graphene field-effect transistors on hexagonal boron nitride … · 2015. 6. 8. · gate sweeps and...
TRANSCRIPT
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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
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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
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Institute of Nanotechnology, KIT 3
Graphene RF applications
High carrier mobility & thinness
Focus on analog RF (small on/off ratio ~2 – 20)
High transit frequencies fT
Christian Benz 13.04.2012
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
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Institute of Nanotechnology, KIT 4
Broadband RF mixer / voltage amplifier
Christian Benz 13.04.2012
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
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Institute of Nanotechnology, KIT 5
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
Christian Benz 13.04.2012
Si/SiO2
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Institute of Nanotechnology, KIT 6 Christian Benz 13.04.2012
Test setup at ENS, Paris
AC AC DC DC
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Institute of Nanotechnology, KIT 7
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
Christian Benz 13.04.2012
S S G D S S
Source Gate Drain Source
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Institute of Nanotechnology, KIT 8
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)
Christian Benz 13.04.2012
~ 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
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Institute of Nanotechnology, KIT 9
RF transistors on hBN
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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
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Institute of Nanotechnology, KIT 10
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)
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-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)
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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)
Christian Benz 13.04.2012
fT = 6.4 GHz
fT ~ 53 GHz
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Institute of Nanotechnology, KIT 12
Ripples in Graphene on hBN
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Institute of Nanotechnology, KIT 13
RF transistors on hBN with graphene gates
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Few-layer graphene gate
Improved flatness
Total device thickness: < 10 nm
Only one metal evaporation step
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Preparation steps – ML graphene gate device
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Exfoilation of (multilayer) graphene
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Preparation steps – ML graphene gate device
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Oxygen plasma etch
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Preparation steps – ML graphene gate device
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Transfer of hBN flake (highlighted)
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Preparation steps – ML graphene gate device
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Transfer of mono-layer graphene flake
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Preparation steps – ML graphene gate device
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Electron beam lithography: PMMA mask
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Preparation steps – ML graphene gate device
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Metal evaporation Ti (10nm) / Al (100 nm)
Gate Drain
Source
Source
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AFM – less ripples / bubbles due to dry transfer
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Source
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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
Christian Benz 13.04.2012
-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
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Institute of Nanotechnology, KIT 22
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
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fT = 4.8 GHz
fT ~ 27 GHz
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Institute of Nanotechnology, KIT 23
Summary & Conclusion
Christian Benz 13.04.2012
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
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Institute of Nanotechnology, KIT 24
E. Pallecchi, A. C. Betz, and B. Plaçais at ENS, Paris K. Watanabe and T. Taniguchi at NIMS, Japan for hBN crystals
Christian Benz 13.04.2012
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
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Institute of Nanotechnology, KIT 25
E. Pallecchi, A. C. Betz, and B. Plaçais at ENS, Paris K. Watanabe and T. Taniguchi at NIMS, Japan for hBN crystals
Christian Benz 13.04.2012
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