transistors for thz systems · real systems→ lnas with low fmin, pas with high psat & high...
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Transistors for THz Systems
Mark Rodwell, UCSB
IMS Workshop: Technologies for THZ Integrated Systems (WMD)
Monday, June 3, 2013, Seattle, Washington (8AM-5PM)
Co-Authors and Collaborators:
UCSB HBT Team: J. Rode, H.W. Chiang, A. C. Gossard , B. J. Thibeault, W. Mitchell Recent Graduates: V. Jain, E. Lobisser, A. Baraskar,
Teledyne HBT Team: M. Urteaga, R. Pierson, P. Rowell, B. Brar, Teledyne Scientific Company
Teledyne IC Design Team: M. Seo, J. Hacker, Z. Griffith, A. Young, M. J. Choe, Teledyne Scientific Company
UCSB IC Design Team: S. Danesgar, T. Reed, H-C Park, Eli Bloch
WMD: Technologies for THZ Integrated Systems RFIC2013, Seattle, June 2-4, 2013 1
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DC to Daylight. Far-Infrared Electronics
Video-resolution radar → fly & drive through fog & rain
How high in frequency can we push electronics ?
...and what we would be do with it ?
100+ Gb/s wireless networks near-Terabit optical fiber links
1982: ~20 GHz 2012: 820 GHz ~2030: 3THz
109
1010
1011
1012
1013
1014
1015
Frequency (Hz)
microwave
SHF*
3-30 GHz
10-1 cm
mm-wave
EHF*
30-300 GHz
10-1 mm
optic
al
385-7
90 T
Hz
sub-mm-wave
THF*
0.3-3THz
1-0.1 mm
far-IR: 0.3-6 THz
near-IR
100
-385
TH
z
3-0
.78
mmid-IR
6-100 THz
50-3 m
*ITU band designations
** IR bands as per ISO 20473
2
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THz Transistors: Not Just For THz Circuits
precision analog design at microwave frequencies → high-performance receivers
500 GHz digital logic → fiber optics
Higher-Resolution Microwave ADCs, DACs, DDSs
THz amplifiers→ THz radios → imaging, communications
3
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THz Communications Needs High Power, Low Noise
Real systems with real-world weather & design margins, 500-1000m range:
3-7 dB Noise figure, 50mW- 1W output/element, 64-256 element arrays
Will require:
→ InP or GaN PAs and LNAs, Silicon beamformer ICs 4
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THz Communications Needs High Power, Low Noise
Real systems→ LNAs with low Fmin, PAs with high Psat & high PAE
InP HEMTs give the best noise. InP HBT & GaN HEMT compete for the PA. Comparing technologies
CMOS is great for signal processing, but noise, power, PAE are poor. Harmonic generation is low power, inefficient. Harmonic mixing is noisy. 5
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III-V PAs and LNAs in today's wireless systems...
http://www.chipworks.com/blog/recentteardowns/2012/10/02/apple-iphone-5-the-rf/
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THz Device Scaling
7
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nm Transistors, Far-Infrared Integrated Circuits
IR today→ lasers & bolometers → generate & detect
It's all about the interfaces: contact and gate dielectrics...
Far-infrared ICs: classic device physics, classic circuit design
...wire resistance,...
...heat,...
...& charge density.
band structure and density of states !
8
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Transistor scaling laws: ( V,I,R,C,t ) vs. geometry
AR contact /
Bulk and Contact Resistances
Depletion Layers
T
AC
v
T
2
2
max)(4
T
Vv
A
I applsat
Thermal Resistance
Fringing Capacitances
~/ LC finging~/ LC finging
dominate rmscontact te
escapacitanc fringing FET )1
escapacitancct interconne IC )2
W
L
LK
PT
th
ln~transistor
LK
PT
th
ICIC
Available quantum states to carry current
→ capacitance, transconductance contact resistance 9
L
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THz & nm Transistors: State Density Limits
2-D: FET 3-D: BJT
current
conductivity
capacitance
2/1
2/1
3
2 2n
qc
3/2
3/22
8
3n
qc
32
23
4
*
VmqJ
22
2/32/12/52/3
3
*2
VmqJ sheet
2
*2
2
mqCDOS
# of available quantum states / energy determines FET channel capacitance FET and bipolar transistor current access resistance of Ohmic contact
10
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Bipolar Transistor Design eW
bcWcTbT
nbb DT 22
satcc vT 2
ELlength emitter
eex AR /contact
2
through-punchce,operatingce,max cesatc TVVAvI /)(,
contacts
contactsheet
612 AL
W
L
WR
e
bc
e
ebb
e
e
E W
L
L
PT ln1
cccb /TAC
11
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Bipolar Transistor Design: Scaling eW
bcWcTbT
nbb DT 22
satcc vT 2
ELlength emitter cccb /TAC
eex AR /contact
2
through-punchce,operatingce,max cesatc TVVAvI /)(,
contacts
contactsheet
612 AL
W
L
WR
e
bc
e
ebb
e
e
E W
L
L
PT ln1
12
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Breakdown: Never Less than the Bandgap
band-band tunneling: base bandgap impact ionization: collector bandgap
13
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FET Design
g
DSWL
RRS/D
contact
gW width gate
gfgsgd WCC ,
)/( gchgm LvCg
)/( vWLR ggDS
)density state /well(2// 2
wellwell qTT
WLC
oxox
gg
chg
masstransport
1
capacitors threeabove the
between ratiodivision voltage2/1
v
14
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FET Design: Scaling
g
DSWL
RRS/D
contact
gW width gate
gfgsgd WCC ,
)/( gchgm LvCg
)/( vWLR ggDS
)density state /well(2// 2
wellwell qTT
WLC
oxox
gg
chg
masstransport
1
capacitors threeabove the
between ratiodivision voltage2/1
v
15
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FET Design: Scaling
g
DSWL
RRS/D
contact
gW width gate
gfgsgd WCC ,
)/( gchgm LvCg
)/( vWLR ggDS
)density state /well(2// 2
wellwell qTT
WLC
oxox
gg
chg
masstransport
1
capacitors threeabove the
between ratiodivision voltage2/1
v
16
2:1 2:1
constant 2:1 2:1
2:1 2:1
2:1 2:1 2:1
2:1
constant
constant
2:1 2:1
constant
2:1 2:1
4:1
constant
constant
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FET parameter change
gate length decrease 2:1
current density (mA/m), gm (mS/m) increase 2:1
transport effective mass constant
channel 2DEG electron density increase 2:1
gate-channel capacitance density increase 2:1
dielectric equivalent thickness decrease 2:1
channel thickness decrease 2:1
channel density of states increase 2:1
source & drain contact resistivities decrease 4:1
Changes required to double transistor bandwidth
GW widthgate
GL
HBT parameter change
emitter & collector junction widths decrease 4:1
current density (mA/m2) increase 4:1
current density (mA/m) constant
collector depletion thickness decrease 2:1
base thickness decrease 1.4:1
emitter & base contact resistivities decrease 4:1
eW
ELlength emitter
constant voltage, constant velocity scaling nearly constant junction temperature → linewidths vary as (1 / bandwidth)2
fringing capacitance does not scale → linewidths scale as (1 / bandwidth )
17
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THz & nm Transistors: what needs to be done
Metal-semiconductor interfaces (Ohmic contacts): very low resistivity Dielectric-semiconductor interfaces (Gate dielectrics---FETs only): thin !
Ultra-low-resistivity (~0.25 W-m2 ), ultra shallow (1 nm), ultra-robust (0.2 A/m2 ) contacts
Mo
InGaAs
Ru
InGaAs
Heat
W
L
LK
PT
th
ln~transistor
LK
PT
th
ICIC
Available quantum states to carry current L
→ capacitance, transconductance contact resistance 18
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THz InP HBTs
19
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Scaling Laws, Scaling Roadmap
HBT parameter change
emitter & collector junction widths decrease 4:1
current density (mA/m2) increase 4:1
current density (mA/m) constant
collector depletion thickness decrease 2:1
base thickness decrease 1.4:1
emitter & base contact resistivities decrease 4:1
scaling laws: to double bandwidth
eW
bcWcTbT
ELlength emitter
150 nm device 150 nm device
20
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HBT Fabrication Process Must Change... Greatly
32 nm width base & emitter contacts...self-aligned
32 nm width emitter semiconductor junctions
Contacts: 1 W-m2 resistivities 70 mA/m2 current density ~1 nm penetration depths → refractory contacts
nm III-V FET, Si FET processes have similar requirements 21
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Needed: Greatly Improved Ohmic Contacts Needed: Greatly Improved Ohmic Contacts
~5 nm Pt contact penetration (into 25 nm base)
Pt/Ti/Pd/Au
22
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Ultra Low-Resistivity Refractory Contacts
10-9
10-8
10-7
10-6
1018
1019
1020
1021
N-InAs
Co
nta
ct
Re
sis
tiv
ity (
W
cm
2)
concentration (cm-3
)
1017
1018
1019
1020
N-InGaAs
concentration (cm-3
)
1018
1019
1020
1021
P-InGaAs
Ir
W
Mo
concentration (cm-3
)
Mo Mo
Barasakar et al IEEE IPRM 2012
32 nm node requirements
Contact performance sufficient for 32 nm /2.8 THz node.
Low penetration depth, ~ 1 nm
In-situ: avoids surface contaminants
Refractory: robust under high-current operation
23
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Ultra Low-Resistivity Refractory Contacts
10-9
10-8
10-7
10-6
1018
1019
1020
1021
N-InAs
Co
nta
ct
Re
sis
tiv
ity (
W
cm
2)
concentration (cm-3
)
1017
1018
1019
1020
N-InGaAs
concentration (cm-3
)
1018
1019
1020
1021
P-InGaAs
Ir
W
Mo
concentration (cm-3
)
Mo Mo
Barasakar et al IEEE IPRM 2012
32 nm node requirements
Schottky Barrier is about one lattice constant
what is setting contact resistivity ?
what resistivity should we expect ?
24
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Ultra Low-Resistivity Refractory Contacts
10-9
10-8
10-7
10-6
1018
1019
1020
1021
N-InAs
Co
nta
ct
Re
sis
tiv
ity (
W
cm
2)
concentration (cm-3
)
1017
1018
1019
1020
N-InGaAs
concentration (cm-3
)
1018
1019
1020
1021
P-InGaAs
Ir
W
Mo
concentration (cm-3
)
Mo Mo
Barasakar et al IEEE IPRM 2012
32 nm node requirements
limit)ty reflectivi-quantum
anddensity (state
:yresistivitcontact barrier -Zero
.cm/107 at m 1.0
tcoefficienon transmissi
ionconcentratcarrier
11
3
8
3192
3/22
3/2
2
W
n
T
n
nTq
c
c
25
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Needed: Greatly Improved Ohmic Contacts Refractory Emitter Contacts
negligible penetration
26
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HBT Fabrication Process Must Change... Greatly
Undercutting of emitter ends
control undercut → thinner emitter
thinner emitter → thinner base metal
thinner base metal → excess base metal resistance
{101}A planes: fast
{111}A planes: slow
tall, narrow contacts: liftoff fails !
27
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HBT: V. Jain. Process: Jain & Lobisser
TiW
W 100 nm
Mo
SiNx
Refractory contact, refractory post→ high-J operation
Sputter+dry etch→ 50-200nm contacts
Sub-200-nm Emitter Contact & Post
Liftoff aided by TiW/W interface undercut
Dielectric sidewalls
28
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RF Data: 25 nm thick base, 75 nm Thick Collector
0
5
10
15
20
25
1010
1011
1012
Ga
ins (
dB
)Frequency (Hz)
H21
U
f = 530 GHz
fmax
= 750 GHz
Required dimensions obtained but poor base contacts on this run
E. Lobisser, ISCS 2012, August, Santa Barbara
29
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DC, RF Data: 100 nm Thick Collector
0
4
8
12
16
20
24
28
32
109
1010
1011
1012
Ga
in (
dB
)
Frequency (Hz)
U
H21
f = 480 GHz
fmax
= 1.0 THz
Aje = 0.22 x 2.7 m
2
Ic = 12.1 mA
Je = 20.4 mA/m
2
P = 33.5 mW/m2
Vcb
= 0.7 V
0
5
10
15
20
25
30
0 1 2 3 4 5
Je (
mA
/m
2)
Vce
(V)
P = 30 mW/m2
Ib,step
= 200 A
BV
P = 20 mW/m2
Aje
= 0.22 x 2.7 m2
10-9
10-7
10-5
10-3
10-1
0
5
10
15
20
0 0.2 0.4 0.6 0.8 1I c
, I b
(A
)
Vbe
(V)
Solid line: Vcb
= 0.7V
Dashed: Vcb
= 0V
nc = 1.19
nb = 1.87
Ic
Ib
Jain et al IEEE DRC 2011
30
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Chart 31
THz InP HBTs From Teledyne
Urteaga et al, DRC 2011, June 31
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Towards & Beyond the 32 nm /2.8 THz Node
Base contact process: Present contacts too resistive (4Wm2) Present contacts sink too deep (5 nm) for target 15 nm base
→ refractory base contacts
Emitter Degeneracy: Target current density is almost 0.1 Amp/m2 (!) Injected electron density becomes degenerate. transconductance is reduced.
→ Increased electron mass in emitter
32
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Base Ohmic Contact Penetration
~5 nm Pt contact penetration (into 25 nm base)
Base Ohmic Contact Penetration
33
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Refractory Base Process (1)
low contact resistivity low penetration depth
low bulk access resistivity
base surface not exposed to photoresist chemistry: no contamination low contact resistivity, shallow contacts low penetration depth allows thin base, pulsed-doped base contacts
Blanket liftoff; refractory base metal Patterned liftoff; Thick Ti/Au
34
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Refractory Base Process (2)
0 100
5 1019
1 1020
1.5 1020
2 1020
2.5 1020
0 5 10 15 20 25
do
pin
g, 1
/cm
3
depth, nm
2 nm doping pulse
1018
1019
1020
1021
P-InGaAs
10-10
10-9
10-8
10-7
10-6
10-5
Hole Concentration, cm-3
B=0.8 eV
0.6 eV0.4 eV0.2 eV
step-barrierLandauer
Co
nta
ct
Res
isti
vit
y,
W
cm
2
32 nm node requirement
Increased surface doping: reduced contact resistivity, but increased Auger recombination. → Surface doping spike at most 2-5 thick. Refractory contacts do not penetrate; compatible with pulse doping. 35
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Refractory Base Ohmic Contacts Refractory Base Ohmic Contacts
<2 nm Ru contact penetration (surface removal during cleaning)
Ru / Ti / Au
36
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Degenerate Injection→ Reduced Transconductance
10-3
10-2
10-1
100
101
102
-0.3 -0.2 -0.1 0 0.1 0.2
J(m
A/
m2)
Vbe
-
Boltzmann
(-Vbe
)>>kT/q
)./exp( kTqVJJ bes
Transconductance is high
)./exp( kTqVJJ bes
JAg Em /
Current varies exponentially with Vbe
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)./exp( kTqVJJ bes
Degenerate Injection→ Reduced Transconductance
10-3
10-2
10-1
100
101
102
-0.3 -0.2 -0.1 0 0.1 0.2
J(m
A/
m2)
Vbe
-
Fermi-Dirac
Boltzmann
(-Vbe
)>>kT/q
Transconductance is reduced
Current varies exponentially with Vbe
38
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Degenerate Injection→ Reduced Transconductance
10-3
10-2
10-1
100
101
102
-0.3 -0.2 -0.1 0 0.1 0.2
J(m
A/
m2)
Vbe
-
Fermi-Dirac
Highly degenerate
(Vbe
->>kT/q
Boltzmann
(-Vbe
)>>kT/q
Highly degenerate limit:
)(8
* 2
32
3
beVmq
J
2* )( beE VmJ
current varies as the square of bias
39
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Degenerate Injection→ Reduced Transconductance
10-3
10-2
10-1
100
101
102
-0.3 -0.2 -0.1 0 0.1 0.2
J(m
A/
m2)
Vbe
-
Fermi-Dirac
Highly degenerate
(Vbe
->>kT/q
Boltzmann
(-Vbe
)<<kT/q
Highly degenerate limit:
)(8
* 2
32
3
beVmq
J
2* )( beE VmJ
Transconductance varies as J1/2
current varies as the square of bias
JmAg EEm
*/
At & beyond 32 nm, we must increase the emitter effective mass.
...and as (m*)1/2
40
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Degenerate Injection→Solutions
At & beyond 32 nm, we must increase the emitter (transverse) effective mass.
Other emitter semiconductors: no obvious good choices (band offsets, etc.).
Emitter-base superlattice: increases transverse mass in junction evidence that InAlAs/InGaAs grades are beneficial
Extreme solution (10 years from now): partition the emitter into small sub-junctions, ~ 5 nm x 5 nm. parasitic resistivity is reduced progressively as sub-junction areas are reduced.
41
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3-4 THz Bipolar Transistors are Feasible.
4 THz HBTs realized by:
Extremely low resistivity contacts
Extreme current densities
Processes scaled to 16 nm junctions
Impact: efficient power amplifiers and complex signal processing from 100-1000 GHz.
42
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InP HBT: Key Features
512 nm node: high-yield "pilot-line" process, ~4000 HBTs/IC
256 nm node: Power Amplifiers: >0.5 W/mm @ 220 GHz highly competitive mm-wave / THz power technology
128 nm node: >500 GHz f , >1.1 THz fmax , ~3.5 V breakdown breakdown* f = 1.75 THz*Volts highly competitive mm-wave / THz power technology
64 nm (2 THz) & 32 nm (2.8 THz) nodes: Development needs major effort, but no serious scaling barriers
1.5 THz monolithic ICs are feasible. 43
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Can we make a 1 THz SiGe Bipolar Transistor ?
InP SiGe
emitter 64 18 nm width
2 0.6 Wm2 access
base 64 18 nm contact width,
2.5 0.7 Wm2 contact
collector 53 15 nm thick
36 125 mA/m2
2.75 1.3? V, breakdown
f 1000 1000 GHz
fmax 2000 2000 GHz
PAs 1000 1000 GHz
digital 480 480 GHz
(2:1 static divider metric)
Assumes collector junction 3:1 wider than emitter.
Assumes SiGe contacts no wider than junctions
Simple physics clearly drives scaling
transit times, Ccb/Ic
→ thinner layers, higher current density
high power density → narrow junctions
small junctions→ low resistance contacts
Key challenge: Breakdown
15 nm collector → very low breakdown
Also required:
low resistivity Ohmic contacts to Si
very high current densities: heat
44
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THz InP Bipolar Transistor Technology Goal: extend the operation of electronics to the highest feasible frequencies
1 THz device Scaling roadmap through 3 THz 220 GHz power amplifiers
ultra-efficient 85 GHz power amplifiers
THz InP Heterojunction Bipolar Transistors 60-600 GHz IC examples; demonstrated & in fab
50 GHz sample/hold 40 GHz op-amp
100 GHz ICs for *electronic* demultiplexing of WDM optical communications
40 Gb/s phase-locked coherent optical receivers
Enabling Technologies : ~30 nm fabrication processes, extremely low resistivity (epitaxial, refractory) contacts, extreme current densities, doping at solubility limits, few-nm-thick junctions
Teledyne Scientific: moving THz IC Technology towards aerospace applications 1.1 THz pilot IC process 204 GHz digital logic (M/S latch) 670 GHz amplifier 300 GHz fundamental phase-lock-loop
Vout
VEE VBB
Vtune
Vout
VEE VBB
Vtune614 GHz fundamental oscillator (VCO)
182 mW 188 mW, 33% PAE
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THz InP HEMTs and
III-V MOSFETs
46
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FET parameter change
gate length decrease 2:1
current density (mA/m), gm (mS/m) increase 2:1
transport effective mass constant
channel 2DEG electron density increase 2:1
gate-channel capacitance density increase 2:1
dielectric equivalent thickness decrease 2:1
channel thickness decrease 2:1
channel density of states increase 2:1
source & drain contact resistivities decrease 4:1
Changes required to double transistor bandwidth
GW widthgate
GL
HBT parameter change
emitter & collector junction widths decrease 4:1
current density (mA/m2) increase 4:1
current density (mA/m) constant
collector depletion thickness decrease 2:1
base thickness decrease 1.4:1
emitter & base contact resistivities decrease 4:1
eW
ELlength emitter
constant voltage, constant velocity scaling nearly constant junction temperature → linewidths vary as (1 / bandwidth)2
fringing capacitance does not scale → linewidths scale as (1 / bandwidth )
47
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FET scaling challenges...and solutions
Gate barrier under S/D contacts → high S/D access resistance addressed by S/D regrowth
High gate leakage from thin barrier, high channel charge density (almost) eliminated by ALD high-K gate dielectric
Other scaling considerations: low InAs electron mass→ low state density capacitance → gm fails to scale increased m* , hence reduced velocity in thin channels minimum feasible thickness of gate dielectric (tunneling) and channel
48
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-0.2 0.0 0.2 0.4 0.60.0
0.4
0.8
1.2
1.6
2.0
2.4
Gm
(mS
/m
)
Cu
rre
nt
De
ns
ity
(m
A/
m)
Gate Bias (V)
0.0
0.4
0.8
1.2
1.6
2.0
2.4 VDS
=0.05 V
VDS
=0.5 V
III-V MOS
Peak transconductance; VLSI-style FET: 2.5 mS/micron ~85% of best THz InAs HEMTs
0.1 10.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8 90 [011]
0 [01-1]
at Vds
=0.5V
Gate length (m)
Pe
ak
Tra
ns
co
nd
uc
tan
ce
(m
S/
m)
Lg = 40 nm (SEM)
III-V MOS will soon surpass HEMTs in RF performance
Sanghoon Lee
40 nm devices are nearly ballistic
49
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In ballistic limit, current and transconductance are set by: channel & dielectric thickness, transport mass, state density
2/3*
,
2/1*
1
2/3
1
)/()/(1 where,
V 1m
mA84
oequivodos
othgs
mmgcc
mmgK
VVKJ
FET Drain Current in the Ballistic Limit
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.01 0.1 1
no
rma
lized
drive
cu
rre
nt
K1
m*/mo
g=2
EET=1.0 nm
0.6 nm
0.4 nm
g=1
InGaAs <--> InP Si
0.3 nm
EET=Equivalent Electrostatic Thickness
=Tox
SiO2
/ox
+Tinversion
SiO2
/semiconductor
/EETε
)/c/c(c oxequiv
2SiO
1
depth
11
2
0
2
, 2/ mqc odos
minima band # g
50
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Low m* gives lowest transit time, lowest Cgs at any EOT.
Transit delay versus mass, # valleys, and EOT
51
2/1*
,
2/1
0
*
2
2/1
72 1 whereVolt 1
cm/s 1052.2
oeq
odos
thgs
g
D
chch
m
mg
c
c
m
mK
VV
LK
I
Q
0
0.5
1
1.5
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
No
rma
lize
d t
ran
sit d
ela
y K
2
m*/mo
EOT=1.0 nm
EOT includes wavefunction depth term
(mean wavefunction depth*SiO2
/semiconductor
)
0.6 nm
0.4 nm
g=1, isotropic bands
g=2, isotropic bands
1 nm
0.4 nm
0.6 nm
/EOTε
)/c/c(c oxequiv
2SiO
1
semi
11
InGaAs
Si, GaN
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FET Scaling: fixed vs. increasing state density
52
0
500
1000
1500
2000
2500
3000 canonical scaling
stepped # of bands
transport only
f , G
Hz
0
500
1000
1500
2000
2500
3000
3500
4000
f ma
x, G
Hz
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50 60
dra
in c
urr
ent
density, m
A/
m
gate length, nm
200 mV gate overdrive
0
200
400
600
800
1000
0 10 20 30 40 50 60
SC
FL
sta
tic d
ivid
er
clo
ck r
ate
, G
Hz
gate length, nm
f fmax
mA/m→ VLSI metric SCFL divider speed
Need higher state density for ~10 nm node
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2-3 THz Field-Effect Transistors are Feasible.
3 THz FETs realized by:
Ultra low resistivity source/drain
High operating current densities
Very thin barriers & dielectrics
Gates scaled to 9 nm junctions high-barrier HEMT MOSFET
Impact: Sensitive, low-noise receivers from 100-1000 GHz.
3 dB less noise → need 3 dB less transmit power.
or
53
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4-nm / 5-THz FETs: Challenges
4 nm
Channel thickness 0.8 nm: UTB 1.6 nm: fin atomically flat
Gate dielectric 0.1 nm EOT: UTB 0.2 nm EOT: fin
Estimated (WKB) tunneling current is just acceptable at 0.2 nm EOT.
How can we make a 1.6 nm thick fin, or a 0.8 nm thick body ? 54
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Thin wells have high scattering rate
Need single-atomic-layer control of thickness Need high quantization mass mq.
Sakaki APL 51, 1934 (1987).
./1y probabilit Scattering 62
wellqTm
55
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III-V vs. CMOS: A false comparison ?
UTB Si MOS UTB III-V MOS III-V THz MOS/HEMT
III-V THz HEMT
III-V MOS has a reasonable chance of future use in VLSI
The real THz / VLSI distinction: Device geometry optimized for high-frequency gain vs. optimized for small footprint and high DC on/off ratio.
56
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Conclusion
57
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THz and Far-Infrared Electronics
IR today→ lasers & bolometers → generate & detect
It's all about classic scaling: contact and gate dielectrics...
Far-infrared ICs: classic device physics, classic circuit design
...wire resistance,...
...heat,...
...& charge density. band structure and density of quantum states (new!).
Even 1-3 THz ICs will be feasible
58
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(backup slides follow)
59
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Electron Plasma Resonance: Not a Dominant Limit
*2kinetic
1
nmqA
TL
T
AC
ntdisplaceme
m
scatterL
Rf
2
1
2
1
frequency scattering
kinetic
bulk
mnmqA
TR
*2bulk
1
2
1
2/1
frequency relaxation dielectric
bulkntdisplaceme
RC
fdielecic
ntdisplacemekinetic
2/1
frequencyplasma
CLf plasma
THz 800 THz 7 THz 74319 cm/105.3
InGaAs-
n
319 cm/107
InGaAs-
pTHz 80 THz 12 THz 13
60