Post on 28-Jul-2020
Company Confidential READY FOR “THE TEST”
On Wafer S-Parameters
& Uncertainties
Dr. Andrej Rumiantsev
Director RF Technologies
MPI Corporation
Company Confidential
visit: www.mtt-archives.org/~mtt11
2 A.Rumiantsev ARFTG86th-NIST SC-
2015
Company Confidential
Outline
• Introduction
• Criteria for the “right method”
• Calibration residual errors
• Conclusion
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Company Confidential
The Last Inch to the DUT
…leads to a different world 4 A.Rumiantsev ARFTG86th-NIST SC-2015
Company Confidential
Coaxial Calibration Standards
• Same media
• Well-defined electrical characteristics at
the calibration plane
Picture: Spinner Group
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Company Confidential
Wafer-Level Standards
• Coplanar design:
– Dispersion
• Not shielded:
– Coupling and
radiation
• Manufacturing
inaccuracy
Picture: FBH, Berlin
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Company Confidential
Wafer-Level Standards (cont.)
Two discontinuities:
• Coaxial media to planar
probe tips
• Probe tips to coplanar
devices (standards)
Picture: FBH, Berlin
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Company Confidential
Outline
• Introduction
• Criteria for the “right method”
• Calibration residual errors
• Conclusion
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Company Confidential
Calibration and Self-Calibration
• Calibration methods: known standards
– SOL, SOLT, QSOLT
• Self-calibration standards:
– Reflect, reciprocal thru, line
• Solution criteria:
– Frequency range
– Self-calibration methods with optimal set of
standards
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Company Confidential
Example: SOLT
Standard Requirements Typical Definition Error Terms
Short Fully known R=0; L=9pH 2
Open Fully known R=inf; C=0.3fF 2
Load Fully known R=50; L=10.6pH 2
Thru Fully known Z0=50Ω
α=0, τ=1ps 4
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Open/Short are not Ideal
0 20 40 60 80 100 120
Frequency (GHz)
Open and Short (multiline TRL)
-1
-0.5
0
0.5
1
Mag(S11) (
dB)
Short
Open
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Company Confidential
0 20 40 60 80 100 120
Frequency (GHz)
Open and Short (multiline TRL)
160
170
180
190
Phase(S11) (
degre
e)
-10
0
10
20
Phase(S11) (
degre
e)
Short (L)
Open (R)
Open/Short are not Ideal
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Company Confidential
Test DUT: SOLT
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Calibration Outcome
Removes systematic
errors: – Shifts the reference plane
– Defines reference impedance
ZREF Error Model DUT
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Reference Impedance: Lumped Methods
• ZREF is defied by the load ZLOAD
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Calibration Plane: Middle of the Thru
• Thru must be fully known – crucial!
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Calibration Challenges at mm-Wave Frequencies
17
• Probe tip Load:
– Less space on the calibration substrate
– More elements on the same size
• Acceptable compromize for low-
frequency measurements
• Load impedance at mm-wave range?
• Calibration accuracy above 110 GHz?
A.Rumiantsev ARFTG86th-NIST SC-2015
Company Confidential
Calibration Challenges at mm-Wave Frequencies
18
?
• Accurate definition of the equivalent impedance requires
uniformed structure of the E/M waves at the reference
point
• Where is the point of the uniformed waves?
1
2 3
A.Rumiantsev ARFTG86th-NIST SC-2015
Company Confidential
Calibration Challenges at mm-Wave Frequencies
• Away from the probe tips:
– Transition to CPW complete
– Uniformed fields
– Well-established traveling
waves
– Well-defied reference
impedance!
• At the probe tip:
– Transition point from tip to
standard
– Discontinuity
– Not-uniformed fields
– Load impedance???
(undefined!)
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2015
Company Confidential
Solution for Calibration at mm-Wave Frequencies
• Move load away from the probe-tips.
• However:
– Load with long offset impractical
– How to define its equivalent impedance in wide
frequency range?
• Solution: NIST multiline TRL
– Load not required!
– Requires just sections of transmission lines
– Calibration standards easy to make on-wafer
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Company Confidential
Distributed Standard-Based Methods:
TRL and mTRL
• Calibration reference impedance is the
characteristic impedance of the line
• Lines are dispersive
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Dispersion Phenomenon
• S-parameters:
– ZREF=ZLINE
• Pseudo S-parameters:
– ZREF=50 Ω
Useful reading: D. Williams, “Traveling waves and power waves”, Microwave Magazine, Nov-Dec 2013.
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Company Confidential
Distributed Standard-Based Methods:
TRL and mTRL
• Transformation to 50 Ω reference impedance
required
• Measurement of line characteristic impedance
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Company Confidential
Probe Tip vs. on-Wafer Calibration
Probe Tip
On-Wafer
DUT (HBT)
Wafer Probe
A. Rumiantsev, “On-Wafer calibration techniques enabling accurate characterization of high-performance silicon devices at the mm-wave range and beyond,” Fakultät für
Maschinenbau, Elektrotechnik und Wirtschaftsingenieurwesen, BTU Cottbus, Cottbus, 2014.
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Company Confidential
Probe Tip vs. on-Wafer Calibration
TMR
TRL
On-wafer: CMOS On-wafer: BiCMOS Off-wafer standards
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On-Wafer Cal: Distributed Standards
Top metal
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On-Wafer Cal: Lumped Standards
Metal1 (2)
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Outline
• Introduction
• Criteria for the “right method”
• Calibration residual errors
• Conclusion
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Company Confidential
Calibration
[A] [B]-1
Error Box Error Box
VNA
Planar Standards
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Real Situation: Residual Errors
[A] [B]-1 [A]* [B]*-1
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VNA
Residual Residual Error Box Error Box
Company Confidential
Example: MAG 2x25μm Cascode Cell
Shinghal, P.; Sloan, R.; Duff, C.I.; Cochran, S., "Observations on the sensitivity of on-wafer cascode cell S-parameter measurements due to probing uncertainties," ARFTG Microwave Measurement Conference (ARFTG), 2014 83rd , vol., no., pp.1,3, 6-6 June 2014
Probe type A
Probe type I
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Sources of Calibration Residual Errors
• Inaccuracies of calibration standards
– Design, fabrication and probe positioning
• Higher-order mode propagation
– Calibration standards and DUT
• Coupling with nearby structures
– Between elements
– RF probes and elements
• Limitations of calibration methods
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Company Confidential
(Co)Planar Calibration Standards
• Dispersion
• Manufacturing
inaccuracy
• Probe positioning
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Dispersion: Example for AC-2
MPI Probe Selection Guide. MPI Corporation, Hsinchu, Taiwan, 2014
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Company Confidential
Operating with Multiple Lines
• Multiline TRL definition:
– Offset of each line vs. Thru.
– Just physical length, not electrical parameters needed
• Wafer-level multiline TRL system requirements:
– Motorized positioner(s)
– Typical positioning error +/- 5 micrometers
– Painful investment
A.Rumiantsev ARFTG86th-NIST SC-2015 35
Company Confidential
Minimize Positioning Error
• Digital gauge for X-axes
• Positioning resolution 1µm
• Set/adjust/measure Δl for
multilne TRL
T
hr
u
Δl
Thr
u
Lin
e
Picture: MPI
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Company Confidential
Membrane CPW Design
for Improved Line Characteristics
U. Arz, M. Rohland, and S. Büttgenbach, Improving the Performance of 110 GHz Membrane-Based Interconnects on Silicon: Modeling, Measurements, and Uncertainty Analysis,
in EEE Trans. on Components, Packaging and Manufacturing Tech., vol. 3, No. 11, Nov. 2013
ε 0
ε r Al2O3
Conventional CPW
Membrane CPW
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Company Confidential
Comparison for Relative Phase Constant
U. Arz, M. Rohland, and S. Büttgenbach, Improving the Performance of 110 GHz Membrane-Based Interconnects on Silicon: Modeling, Measurements, and Uncertainty Analysis,
in EEE Trans. on Components, Packaging and Manufacturing Tech., vol. 3, No. 11, Nov. 2013
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Company Confidential
CPW Boundary Conditions
Ceramic Metal
Courtesy: FBH, Berlin
• Multi-mode propagation at mm-wave frequencies
• Critical for every calibration method
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Optimized Chuck Material
0 20 40 60 80 100 120
Frequency (GHz)
-0.8
-0.6
-0.4
-0.2
0
Imag(Z0) (
Ohm
)
On Metal
On Absorber
On Ceramic
A. Rumiantsev, R. Doerner, and E. M. Godshalk, "The influence of calibration substrate boundary conditions on CPW characteristics and calibration accuracy at mm-wave frequencies,"
ARFTG Microwave Measurements Conference-Fall, 72nd, pp. 168-173, 2008.
Picture: MPI
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Coupling with Nearby Structures
• Ex-field in the CPW
• CPW mode in the
neighborhood
V. Krozer, R. Doerner, A. Rumaintsev, N. Weinmann, F. Schmückle, and W. Heinrich, On-Wafer Small- and Large- Signal Measurement Systems at sub-THz Frequencies, BCTM-2014, pp. 1-
8, 2014.
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Higher-Order Modes
• Coupling between probe ground and on-
wafer ground:
– Parasitic propagating signal
• Parallel-plate mode in substrate:
– CPW ground and the backside ground
• Other modes guiding:
– Between coaxial probe ground and wafer
backside metallization
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Company Confidential
Coupling and Higher Modes
G.N. Phung, F.J. Schmückle, W. Heinrich, “Parasitic Effects and Measurement Uncertainties in Multi-Layer Thin-Film Structures,” Proc. 43th European Microwave Conf.
(EuMC 2013), Nuremberg, Germany, Oct. 7-10, pp. 318-321
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PPL tube mode
MS mode
PPL mode
CPW needle mode
Coupling and Higher Modes:
Microstip Elements
G.N. Phung, F.J. Schmückle, W. Heinrich, “Parasitic Effects and Measurement Uncertainties in Multi-Layer Thin-Film Structures,” Proc. 43th European Microwave Conf. (EuMC
2013), Nuremberg, Germany, Oct. 7-10, pp. 318-321
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Company Confidential
110 GHz RF Probe:
Similar Concept, Different Tip Design
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RF Probe Design:
Coax-to-CPW Transmission Variety
Picoprobe
A. Rumiantsev and R. Doerner, "RF probe technology," Microwave Magazine, IEEE, vol. 14, pp. 46-58, 2013.
ACP Infinity TITAN (Allstron)
Company Confidential
Impact of the Probe Tip Design
0 10 20 30 400.0
0.5
1.0
1.5
2.0
2.5
Att
enuation C
onsta
nt
(dB/c
m)
Frequency (GHz)
'A' 'I'
'P' 'AL'
0 10 20 30 402.200
2.225
2.250
2.275
2.300
'A' 'I'
'P' 'AL'
Rela
tive P
hase C
onsta
nt
(unitle
ss)
Frequency (GHz)
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A. Rumiantsev, R. Doerner, Method for Estimating Probe-Dependent Residual Errors of Wafer-Level TRL Calibration, ARFTG-83rd, 2014.
Company Confidential
Worst-Case Estimate:
Error for Four Probe Technologies
0 20 40 60 80 100 120-1.5
-1.0
-0.5
0.0
0.5
M
ag(S
21)
(dB)
Frequency (GHz)
'I' 'A'
'P' 'AL'
SMAX
, SMIN
A. Rumiantsev, R. Doerner, Method for Estimating Probe-Dependent Residual Errors of Wafer-Level TRL Calibration, ARFTG-83rd, 2014.
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Company Confidential
Outline
• Introduction
• Criteria for the “right method”
• Calibration residual errors
• Conclusion
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Company Confidential
Conclusion
• Calibration residual errors have complex nature
• Contributing factors:
– Design of standards
– Probe type
• Solutions for reference CPW line available
• Design optimization of the calibration chip:
– Reduce support of higher-order modes
– Minimize coupling effects
50 A.Rumiantsev ARFTG86th-NIST SC-2015
Company Confidential READY FOR “THE TEST”
THANK YOU
FOR YOUR ATTENTION For more information, please visit:
www.mpi-corporation.com