Operation of MEMS based devices in space

1
Operation of MEMS based devices in space
Literature review on

• Felix Lu
• Duke University
• January 18, 2007

2
Outline

• Motivation and background
• Radiation types and effects
• Radiation testing
• Effects on materials
• Effects on Devices
• Examples
• Mitigation techniques
• Summary

3
Background Components

• Radiation
• Degrades electrical and optical components
• Induces noise in detectors
• Induces errors and latch-ups in digital circuits
• Builds up charge in insulators
• Harmful to organisms

• MEMS based device components
• include
• Mechanical properties of semiconductors
• Electrically insulating oxides
• P-n junctions
• Oxides for optical fibers

• MEMS based systems include
• Inertial navigation
• Bolometers
• RF switches and Variable capacitors
• Optical switching and communications
• Propulsion
• Biomicro fluidics

4
MEMS in harsh environments

• Adverse Environment features
• Large temperature swings
• Corrosive elements
• Materials need to be corrosion resistant and/or
  kept away from corrosive elements
• Radiation
• Radiation hardened
• Remote location (not easily serviceable)
• power conservation, robustness of devices
  important
• Large amplitude vibrations (20 gs)
• MEMS considered a good candidate for operation in
  adverse environments (4-10K/lb. for launch)
• Small, lightweight, low power, robust, low cost
• Small mass ? small forces (e.g. mN for 1000G)8

http//http//www.spaceref.com/news/viewnews.htm
l?id301
5
Radiation in space

• From Solar wind and flares
• Electrons, protons, and heavy ions
• From Van Allen belts
• Inner belt primarily protons gt 10-100 MeV
• Reaches in about 250 km above Brazilian coast
• Outer belt primarily electrons lt 10 MeV
• http//www.oulu.fi/spaceweb/textbook/radbelts.htm
  lMagnetosphere
• Cosmic rays
• Electromagnetic pulse

(mostly protons, up to 1020 eV)
Contains also helium, heavy ions, gamma rays,
electrons(from wikipedia)
6
Annual Dose vs. altitude
Assuming 4 mm of spherical aluminum shielding
Rad radiation absorbed dose
1 rad .01 J per kg of absorbing matter (e.g.
tissue, Si, Al)
Source E.J. Daly, A. Hilgers, G. Drolshagen, and
H.D.R. Evans, "Space Environment Analysis
Experience and Trends," ESA 1996 Symposium on
Environment Modelling for Space-based
Applications, Sept. 18-20, 1996, ESTEC,
Noordwijk, The Netherlands
http//www.eas.asu.edu/holbert/eee460/tiondose.ht
ml
7
Radiation Dose and Dose Rates

• Total Ionizing Dose long term failure
• Threshold shifts
• Increased leakage currents
• Timing changes
• Units of rad (R) (radiation absorbed dose) or
  grays
• 1 Rad(Si) 1 R 100 ergs/g in silicon,
  1 Gray (Gy) 1 J/Kg
  100 R
• Dose Rate
• Effects on dose rate seem to be different for
  different materials6
• Simulating low dose rate effects using high dose
  rate irradiation is not well understood.

8
Radiation testing

• Radiation sources
• Particles (cyclotron 3 MeV to 3 GeV)
• Low energy x-rays
• 8-160 keV
• Flash x-rays
• 250 keV x-rays, 1.4 MeV electrons
• Cobalt60 gamma source
• 2.5 Mev photons, 97 keV b particles

Texas AM at College Station, TX
9
Examples of radiation induced failure modes

• Mechanical fracture by damage by high energy
  heavy ions
• Dielectric rupture by high charges across thin
  dielectrics
• Performance degradation caused by change in
  material properties
• Electrical Latch-up causing high currents to flow

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Effects on Materials

• Mechanical properties
• Defects
• Dislocations
• Probably does not affect much but not much data
  on this.
• Electrical properties
• Oxides
• p-n junctions
• SOI

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Effects on silica optical fiber

• Defects ? Color centers
• More easily radiation induced with more
  impurities 7
• Literature presents seemingly conflicting
  results
• Fibers rad hard with low OH content 11
• Fibers rad hard with high OH content7
• Self annealing properties
• Offsets color center generation rate
• Thermally activated
• Silica fibers that are not doped with P or B
  display this characteristic
• Annealing rate increased with light
• Mechanism not well understood

12
Effects on electronic devices

• Transient errors
• Single Event Effects (SEEs)
• Single ions hitting the device
• Single Event Upsets (SEUs)
• flipped bits
• Charging

13
Effects on Devices and circuits
14
Transient Effects
Effects of Quartz crystal oscillator
Atomic displacements lead to change in elastic
properties of material
Low doses shift fss more than high doses (not
well understood)
Dfss varies nonlinearly with dose
15
Example of clamping circuit
Protected node
Protecting node
Protected node
Protecting node
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Effect on mechanical properties of materials

• Not much published data on effect of radiation on
  mechanical properties
• Shea8 says that
• even at high end of space mission doses, the
  mechanical properties of silicon and metals are
  mostly unchanged (Youngs modulus, yield strength
  not significantly affected).

17
MEMS piston actuator 2

• Under low energy X-rays and gamma rays
• 250, 500, 750, 1000 krad (Si)

No change with Gamma rays Attributed to energy
being deposited in silicon substrate away from
actuators.
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Effects on MEMS piston actuator 2

• X-ray irradiated samples under positive and
  negative bias
• increased voltage/deflection
• - decreased voltage/deflection
• Radiation induced charge trapped in SiN layer.
• Negative bias effects ? long lived
• Positive bias effects ? lasted 7 days

19
Mitigation techniques and tradeoffs

• Shielding
• High density material (HDM) , e.g. Lead
• not always practical due to weight
• Bremsstrahlung radiation from HDM may be harmful
  due to short wavelengths from secondary emission.
  J.H. Adams, The variability of single event
  upsets rate sin the natural environment, IEE
  Trans. On Nuclear Science, vol., NS-30, no.6, Dec
  1983
• Low density Material (LDM), e.g. Aluminum
• high energy ions (gt 30 MeV H) pass through LDM
• Ions which are slowed down can cause more damage
  due to longer interaction time
• Material structure
• Semiconductor on Insulator (SOI)
• Reduced bulk material reduces e-h pairs generated
  by passing particles.

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Mitigation techniques and tradeoffs

• Minimizing use of dielectrics
• Trapped charge causes permanent electric field
• Minimize fatigue and plastic deformation8
• No metal on silicon suspension beams
• Dry ambient
• Maximum strain of less than 20 of yield strength

• Radiation hardening by design
• Redundancy and comparison, CMOS on SOI resistant
  to latchup
• Rad hard processors
• Slower and more power hungry due to redundancy
  and scrubbing programs which are error correcting
  programs which scan the memory.
• At least 10 slower than Commercial Off The Shelf
  (COTS) processors.
• Software
• Periodic scanning programs to catch errors
• Eat up CPU cycles and slow down the system

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Summary

• TID, dose rate, radiation type(s) depend on
  orbit.
• Techniques for mitigating detrimental effects are
  available but no panacea is offered
• Radiation induced effects are often complex and
  difficult to model mitigation done on a case by
  case basis.

22
References

• Peter C. Mehlitz, John Penix, Expect the
  unexpected Radiation hardened software, 2005,
  Intelligent systems Division, AMES Research
  center, http//ic.arc.nasa.gov/ase/papers/AIAA05/r
  hs.pdf
• J.R. Caffey and P. E. Kladitis, The Effects of
  ionizing radiation on microelectromechanical
  systems (MEMS) actuators electrostatic,
  electrothermal, and Bimorph, 2004 IEEE, p. 133-6
• Space Radiation effect in microelectronics,
  Presented by the Radiation effects group Sammy
  Kayali, Section Manager, http//parts.jpl.nasa.gov
  /docs/Radcrs_Final.pdf
• Brian Stark (Editor), MEMS Reliability Assurance
  guidelines for Space Applications, Jet
  Propulsion Laboratory, JPL Publication 99-1,
  1999 http//parts.jpl.nasa.gov/docs/JPL20PUB209
  9-1.pdf
• Mario Jorge Moura David, Low Dose Rate Effects
  in scintillating and WLS fibers by ionizing
  radiation, Masters Thesis, University of Lisbon,
  1996
• http//nepp.nasa.gov/photonics/spietre/reffects.ht
  m
• H. Henschel, O. Kohn, U. Weinand, A new
  radiation hard optical fiber for high dose
  values, IEEE Trans. On Nuc. Sci, vol. 49, no. 3,
  2002, pg. 1432
• Madsen, Anne Design Techniques for the
  prevention of radiation induced latchup in bulk
  CMOS processes, 1995, Naval postgraduate school
• Herbert R. Shea, Reliability of MEMS for space
  applications, Reliability, Packaging, Testing
  and Characterization of MEMS/MOEMS V, edited by
  Danele M. Tanner, Rajeshuni, Ramesham, Proc. Of
  SPIE Vol 6111, 61110A, (2006)
• Rajesh Garg, Nikhil Jayakumar, Sunil P. Khatri,
  Gwan Choi, A Design Approach for radiation hard
  digital electronics, DAC 2006, July 24.28, 2006,
  San Francisco, California, USA, p. 773