Transcript Design and Scaling of SiGe BiCMOS VCOs Above 100GHz S. T. Nicolson1, K.H.K Yau1, K.A.

Design and Scaling of SiGe BiCMOS
VCOs Above 100GHz
S. T. Nicolson1, K.H.K Yau1, K.A. Tang1, P. Chevalier2, A. Chantre2
B. Sautreuil2, and S. P. Voinigescu1
1) Edward S. Rogers Sr. Dept. of Elec. & Comp. Eng., Univ. of Toronto
2) STMicroelectronics
© Sean Nicolson, BCTM 2006
Outline
•
•
•
•
•
Motivation for W-band SiGe integrated circuits
VCO design methodology for low phase noise in W-band
Layout considerations
Measurement results
Conclusions and future work
© Sean Nicolson, BCTM 2006
Motivation for W-band SiGe ICs
• Typical applications: 77GHz auto radar, 94GHz weather radar, imaging
– Central to these applications is the low phase noise VCO
• Process development: NFmin, Rn & Ysopt difficult to measure in W-band
– Use VCO as a process monitor for the noise performance of SiGe technologies
• Explore VCO scaling/yield in SiGe
© Sean Nicolson, BCTM 2006
VCO Topology
• No cascode
2.5 V VCC
LC
CM
– lower phase noise, lower supply voltage
• Colpitts topology
– maximize fosc relative to other topologies
• Augment Cbe with Cext
LB
Q1
CextVBB
24mA
VTUNE+
Cvar
– Reduces phase noise
VTUNE- LEE
• Add negative Miller capacitors
REE
– Increases fosc by cancelling Cm
CEE
VTUNE
• Differential tuning
– reduces supply induced noise
B
bib
RB
cp rp
E
© Sean Nicolson, BCTM 2006
C
Cext
W-Band VCO Design Methodology
• Use smallest realizable LB with adequate Q
• Given fosc, maximize tuning range using large Cext
f osc 
1
Ceq 
2p LB Ceq
Cext  Cp C var
Cext  Cp  C var
 Cm
• Negative resistance
Rneg  RB 
I C VT
 2 Cext   F I C VT Cvar
Max. Rneg occurs at
peak fT/fMAX bias
• Phase noise formula
S out  2
In
2
Vtank
1
2
1
2
2




C

C
Cext  Cp 2  ext p  1
 C var

• Phase noise trade-off when HBT pushed to limit
– Minimize HBT noise  bias at NFmin current density
– Maximize Vtank and Cext bias at peak fT current density
© Sean Nicolson, BCTM 2006
VCO Fabrication
• Fabricated in three technology splits:
BiC9
fT = 150GHz
fMAX = 160GHz
BipX
fT = 230GHz
fMAX = 300GHz
BipX1
fT = 270GHz
fMAX = 260GHz
emitter
4×5mm×0.17mm
emitter
4×5mm×0.13mm
emitter
4×5mm×0.13mm
• All VCO layouts and bias currents are identical – no redesign
• Directly compare VCOs fabricated in different processes
• Use the VCO to optimize HBT profile
– Noise parameters from phase noise
– fMAX from VCO output power
© Sean Nicolson, BCTM 2006
VCO Layout
• VCO core area: 100mm × 100mm
• Spiral inductors where necessary to reduce area
• Plenty of supply decoupling (MiM and metal-metal)
70mm
100mm
© Sean Nicolson, BCTM 2006
Technology Overview – fT/fMAX Scaling
• Peak fT/fMAX current density increases at each technology node
– 0.17mm SiGe JpeakfT = 7mA/mm2 where fT = 150GHz
– 0.13mm SiGe JpeakfT = 14mA/mm2 where fT = 230GHz (or 250GHz)
• Contrast with CMOS…
– JpfT = 0.3mA/mm, JpfMAX = 0.2mA/mm, JNFmin = 0.15mA/mm for 180-65nm nodes
© Sean Nicolson, BCTM 2006
Measurement Results
•
•
•
•
VCO performance comparison in 3 SiGe technologies
Phase noise performance
Temperature testing
Wafer mapping
© Sean Nicolson, BCTM 2006
Performance Comparison Across Technology
BiCMOS9
MOS var.
BiCMOS9
HBT var.
BipX
HBT var.
BipX1
HBT var.
150/160
150/160
230/300
250/260
Differential Pout
(dBm)
+0.7
-1.3
+2.7
+2.5
SSB PN @
1MHz (dBc/Hz)
-101.6
-80
-98
-101.3
Osc. Freq. (GHz)
96
100
106
104
Tech. fT/fMAX
(GHz)
•
•
•
•
LC-oscillator frequency insensitive to technology fT/fMAX
MOS varactors give less phase noise than HBT (CBC) varactors
Higher fMAX  more output power, higher frequency
BipX1 results in lowest phase noise
© Sean Nicolson, BCTM 2006
Phase Noise Performance
• Oscillation frequency of 104GHz
• Phase noise of 101.3dBc/Hz @ 1MHz offset
Phase Noise in W-Band
SiGe VCOs
FMCW modulation
Averaged
Spectral Plot
Phase noise at 1MHz offset
(dBc/Hz)
-80
-85
fT=155
fmax =155
-90
-95
fT=175
fmax =275
-100
130nm
CMOS
fT=175
fmax =275
fT=205
fmax =290
fT=230
fmax =300
90nm CMOS
fT=150 fT=270
fmax =160 fmax =260
fT=200GHz
fmax =275GHz
-105
fT=206
fmax =197
-110
65
70
75
80
85
90
95
100 105 110
Oscillation frequency (GHz)
**References provided in abstract**
© Sean Nicolson, BCTM 2006
Biasing W-Band VCOs for Low Noise
• NFmin current density scales with technology and fosc
– Emitter width
JNFmin
(scales with JpeakfT)
– Frequency
JNFmin
(gets closer to JpeakfT)
– Noise correlation further increases JNFmin [K. Yau, SiRF, 2006]
B
RB
<inB>
bib
cp
C
<inC>
E
The B and C shot noise
currents are correlated
*
inB inC
 2qIC exp  j n   1
© Sean Nicolson, BCTM 2006
Phase Noise Performance Across Bias
• What is the minimum phase noise current density in W-band VCOs?
• Measure output power and phase noise w.r.t current density (vary VBB)
• Looks like phase noise is minimum at peak fT current density
2.5 V VCC
output
power
LC
CM
LB
phase
noise
JNFMIN increases
with frequency
Q1
CextVBB
VTUNE+
Cvar
VTUNE- LEE
REE
© Sean Nicolson, BCTM 2006
CEE
W-Band Manufacturability Challenges
• Manufacturability specifications for automotive radar are stringent
– Outdoors  wide temperature variations
– Must last for car’s lifetime
– Low cost per part requires high yield
• Is SiGe on the way to meeting such challenges?
Output power (dBm) .
2
25ºC
25ºC
0
25ºC
70ºC
70ºC
125ºC
-2
BiC9
-4 MOS var.
BiC9
HBT var.
50ºC
BipX
-6
92
96
100
104
Center frequency (GHz)
108
© Sean Nicolson, BCTM 2006
Wafer Mapping – BiCMOS9
• Tested 120 VCOs on 4 wafers
• Summary of BiC9 VCOs with MOS varactors (60 dice averaged)
Wafer
1
2
3
4
Center freq. (GHz)
94.7
94.9
94.9
95.0
Tuning range (GHz)
4.6
4.6
4.6
4.6
Output power (dBm)
0.2
0.7
0.6
0.8
DC power (mW)
133.8 133.2 137.3
132.6
• Summary of BiC9 VCOs with HBT varactors (60 dice averaged)
Wafer
1
2
3
4
Center freq. (GHz)
99.6
100.5
100.1
100.5
Tuning range (GHz)
3.4
3.6
3.6
3.7
Output power (dBm)
-1.1
-1
-1.4
-0.9
DC power (mW)
133.0 133.0
136.2
132.8
• 4 VCOs had significantly below average performance (outliers)
• 2 of the 4 outlier VCOs failed to oscillate entirely
© Sean Nicolson, BCTM 2006
Wafer Mapping – BipX
Oscillation Frequency
Phase Noise at 1MHz offset
Wafer flat
Location of
VCO in reticule
VCO not present
Die not tested
104.5-105.0 GHz
104.0-104.5 GHz
103.5-104.0 GHz
103.0-103.5 GHz
© Sean Nicolson, BCTM 2006
VCO not present
Die not tested
< -98 dBc/Hz
-95 – -98 dBc/Hz
-92 – -95 dBc/Hz
> -92 dBc/Hz
Figures of Merit
• Comparison of our work to other state of the art W-Band VCOs
References [1] Huang P. et al, ISSCC 2006 [2] Kobayashi K. W. et al, JSSC 1999
[3] Tang K. W. et al. CSICS 2006 [4] Huang P. et al, ISSCC 2006
© Sean Nicolson, BCTM 2006
Conclusions
• Demonstrated a design methodology for low phase noise in W-Band
VCOs
– Biasing at JpeakfT minimizes phase noise in W-band VCOs
• Performed a direct comparison of identical VCOs fabricated in different
technologies
– LC-oscillator frequency is insensitive to technology scaling
– Higher fT technology yielded VCO with lower phase noise
– Higher fMAX technology yielded VCO with improved output power
• Future work is required to fully support these conclusions
– Noise figure measurements in the W-Band (correlate to Y-parameter method)
– Verify JNFmin in the W-Band and support biasing near JpeakfT for min. phase noise
© Sean Nicolson, BCTM 2006
Technology Overview – fT/fMAX Scaling
• Improvement in peak fT/fMAX has two contributions
– Layout  stripe contact, decreased emitter width 0.17mm to 0.13m
– Vertical profile and processing  doping, materials, epitaxy, etc.
• How much of the speed improvement is due to each contribution?
– Measure the 0.13mm HBT layouts fabricated in the 0.17mm process
© Sean Nicolson, BCTM 2006