surface micromachining iii · 2003. 9. 11. · brosnihan et al. analog devices 14 u. srinivasan ......
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Surface Micromachining III
Dr. Thara SrinivasanLecture 5
Picture credit: Sandia National Lab
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Lecture Outline
• Reading• From reader: Bustillo, J. et al., “Surface Micromachining of
Microelectromechanical Systems,” pp. 1564-9.
• Problem set #2 on website, due next Tuesday 9/16
• MUMPS Labs after class: 4-5, 5-6 pm• Where Prof. Howe’s grad students demonstrate MUMPS devices and you
help…• 6-10 students per session
• Today’s Lecture• MEMS Test Structures for Film Characterization (from Lecture 4)• Stiction and Friction in MEMS (from Lecture 4)• 3-D Microstructures
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• Today’s Lecture• MEMS Test Structures for Film Characterization (from Lecture 4)• Stiction and Friction in MEMS (from Lecture 4)• 3-D Microstructures
Lecture Outline
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• Today’s Lecture• MEMS Test Structures for Film Characterization (from Lecture 4)• Stiction and Friction in MEMS (from Lecture 4)• 3-D Microstructures
Lecture Outline
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53-D Microstructures
• Approaches• Hinges• Molding: Hexsil• Silicon-on-Insulator Process• Sealed-cavity Deep RIE Process• SCREAM
StaplePolysilicon level 2
Polysilicon level 1
Silicon substrate
Polysilicon level 1
Polysilicon level 2
Hinge staple
Plate
Silicon substrate
Support arm K.S.J. Pister et al., Sensors and Actuators A, Vol. A33, p. 249, 1992.
Hexsil molding
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Hinge Process FlowDeposit first sacrificialDeposit and pattern first poly
Pattern contactsDeposit and pattern second poly
Deposit and pattern second sacrificial
Etch sacrificialAssemble part
Pister
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Pop-Up MEMS
First MEMS hinge, K. Pister, et al. 1992
Corner Cube Reflector : V. Hsu, 1999
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Pop-Up MEMS
Hinged Campanile made in SUMMiT process,
assembled using probes Elliot Hui et al.
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5Assembling Hinges
• Assembly using• Grad students’ eyebrows!• Fluidic agitation• On-chip actuators• Magnetic forces• Surface tension of precisely
located droplets
Muller & Lau groups Pister group
Syms, Imperial College
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Deformable Hinges and Flexures
Helmbrecht, Srinivasan et al.
• Flexible hinges• Rigid polySi plates (E =
140 GPa) connected by elastic polyimide hinges (E = 3 GPa), Suzuki et al.
• Aluminum hinges fabricated in standard CMOS process, released with XeF2, Pister et al.
• Pop-up flexures• Nickel film has tensile
stress• Nickel-polySi “bimorph”
legs
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5Molding Hexsil
• Makes high aspect ratio structures using conformal thin films in mold trenches
• Parts are demolded(and transferred to another wafer)
• Mold can be reused• Honeycomb
structure
C. Keller et al.
J. Heck, Ph.D.
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Hexsil MEMS
MEMS Precision Instruments
Heck, Muller and Howe
A. Singh et al.
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5Silicon on Insulator Process
• Silicon-on-Insulator (SOI) wafer• Thin layer of SCS (10’s of nm – 10’s of
µm) on oxide layer (few 100’s of nm) on handle Si wafer
• SIMOX• Bonded SOI
• CMOS compatible• Cost: ~$200 per wafer
• Fabrication• Dry etching to pattern Si layer• Etch buried SiO2 to release
Si wafer
SiO2
Si (100) layer
Silicon-on-Insulator wafer
Brosnihan et al.
Analog Devices
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Proof mass 52 µg
SOI Process
Lemkin et al.
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5SCREAM Process (!)
Shaw, MacDonald et al.
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Sealed-cavity Deep RIE Process• Si substrates are polished to
desired thickness, micromachined, and fusion-bonded together in a stack.
200 µm-deep thermal actuator
Lucas NovaSensor