Transcript No Slide Title

Overview
• Quick look at some common MEMS actuators
• Piezoelectric
• Thermal
• Magnetic
• Next:
MEMS Design & Fab
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• Electrostatic actuators
• Actuators and mechanism
• Beams
MEMS Actuation Options
• Piezoelectric
• Thermal
• Magnetic
• Electrostatic
• Dynamics
MEMS Design & Fab
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• Beam bending
• Damping
Ferroelectrics (piezoelectrics)
• Huge energy densities
• Good efficiency
• Huge force, small displacement
• Major fabrications challenges
MEMS Design & Fab
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• Continuously promising technology
Piezoelectric effect
V
L
A
dL
V
F
 0 A
• Polyvinylidene flouride (PVDF)
• Zinc oxide - ZnO
• Lead zirconate titanate – PZT
• PMNPT
MEMS Design & Fab
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d - piezoelectric coefficient
rank 2 tensor: e.g. d11, d31
Piezoelectric products
V
A
L
• E.g. crystal oscillators
• ~10Million/day, $0.10 each, vacuum packaged
MEMS Design & Fab
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• Quartz resonators (single crystal)
Bimorph for STM and AFM
Aluminum electrodes
After Akamine, Stanford, ~90
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ZnO
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
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• “Continuously promising”
Thermal Expansion
L
 = g DT is the thermal expansion strain (dL/L)
= E  is the thermal expansion stress
F = A  is the thermal expansion force
A
.
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gsilicon ~ 2.3x10-6/K
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 .
MEMS Design & Fab
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Area=
= g DT =
= E  =
F=A=
dL=  L=
Plot by: R. Conant, UCB.
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Thermal expansion: The heatuator
Thermal Actuators
Uses thermal expansion for actuation
Very effective and high force output per unit area
Actuator translates
in this direction
Cold arm
Current output pad
Hot arm
Current input pad
MEMS Design & Fab
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Cascaded thermal actuators
for high force
Thermal actuators in CMOS
Shen, Allegretto, Hu, Robinson, U. Alberta
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Joule heating of beams leads to differential thermal
expansion, changing the angle of the mirror
Bubble actuators (thermal and other)
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• Lin, Pisano, UCB, ~92?
• HP switch
• Papavasiliu, Pisano, UCB - electrolysis
Thermal actuator summary
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•
•
•
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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
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• Easy process integration!
• Large forces, small displacements
• Need lever mechanisms to trade off force for
Magnetic actuators
• Lorentz force
• Internal current in an external (fixed) magnetic
field
• Dipole actuators
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• Internal magnetic material in an external (varying)
field
Magnetic Actuation (external field)
External magnetic
field
NiFe electroplated
on polysilicon
• Fabrication: NiFe electroplating
• Switching external field
• Packaging
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Silicon substrate
Magnetic Parallel Assembly
Parallel assembly of Hinged Microstructures Using Magnetic Actuation
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.
Solid-State Sensor and Actuator Workshop
Hilton Head 1998
Figure 2. (a) SEM micrograph of a Type II structure. (b) Schematic
cross-sectional view of the structure at rest; (c) schematic crosssectional view of the structure when Hext is increased.
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Yong Yi and Chang Liu
Microelectronics Laboratory
University of Illinois at Urbana-Champaign
Urbana, IL 61801
Parallel assembly
Parallel assembly of Hinged Microstructures Using Magnetic Actuation
Yong Yi and Chang Liu
Microelectronics Laboratory
University of Illinois at Urbana-Champaign
Urbana, 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 ).
Solid-State Sensor and Actuator Workshop
Hilton Head 1998
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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.
Magnetic actuators – Onix switch?
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• Magnetic actuation, electrostatic hold
Magnetic actuators in CMOS
Resonant Magnetometer
B. Eyre, Pister, Judy
Lorentz force excitation
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Piezoresistive detection
LIGA: synchrotron lithography, electroplated metal
Closed Loop Controlled, Large
Throw, Magnetic Linear
Microactuator with 1000 mm
Structural Height
H. Guckel, K. Fischer, and E. Stiers
Micro Electro Mechanical Systems
Jan., 1998 Heidelberg, Germany
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U. Wisconsin
Magnetic Actuation in LIGA
Micro Electro Mechanical Systems
Jan., 1998 Heidelberg, Germany
MEMS Design & Fab
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U. Wisconsin
Magnetic Actuation in LIGA
Micro Electro Mechanical Systems
Jan., 1998 Heidelberg, Germany
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U. Wisconsin
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Maxell (Hitachi) RF ID Chip
Magnetic actuator summary
• High current, low voltage (contrast w/
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•
•
electrostatics)
Typically low efficiency
Potentially large forces and large
displacements
Some process integration issues