Radiation Hardening Of Mems Based Devices

Literature review on

Operation of MEMS based devices in space Felix Lu Duke University January 18, 2007 http://www.sandia.gov/mstc/images/galileo.gif

From wikipedia

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 - Bioµ fluidics 3

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 rays (mostly protons*, up to 10 Electromagnetic pulse

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

eV)

After Mehlitz[1] * Contains also helium, heavy ions, gamma rays, electrons…(from wikipedia)

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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.html

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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. 7

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

• 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 Increasing loss during • Offsets color center generation rate gamma irradiation • Thermally activated • Silica fibers that are not doped with P or B display this characteristic • Annealing rate increased with light • Mechanism not well understood

Recovery – after irradiation

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

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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]

SEL – Single event Latchup SEB – Single event burnout SEFI – Single event function interrupt

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

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Effects on Devices and circuits Radiation induced photocurrent shorts out Vdd

http://www.aero.org/publications/cr osslink/summer2003/03.html

From Space Radiation Effects in microelectronics, JPL/NASA

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

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

- 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.

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Transient Effects

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

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)

∆fss varies nonlinearly with dose

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

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Example of clamping circuit Protected node

Protecting node

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

Protecting node

Garg et al., 2006 [10]

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

– Radiation induced charge trapped in SiN layer. – Negative bias effects
long lived Differences not known, but interfaces at air and – Positive bias effects
lasted 7 days substrate are different

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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 (> 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.

From Space Radiation Effects in microelectronics, JPL/NASA

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Mitigation techniques and tradeoffs •

Minimizing use of dielectrics –

•

Minimize fatigue and plastic deformation[8] – – –

•

Redundancy and comparison, CMOS on SOI resistant to latchup

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

Rad hard processors – –

•

No metal on silicon suspension beams Dry ambient Maximum strain of less than 20% of yield strength

Radiation hardening by design –

•

Trapped charge causes permanent electric field

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. 21

References 1.

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 991, 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

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