Operation of MEMS based devices in space

Felix Lu

Duke UniversityJanuary 18, 2007

http://www.sandia.gov/mstc/images/galileo.gif

Literature review on

From wikipedia

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Outline

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

http://see.msfc.nasa.gov/pf/pf.htm

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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- Bio&micro fluidics

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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 g’s)

• 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.html?id=301

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Radiation in space

From Solar wind and flares• Electrons, protons, and heavy ions

From Van Allen belts• Inner belt : primarily protons > 10-100 MeV

– Reaches in about 250 km above Brazilian coast

• Outer belt: primarily electrons < 10 MeV– http://www.oulu.fi/~spaceweb/textbook/radbelts.htmlMagnetosphere

Cosmic raysElectromagnetic pulse

After Mehlitz[1]

http://www.eas.asu.edu/~holbert/eee460/tiondose.html

* Contains also helium, heavy ions, gamma rays, electrons…(from wikipedia)

(mostly protons*, up to 1020 eV)

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Annual Dose vs. altitude

http://www.eas.asu.edu/~holbert/eee460/tiondose.html

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

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…)

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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 materials[6]• Simulating low dose rate effects using high dose

rate irradiation is not well understood.

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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 β particles

http://www.ilhamalqaradawi.com/physics-dept/gamma_cell.htm

*Texas A&M at College Station, TX

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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

From Space Radiation effects on microelectronics, JPL

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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 content[7]

• 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

http://www.fiber-optics.info/fiber-history.htm

H. Henschel, et al., 2002 [7]

Increasing loss during gamma irradiation

Recovery – after irradiation

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Effects on electronic devices

• Transient errors• Single Event Effects (SEEs)

– Single ions hitting the device• Single Event Upsets (SEUs)

– flipped bits• Charging

After Mehlitz [1]

http://www.aero.org/publications/crosslink/summer2003/03.html

SEL – Single event LatchupSEB – Single event burnoutSEFI – Single event function interrupt

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Effects on Devices and circuits

In CMOS circuits: Latch-up can occur (PMOS and NMOS are both on at the same time)

- Coupled by parasitic BJTs: This draws large currents which can burn out the circuit.- Using an SOI structure reduces coupling and makes it latch-up resistant.

From Space Radiation Effects in microelectronics, JPL/NASA

http://www.eng.uwaterloo.ca/~asultana/PROJECT_SOI_MOSFET.doc.pdf

http://www.aero.org/publications/crosslink/summer2003/03.html

Radiation induced photocurrent shorts out Vdd

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Transient Effects

http://www.ieee-uffc.org/freqcontrol/quartz/vig/vigrad.htm

Effects of Quartz crystal oscillator

∆fss varies nonlinearly with dose

Low doses shift fss more than high doses

(not well understood)

Atomic displacements lead to change in elastic properties of material

http://www.aero.org/publications/crosslink/summer2003/03.html

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Example of clamping circuit

Garg et al., 2006 [10]

Protected node

Protected node

Protecting node

Protecting node

If particle causes protected gate (G) to turn on:D2 turns on and clamps voltage

If particle causes protecting gate (GP) to turn on:The lower login 0 level means that an error is more unlikely.

Under normal operation, both G and GP are used simultaneously.

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Effect on mechanical properties of materials

• Not much published data on effect of radiation on mechanical properties

• Shea[8] says that:– “even at high end of space mission doses, the

mechanical properties of silicon and metals are mostly unchanged (Young’s modulus, yield strength not significantly affected).”

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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 negativebias

• +: increased voltage/deflection• -: decreased voltage/deflection

– Radiation induced charge trapped in SiN layer.– Negative bias effects � long lived– Positive bias effects � lasted 7 days

Differences not known, but interfaces at air and substrate are different

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Mitigation techniques and tradeoffs

From Space Radiation Effects in microelectronics, JPL/NASA

• 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 (> 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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• Minimizing use of dielectrics– Trapped charge causes permanent electric field

• Minimize fatigue and plastic deformation[8]– No metal on silicon suspension beams– Dry ambient– Maximum strain of less than 20% of yield strength

Mitigation techniques and tradeoffs

• 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

http://www.us.design-reuse.com/news/?id=10962&print=yes

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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.

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References1. 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/rhs.pdf

2. 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

3. “Space Radiation effect in microelectronics”, Presented by the Radiation effects group; Sammy Kayali, Section Manager, http://parts.jpl.nasa.gov/docs/Radcrs_Final.pdf

4. Brian Stark (Editor), “MEMS Reliability Assurance guidelines for Space Applications”, Jet Propulsion Laboratory, JPL Publication 99-1, 1999; http://parts.jpl.nasa.gov/docs/JPL%20PUB%2099-1.pdf

5. Mario Jorge Moura David, “Low Dose Rate Effects in scintillating and WLS fibers by ionizing radiation”, Masters Thesis, University of Lisbon, 1996

6. http://nepp.nasa.gov/photonics/spietre/reffects.htm

7. 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

8. Madsen, Anne; Design Techniques for the prevention of radiation induced latchup in bulk CMOS processes, 1995, Naval postgraduate school

9. 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)

10. 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