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.

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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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dC

Network Analyzer Basicsy

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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

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Test port 2Test port 1

Lightwave Analogy to RF Energy

IncidentTransmitted

Reflected Lightwave

DUT

RF

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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

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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

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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

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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

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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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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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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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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

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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

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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

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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

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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

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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

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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

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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

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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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• 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