Ksjp, 7/01 MEMS Design & Fab Overview Quick look at some common MEMS actuators Piezoelectric Thermal...
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Transcript of Ksjp, 7/01 MEMS Design & Fab Overview Quick look at some common MEMS actuators Piezoelectric Thermal...
ksjp
, 7/0
1
MEMS Design & Fab
Overview
• Quick look at some common MEMS actuators• Piezoelectric• Thermal• Magnetic
• Next:• Electrostatic actuators• Actuators and mechanism• Beams
ksjp
, 7/0
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MEMS Design & Fab
MEMS Actuation Options• Piezoelectric
• Thermal
• Magnetic
• Electrostatic
• Dynamics• Beam bending• Damping
ksjp
, 7/0
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MEMS Design & Fab
Ferroelectrics (piezoelectrics)• Huge energy densities
• Good efficiency
• Huge force, small displacement
• Major fabrications challenges• Continuously promising technology
ksjp
, 7/0
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MEMS Design & Fab
Piezoelectric effect
• Polyvinylidene flouride (PVDF)
• Zinc oxide - ZnO
• Lead zirconate titanate – PZT
• PMNPT
V d L0A
FL
A
d - piezoelectric coefficient rank 2 tensor: e.g. d11, d31
V
ksjp
, 7/0
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MEMS Design & Fab
Piezoelectric products
• Quartz resonators (single crystal)• E.g. crystal oscillators• ~10Million/day, $0.10 each, vacuum packaged
L
AV
ksjp
, 7/0
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MEMS Design & Fab
Bimorph for STM and AFM
ZnO
Aluminum electrodes
After Akamine, Stanford, ~90
ksjp
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MEMS Design & Fab
Piezoelectric Actuator Summary• High voltage, low current
• ~100V/um• No static current (excellent insulator)
• Highest energy density of any MEMS actuator but• Large force, small displacement• Typically very difficult to integrate with other
materials/devices
• “Continuously promising”
ksjp
, 7/0
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MEMS Design & Fab
Thermal Expansion
.
= T is the thermal expansion strain (L/L)= is the thermal expansion stressF = A is the thermal expansion force
silicon ~ 2.3x10-6/K
AL
ksjp
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MEMS Design & Fab
Thermal actuator worksheet• Assume that you have a silicon beam that is 100 microns long,
and 1um square. You heat it by 100K. How much force do you get if you constrain it? How much elongation if you allow it to expand? TCE for silicon is 2.3x10^-6/K .
Area== T == =F = A =L= L=
ksjp
, 7/0
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MEMS Design & Fab
Plot by: R. Conant, UCB.
Thermal expansion: The heatuator
ksjp
, 7/0
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MEMS Design & Fab
Thermal Actuators
Current input pad
Actuator translatesin this direction
Cold arm
Hot arm
Current output pad
Uses thermal expansion for actuationVery effective and high force output per unit area
Cascaded thermal actuators for high force
ksjp
, 7/0
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MEMS Design & Fab
Thermal actuators in CMOS
Shen, Allegretto, Hu, Robinson, U. Alberta
Joule heating of beams leads to differential thermal expansion, changing the angle of the mirror
ksjp
, 7/0
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MEMS Design & Fab
Bubble actuators (thermal and other)• Lin, Pisano, UCB, ~92?
• HP switch
• Papavasiliu, Pisano, UCB - electrolysis
ksjp
, 7/0
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MEMS Design & Fab
Thermal actuator summary• Easy process integration!
• Large forces, small displacements
• Need lever mechanisms to trade off force for displacement
• Typically very inefficient
• Time constants ~1ms
• Substantial conduction through air
• Minimal convection in sub-millimeter designs
• Radiation losses important above ~300C
• Instant heating, slow cooling• Except when radiative losses dominate
ksjp
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MEMS Design & Fab
Magnetic actuators• Lorentz force
• Internal current in an external (fixed) magnetic field
• Dipole actuators• Internal magnetic material in an external (varying)
field
ksjp
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MEMS Design & Fab
Magnetic Actuation (external field)
Silicon substrate
NiFe electroplatedon polysilicon
External magneticfield
• Fabrication: NiFe electroplating
• Switching external field
• Packaging
ksjp
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MEMS Design & Fab
Magnetic Parallel Assembly
Solid-State Sensor and Actuator WorkshopHilton Head 1998
Figure 1. (a) An SEM micrograph of a Type I structure. The flap is allowed to rotate about the Y- axis. (b) Schematic cross-sectional view of the structure at rest; (c) schematic cross-sectional view of the flap as Hext is increased.
Figure 2. (a) SEM micrograph of a Type II structure. (b) Schematic cross-sectional view of the structure at rest; (c) schematic cross-sectional view of the structure when Hext is increased.
Parallel assembly of Hinged Microstructures Using Magnetic Actuation
Yong Yi and Chang LiuMicroelectronics Laboratory
University of Illinois at Urbana-ChampaignUrbana, IL 61801
ksjp
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MEMS Design & Fab
Parallel assembly
Solid-State Sensor and Actuator WorkshopHilton Head 1998
Parallel assembly of Hinged Microstructures Using Magnetic Actuation
Yong Yi and Chang LiuMicroelectronics Laboratory
University of Illinois at Urbana-ChampaignUrbana, IL 61801
Figure 8. Schematic of the assembly process for the flap 3-D devices. (a) Both flaps in the resting position; (b) primary flap raised to 90º at Hext = H1; (c) full 3-D assembly is achieved at Hext = H2 (H2 > H1 ).
Figure 9. An SEM micrograph of a 3-D device using three Type I flaps. The sequence of actuation is not critical to the assembly of this device.
ksjp
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MEMS Design & Fab
Magnetic actuators – Onix switch?
• Magnetic actuation, electrostatic hold
ksjp
, 7/0
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MEMS Design & Fab
Magnetic actuators in CMOS
Resonant Magnetometer
B. Eyre, Pister, Judy
Lorentz force excitation
Piezoresistive detection
ksjp
, 7/0
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MEMS Design & Fab
LIGA: synchrotron lithography, electroplated metal
Micro Electro Mechanical SystemsJan., 1998 Heidelberg, Germany
Closed Loop Controlled, Large Throw, Magnetic Linear
Microactuator with 1000 m Structural Height
H. Guckel, K. Fischer, and E. Stiers
U. Wisconsin
ksjp
, 7/0
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MEMS Design & Fab
Magnetic Actuation in LIGA
Micro Electro Mechanical SystemsJan., 1998 Heidelberg, Germany
U. Wisconsin
ksjp
, 7/0
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MEMS Design & Fab
Magnetic Actuation in LIGA
Micro Electro Mechanical SystemsJan., 1998 Heidelberg, Germany
U. Wisconsin
ksjp
, 7/0
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MEMS Design & Fab
Maxell (Hitachi) RF ID Chip
ksjp
, 7/0
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MEMS Design & Fab
Magnetic actuator summary• High current, low voltage (contrast w/
electrostatics)
• Typically low efficiency
• Potentially large forces and large displacements
• Some process integration issues