Structural Analysis of a Magnetically Actuated Silicon Nitride Micro-Shutter for Space Applications James P. Loughlin a , Rainer K. Fettig b , S. Harvey Moseley a , Alexander S. Kutyrev b , D. Brent Mott a Simulation: Timothy Carnahan a a NASA/Goddard Space Flight Center, Greenbelt, MD 20771 b Raytheon ITSS, Greenbelt, MD 20771
18
Embed
Structural Analysis of a Magnetically Actuated Silicon Nitride Micro-Shutter for Space Applications James P. Loughlin a, Rainer K. Fettig b, S. Harvey.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Structural Analysis of a Magnetically Actuated Silicon Nitride
Micro-Shutter for Space Applications
James P. Loughlina, Rainer K. Fettigb, S. Harvey Moseleya, Alexander S. Kutyrevb, D. Brent Motta
Simulation: Timothy Carnahana
aNASA/Goddard Space Flight Center, Greenbelt, MD 20771bRaytheon ITSS, Greenbelt, MD 20771
FEMCI 2002 2
Next Generation Space Telescope (NGST)
• Next Generation Space Telescope
– Mission: Investigate Galactic Origins
– Key Instrument: NIR MOS• Near Infrared Multi-Object Spectrometer
– MOS Requirement:
Addressable “Field Selector”
FEMCI 2002 3
Micro-shutter Attributes and Requirements
• Pixel Size Requirement: 100µm x 100µm• Torsion Strap: 90µm x 3µm x 0.5µm thick• Mirror Material: Silicon Nitride
– silicon nitride is linear until fracture
• Operational Temperature: 30°K• Rotation
– micro-shutter will rotate 90° to the open position
– micro-shutter will be closed in the off position
FEMCI 2002 4
Micro-shutter Array
FEMCI 2002 5
Electrostatic Analysis
• 2D Structural/Electrostatic FEM Using ANSYS/Multiphysics v5.7
0 Volts 625 Volts
FEMCI 2002 6
Electrostatic Analysis– ANSYS Predicts 625+ Volts Required for 90º Actuation
‼ Limit ~ 100 V
– Parametric Study for Determining Max. Rotation with Limiting Actuation Voltage:
Electrostatic Forces
0.0E+00
1.0E-10
2.0E-10
3.0E-10
4.0E-10
5.0E-10
6.0E-10
7.0E-10
8.0E-10
0 20 40 60 80 100Angle
Torq
ue
(N
-m)
Torsion Strap K
20 volts
40 volts
60 volts
80 volts
100 volts
•100 V Limit Allows for 10º rotation, from 80º to 90 º
FEMCI 2002 7
Mechanical Operation
• Produced by Timothy Carnahan, GSFC Code 542
FEMCI 2002 8
Electromagnetic Analysis
Magnet Width = 0.03m
• Proposed Tripole Electromagnet
FEMCI 2002 9
Micro-shutter Size Relative to Magnetic Poles
FEMCI 2002 10
Electromagnetic Analysis
d
• d=distance between shutters and magnet; 40µm ≤ d ≤ 120µm• peak magnetic flux density = 0.23 tesla at magnet centerline
FEMCI 2002 11
Deflected Micro-shutters
• Magnetic forces are Applied to the Micro-Shutters. • The force deflects and rotates theShutters.
FEMCI 2002 12
Electromagnetic Analysis
• Shutter Hinge Reaction Torque Relative to Magnet Centerline
Shutter Hinge Moment vs. Magnet Centerline
-3.00E-09
-2.50E-09
-2.00E-09
-1.50E-09
-1.00E-09
-5.00E-10
0.00E+00
5.00E-10
1.00E-09
1.50E-09
2.00E-09
-800 -600 -400 -200 0 200 400 600 800 1000
Hinge Location Relative to Magnet Centerline (m)
Hin
ge
Mo
me
nt
(N-m
)
0 degree
45 degree
90 degree
60 degree
70 degree
80 degree
FEMCI 2002 13
Electromagnetic Analysis• Shutter Hinge Reaction Torque (N-m) vs. Angular
Deflection
Shutter Torsion Strap
-1.0E-09
-5.0E-10
0.0E+00
5.0E-10
1.0E-09
1.5E-09
2.0E-09
0 20 40 60 80 100
Rotation Angle of Shutter Tip
Ro
tatio
na
l Mo
me
nt
Torsion Strap K
100um
50um
35um
15um
FEMCI 2002 14
Model Correlation
• Electromagnetic FEA Indicates Maximum Achievable Degree of Rotation = 86º
• Electrostatic Parametric Study Indicates Required Voltage to Capture Shutter (at 86º Position) = 43 V– Lab Tests Show “Capture” Voltage = 50 V
• Electrostatic FEA Indicates 15 V Required to Maintain 90º “Open” Position– Lab Tests Show “Release” Voltage = 23 V
FEMCI 2002 15
Stress Analysis• 3D Structural FEM Using ANSYS/Multiphysics v5.7• Assumed Silicon Nitride Fracture Strength = 6.4 GPa[1]
• Peak Resultant Stress = 1.5 GPa
FEMCI 2002 16
Weibull Fracture Probability
Weibull Distribution
-2.00E-01
0.00E+00
2.00E-01
4.00E-01
6.00E-01
8.00E-01
1.00E+00
1.20E+00
0 2000 4000 6000 8000 10000
Stress
Pro
bab
ilit
y o
f F
ailu
re
weibull
• Many SiN cantilevered test samples were manufactured and tested.• Probability of failure is dependent on the surface area of the test structure relative to the surface area of the device.• test/torsion = (Surface Area test/Surface Area torsion)1/m
• Stresses in the 3m x 0.5m torsion strap are approximately 1500 MPa when the shutter is open.• The Probability of Failure at 1500 Mpa is 9.48e-5. (99.99% success rate)
FEMCI 2002 17
Conclusions
• FEA Predicts:– Electromagnetic Tripole Will Open a
Magnetized Shutter to 90º Position– Shutter Electrostatically Captured When
Opened >80º Using <100V– Shutter Maintained at 90º for 15V
• Test Data Correlates with Predicts
• Coupled-Field FEA May Be Used for Design Optimization
FEMCI 2002 18
References
1) G. Coles, R. L. Edwards, W. Sharpe, The Johns Hopkins University. “Mechanical Properties of Silicon Nitride”. SEM Annual Conference. June 2001.
2) R. Fettig, J. Kuhn, S. H. Moseley, A. Kutyrev, J. Orlof, S. Lu. “Some Aspects on the Mechanical Analysis of Microshutters”. Micromachining and Fabrication, Vol. 3875. September 1999