2008 ASPE Annual Meeting

1. DESIGN AND FABRICATION OF A
MULTIFUNCTIONAL SCANNING PROBE WITH
INTEGRATED TIP CHANGER FOR FULLY
AUTOMATED NANOFABRICATION
Curtis R. Taylor1 and Kam K. Leang2
1Department of Mechanical and Aerospace Engineering
University of Florida, Gainesville, FL
2Department of Mechanical Engineering
University of Nevada-Reno, Reno, NV
23rd ASPE Annual Meeting
October 19-24, 2008, Portland, Oregon

2. Outline
1. Need for Probe-based Nanoscale Tools
• Challenges for nanoscale fabrication
• Advantages of probe-based tools
• Limitations and challenges of probe-based tools
2. Automated Tip Changing System Concept
• MEMS Thermally-Actuated Gripper and Integrated Proximity Sensor
• Advantages/Benefits/Novelty
• Key Applications Enabled by System
3. Design, Modeling, and Fabrication Results
• Cantilever Design
• Dynamic Modeling
• Coupled Electro-Thermo-Mechanical Modeling
• Fabrication Process
• Fabrication of Prototype
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 2

3. Nanoscale Fabrication Tools
• TOP DOWN Fab Tools
Non-Planar Surface Features
– Mesas, Trench, Line and Hole FIB
geometries via:
– E-beam lithography
– FIB sculpting
– Micromachining/fabrication
• BOTTOM UP Fab Processes
Strain and Chemical Surface
Modification MicroFab
– Heteroepitaxial Strain
– Ion Implantation
– Self-Assembly Self-Assembly
Expensive Tools
require large fabs/cleanrooms
Complex Processes
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 3

4. Advantages of Fabrication Via Probe Tip Tools
IBM’s Probe-based Memory
Technology >1 Tb/in2
T. Kenny, 2007
Arrays of 1,000s of
probes can be used to:
manipulate, pattern, machine, scribe,
write, deposit, and
engineer material surfaces
Mirkin et. al., at the nanoscale with:
Angew. Chem. ,
2006 (45), 7720
<1 nm resolution
on diverse materials
without costly cleanroom processes
55,000 replicas (88 million nanofeatures) over 1
cm2 in less than 30 minutes
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 4

5. Limitations and Challenges for Probe
Tip NanoManufacturing
1. Tip Wear 1.
2. Cross-contamination
3. Throughput
•
single tip
•
> 5 minutes to change tip
new tip worn tip
3. nanolithography
tip 2.
fouled tip
nanomachining
tip 10 um
debris
r ~ 10 nm
• 50+ different probe tips and microscopy modes - no integrated platform/
manual tip change produces slow throughput
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 5

6. Probe Tip Changer For Fully
Automated Nanofabrication
Funded by NSF CMMI Grant #0726778
To address the critical issues of throughput, tip wear,
APPLICATIONS:
repeatability, scalability, and limited functionality of
probe-based nanofabrication • Nanoscale Rapid Prototyping
• Desktop Nanofactory
• Enhance throughput • Hybrid Printing of Nanostructures
• Expand functionality
• Enable fully automated nanofabrication
• Provide method for scalability and robust fabrication
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 6

7. Tip Changing System Concept
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 7

8. Cantilever Design
Specifications
• Design Specs and
Requirements
– compatible with existing
AFMs
– actuation
– stiffness
– resonant frequency
– gripping force and tip
stability
• Thermally-Actuated
Gripper
– High current density in smaller
arm results in higher heating
and thermal expansion.
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 8

9. Thermally-Actuated
Cantilever Design Concepts
V-flexure
flexures
Single Flexure Multiple Flexure V-Flexure
High current density in smaller arm results in higher heating and thermal expansion
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 9

10. Static/Dynamic Modeling
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 10

11. Analytical Model of Cantilever Thermal-Actuation
Huang et. al., J. Micromech. Microeng., 9 (1999) 64-70
 dT  2  dT  T − Ts
−kA   + J ρ AΔx = −k p A   + SΔxw
 dx  x  dx  x + Δx RT
joule heating conductive heat transfer
(
ΔL = α L T − Tref )
δ
deflection
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 11

12. FEA Electro-Thermal-Mechanical Model
COMSOL Q T
δ
Multiphysics joule heating temperature
deflection
electric potential distribution, conduction, thermal strain, Hooke’s
current density convection heat law, deflection
transfer, temperature
r r h σ = Dε
Governing J = σE
Equation r r
−∇gk∇T ) = Q +
( (Text − T )
dA −∇g = F
σ
Jg = Q
E
Constants V, ρ(T ) k, h α ,Ε
B.C.s V (0) = 0 T (0) = T (L) = 298K δ (0) = δ (L) = 0
V (L) = V0 heat flux on other boundaries
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 12

13. Comparison of FEA and Analytical Model
Same dimensions and parameters used in
Huang model
Results of ‘multiphysics’ FEA model in agreement with analytical model
*Note: FEA model includes convective contribution
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 13

14. Application of FEA Model to Design of Cantilevers
Q T
joule heating temperature
δ
deflection
electric potential conduction, thermal strain,
distribution, current convection heat Hooke’s law,
density transfer, temperature deflection
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 14

15. FEA Modeling of Design Concepts
V-flex fails by contact of hot arms
max ~ 3
um
1200 K = thermal max ~
failure 2V
single multiple
flex flex
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 15

16. Fabrication of Prototype
• 3 mask, SOI process
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 16

17. Prototype Fabrication
• Rapid Prototyping of Cantilever
concept has been performed
• Prototype of Silicon probe
fabricated
Future Work
• Testing
• Optimization
• Modular Tip Design and Fab
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 17

18. Summary
1. Need for Probe-based Nanoscale Tools
• Sub 1 nm resolution
• Low cost versus energetic beam tools and bottom up processes
2. Automated Tip Changing System Concept
• Addresses key issues of tip wear, cross-contamination, and
throughput
• MEMS Thermally-Actuated Gripper and Integrated Proximity Sensor
• Key Applications Enabled by System
• Nanoscale Rapid Prototyping
• Nanofactory
3. Design, Modeling, and Fabrication Results
• Prototype cantilever designed
• Coupled Electro-Thermo-Mechanical model developed and validated
• Fabrication of prototype
23rd ASPE Annual Meeting, Oct. 19-24, 2008 Slide 18