

SP38_1_-1.00Vg»[email protected] SP38_2_1.00Vg»[email protected]

Small hysteresis

Linear IV characteristics


Gate length 100 nm, channel width ~ 27 µm

1 10 100

1

10

100

h21

Frequency (GHz)

SP48 (Vds = 0.53V, Vg = 0.46V)fT = 4.8 GHz h21fT = 27.1 GHz h21 (deembedded)

Experimental results from SP48


fT = 4.8 GHz

fT ~ 27 GHz


Summary & Conclusion


Sapphire – suitable low loss substrate for RF

hBN – substrate and gate dielectric < 4 nm

Few-layer graphene gates applicable

Device thicknesses < 10 nm

Future applications & experiments

Monolayer graphene gate / bilayer channel

Transparent electronics

Integration into cryogenic amplifier


E. Pallecchi, A. C. Betz, and B. Plaçais at ENS, Paris K. Watanabe and T. Taniguchi at NIMS, Japan for hBN crystals


Romain Danneau, Kristina Hönes, Jens Mohrmann, Christian Benz, Simon Ketterer, Julien Bordaz, Pablo Robert, Zeineb Ben Aziza and Renjun Du

Acknowledgments

Appl. Phys. Lett. 99(11):113502


E. Pallecchi, A. C. Betz, and B. Plaçais at ENS, Paris K. Watanabe and T. Taniguchi at NIMS, Japan for hBN crystals


Romain Danneau, Kristina Hönes, Jens Mohrmann, Christian Benz, Simon Ketterer, Julien Bordaz, Pablo Robert, Zeineb Ben Aziza and Renjun Du

Acknowledgments

Appl. Phys. Lett. 99(11):113502

Thank you for your attention!

Slide Number 1OutlineGraphene RF applicationsBroadband RF mixer / voltage amplifierProblems / our approachSlide Number 6Microwave measurementsRF performance of our GFET on sapphireRF transistors on hBNGate sweeps and IV curves for SP34 (hBN)RF results from SP34 (hBN)Ripples in Graphene on hBNRF transistors on hBN with graphene gatesPreparation steps – ML graphene gate devicePreparation steps – ML graphene gate devicePreparation steps – ML graphene gate devicePreparation steps – ML graphene gate devicePreparation steps – ML graphene gate devicePreparation steps – ML graphene gate deviceAFM – less ripples / bubbles due to dry transferGate sweeps and IV curves for SP38Experimental results from SP48Summary & ConclusionSlide Number 24Slide Number 25

Documents

Graphene Field-Effect Transistors on Hexagonal Boron Nitride … · 2015. 6. 8. · Gate sweeps and IV curves for SP34 (hBN) 13.04.2012. Christian Benz-2,5 -2,0 -1,5 -1,0 -0,5 0,0