# Presentation: 751416

## Structural Analysis of a Magnetically Actuated Silicon Nitride Micro-Shutter for Space Applications

- _James P. Loughlin__a_, Rainer K. Fettigb, S. Harvey Moseleya, Alexander S. Kutyrevb, D. Brent Motta
- Simulation: Timothy Carnahana
- aNASA/Goddard Space Flight Center, Greenbelt, MD 20771
- bRaytheon ITSS, Greenbelt, MD 20771

## Next Generation Space Telescope (NGST)

**N**ext **G**eneration **S**pace **T**elescope
- Mission: Investigate Galactic Origins
- Key Instrument: NIR MOS
- Near Infrared Multi-Object Spectrometer
- MOS Requirement:
- 	Addressable “Field Selector”

## 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

## Micro-shutter Array

## Electrostatic Analysis

- 2D Structural/Electrostatic FEM Using ANSYS/Multiphysics v5.7

- 0 Volts

- 625 Volts

## Electrostatic Analysis

- ANSYS Predicts 625+ Volts Required for 90o Actuation
- Limit ~ 100 V
- Parametric Study for Determining Max. Rotation with Limiting Actuation Voltage:

- 100 V Limit Allows for 10o rotation, from 80o to 90 o

## Mechanical Operation

- Produced by Timothy Carnahan, GSFC Code 542

## Electromagnetic Analysis

- • Proposed Tripole Electromagnet

## Micro-shutter Size Relative to Magnetic Poles

## Electromagnetic Analysis

- • d=distance between shutters and magnet; 40μm ≤ d ≤ 120μm
- • peak magnetic flux density = 0.23 tesla at magnet centerline

## Deflected Micro-shutters

- • Magnetic forces are Applied to the Micro-Shutters.
- • The force deflects and rotates the
- Shutters.

## Electromagnetic Analysis

- Shutter Hinge Reaction Torque Relative to Magnet Centerline

## Electromagnetic Analysis

- Shutter Hinge Reaction Torque (N-m) vs. Angular Deflection

## 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

## 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

## Weibull Fracture Probability

- • 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 3m x 0.5m 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**)

## 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

## References

- G. Coles, R. L. Edwards, W. Sharpe, The Johns Hopkins University. “Mechanical Properties of Silicon Nitride”. SEM Annual Conference. June 2001.
- 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