Flextester II Final Presentation

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Flextester II?Final Presentation
A Precision Metrology Instrument for Stiffness
Characterization of Micro Mechanisms
Precision Engineering Research Group
Jian Li Eun Suk Suh
12/12/2001
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Contents

• Introduction
• Functional Requirements
• Theory of Operation
• Mechanical Design Overview
• Calibration And Measurement
• Experimental Data From Flextester II?
• Conclusion and Future Works

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Introduction
Background for Development
In Need of a Machine which can accurately measure
the F - d of small MEMS micro structure, as shown
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Introduction
Background for Development
The objective of this project is to improve upon
the original Flextester?, which was built for
2.75-1999 (Shown in the Picture)
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Functional Requirements
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Theory Of Operation
d1 - d3
d1 d3
Optical Sensor
Optical Sensors
Reference Flexure
d1
MEMS Beam (represented by a spring)
Force
d1 - d2
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Improved Design of the F-II
Main Body (More compact and accurate flexures)
Linear Stages
Probe Head (X and Z force measurement)
Vacuum Chuck
Micrometer
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Improved Design of the F-II
Main Body
Probe Head
Linear Stages
Micrometer
Vacuum Chuck
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Mechanical Design Overview

• Main Body Specification
• - Wn 110 Hz
• - Crab leg flexures for
• non-parasitic motion
• - Optimized flexure layout
• for decoupled X-Z motion
• - Optimized flexure dimension
• - KC probe interface with
• magnetic preload

Coupling Interface
Crab Leg Flexures
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Mechanical Design Overview

• 2. Probe Head Specification
• - Wn 55 65 Hz
• - KC for repeatable mtg.
• - Parasitic free X-Z F-d
• measurement
• - Sensors in differential
• configuration mounting
• for better noise rejection

Sensors
Magnet
KC
Reference Flexure
Needle
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Mechanical Design Overview
3. Main Assembly - Probe head and main
body are held together by magnet at the
coupling interface - Probe tip moves
with straightness error 0.6
Micrometer
Magnet
Probe Tip
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Calibration And Measurement

• Principle Procedure
• - Optical Barcode Sensors are used.
• - By creating calibration look-up tables of
  voltage vs. displacement, very accurate
  displacement measurements can be achieved.

Vo
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Calibration And Measurement
Create a first look-up table
V2
V3
Displacement (micrometer reading)
Voltage V1
X X X X . . .
Y Y Y Y . . .
V1
Reference flexure
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Calibration And Measurement
Create a second look-up table
V2
V3
Displacement (micrometer reading)
Voltage V1
Voltage V2-V3
Z Z Z Z . . .
X X X X . . .
Y Y Y Y . . .
V1
Tip locked
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Calibration And Measurement
V2
Add force calibration data to the look up table
V1
Precision Force Gauge (represented by a spring)
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Experimental Data
2. Calibration Data
In-plane calibration
Out-of plane calibration
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Experimental Data
3. MEMS Bi-stable Beam Ideal F-d Curve
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Experimental Data
4. Experimental Results
FEA Result
Experimental Result
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Conclusion

• Flextester-II? can measure F-d in and out of
  plane with the same probe head.
• Improved, smaller probe head assembly with
  differential sensor configuration for signal
  noise reduction (CNR)
• Incorporation of KC magnet for easily
  exchangeable probe head assembly.
• Overall smaller design than original Flextester?
• Incorporation of a vacuum chuck for holding
  silicon wafers.