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Design of a compact AFM scanner. Compact, high speed and high accuracy AFM scanner K. J. Kamp June 26, 2013 Committee: Prof . Ir. R.H. Munnig Schmidt Dr. Ir. S. Kuiper Dr. Ir. J. L. Herder Dr. Ir. J. F. L. Goosen. Outline. Introduction to Atomic Force Microscopes (AFM)

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design of a compact afm scanner

Design of a compact AFM scanner

Compact, high speed and high accuracy AFM scanner K. J. KampJune 26, 2013

Committee:

Prof. Ir. R.H. MunnigSchmidt

Dr. Ir. S. Kuiper

Dr.Ir. J. L. Herder

Dr. Ir. J. F. L. Goosen

outline
K. J. Kamp Design of a compact AFM scannerOutline
  • Introduction to Atomic Force Microscopes (AFM)
  • Research questions
  • Requirements and specifications
  • Concept 1
  • Concept 2
  • Detailed Design
  • Conclusion
introduction
K. J. Kamp Design of a compact AFM scanner
  • Introduction
  • Research Questions
  • Requirements specifications
  • Concept 1
  • Concept 2
  • Detailed Design
  • Conclusion
Introduction
introduction1
K. J. Kamp A compact AFM scannerIntroduction

The atomic force microscope (AFM)

  • Basic operation principle
    • Probe tip attached to a cantileveris scanned over a sample
    • Cantilever deflects due to the atomic forces
    • The cantilever deflectionmeasures the surface topography
introduction2
K. J. Kamp A compact AFM scannerIntroduction

The AFM scannerLateral scanning

  • Triangularpattern
  • Constant tip speed

x

z

y

introduction3
K. J. Kamp A compact AFM scannerIntroduction

The AFM scannerVertical scanning

  • Feedback loop
  • Cantilever deflection signal minimal
  • The probe tip tracks the topography

DOI wafer AFM measurement

introduction4
K. J. Kamp A compact AFM scannerIntroduction

AFM system specifications

  • Surface area (x,y) <15mm x 15mm
  • Measurement range (x,y,z) >10 x 10 x 2 microns
  • Imaging time < 1 s
  • Measurement uncertainty < 1 nm
introduction5
K. J. Kamp A compact AFM scanner

Top View

Introduction

z

y

Concept 1:The tripod scanner

x

Sensor

Sensor

Actuator 3

u3

Actuator 1

Actuator 2

u2

u1

Sensor

research questions
K. J. Kamp A compact AFM scanner
  • Introduction
  • Research Questions
  • Requirements specifications
  • Concept 1
  • Concept 2
  • Detailed Design
  • Conclusion
Research Questions
research questions1
K. J. Kamp A compact AFM scannerResearch questions
  • How do the specifications of the AFM system translate to the requirements of the AFM scanner?
  • Does the first scanner concept meet the requirements?
  • Does the second scanner concept meet the requirements?
  • Is the second scanner concept valid as a real world design?
requirements
K. J. Kamp A compact AFM scanner
  • Introduction
  • Research Questions
  • Requirements specifications
  • Concept 1
  • Concept 2
  • Detailed Design
  • Conclusion
Requirements
requirements1
K. J. Kamp A compact AFM scannerRequirements

Research question 1:How do the specifications of the AFM system translate to the requirements of the AFM scanner?

  • Measurement uncertainty < 1 nm  Translate to scanner roll angles
  • Imaging time < 1 s  Translate to scanner resonance frequencies
requirements2
K. J. Kamp A compact AFM scannerRequirements

Measurement uncertainty to roll angle

  • Misalignment sensors and probe tip: 0,5 mm
  • Scanner will rotate (roll angle)

→ This causes an Abbeerror (measurement uncertainty)

requirements3
K. J. Kamp A compact AFM scannerRequirements

Abbe error

  • Platform roll angle φ
  • Sensor offset δ
  • Abbe error: eabbe = δ tan(φ)Assumptions:

δ = 0,5 mmeabbe < 1,0 nm φ < 2 microrad

requirements4
K. J. Kamp A compact AFM scannerRequirements

Imaging time to resonance frequencies

  • Lateral resonance frequency > 10 kHz

Triangular wave frequency content

  • Vertical resonance frequency > 30 kHzTracking error, scanning speed

x

z

y

concept 1
K. J. Kamp A compact AFM scanner
  • Introduction
  • Research Questions
  • Requirements specifications
  • Concept 1
  • Concept 2
  • Detailed Design
  • Conclusion
Concept 1
concept 11
Design of a compact AFM scannerConcept 1

Analysis of the tripod concept

Kinematics related to scanner stroke

Statics related to scanner roll angles (Abbe error)

Dynamics related to scanner resonance frequencies

concept 12
K. J. Kamp A compact AFM scannerConcept 1

z

y

Kinematics analysis

Required stroke: 10 x 10 x 2 microns

  • Relation is found between

x, y, z (platform position)

u1, u2, u3 (actuators)

x

u3

u1

u2

concept 13
K. J. Kamp A compact AFM scannerConcept 1

Example

  • Ten scan lines 10 x 10 microns
  • Actuatordisplacement~ 6 microns
  • Mechanical amplification 10 / 6 = 1.66
concept 14
K. J. Kamp A compact AFM scannerConcept 1

z

y

Scanner roll angle

  • Hinges are not perfect
  • Lateral motion will cause the scanner to roll

x

u3

u1

u2

concept 15
Titel van de presentatieConcept 1

2D Statics analytical model

concept 16
K. J. Kamp A compact AFM scannerConcept 1

Main cause of AFM scanner roll

  • Stiffness ratio between longitudinal and lateral stiffness of a rod

Normalized stiffness ratio []

concept 17
K. J. Kamp A compact AFM scannerConcept 1

Statics

  • Flexure notch hinges
      • Increase longitudinal to lateral stiffness ratio
      • Decreases the roll angle
concept 18
K. J. Kamp A compact AFM scannerConcept 1

Statics FEM analysis

  • 3D FEM model
concept 19
K. J. Kamp A compact AFM scannerConcept 1

Statics FEM results

  • u1 = 5 microns
  • x = 5 microns
  • φ = ~ 460 microrad
concept 110
K. J. Kamp A compact AFM scannerConcept 1

Statics FEM results

  • Roll angle is lower
  • φ = ~ 360 microrad
concept 111
K. J. Kamp A compact AFM scannerConcept 1

Statics FEM results

  • Circular notch hinge
  • Roll angle even lower
  • φ=~ 60 microrad
concept 112
K. J. Kamp A compact AFM scannerConcept 1

Dynamics

  • First four resonances:
concept 113
K. J. Kamp A compact AFM scannerConcept 1

FEM Modal analysis

  • Eigenmode results

Yaw9,8 kHz

Lateral9,3 kHz

Roll42 kHz

Vertical 48 kHz

slide30
K. J. Kamp A compact AFM scanner

Concept 1

SummaryCan the requirements be met?

  • Trade-off low roll angle vs. high resonance frequencies
  • Low roll angles require a high stiffness ratio (low lateral stiffness)
  • High resonance frequencies require high stiffness overall

Conclusion: The individual requirements can not all be met. Concept 1 is not feasible

concept 2
K. J. Kamp A compact AFM scanner
  • Introduction
  • Research Questions
  • Requirements specifications
  • Concept 1
  • Concept 2
  • Detailed Design
  • Conclusion
Concept 2
concept 21
K. J. Kamp A compact AFM scannerConcept 2
  • Orthogonal scanning conceptLateral motion

Side view

Top view

Probe tip

Sensor

Sensor

Actuator

Actuator

concept 22
K. J. Kamp A compact AFM scannerConcept 2
  • Orthogonal scanning conceptVertical motion

Side view

Top view

Probe tip

Sensor

Sensor

Actuator

Actuator

concept 23
K. J. Kamp A compact AFM scanner

x

Concept 2

Kinematics

Lateral stroke:mechanical amplification = lever ratio b to a

ulever

b

a

concept 24
z

K. J. Kamp A compact AFM scanner

φ

x

L

ux

Concept 2

uz

K1

ux

uz

Statics analysis

Analytical model adapted to the orthogonal concept

L2

K2

K2

ulever

concept 25
K. J. Kamp A compact AFM scannerConcept 2

Analytical model and FEM analysis

  • Pure lateral input (no lever)ux = 5 microns
  • Analytical model: φ = 21,7 microrad
  • FEM resultφ = 22,9 microradThe roll angle φ is positive
concept 26
K. J. Kamp A compact AFM scanner

ux

uz

Concept 2

b

a

Including the lever

  • Input uxresults in a positive roll angle
  • Input uφresults in a negative roll angle

ulever

positive

negative

ux

concept 27
K. J. Kamp A compact AFM scannerConcept 2
  • Analytical model and FEM results
  • The length of the vertical rods is varied:
  • The roll angle shifts from negative to positive
concept 28
K. J. Kamp A compact AFM scannerConcept 2
  • The analytical model is used to find zero roll angle

Vertical rod length [m]

concept 29
K. J. Kamp A compact AFM scannerConcept 2

Resulting roll angle

Final iteration

L1 = 3,0 mmL2 = 4,0 mm

ulever= 10 microns

x = 4,9 microns

Roll angleφ = -0,63 microrad

concept 210
K. J. Kamp A compact AFM scannerConcept 2

Lateral:

Dynamics

FEM modal results

Lateral eigenmodes(x,y):~12,3 kHzVertical mode (z):

~36,5 kHz

Vertical:

concept 211
K. J. Kamp A compact AFM scannerConcept 2

Summary

  • The orthogonal scanner concept meets all the requirements
  • The stroke of 10 x 10 x 2 microns can be achieved
  • The roll angle is ~ 0,64 microrad
  • The resonance frequencies are 12,3 kHz lateral

43,4 kHz vertical

detailed design
K. J. Kamp A compact AFM scanner
  • Introduction
  • Research Questions
  • Requirements specifications
  • Concept 1
  • Concept 2
  • Detailed Design
  • Conclusion
Detailed design
detailed design1
K. J. Kamp A compact AFM scannerDetailed design

Component selection

  • Piezo actuators
  • Triangulation sensors
  • AFM chip holder
detailed design2
K. J. Kamp A compact AFM scannerDetailed design

Piezo actuators

  • PI (PhysikInstrumente)
  • 5 x 5 x 9 mm for vertical motion
  • 3 x 3 x 13,5 mm for lateral motion
detailed design3
K. J. Kamp A compact AFM scannerDetailed design

Triangulation sensors

  • Lion Precision capacitive sensors
detailed design4
K. J. Kamp A compact AFM scannerDetailed design

AFM chip holderBrukerDAFMCH probe holder

Piezo holder measures 4 x 5 mm at the base.

detailed design5
K. J. Kamp A compact AFM scannerDetailed design

Probe holder

Final design overview

  • Outer dimensions (x,y): 26 x 26 mm

Lever

Sensor

Piezo actuator

detailed design6
K. J. Kamp A compact AFM scannerDetailed design

Cross-section view (no piezo actuators)

detailed design8
K. J. Kamp A compact AFM scannerDetailed design

Summary

Specifications

  • Dimensions (x,y) 26 x 26 mm
  • Stroke (microns) 16 x 16 x 6,5
  • Roll angle 5,4 microrad
  • Resonances lateral 9,8 kHz
  • Resonances vertical 30,4 kHz
detailed design9
K. J. Kamp A compact AFM scannerDetailed design

Summary

Specifications Requirements

  • Dimensions (x,y) 26 x 26 mm 15 x 15 mm
  • Stroke (microns) 16 x 16 x 6,5 10 x 10 x 2
  • Roll angle 5,4 microrad< 2 microrad
  • Resonances lateral 9,8 kHz > 10 kHz
  • Resonances vertical 30,4 kHz > 30 kHz
conclusion
K. J. Kamp A compact AFM scanner
  • Introduction
  • Research Questions
  • Requirements specifications
  • Concept 1
  • Concept 2
  • Detailed Design
  • Conclusion
Conclusion
conclusion1
K. J. Kamp A compact AFM scannerConclusion
  • The requirements have been set up for the AFM scanner
  • The first concept is not feasible
  • The second concept meets all the requirements and is feasible
  • The detailed design is limited by the selected components:

1. The required size can not be achieved

2. The required roll angle is exceeded by a factor 2

questions
K. J. Kamp A compact AFM scanner
  • Introduction
  • Research Questions
  • Requirements specifications
  • Concept 1
  • Concept 2
  • Detailed Design
  • Questions?
Questions?
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