transistors for thz systems - ucsb...rf data: 25 nm thick base, 75 nm thick collector 0 5 10 15 20...
TRANSCRIPT
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
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
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
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
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
III-V PAs and LNAs in today's wireless systems...
http://www.chipworks.com/blog/recentteardowns/2012/10/02/apple-iphone-5-the-rf/
THz Device Scaling
7
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
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
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
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
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
Breakdown: Never Less than the Bandgap
band-band tunneling: base bandgap impact ionization: collector bandgap
13
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
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
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
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
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
THz InP HBTs
19
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
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
Needed: Greatly Improved Ohmic Contacts Needed: Greatly Improved Ohmic Contacts
~5 nm Pt contact penetration (into 25 nm base)
Pt/Ti/Pd/Au
22
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
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
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
Needed: Greatly Improved Ohmic Contacts Refractory Emitter Contacts
negligible penetration
26
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
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
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
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
Chart 31
THz InP HBTs From Teledyne
Urteaga et al, DRC 2011, June 31
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
Base Ohmic Contact Penetration
~5 nm Pt contact penetration (into 25 nm base)
Base Ohmic Contact Penetration
33
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
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
Refractory Base Ohmic Contacts Refractory Base Ohmic Contacts
<2 nm Ru contact penetration (surface removal during cleaning)
Ru / Ti / Au
36
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
37
)./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
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
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
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
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
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
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
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
THz InP HEMTs and
III-V MOSFETs
46
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
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
-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
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
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
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
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
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
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
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
Conclusion
57
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
(backup slides follow)
59
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