Lecture 22 - Mechanical Engineeringzleseman/teaching/me260/lectures/Lecture22.pdf · 1 Lecture 22...
Transcript of Lecture 22 - Mechanical Engineeringzleseman/teaching/me260/lectures/Lecture22.pdf · 1 Lecture 22...
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Lecture 22Chapter 29
Microelectromechanical Systems (MEMS)
The University of New Mexico
zcl ME260L ‘06
IntroductionThe University of New Mexico
zcl ME260L ‘06
• MEMS– Micro – scale on which the devices exist
– Electro – devices have electrical input/output
– Mechanical – devices have mechanically moving parts
– System – integration of components
• Why develop MEMS?– Sensors (Analog Devices – Accelerometer (Airbag Sensor)
• Small package– Lightweight
– Higher sensitivity
» Small forces – sub-mN
» Small displacements – sub-μm
– Actuators (Texas Instr. Micromirror Device)
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Types of MEMSThe University of New Mexico
zcl ME260L ‘06
• Bulk Micromachining
– Removal of bulk Si from wafer to define
a device
– Examples
• SCREAM
• SCALPEL
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Conceptual Design for Thin Film Tester
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Load Cell Fabrication
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Load Cell Force Calibration
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Gold Nanofilm Characterization• Analysis of Au Film
– Au film sputtered on Si (100) substrate
– Stoney’s Formula• ~10 MPa residual
compressive stress
– XRD• Main orientation (111)• ~2.5 MPa residual
compressive stress
– TEM• Average grain size
~57nm
The University of New Mexico
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Gold Nanofilm Characterization• Average grain size ~57nm
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The University of New Mexico
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Experimental Setup
Leseman, Z. C. and Mackin, T. J. Indentation testing of axisymmetric freestanding nanofilms using a MEMS load cell, Sensors and Actuators A, in press. (Invited paper)
The University of New Mexico
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Gold Nanofilm Data
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The University of New Mexico
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Fracture
500 μm
•Au Film–100 nm thick
–(111) Texture
–10 MPacompressive residual stress
The University of New Mexico
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Creep of Au Films
0
5
10
15
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25
30
35
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45
50
0 2 4 6 8 10 12 14
Time (minutes)
Dia
met
er o
f Are
a C
reep
ing
( μm
)
Creep Behavior of 100 nm Thick Au Film at Room Temperature
Thickness = 100 nmDiameter = 500 μmAverage Grain Size = 20 nmIndenter Diameter = 300 μmMax Applied Load = 761 μNTemperature = 20 oC
t = 0 minφ = 48.6 μm
t = 1.5 minφ = 32.2 μm
t = 12 minφ = 0 μm
57 nm
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Types of MEMSThe University of New Mexico
zcl ME260L ‘06
• Surface Micromachining
– Selective deposition and removal of thin films from a substrate (Si)
to create a multi-level device
– SUMMiTTM Process (Sandia)
– DMD Process (Texas Instruments)
Stiction
• Stiction- Unintended structural collapse due to secondary forces
• Causes– During etching of
sacrificial layers– Application of surface
treatments
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Experimental Concept
Fixed PositionMoves Incrementally in y-direction (50 nm)
• Stiction failed cantilever (s-shaped failure)– Fixed end of beam raised incrementally– Crack length (s) is measured before and after increment
• Arrest value for the critical strain energy release rate is found
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Experimental SetupThe University of New Mexico
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Microcantilevers Used in this Work
•SUMMiT IVTM from Sandia•Beam dimensions: 30 μm wide and 1500 μm long
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0
2
4
6
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10
12
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Substrate = poly-SiLiquid = IPA
Substrate = poly-SiLiquid = DI
Substrate = hydrophobicLiquid = IPA
Substrate = hydrophobicLiquid = DI
Substrate = hydrophilicLiquid = IPA
Substrate = hydrophilicLiquid = DI
G (mJ/m2) 47% RH
at 20oC
47% RHat 20oC
58% RHat 20oC
58% RHat 20oC
58% RHat 20oC
58% RHat 20oC
‘Wet’ Experimental Results
• Wet experiments in IPA vs. DI– GIPA < GDI
• poly-Si substrate• Hydrophilic gold• Hydrophobic gold
} Surface Tension EffectσDI = 73 mJ/m2 ; σIPA = 21.7 mJ/m2
The University of New Mexico
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Types of MEMSThe University of New Mexico
zcl ME260L ‘06
• LIGA – Lithographie Galvanoformung und abformung1. Deposit PMMA onto a substrate
2. Develop PMMA
3. Deposition of metal onto primary substrate
4. PMMA removed
5. Injection molding of another plastic
– Forms• Freestanding metal structure
• Plastic injection-molded structure
• Investment-cast metal structure from injection-molded structure
• Slip-cast ceramic part from injection-molded structure
LIGA DynamometerThe University of New Mexico
zcl ME260L ‘06