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S2DEL - Solid State and Diamond Electronics LabROMATRE
Università degli Studi
1/26
Gennaro (Rino) Conte
E. Giovine
A. Bolshakov, V.G. Ralchenko, V. Konov
Surface Channel MESFETs
on H-Terminated Diamond
Nano and Giga Challengesin Electronics, Photonics and Renewable EnergyMoscow - Zelenograd, Russia, September 12-16, 2011
S2DEL - Solid State and Diamond Electronics LabROMATRE
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Outline
Why Diamond ?
Hydrogenated Diamond: 2DHG ?
Technology Issues
DC and RF MESFETs performance
Fast optically triggered switches?
Conclusions
S2DEL - Solid State and Diamond Electronics LabROMATRE
Università degli Studi
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Wide Band Gap Semiconductors: an overview
MaterialBand gap
Thermal
conductivity
Breakdown
electric field
EBD
Mobility
holes
Carriers sat.
velocity vsat
Dielectric
constant εr
eV W/cmK 106 V/cm cm2/Vs 107 cm/s -
Diamond 5.5 22 10 1900 2.7 5.7
Gallium nitride 3.45 1.3 2.5 130 2.5 8.9
Silicon carbide 3.27 4.9 3.0 50 2.0 9.7
Gallium Arsenide 1.42 0.46 0.4 320 0.8 12.9
Silicon 1.12 1.5 0.3 480 1.0 11.8
Germanium 0.67 0.58 0.1 1900 1.0 16.2
Johnson[a] FoM = (EBD2vsat
2)/(4π2) EBD vsat = Vmax fmax
Keyes[b] FoM = λ (c vsat/4πε0)1/2
λ: thermal conductivity, c: speed of light
a) E. O. Johnson, "Physical Limitations on Frequency and Power Parameters of Transistors," RCA Review, vol. 26, pp. 163-177, 1965.
b) R. W. Keyes, "Figure of Merit for Semiconductors for High Speed Switches," Proc.IEEE, vol. 60, pp. 225-232, 1972.
Why diamond ?
S2DEL - Solid State and Diamond Electronics LabROMATRE
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Si InP GaAs SiC GaN C
JFoM
KFoM(normalized to Si)
Wide Band Gap Semicondutors: an overview
Communications
Satellite
Wireless
stations
Mobile
terminals
Wireless
LAN
Broadcasting
Stations
Radar
Wide Band Gap Semicondutors are the answer for
High-frequency and High-power applications
Why diamond ?
S2DEL - Solid State and Diamond Electronics LabROMATRE
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Diamond samples grown by Chemical Vapor Deposition (CVD) with CH4 + H2
Single Crystal Plates on HPHT (high pressure high temperature) 5x5 mm2 substrate (SCD)
Polycrystalline diamond on 2-4“ Silicon wafers (PCD)
CVD Diamond for Electronics
Ulm University, Germany
Diamond MaterialsFraunhofer Institute IAF in Freiburg, Germany
Delaware Diamond Knives, DDK Inc.Wilgminton, USA
SCD PCD
element six ltdAscot, Berkshire, UK
General Physics Institute RASMoscow (Russia)
Why diamond ?
S2DEL - Solid State and Diamond Electronics LabROMATRE
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• 1982: diamond based PNP transistorJ. Prins, Appl. Phys. Lett. 41
• 1987: boron doped diamond FETM. W. Geis et al., IEEE Elect. Dev. Lett., 8
• 1991: ion-implanted diamond FETC. Zeisse et al., IEEE Elect. Dev. Lett., 12
• 1992: polycrystalline diamond FETA. J. Tessmer, et al., Diamond Relat. Mater., 1
• 1992: delta-doped diamond FETsN. Fujimori, et al., Diamond Relat. Mater., 1
Diamond based transistors history
• 1994: H-terminated diamond based FETH. Kawarada, et al., Appl. Phys. Lett. 65
• 1997-1999: H-terminated diamond FETs improvementsP. Gluche, et al. IEEE Elect. Dev. Lett., 18 (1997), T. Yun, et al. J. Appl. Phys. 82 (1997)
• 1999: results for -doped technologyA. Aleksov, E. Kohn et al., Diamond Relat. Mat. 8
• 2001: RF performances reported for H-terminated Single Crystal DiamondH. Taniuchi, et al., IEEE Elect. Dev. Lett. 22
• 2005: RF Power performances reported for H-terminated Single Crystal DiamondM. Kasu, et al., Elect. Letters, 41
• 2006: best RF performances reported for H-terminated polycrystalline diamondK. Ueda, et al., IEEE Elect. Dev. Lett. 27
• 2008: RF performances achievement for delta-doped diamond technologyA. El-Hajj, et al., Diamond Relat. Mater. 17
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RF Record performances
K. Ueda et al., Diamond FET using high-quality polycrystalline diamond with fT of
45 GHz and fMax of 120 GHz, IEEE Electron Device Letters, 27 (2006) 570.
Polycrystalline Diamond
21 2
12
2
2 2121
21 12 11 22
11 22 21 12
2 2
11 22
1
2
1 1
1 1
'
SMAG K K
S
SH
S S S S
S S S SU
S S
K Rollett s Stability Factor
Figures of Merit
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Plasma assisted Hydrogen termination of CVD Diamond induces p-type conductive channel [a]
a) M.I. Landstrass & K.V. Ravi “The Resistivity of CVD Diamond Films” Appl. Phys. Lett. 55, 975 (1989)
b) F. Maier, M. Riedel, B. Mantel, J. Ristein, L. Ley “Origin of Surface Conductiviy in Diamond” Phys. Rev. Lett. 85, 16 (2000)
c) C. E. Nebel, B. Rezek, A. Zrenner “2D-hole accumulation layer in hydrogen terminated diamond” Phys. Stat. Sol. 201, 11 (2004)
d) V. Chakrapani, J. C . Angus, et al. “Charge Transfer Equilibria between diamond and an acqueous Oxygen Electrochemical redox couple” Science 318 (2007)
e) T. Maki, S. Shikama. M. Komori, et al “Hydrogenating Effect of Single-Crystal Diamond Surface” Jap. J. Appl. Phys. 31 (1992)
• Surface band bending where valence-band electrons transfer into an adsorbate layer: “transfer doping model”[b,c,d]
• Shallow hydrogen induced acceptors[e]
Diamond surface hydrogenationHydrogenated Diamond: 2DHG ?
Electrons from the valence-band diffuse into empty electronic states of the adsorbate layer as long as the chemical
potential µe is lower than the Fermi energy
S2DEL - Solid State and Diamond Electronics LabROMATRE
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10-15
10-14
10-13
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
0 5 10 15 20
Co
nd
uctiv
ity (S
/cm)
1000/T (K-1
)
Co
nd
uct
ivit
y (
S/c
m)
Ea= 0.9 eV
Ea= 3 meV
Polycrystalline Diamond
1 cm2, Ag 200 nm
Average Roughness 2-8 nm
H-Terminated Surface
O-Terminated Surface
Hydrogen Termination Analysis
0
5
10
15
20
0 50 100 150 200
Poly-Ra270
Hydrogenated
TLM-Au
Z=150 m
C3-B
C5-B
C14-B
y = 0.084211 + 0.10279x R= 0.99779
RT (
k
Distance, d ( m)
(2RC) (R
Sh/Z)
LT=2.5 m
C=2.5x10
-5 cm
2
S2DEL - Solid State and Diamond Electronics LabROMATRE
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0
20
40
60
80
100
120
140
0 10 20 30 40 50
E6 High Quality SCD
E6 Standard SCD
RAS SCD P14MS
RAS PolyD4
Hall
Mo
bil
ity (
cm
2/V
s)
1000/T (K-1
)
EA=1.6 meV
EA
=1.8 meV
EA=4.1 meV
EA<0.2 meV
1012
1013
1014
0 10 20 30 40 50 60
RAS Polycrystalline D4
RAS SCD P14MS
E6 High Quality SCD
E6 Standard SCD
Ho
le d
en
sity
(cm
-2)
1000/T (K-1
)
Carriers density value of 1013 cm-2 is
temperature independent, as expected
for 2D transport in extended states
and in the absence of localizations.
Mobility activation occurs around 50-60 K
When T<50 K, µ is T independent with very low EA
Mobility and carriers activation energy EA are in relation with diamond surface
quality, in particular to surface roughness and crystallographic defects
Hydrogen Termination AnalysisHall mobility
S2DEL - Solid State and Diamond Electronics LabROMATRE
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a) C.E. Nebel, F. Ertl , C. Sauerer , M. Stutzmann , C.F.O. Graeff , P. Bergonzo , O.A. Williams, R.B. Jackman Diamond Relat. Mater. 11 (2002) 351–354
b) K. Hayashi, S. Yamanaka, H. Watanabe, T. Sekiguchi, H. Okushi, K. Kajimura J. Appl. Phys. 81 (1997) 744-753
c) J. A. Garrido, T. Heimbeck, And M. Stutzmann Phys. Rev. B71 (2005) 245310
100
101
102
101
102
103
E6 HQ SCD
E6 St SCD
RAS SCD P14MS
RAS PolyD4
PolyCVD (A) Ref.[a]
Nat.IIa (C) Ref.[a]
SCD Ref.[b]
SCD Ref.[c]
Hall
Mo
bil
ity (
cm2/V
s)
1000/T (K-1
)
Higher RT values have been
found with different techniques
Hydrogen Termination AnalysisSurface doping
10-13
10-11
10-9
10-7
10-5
-6 -4 -2 0 2 4 6
H-Terminated
SCD SQ E6
4.5x4.5x0.5 mm
Al/Au 205K
207.5
220K
240K
260K
280K
292K
300K
Cu
rren
t (A
)
Voltage (V)
B=0.75 0.05 eV
Rs= 38 k
n= 1.3
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diamondReactive Ion Etching (RIE)
Ar + O2 Ar + O2
Resist
H
diamond Hydrogen Termination:
H-terminated layer
Device Technology Issues
Ohmic Contact
Au
Drain-Source Channel
Wet etching: KI+O2+H20
EBL resist
Gate Electrode EBL resist
Aluminum
After EBL resist stripping
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Device Layout
25 μm ≤ WG ≤ 200 μm
0.2 μm ≤ LG ≤ 1 μm
Small H-terminated area for leakage current reduction and
electric field confinement.
2D Hole Channel
Drain(Au)
Gate(Al)Source
(Au)Source
(Au)
CVD Diamond
WG
Device Technology Issues
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C-V and charge carriers depth profile
130
20
; sd d
s
AdN x x
qA dVC C
C
-4 -3 -2 -1 0 1 2 3 4
SAG FET
L=400 nm, W=50 m
1MHz
Cap
aci
tan
ce (
pF
) C-2 x
10
24 (F
-2)
Voltage, VGS
(V)
10
5
15
20
25
0
0.6
0.4
0.8
1
1.2
0
0.2
0.93 pF
VBi
=-0.1V
Device Technology Issues
1 10 100
100 kHz
10 kHz
1 MHz
Ho
le D
en
sity
x1
01
3 (
cm
-2)
xd (nm)
10
1.0
0.1
0.01
Self-Aligned Gate FET
LG
=1 m
WG
=200 mf
Tail
Channel
Increasing frequency the channel is
pushed down below the surface
1/2
0dx x
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0
5
10
15
20
-3 -2 -1 0 1 2
TM180 E6 IV21
L = 2 m W = 50 m
Vds=0.00
-0.50
-1.00
-1.50
-2.00
-2.50
-3.00
-3.50
-4.00
-4.50
-5.00
-5.50
-6.00
-6.50
-7.00
-8.00
-10.00
-13.00
-20.20
-25.00
|ID
S| (
mA
/mm
)
VGS
(V)
Vth
Thermal Management Grade E6 No-SAG
0
1
2
3
4
5
6
7
8
-3 -2 -1 0 1 2
TM180 E6 IV21
L = 2 m
W = 50 m0.00
-0.50
-1.00
-1.50
-2.00
-2.50
-3.00
-3.50
-4.00
-4.50
-5.00
-5.50
-6.00
-6.50
-7.00
-8.00
-10.00
-13.00
-20.20
-25.00
gm
(m
S/m
m)
VGS
(V)
VDS
Mobility degradation and/or
series resistance effects
Short channel effects are visible
Polycrystalline Diamond
DC and RF MESFETs performances
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-20
-10
0
10
20
30
40
0,1 1 10 100
MAG [dB]
|H21
|2 [dB]
VDS
= -18 V VGS
= 0.0 V
Gain
(d
B)
Frequency (GHz)
LG= 200 nm
WG=200 µm
fMAX=14.1 GHz
fT=4.1 GHz
Thermal Management Grade TM180 by Element Six
-20 dB/dec.
Gain@1GHz
11 dB
Old RF Layout
fMAX/fT=3.5
-20
-10
0
10
20
30
40
0,1 1 10 100
MAG [dB]
|H21
|2 [dB]
VDS
= -14 V VGS
= -0.3 V
Gain
(d
B)
Frequency (GHz)
New RF Layout
LG= 200 nm
WG=50 µm
fMAX=14.9 GHz
fT=6.1 GHz
-20 dB/dec.
Gain@1GHz
15 dB
fMAX/fT=2.4
DC and RF MESFETs performances TM180 by Element Six SAG FET
Slight dependence on VDS addresses not yet saturated carrier velocity
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TM180 by Element Six SAG FET
Better performance is obtained
near the threshold voltage VTh
New RF Layout
Near the threshold, CGS decreases
faster than gm,p: holes channel charge
is pushed into the substrate down to a
region of higher mobility.
0,1
1
10
-4-3-2-10123
fMax
fT
Freq
uen
cy (
GH
z)
VGS
(V)
VDS
=-14V
VGS
=-0.3V
10-13
10-12
1
10
-4-3-2-10123
Ca
pa
cita
nce
(F/m
m) g
m,p (m
S/m
m)
VGS
(V)
gm,p
CGS
gm,max
LG= 200 nm
WG=50 µm
0
5
10
15
20
25
30
35
0 2 4 6 8 10 12 14
New Layout
Old Layout
f Ma
x (G
Hz)
fT (GHz)
=3.3
=2.0
DC and RF MESFETs performances
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0
20
40
60
80
100
120
140
0 20 40 60 80 100
0.0 V
-0.25 V
-0.5 V
-0.75 V
-1.0 V
-1.25 V
-1.5 V
-1.75 V
-2.0 V
-2.25 V
-2.5 V
-2.75 V
-3.0 V
-3.25 V
-3.5 V
I DS (
mA
/mm
)
VDS
(V)
RAS P7MS SAG
LG
=0.4 m, WG
=25 m
VGS
RAS Single Crystal Diamond
Channel conductance is always positive. No self-heating effects!
70VFappl = 1.87 MV/cm
0
20
40
60
80
100
120
0
10
20
30
40
50
-4 -3 -2 -1 0 1
RAS P7MS SAG
LG=0.4 m
WG=25 m
-5V
-20V
-60V
gm (mA/mm/V) Vds=-5V
gm (mA/mm/V) Vds=-20V
gm (mA/mm/V) Vds=-60V
I DS (
mA
/mm
)
gm
(mS
/mm
)
Vgs (V)
VTh
=-0.4V
Threshold Voltage=-0.4V
DC and RF MESFETs performances
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-10
0
10
20
30
40
0,1 1 10 100
MAG [dB]
|H21
|2 [dB]
Ga
in (
dB
)
Frequency (GHz)
-20 dB/dec.
VGS=-0.2 V, VDS=-10 V
Gain = 15 dB@ 1 GHz
Eapplied= 0.5 MV/cm
WG=25 μm
fMAX = 23.7 GHz
fT = 6.9 GHz
Polycrystalline Diamond
RAS PolyD4
fMAX/fT=3.5-10
0
10
20
30
40
0,1 1 10 100
MAG [dB]
|H21
|2 [dB]
Ga
in (
dB
)
Frequency (GHz)
Single Crystal Diamond
RAS P7MS
Wg=50 μm
fMAX =26.3 GHz
fT = 13.2 GHz
Gain = 22 dB @ 1 GHz
fMAX/fT=1.8
LG=0.2 μm
RF PerformancesDC and RF MESFETs performances
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-20
-10
0
10
20
30
40
0,1 1 10 100
MAG [dB]
|H21
|2 [dB]
Ga
in (
dB
)
Frequency (GHz)
-20 dB/dec.
Lg=0.2 μm, Wg=25 μm
VGS=0.0V, VDS=-35V
Gain =
16 dB @1GHzfMax = 35 GHz
fT = 9.3 GHz
Eapplied= 1.75 MV/cm
Cut-off frequencies increase according
to drain source applied electric field,
suggesting that charge carriers
saturation velocity is not reached yet
P. Calvani, A. Corsaro, M. Girolami, F. Sinisi, D.M. Trucchi, M.C. Rossi, G. Conte, S. Carta, E. Giovine, S. Lavanga , E. Limiti , V. Ralchenko “DC and RF
Performance of surface channel MESFETs based on hydrogen terminated polycrystalline diamond”, Diamond Relat. Mater. 18, (2009) 786-788
PolyD4 by Russian Academy of Sciences
RF PerformancesDC and RF MESFETs performances
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Class A @ 1GHz
Pout=0.8 W/mm
G. Conte, et al. “RF Power Performance Evaluation of
Surface Channel Diamond MESFETs”, Solid State Electr.
55 (2011) 19-24
Best reported result on SCD: Pout @1GHz=2.1 W/mm [Lg=0.1 μm, Wg=100 μm, VGS=-1.5 V, VDS=-20 V]M. Kasu, et al.,“2 W/mm Output Power Density At 1 GHz For Diamond FETs” Electr. Lett. 41 (2005) 1249
-20
-15
-10
-5
0
5
10
15
0
5
10
15
20
25
-25 -20 -15 -10 -5 0 5 10
Pout
(dBm)
Gain (dB)
PAE %
Pin
(dBm)
Po
ut (d
Bm
), G
ain
(d
B)
PA
E %
Best reported RF result for Polycrystalline Diamond
LG=200nm
WG=50um
VDS=-14 V,
VGS=-0.3 V
fMAX = 15.2 GHz
ft = 6.2 GHzLinear Gain=8 dB (–25 to 0 dBm).
This indicates the possibility of
power amplification without
distortion in a wide input range.
Power output can be increased by
reducing impedance mismatch
between the output side of the
diamond FETs and the input side of
the tuner in the power measurement
system.
DC and RF MESFETs performances
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First device
Year1995 2000 2005 2010
1
10
1002009
Diam. Relat. Mater. 18
2008 - IJMOT 3
SCD 2007
Graduate Thesis
2006
Diam. Relat. Mater. 16
PolyD 2005
Graduate Thesis
H. Kawarada et al.
Appl. Phys. Lett. 65
H. Taniuchi et al.
IEEE EDL 22
K. Ueda, M. Kasu et al.
IEEE EDL 27
A. Aleksov, E. Kohn et al.
Diam. Relat. Mater. 13
RF
per
form
an
ces
(GH
z)
10-1
100
101
102
103
0,1 1 10
fMAX
- PolyD - Kasu et al. (IEEE El. Dev. Lett., 27 - 2006)
fMAX
- SCD - Kawarada et al. (APL, 92 - 2008)
fMax
- SCD - Aleksov et al. (Diam. Relat. Mater. 11 - 2002)
All fT
fMAX
- PolyD - S2DEL
fMAX
- SCD - S2DEL
Fre
qu
ency
(G
Hz)
1/LG
( m-1
)
fT
fMax
RF Power PerformancesGate length scaling
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Poly Ra270 DiamondFast optically triggered switches
0
0,5
1
1,5
2
Vds
=Floating
-1V
-2V
-3V
-4V
-5V
-6V
-7V
-8VSig
nal
(V)
Time (ns)
0 10 20 30 40-20 -10
OpFET
=193 nm
WG
=200 m; LG
=4 m
G-D=12 m
G-S=~1 m
VGS
=-2V
0
0,5
1
1,5
2
-1.0V
-1.25V
-1.5V
-1.75V
-2.0V
0.0V
-0.5V
0.5VSig
nal
(V)
Time (ns)0-5 105 2015 25
OpFET
=193 nm
WG
=200 m; LG
=4 m
G-D=12 m
G-S=~1 m
VDD
=-8V
VGS
S G D
193 nm
Strong asymmetric design and low hydrogenation
level aimed to reduce current in the dark
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-0,01
0
0,01
0,02
0,03
0,04
0,05
0,06
0,07
Vds=0
Vds=-0.5
Vds=-1.0
Vds=-1.5
Vds=-2.0
Vds=-2.5
Vds=-3.0
Vds=-3.5
Vds=-4.0
Vds=-4.5
Vds=-5.0
Vds=-6.0
Vds=-7.0
Vds=-8.0
Peak
Am
pli
tud
e (
V)
Vdd
(V)
0 -2 -4 -6 -8
Diamond UV-FET
l = 20 um
w = 200 um
ArF 193 nm
-1 -3 -5 -7
Vgs
- Vdd
100 kLeCroy
UV
RAC=1 M
Polycrystalline DiamondUV triggered MESFETs
WG=200 µm LG=4 µm
Vgs=-0.9 VG-S =4 µm, G-D=12 µm
G. Conte, G. Ricciotti, P. Calvani, E. Giovine,
Diamond FET: high-speed optical switch
Electronics Lett., 46 (2010) 1614-1616
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Conclusions
MESFETs on H-terminated poly-diamond are ready for technogical transfer
to the industry (at least for High Frequency low-Power applications)
Polished substrates up to 2x2 cm2 are today available
Best reported microwave performances
Large grains substrates show better H-termination
Low roughness for scaling down the gate-contact by EBL is requested
SCD could be used to study new device architectures (i.e. -doping)
Limited dimension
Replica of crystallographic defects from HPHT substrates
Difficulty to grow i-Diamond on B-doped layers
Mathematical modeling is welcome for devices performance improvement
Fast optical switch behavior has been demonstrated
Opaque gate three-terminal devices are suitable for application in emerging
photonic technologies, for power-management systems optical receivers,
where copper wires and EM shielding can be replaced by lightweight optical
fibres
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Thanks for your attention
Authors would like to acknowledge:
E. Limiti, W. Ciccognani
G. Ghione, F. Cappellutti
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