THz Indium Phosphide Bipolar Transistor Technology
[email protected] 805-89-44, 805-89-5705 fax
IEEE Compound Semiconductor IC Symposium, October 4-7, La Jolla, California
Mark Rodwell University of California, Santa Barbara
Coauthors:
J. Rode, H.W. Chiang, P. Choudhary, T. Reed, E. Bloch, S. Danesgar, H-C Park, A. C. Gossard, B. J. Thibeault, W. Mitchell UCSB M. Urteaga, Z. Griffith, J. Hacker, M. Seo, B. Brar Teledyne Scientific Company
Why THz Transistors ?
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
THz Communications Needs High Power, Low Noise
Real systems with real-world weather & design margins, 500-1000m range:
3-7 dB Noise figure, 50-500 mW power/element, 64-256 element arrays
Will require:
→ InP or GaN PAs and LNAs, Silicon beamformer ICs
THz InP HBTs
THz & nm Transistors: what it's all about
Metal-semiconductor interfaces (Ohmic contacts): very low resistivity Dielectric-semiconductor interfaces (Gate dielectrics---FETs only): thin !
Ultra-low-resistivity (~0.25 W-mm2 ), ultra shallow (1 nm), ultra-robust (0.2 A/mm2 ) 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
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
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
Scaling Laws, Scaling Roadmap
HBT parameter change
emitter & collector junction widths decrease 4:1
current density (mA/mm2) increase 4:1
current density (mA/mm) 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
HBT Fabrication Process Must Change... Greatly
32 nm width base & emitter contacts...self-aligned
32 nm width emitter semiconductor junctions
Contacts: 1 W-mm2 resistivities 70 mA/mm2 current density ~1 nm penetration depths → refractory contacts
nm III-V FET, Si FET processes have similar requirements
Needed: Greatly Improved Ohmic Contacts
textbook with surface oxide
Interface barrier → resistance
Further intermixing during high-current operation → degradation
with metal penetration
Needed: Greatly Improved Ohmic Contacts Needed: Greatly Improved Ohmic Contacts
~5 nm Pt contact penetration (into 25 nm base)
Pt/Ti/Pd/Au
Ultra Low-Resistivity Refractory In-Situ 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
Needed: Greatly Improved Ohmic Contacts Refractory Emitter Contacts
negligible penetration
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 !
Sub-200-nm Emitter Anatomy
slide: E. Lobisser. HBT: V. Jain. Process: Jain & Lobisser
TiW
W 100 nm
Mo
High-stress emitters fall off
during subsequent lift-offs
TiW W
Single sputtered metal has
non-vertical etch profile
SiNx
Refractory contact: high-J operation
Liftoff Sputter+dry etch→ sub-200nm contacts
Sub-200-nm Emitter Anatomy
slide: E. Lobisser. HBT: V. Jain. Process: Jain & Lobisser
TiW
W 100 nm
Mo
Hybrid sputtered metal stack for
low-stress, vertical profile
W/TiW interfacial discontinuity
enables base contact lift-off
Interfacial Mo blanket-evaporated for low ρc SiNx
SiNx sidewalls protect emitter contact,
prevent emitter-base shorts during liftoff
Semiconductor wet etch
undercuts emitter contact
Very thin emitter epitaxial layer
for minimal undercut
Sub-200-nm Emitter Anatomy
slide: E. Lobisser. HBT: V. Jain. Process: Jain & Lobisser
emitter-base gap: only ~10 nm → greatly reduces link component of Rbb. emitter-base gap: only ~10 nm → greatly reduces link component of Rbb
Web = 155 nm
Wbc = 150 nm
TiW
W
Pt/Ti/Pd/Au
SiNx sidewall
RF Data: 25 nm thick base, 75 nm Thick Collector
0
5
10
15
20
25
1010
1011
1012
Gain
s (
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
DC, RF Data: 100 nm Thick Collector
0
4
8
12
16
20
24
28
32
109
1010
1011
1012
Gain
(d
B)
Frequency (Hz)
U
H21
f = 480 GHz
fmax
= 1.0 THz
Aje = 0.22 x 2.7 mm
2
Ic = 12.1 mA
Je = 20.4 mA/mm
2
P = 33.5 mW/mm2
Vcb
= 0.7 V
0
5
10
15
20
25
30
0 1 2 3 4 5
Je (
mA
/mm
2)
Vce
(V)
P = 30 mW/mm2
Ib,step
= 200 mA
BV
P = 20 mW/mm2
Aje
= 0.22 x 2.7 mm2
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
Chart 22
THz InP HBTs From Teledyne
Urteaga et al, DRC 2011, June
Towards & Beyond the 32 nm /2.8 THz Node
Base contact process: Present contacts too resistive (4Wmm2) 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/mm2 (!) Injected electron density becomes degenerate. transconductance is reduced.
→ Increased electron mass in emitter
Base Ohmic Contact Penetration
~5 nm Pt contact penetration (into 25 nm base)
Base Ohmic Contact Penetration
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
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.
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/m
m2)
Vbe
-
Boltzmann
(-Vbe
)>>kT/q
)./exp( kTqVJJ bes
Transconductance is high
)./exp( kTqVJJ bes
JAg Em /
Current varies exponentially with Vbe
)./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/m
m2)
Vbe
-
Fermi-Dirac
Boltzmann
(-Vbe
)>>kT/q
Transconductance is reduced
Current varies exponentially with Vbe
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/m
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
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/m
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
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.
IC Results
InP HBT Integrated Circuits: 600 GHz & Beyond
614 GHz fundamental VCO
340 GHz dynamic frequency divider
Vout
VEE VBB
Vtune
Vout
VEE VBB
Vtune
565 GHz, 34 dB, 0.4 mW output power amplifier
J. Hacker, TSC
M. Seo,
M. Seo, UCSB/TSC IMS 2010
204 GHz static frequency divider (ECL master-slave latch)
Z. Griffith, TSC CSIC 2010
300 GHz fundamental PLL M. Seo, TSC IMS 2011
220 GHz 90 mW power amplifier T. Reed, UCSB
600 GHz Integrated Transmitter PLL + Mixer M. Seo
Integrated 300/350GHz Receivers: LNA/Mixer/VCO
M. Seo
Chart 34
Teledyne: 560 GHz Common-Base Amplifier IC
S-parameters Output Power
•10-Stage Common-base using
inverted CPW-G architecture
•34 dB at 565 GHz
•Psat -3.9 dBm at 560 GHz
1200x230 mm2
J Hacker et al, Teledyne Scientific
90 mW, 220 GHz Power Amplifier
active area, 1.02 x 0.85 mm die: 2.42 x 1.22 mm
Reed (UCSB) and Griffith (Teledyne): CSIC 2012 Teledyne 250 nm InP HBT
-20
-10
0
10
20
210 220 230 240 250 260
Am
plif
ier
ga
ins (
dB
)
frequency (GHz)
3dB bandwidth = 240GHz
S21,mid-band
= 15.4dB
S11
S22
8-cell, 2-stage PA
PDC
= 4.46W
0
20
40
60
80
100
0 2 4 6 8 10 12 14
Po
ut , m
W
Pin
, mW8-cell, 2-stage PA PDC
= 4.46W
88mW Pout
84mW
80mW
72mW
62mW
42mW
90mW
220GHz operation
RF output power densities up to 0.5 W/mm @ 220 GHz. → InP HBT is a competitive mm-wave / sub-mm-wave power technology.
220 GHz 330mW Power Amplifier Design
0
5
10
15
20
25
30
35
40
0
50
100
150
200
250
300
350
400
-30 -25 -20 -15 -10 -5 0 5 10
Ga
in (
dB
), P
ou
t (d
Bm
)
Po
ut (m
W)
Pin (dBm)
Operating Frequency = 220 GHz
Pdc = 12 W
-20
-10
0
10
20
30
0 50 100 150 200 250 300 350 400
-20
-10
0
10
20
30
S-p
ara
me
ters
(d
B)
Frequency (GHz)
2.3 mm x 2.5 mm
T. Reed, UCSB Z. Griffith, Teledyne Teledyne 250 nm InP HBT
50-G/s Track/Hold Amplifier; 250 nm InP HBT
20.5 GHz input, 10 GHz clock
S. Daneshgar, this conference
Linearity test (third-order intercept)
Where Next ? → 2 THz Transistors, 1 THz Radios.
transmitter receiver
interconnects
DIVOUT
VEF
RFIN
VEE
C1
C2
C3
C4
Q3,4 Q5,6
Q1 Q2
Q7 Q8
Q9
Q10
Q11
L1 L2
L3 L4
L5 L6
R1
R2R3 R4
R5
R6 R7
circuits
VVEEEE VVTUNETUNE
VVOUTOUT
VVBBBB
Q3Q3 Q4Q4
Q1Q1 Q2Q2Q6Q6
C1C1 C2C2 C3C3
RREE
Q5Q5Q5Q5
LLE1E1
LLE2E2
RR11
CCVarVar CCVarVar
RR22
RR33
RR44
LLBB
LLC1C1
LLC2C2LLC3C3
LLout1out1
LLout2out2
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
(backup slides follow)
Weakly Degenerate→ Effective Added Resistance
10-3
10-2
10-1
100
101
102
-0.3 -0.2 -0.1 0 0.1 0.2
J(m
A/m
m2)
Vbe
-
Fermi-Dirac
Boltzmann
(-Vbe
)<<kT/q
Fit:
equivalent
series
resistanceeqsbe RIIIqkTV )/ln()/(
*/1 Eeq mR
At & beyond 32 nm, we must increase the emitter effective mass.
HBT Scaling Roadmap
emitter 128 64 32 nm width
4 2 1 Wmm2 access
base 120 60 30 nm contact width,
5 2.5 1.25 Wmm2 contact
collector 75 53 37.5 nm thick,
18 36 72 mA/mm2 current density
3.3 2.75 2-2.5 V, breakdown
f 730 1000 1400 GHz
fmax 1300 2000 2800 GHz
RF-ICs 660 1000 1400 GHz
digital divider 330 480 660 GHz
140 nm Device: RF Results
140 nm emitter junction
120 nm wide base contacts 75 nm thick collector 25 nm thick base
fmax impaired (780 GHz) : excessive contact penetration into base
Chiang & Rode unpublished
433 GHz f 780 GHz fmax
DC to Daylight. Far-Infrared Electronics
0.1-0.4 THz imaging systems
109
1010
1011
1012
1013
1014
1015
Frequency (Hz)
microwave
3-30 GHz
mm-wave
30-300 GHz
far-IR
(sub-mm)
0.3-3THz
mid-IR
3-30 THz
near-IR
30-450 THz
op
tica
l
45
0-9
00
TH
zHow high in frequency can we push electronics ?
...and what would be do with it ?
0.3-3 THz radio: vast capacity bandwidth, # channels
0.1-1 Tb/s optical fiber links