1. Design of a compact AFM scanner
Titel van de presentatie
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Design of a compact 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

2. Outline Introduction to Atomic Force Microscopes (AFM)
Design of a compact AFM scanner
Outline
Introduction to Atomic Force Microscopes (AFM)
Research questions
Requirements and specifications
Concept 1
Concept 2
Detailed Design
Conclusion

3. Titel van de presentatie
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Design of a compact AFM scanner
Introduction
Research Questions
Requirements specifications
Concept 1
Concept 2
Detailed Design
Conclusion
Introduction

4. Introduction The atomic force microscope (AFM)
A compact AFM scanner
Introduction
The atomic force microscope (AFM)
Basic operation principle
Probe tip attached to a cantilever is scanned over a sample
Cantilever deflects due to the atomic forces
The cantilever deflection measures the surface topography

5. x z y Introduction The AFM scanner Lateral scanning Triangular pattern
A compact AFM scanner
Introduction
The AFM scanner Lateral scanning
Triangular pattern
Constant tip speed y x z

6. Introduction The AFM scanner Vertical scanning Feedback loop
A compact AFM scanner
Introduction
The AFM scanner Vertical scanning
Feedback loop
Cantilever deflection signal minimal
The probe tip tracks the topography
DOI wafer AFM measurement

7. Introduction AFM system specifications
A compact AFM scanner
Introduction
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

8. Introduction z y x u3 u2 u1 Top View Concept 1:The tripod scanner
A compact AFM scanner
Top View
Introduction
Concept 1:The tripod scanner
Actuator 1
Actuator 2
Actuator 3 u1 u2 u3 y z
Sensor x

9. Research Questions Introduction Research Questions
A compact AFM scanner
Introduction
Research Questions
Requirements specifications
Concept 1
Concept 2
Detailed Design
Conclusion
Research Questions

10. A compact AFM scanner
Research 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?

11. Requirements Introduction Research Questions
A compact AFM scanner
Introduction
Research Questions
Requirements specifications
Concept 1
Concept 2
Detailed Design
Conclusion
Requirements

12. A compact AFM scanner
Requirements
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

13. Titel van de presentatie
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A compact AFM scanner
Requirements
Measurement uncertainty to roll angle
Misalignment sensors and probe tip: 0,5 mm
Scanner will rotate (roll angle)
→ This causes an Abbe error (measurement uncertainty)

14. Requirements Abbe error Platform roll angle φ Sensor offset δ
A compact AFM scanner
Requirements
Abbe error
Platform roll angle φ
Sensor offset δ
Abbe error: eabbe = δ tan(φ) Assumptions:
δ = 0,5 mm eabbe < 1,0 nm φ < 2 microrad

15. Requirements Imaging time to resonance frequencies
A compact AFM scanner
Requirements
Imaging time to resonance frequencies
Lateral resonance frequency > 10 kHz
Triangular wave frequency content
Vertical resonance frequency > 30 kHz Tracking error, scanning speed y x z

16. Concept 1 Introduction Research Questions Requirements specifications
A compact AFM scanner
Introduction
Research Questions
Requirements specifications
Concept 1
Concept 2
Detailed Design
Conclusion
Concept 1

17. Concept 1 Analysis of the tripod concept
Design of a compact AFM scanner
Concept 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

18. Concept 1 Kinematics analysis Required stroke: 10 x 10 x 2 microns
A compact AFM scanner
Concept 1
Kinematics analysis
Required stroke: 10 x 10 x 2 microns
Relation is found between
x, y, z (platform position)
u1, u2, u3 (actuators) u1 u2 u3 y z x

19. Concept 1 Example Ten scan lines 10 x 10 microns
A compact AFM scanner
Concept 1
Example
Ten scan lines 10 x 10 microns
Actuator displacement ~ 6 microns
Mechanical amplification 10 / 6 = 1.66

20. Titel van de presentatie
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A compact AFM scanner
Concept 1
Scanner roll angle
Hinges are not perfect
Lateral motion will cause the scanner to roll u1 u2 u3 y z x

21. Titel van de presentatie
Concept 1
2D Statics analytical model

22. Titel van de presentatie
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A compact AFM scanner
Concept 1
Main cause of AFM scanner roll
Stiffness ratio between longitudinal and lateral stiffness of a rod
Normalized stiffness ratio []

23. Concept 1 Statics Flexure notch hinges
A compact AFM scanner
Concept 1
Statics
Flexure notch hinges
Increase longitudinal to lateral stiffness ratio
Decreases the roll angle

24. A compact AFM scanner
Concept 1
Statics FEM analysis
3D FEM model

25. Concept 1 Statics FEM results u1 = 5 microns x = 5 microns
A compact AFM scanner
Concept 1
Statics FEM results
u1 = 5 microns
x = 5 microns
φ = ~ 460 microrad

26. Concept 1 Statics FEM results Roll angle is lower φ = ~ 360 microrad
A compact AFM scanner
Concept 1
Statics FEM results
Roll angle is lower
φ = ~ 360 microrad

27. Concept 1 Statics FEM results Circular notch hinge
A compact AFM scanner
Concept 1
Statics FEM results
Circular notch hinge
Roll angle even lower
φ = ~ 60 microrad

28. A compact AFM scanner
Concept 1
Dynamics
First four resonances:

29. Concept 1 FEM Modal analysis Eigenmode results Lateral9,3 kHz
A compact AFM scanner
Concept 1
FEM Modal analysis
Eigenmode results
Lateral9,3 kHz
Yaw 9,8 kHz
Roll 42 kHz
Vertical 48 kHz

30. Concept 1 Summary Can the requirements be met?
A compact AFM scanner
Concept 1
Summary Can 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

31. Concept 2 Introduction Research Questions Requirements specifications
A compact AFM scanner
Introduction
Research Questions
Requirements specifications
Concept 1
Concept 2
Detailed Design
Conclusion
Concept 2

32. Concept 2 Side view Top view
A compact AFM scanner
Concept 2
Orthogonal scanning concept Lateral motion
Side view
Top view
Probe tip
Sensor
Sensor
Actuator
Actuator

33. Concept 2 Side view Top view
A compact AFM scanner
Concept 2
Orthogonal scanning concept Vertical motion
Side view
Top view
Probe tip
Sensor
Sensor
Actuator
Actuator

34. A compact AFM scanner
Concept 2
Kinematics Lateral stroke: mechanical amplification = lever ratio b to a x
ulever a b

35. A compact AFM scanner
Concept 2
Statics analysis Analytical model adapted to the orthogonal concept L2 x z φ ux K2 L K1 uz uφ uφ ux uz
ulever

36. Concept 2 Analytical model and FEM analysis
A compact AFM scanner
Concept 2
Analytical model and FEM analysis
Pure lateral input (no lever) ux = 5 microns
Analytical model: φ = 21,7 microrad
FEM result φ = 22,9 microrad The roll angle φ is positive

37. Concept 2 ux uφ uφ a b ux uz ulever Including the lever
A compact AFM scanner
Concept 2 uφ a b ux uz
ulever
Including the lever
Input ux results in a positive roll angle
Input uφ results in a negative roll angle
positive
negative ux uφ

38. Concept 2 Analytical model and FEM results
A compact AFM scanner
Concept 2
Analytical model and FEM results
The length of the vertical rods is varied:
The roll angle shifts from negative to positive
Vertical rod length
φ Analytical
φ FEM
10 mm
-82,1 μrad
-17,8 μrad
6 mm
-28,4 μrad
+19,5 μrad
3 mm
+123,1 μrad
+73,2 μrad

39. Concept 2 The analytical model is used to find zero roll angle
A compact AFM scanner
Concept 2
The analytical model is used to find zero roll angle
Vertical rod length [m]

40. Compact AFM
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A compact AFM scanner
Concept 2
Resulting roll angle Final iteration L1 = 3,0 mm L2 = 4,0 mm ulever = 10 microns x = 4,9 microns Roll angle φ = -0,63 microrad

41. Compact AFM
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A compact AFM scanner
Concept 2
Dynamics FEM modal results Lateral eigenmodes (x,y): ~12,3 kHz Vertical mode (z): ~36,5 kHz
Lateral:
Vertical:

42. Compact AFM
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A compact AFM scanner
Concept 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

43. Titel van de presentatie
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A compact AFM scanner
Introduction
Research Questions
Requirements specifications
Concept 1
Concept 2
Detailed Design
Conclusion
Detailed design

44. Detailed design Component selection Piezo actuators
A compact AFM scanner
Detailed design
Component selection
Piezo actuators
Triangulation sensors
AFM chip holder

45. Detailed design Piezo actuators PI (Physik Instrumente)
A compact AFM scanner
Detailed design
Piezo actuators
PI (Physik Instrumente)
5 x 5 x 9 mm for vertical motion
3 x 3 x 13,5 mm for lateral motion
Type
Dimensions
Nom. displ.
P885.11
5 x 5 x 9 mm
~6,5 micron
P883.31
3 x 3 x 13,5 mm
~13 micron

46. Detailed design Triangulation sensors
A compact AFM scanner
Detailed design
Triangulation sensors
Lion Precision capacitive sensors
Type
Dimensions
Range
C3R-0,8
Ø3 x 15 mm
25 microns

47. Detailed design AFM chip holder Bruker DAFMCH probe holder
A compact AFM scanner
Detailed design
AFM chip holder Bruker DAFMCH probe holder
Piezo holder measures 4 x 5 mm at the base.

48. Detailed design Probe holder Final design overview Lever Sensor
A compact AFM scanner
Detailed design
Probe holder
Final design overview
Outer dimensions (x,y): 26 x 26 mm
Lever
Sensor
Piezo actuator

49. Detailed design Cross-section view (no piezo actuators)
A compact AFM scanner
Detailed design
Cross-section view (no piezo actuators)

50. A compact AFM scanner
Detailed design

51. Detailed design Summary Specifications Dimensions (x,y) 26 x 26 mm
A compact AFM scanner
Detailed 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

52. Detailed design Summary Specifications Requirements
A compact AFM scanner
Detailed 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

53. Titel van de presentatie
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A compact AFM scanner
Introduction
Research Questions
Requirements specifications
Concept 1
Concept 2
Detailed Design
Conclusion
Conclusion

54. Conclusion The requirements have been set up for the AFM scanner
A compact AFM scanner
Conclusion
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

55. Titel van de presentatie
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A compact AFM scanner
Introduction
Research Questions
Requirements specifications
Concept 1
Concept 2
Detailed Design
Questions?
Questions?