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
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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
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)