Transcript low power electronics device considerations

2D BEAM STEERING USING
ELECTROSTATIC AND THERMAL
ACTUATION FOR NETWORKED CONTROL
Jitendra Makwana1, Stephen Phillips1, Lifeng Wang1,
Nathan Wedge2, and Vincenzo Liberatore2
1
2
Department of Electrical Engineering
Arizona State University
Tempe, Arizona
Department of Electrical Engineering and Computer Science
Case Western Reserve University
Cleveland, Ohio
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OUTLINE
 Networked
Control Systems
 NCS and MEMS
 Example Testbed
 Beam Steering Actuator
 Modelling and Proposed Fabrication
 Simulated Performance
 Conclusion and Future Work
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Feedback Control
A Physical System S
Controller

Traditional feedback
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–
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Multiple sensors/actuators
Dedicated channels with deterministic delays
Predictable performance without failures
Robust to physical system variations
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Networked Control System (NCS)

NCS feedback
– Reconfigurable structure
– Communication with nondeterministic delays
– Robust to communication failures
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NCS and MEMS

In MEMS
– NCS enables operation distant from its control
– Complex control strategies achieved by leveraging
remote computational power
– Extends the capability of an integrated MEMS device
– Beam steering device as actuator for NCS testbed
– One example testbed involves a mobile agents
performing laser tracking
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Battlefield Application

Steered Beam
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–
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Secure communications
Resource tracking
Target tracking
Robust to obstacles, node failures, communication failures
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Actuator and Sensor

Implementation
– 2DoF Tilting mirror actuator
– Measured beam position sensor
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REQUIREMENTS

For a beam steering actuator
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–
–
–
–
–
2 Degrees of freedom
Low power consumption/dissipation
Low voltage for electrostatic actuation
Low current for thermal actuation
Fast steering capabilities
Adequate tilt angle
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ELECTROSTATIC ACTUATION

Zipper actuator top view
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–
–
–
Large deflections at low voltages
Four cantilever beams
Two springs per beam
Mirror
SPRING
CANTILEVER BEAM
MIRROR
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ELECTROSTATIC ACTUATION
 Zipper actuator side view
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–
–
–
Sputtered aluminum for structure, conductivity, reflectivity
Anti-reflective coating (ARC) allows for only mirror reflectivity
Sacrificial Oxide for air-gap between the top and bottom plates
Silicon nitride (SiN) prevents top and bottom plate shorting
ARC
ALUMINUM
MIRROR
SPRING
AMORPHOUS SILICON
LENGTH, L2
LENGTH, L1
GAP, g
NITRIDE
LENGTH, L
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ELECTROSTATIC ACTUATION

Zipper actuator side view
– Mirror held by beams through springs
– Beams at ground potential
– Bottom plates positive actuation voltage
ARC
ALUMINUM
MIRROR
SPRING
AMORPHOUS SILICON
LENGTH, L2
LENGTH, L1
GAP, g
NITRIDE
LENGTH, L
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ELECTROSTATIC ACTUATION

Zipper actuator after release: Simulated
– Al vs. a-Si coefficients of thermal expansion
– Beams bend upwards
D
– Mirror elevation is 25 mm
D
D
θ  0o at V  0 V
Max. stress at supports D is 43 MPa
Max. stress in springs is 60 MPa
D
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ELECTROSTATIC ACTUATION

Zipper actuator design and model
Fe ~ E1 / 4
W
xdef
 εrV 2 H 


g


3/ 4
Fe: Electrostatic force
V : Voltage applied
W : Width of cantilever beam = 100 mm
H : Top electrode thickness = 0.5 mm
g : Air gap = 1 mm
xdef = Cantilever beam deflection
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ELECTROSTATIC ACTUATION

Zipper actuator design and model
ε0V 2W
- Electric field
E
2
2[ g / ε r ]
tan( θ ) 
x def
L2
xdef = 8.75 mm for θ = 5o tilt
L2 = Mirror length = 100 mm
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ELECTROSTATIC ACTUATION

Zipper actuator design and model
Fe = Fb
Fb: Cantilever beam force = kcxdef
kc 
EeqWH 3
3
4L
L = Mirror length = 505 mm
kc: Composite cantilever beam spring constant = 146 x 10-9 N/mm
Eeq: 94 GPa (from simulation)
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ELECTROSTATIC ACTUATION
 θ
vs. V: Simulated
θ  5o at V  43 V
12
o
Tilt Angle ( )
10
8
6
4
2
0
0
20
40
60
80
100
Voltage (V)
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ELECTROSTATIC ACTUATION


Gap much less than beam width
Squeeze-film damping effects are dominant.
The quality factor and the damping coefficient are:
1
2
( Eeq  ave ) WH 2 g 3
Q
( )  2.9
2
L
W
1

 0.17
2Q
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ELECTROSTATIC ACTUATION

Zipper actuator switching capability
- Rise time (tr) and Settling time (ts) for a
second order system is given by
D
1
tr 
ωd
2

1

ξ
   arctan

ξ


    62.5 ms
 2ωd

3
ts 
 702 ms
ξωn
ωn ≈ ωd =2.5×104 rad/s (simulation)
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D
ELECTROSTATIC ACTUATION

Zipper actuator tilt: Simulated
D
Room temperature
θ  5o at V  43 V
D
D
Max. stress at supports D is 130 MPa
Max. stress at springs is 500 MPa
D
Rise time 63 ms
Settling time 702 ms
D
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THERMAL ACTUATION
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Thermal actuator side view
– Al and SiN multilayer cantilever beams
– Joule heating in serpentine top layer
– Nitride layer used for thermal insulation
ALUMINUM
MIRROR
SPRING
SILICON NITRIDE
LENGTH, L2
GAP, g
LENGTH, L
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THERMAL ACTUATION

Thermal actuator side view
– Top Al is much thinner than bottom Al layer
– Release at room temperature, all beams bend upwards
– Similar to electrostatic zipper actuator
ALUMINUM
MIRROR
SPRING
SILICON NITRIDE
LENGTH, L2
GAP, g
LENGTH, L
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THERMAL ACTUATION

Thermal actuator thermal energy
– Heat energy (J) required to heat
J  CT T
CT  Heat capacity of the resistor  ρm aWLCm
m = Density of aluminum = 2700 kg/m3
a = Aluminum thickness of serpentine = 0.1 mm
W = Aluminum width of serpentine = 15 mm
L = Aluminum length of serpentine= 3.64 x 103 mm
Cm = Specific heat per unit mass for aluminum = 900 J/(kg-K)
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THERMAL ACTUATION

Thermal actuator heating/power dissipation
P  I 2R
J R  Energy dissipated as function of time  I 2 Rt
where
R  Ro [1  α (T  To )]
Ro at 20o C  64.3 
α  Temp. coefficien t of resistance  3.9 x 10-3 / oC
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THERMAL ACTUATION
T = T - 298 K
12.00
D
o
Mirror Tilt ( )
10.00
D
8.00
6.00
4.00
2.00
0.00
0
θ  5o at ΔT  60 K
θ  10o at ΔT  100 K
20
D
40
60
80
 Temperature (K)
100
D120
Max. stress at supports D is 300 MPa
Max. stress at springs is 230 MPa
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THERMAL ACTUATION

Time (t) required to heat resistor at 1 mA of
current using voltage variable source
mCm T
t
I 2R
where
m  Mass of aluminum
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THERMAL ACTUATION
14
12
θ  5 at ΔT  60 K  t  10.2 ms
o
θ  7 at ΔT  80 K  t  12.8 ms
t (ms)
10
8
6
o
4
2
0
0
20
40
60
T (K)
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80
100
SUMMARY

Beam steering using electrostatic, thermal actuation.
Four cantilever beams with spring suspended mirror
Electrostatic tilt angle of 5oat 43 V.
Electrostatic actuator tr and ts are 63 ms and 702 ms
Thermal actuator T = 60 K for 5o tilt in 10 ms.
Fabrication in progress
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NSF funding through grant CCR-0329910
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