Agilent E Seminar

August 2008Page 1

Expanding Impedance Measurement to Nanoscale:

Coupling the Power of Scanning Probe Microscopy with Performance Network Analyzer (PNA)

Hassan Tanbakuchi Senior Research Scientist Agilent Technologies

Agilent E-Seminar

August 2008Page 2

Outline

•SCM Basics.

•Microwave Network Analyzer Basics (VNA).

•Challenges of VNA as a SMM measurement engine.

•Addressing the measurement challenge.

•Electromechanical coupling challenge and solution

•Mechanical design.

•DPMM (Dopant Profile Measurement Module)

•System overview.

•Some interesting images.

Agilent E-Seminar

August 2008Page 3

Traditional SCM

dV

dC

VCO Detector

• Scanning only• qualitative• poor sensitivity• limited 1015-1020 Atoms/cm3• No Conductors/Insulators

Agilent E-Seminar

August 2008Page 4

Network Analyzer Basics

Agilent E-Seminar

August 2008Page 5

What is a Vector Network Analyzer?Vector network analyzers (VNAs)…• Are stimulus-response test systems• Characterize forward and reverse reflection and transmission responses

(S-parameters) of RF and microwave components• Quantify linear magnitude and phase• Are very fast for swept measurements• Provide the highest level

of measurement accuracy

S21

S12

S11 S22

R1 R2

RF Source

LO

Test port 2

BA

Test port 1

Phase

Magnitude

DUT

Reflection

Transmission

Agilent E-Seminar

August 2008Page 6

Lightwave Analogy to RF Energy

RF

Incident

Reflected

Transmitted

Lightwave

DUT

Agilent E-Seminar

August 2008Page 7

Transmission Line Terminated with Zo

For reflection, a transmission line terminated in Zo behaves like an infinitely long transmission line

Zs = Zo

Zo

Vrefl = 0! (all the incident poweris absorbed in the load)

V inc

Zo = characteristic impedance of transmission line

Agilent E-Seminar

August 2008Page 8

Transmission Line Terminated with Short, Open

Zs = Zo

Vrefl

Vinc

For reflection, a transmission line terminated in a short or open reflects all power back to source

In-phase (0o) for open, out-of-phase (180o) for short

Agilent E-Seminar

August 2008Page 9

Transmission Line Terminated with 25 Ω

Vrefl

Standing wave pattern does not go to zero as with short or open

Zs = Zo

ZL = 25 Ω

V inc

Agilent E-Seminar

August 2008Page 10

High-Frequency Device Characterization

Transmitted

Incident

TRANSMISSION

Gain / Loss

S-ParametersS21, S12

GroupDelay

TransmissionCoefficient

Insertion Phase

Reflected

Incident

REFLECTION

SWR

S-ParametersS11, S22 Reflection

Coefficient

Impedance, Admittance

R+jX, G+jB

ReturnLoss

Γ, ρΤ,τ

Incident

Reflected

TransmittedRB

A

A

R=

B

R=

Agilent E-Seminar

August 2008Page 11

Standard Vector Network Analyzeras a reflectometer

Highly resistive load High SNRLow Resolution

Low resistive loadHigh SNRLow Resolution

Load close to 50 OhmsLow SNRHigh Resolution Figure 1: reflection

coefficient vs.. impedance

0

011 ZZ

ZZSL

L

+−

=

Ωk

A BLO LO

A/D A/D

Source

Probe

Very small capacitor High SNRLow Resolution

Agilent E-Seminar

August 2008Page 12

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

A-in

Extreme Load Impedance

Balun

Source

Variable Attenuator

Ref-In Diff Amp

Amp

a1 b1

Delay line

Agilent E-Seminar

August 2008Page 13

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 DSP.

A BLO1 LO1

DUTSource

LO2 LO2

ECAL

10 KHzIF

10 KHzIF

DAC

A/D1

DSP1 DSP2

+

-

DIF1

A/D

A/D

+

-

U93

DAC

High resolutionamplitudetweaker

Agilent E-Seminar

August 2008Page 14

Simplified Single Frequency Solution

A BLO LO

A/D A/D

Source

Half wave lengthCoaxial resonator

50 Ohm

Probe

freq (500.0MHz to 3.000GHz)

S(1

,1) m1

m1freq=S(1,1)=0.001 / -90.076impedance = Z0 * (1.000 - j0.003)

1.910GHz

1.0 1.5 2.0 2.50.5 3.0

-40

-20

-60

0

freq, GHz

dB(S

(1,1

))

m2

m2freq=dB(S(1,1))=-57.550

1.910GHz

Agilent E-Seminar

August 2008Page 15

Electromechanical couplingBalanced Pendulum: How Does It Work

Y scan

• Laser tracking spot remains fixed relative to Z-piezo & AFM cantilever• Z-piezo does not bend

Tube Design Pendulum Design

Agilent E-Seminar

August 2008Page 16

RF to PNA

Load Diplexer

Scanner head With Conductive Tip

Early Design Suffers from Abrupt Localized Bend of Coax Connecting TIP to Diplexer

Coax from the Tip to diplexer

Agilent E-Seminar

August 2008Page 17

Distribution of Electromechanical Coupling Through Coaxial Loop

Diffusion of electrical/mechanical coupling with integration of enhanced VNA and Precision Machining

Half Wavelength Cable

Diplexer 50 Ohm CKT

Looped cable

Looped cable

Extraction tool

Conductive TipConductive Tip

Agilent E-Seminar

August 2008Page 18

Speedy Conductive Tip Replacement

Magnetic Jaw

RF Connection

Conductive Tip

Pt/Rb Cantilever

Alumina Carrier

Agilent E-Seminar

August 2008Page 19

DPMM Dopant Profile Measurement Module

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 function of the dopant density.

Agilent E-Seminar

August 2008Page 20

DPMM Block Diagram/Physical Realization

A

LO

A/D

Source

B

LO

A/D

Half wave lengthCoaxial resonator

50 Ohm

ProbeAMP

AMPAMP AMP

AMP

Signal outTo Lock in

RCVR IN

CPLR OUT

CPLR Thru

DPMM

dopant

Signal IN

Source Out

Agilent E-Seminar

August 2008Page 21

DPMM Internal Structure and as an add on Module to PNA

DPMM Internal MIC detail DPMM as an add measurement module to PNA

DPMM PNA PORT1

Agilent E-Seminar

August 2008Page 22

System Overview

Coaxial cable

Network Analyzer

• 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 andreflected are calculatedApply a model to calculate the electrical properties• AFM scans• AFM moves tip to specific locations to do point probing

Photodetector

Sample

Coaxial Resonator

The MW diplexer

Ground/Shield

Sample scanning AFM in X and Y and Z (closed loop)

Agilent E-Seminar

August 2008Page 23

SRAM Image

Agilent E-Seminar

August 2008Page 24

Agilent E-Seminar

August 2008Page 25

• Scanning only• qualitative• poor sensitivity• limited 1015-1020 Atoms/cm3• No Conductors/Insulators