Post on 19-Aug-2018
Expanding ImpedanceExpanding Impedance Measurement to Nanoscale:Nanoscale:
Coupling the Power of Scanning Probe Microscopy with Performance Network Analyzer (PNA)(PNA)
Hassan Tanbakuchi Senior Research Scientist Agilent Technologies, Inc.
Agilent E Seminar
August 2008Page 1
Outline
• SCM Basics.
• Microwave Network Analyzer Basics (VNA).Microwave Network Analyzer Basics (VNA).
• Challenges of VNA as a SMM measurement engine.
• Addressing the measurement challenge.g g
• Electromechanical coupling challenge and solution
• Mechanical design.
• DPMM (Dopant Profile Measurement Module)
• System overview.
• Some interesting images.
Agilent E-Seminar
August 2008Page 2
Traditional SCM
VCO Detector
• Scanning only• qualitative• poor sensitivity• limited 1015-1020 Atoms/cm3• No Conductors/Insulators
dV
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August 2008Page 3
dC
Network Analyzer Basicsy
Agilent E-Seminar
August 2008Page 4
What is a Vector Network Analyzer? S21
Vector network analyzers (VNAs)…• Are stimulus-response test systems
21
S12
S11 S22DUT
Reflection
Transmission
• Characterize forward and reverse reflection and transmission responses (S-parameters) of RF and microwave components
• Quantify linear magnitude and phase
12
• Are very fast for swept measurements• Provide the highest level
of measurement accuracy RF So rce
Magnitude
of measurement accuracy RF Source
LO
Phase
R1 R2LO
BA
Agilent E-Seminar
August 2008Page 5
Test port 2Test port 1
Lightwave Analogy to RF Energy
IncidentTransmitted
Reflected Lightwave
DUT
RF
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August 2008Page 6
Transmission Line Terminated with Zo
Zs = ZoZo = characteristic impedance of transmission line
Zo
of transmission line
Vinc
Vrefl = 0! (all the incident poweris absorbed in the load)
Vinc
For reflection, a transmission line terminated in Zo behaves like an infinitely long transmission line
Agilent E-Seminar
August 2008Page 7
behaves like an infinitely long transmission line
Transmission Line Terminated with Short, Open
Zs = Zo
V
Vrefl
Vinc
In-phase (0o) for open, Vrefl
For reflection, a transmission line terminated in a short or open reflects all power back to source
out-of-phase (180o) for short
Agilent E-Seminar
August 2008Page 8
short or open reflects all power back to source
Transmission Line Terminated with 25 Ω
Zs = Zo
Z 25 ΩZL = 25 Ω
Vrefl
Vinc
Vrefl
Standing wave pattern does not go t ith h t
Agilent E-Seminar
August 2008Page 9
to zero as with short or open
High-Frequency Device Characterization
Incident
Reflected
TransmittedR BA
TRANSMISSIONREFLECTION
TransmittedIncident
Gro p
ReflectedIncident
AR
=BR
=
Gain / Loss
S-ParametersS21, S12
GroupDelay
TransmissionC ff
Insertion Phase
SWR
S-ParametersS11, S22 Reflection
Coefficient
Impedance, Admittance
R+jX,
ReturnLoss
Agilent E-Seminar
August 2008Page 10
CoefficientR jX, G+jB Γ, ρ
Τ,τ
Standard Vector Network Analyzeras a reflectometeras a reflectometer
Ωk
A BSource
Very small capacitor High SNRLow Resolution
0
011 ZZ
ZZSL
L
+−
=
A BLO LO
A/D A/DProbe
Highly resistive load High SNRLow Resolution
Load close to 50 OhmsLow SNRHigh Resolution Figure 1: reflection
coefficient vs.. impedance
Low resistive loadHigh SNRLow Resolution
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August 2008Page 11
Proposed solutions
Cancellation (Nulling) of the reflected wave can be done either in the RF front end or the IF stage:
RF techniques: 1) Balun and amp 2) Differential Amp
Extreme Load ImpedanceSource
Ref-In Diff Amp
a1 b1
Variable Attenuator
AmpDelay lineA-inBalun
Delay line
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August 2008Page 12
Fully Automated Proposal
System drift correction via ECAL
Phase shifting and Attenuation are done through DSP
Low IF frequency, and High speed ADC are chosen to minimize the computational round off error in DSPDSP.
A B
DUTSource ECAL
A BLO1 LO1
LO2 LO210 KHz
IF
10 KHzIF
A/
DAC
/D1
DSP1 DSP2
+
-
DIF1
A/D+
-
U93
DAC
High resolution
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August 2008Page 13
A/D
High resolutionamplitudetweaker
Simplified Single Frequency Solution
A B
Source
Half wave length 50 Ohm
LO LO
A/D A/D
Half wave lengthCoaxial resonator
50 Ohm
Probe
m1freq=S(1,1)=0.001 / -90.076
1.910GHzm2freq=dB(S(1,1))=-57.550
1.910GHz
S(1
,1) m1
( , )impedance = Z0 * (1.000 - j0.003)
-40
-20
0
dB(S
(1,1
))
f (500 0MH t 3 000GH )
1.0 1.5 2.0 2.50.5 3.0
-60
freq, GHz
m2
Agilent E-Seminar
August 2008Page 14
freq (500.0MHz to 3.000GHz)
Electromechanical couplingBalanced Pendulum: How Does It WorkBalanced Pendulum: How Does It Work
• Laser tracking spot remains fixed relative to Z-piezo & AFM cantilever
• Z-piezo does not bend
Y scan
Tube Design Pendulum Design
Agilent E-Seminar
August 2008Page 15
Early Design Suffers from Abrupt Localized Bend of Coax Connecting TIP to Diplexer
Load Diplexer
of Coax Connecting TIP to Diplexer
RF to PNARF to PNA
Coax from the
Scanner head With Conductive Tip
Coax from the Tip to diplexer
With Conductive Tip
Agilent E-Seminar
August 2008Page 16
Distribution of Electromechanical Coupling Through Coaxial Loop
Extraction tool
Conductive TipConductive TipConductive Tip
Diplexer 50 Ohm CKT
Looped cable
Looped cable
H lf W l th C bl
Diff i f l t i l/ h i l li ith i t ti f h d VNA d P i i M hi i
Half Wavelength Cable
Agilent E-Seminar
August 2008Page 17
Diffusion of electrical/mechanical coupling with integration of enhanced VNA and Precision Machining
Speedy Conductive Tip Replacement
RF Connection
Pt/Rb Cantilever
Al i C iAlumina Carrier
Magnetic JawConductive Tip
Agilent E-Seminar
August 2008Page 18
DPMM Dopant Profile Measurement ModuleDopant Profile Measurement Module
DPMM approach:DPMM approach:Use the Flatband transfer function
that is function of dopant density ( variable capacitor) that can be used as an AM mixer to modulate the reflected MW signal at the rate of Flatband drive frequency (<100 KHz). The said AM modulation index is
Agilent E-Seminar
August 2008Page 19
function of the dopant density.
DPMM Block Diagram/Physical Realization
ACPLR OUT
CPLR Thru
Source Out
A
LO
A/D
SourceHalf wave lengthCoaxial resonator
50 Ohm
ProbeAMP
Signal IN
B
AMPAMP AMP
AMP
dopant
LO
A/D
AMP
Signal outT L k i
RCVR IN
DPMM
To Lock in
Agilent E-Seminar
August 2008Page 20
DPMM Internal Structure and as an add on Module to PNAto PNA
DPMM PNA PORT1
DPMM Internal MIC detail DPMM as an add measurement module to PNA
Agilent E-Seminar
August 2008Page 21
System OverviewPhotodetector
Coaxial cableCoaxial Resonator
Sample
Coaxial Resonator
The MW diplexer
Network Analyzer
Ground/Shield
Sample scanning AFM in X and Y and Z (closed loop)
• Network analyzer sends an incident RF signal to the tip throughthe diplexer.
• RF signal is reflected from the tip and measured by the Analyzer.• The magnitude and the phase of the ratio between the incident andThe magnitude and the phase of the ratio between the incident and
reflected are calculated• Apply a model to calculate the electrical properties• AFM scans
AFM ti t ifi l ti t d i t bi
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August 2008Page 22
• AFM moves tip to specific locations to do point probing
SRAM Image
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S i l• Scanning only• qualitative• poor sensitivity• limited 1015-1020 Atoms/cm3
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• No Conductors/Insulators