Radiation Effects in Microelectronics

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Radiation Effects in Microelectronics

• EE-698a Course Seminar by
• Aashish Agrawal

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Radiation Environments

• Galactic Cosmic Rays (heavy ions)
• Cosmic Solar particles (influenced by solar
  flares).
• Trapped protons in radiation belts (Van Allen
  Belts).
• Trapped electrons in radiation belts.

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Single Event Upset (SEU)

• Single event upset (SEU) is defined by NASA as
  "radiation-induced errors in microelectronic
  circuits caused when charged particles (usually
  from the radiation belts or from cosmic rays)
  lose energy by ionizing the medium through which
  they pass, leaving behind a wake of electron-hole
  pairs."
• Is a soft SEE.

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Linear Energy Transfer (LET)

• high LET radiation Radiation with high linear
  energy transfer,normally assumed to comprise
  protons, neutrons and alpha particles (or other
  particles of similar or greater mass).
• low LET radiation Radiation with low linear
  energy transfer,normally assumed to comprise
  photons (including X rays and gamma radiation),
  electrons, positrons and muons.

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Total Ionizing Dose (TID) Damage

• Electrons and Protons produce ionization in
  semiconductors.
• Ionization excites carriers from conduction to
  valence band
• Charge is trapped at interface regions
• Units rad(material) 1 rad 100 ergs/g of
  material
• Depends on bias conditions and device technology
• Typical effect threshold shift in MOS
  transistors.

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Unit of Total Ionizing Dose (RAD)

• Total ionizing dose in electronics is similar to
  a sunburn to humans. Total dose is the cumulative
  ionizing radiation that an electronic device
  receives over a specified period of time. Like a
  sunburn to humans, the damage is dependant on the
  amount of radiation and how long it took to
  accumulate the total dose. Its Unit is RAD
  (Radiation Absorbed Dose).

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Displacement Damage

• Collision between incoming particle and
  lattice atom.
• Lattice atom is moved out of normal position.
• Degrades minority carrier lifetime.
• Typical effect degradation of gain and leakage
  current in bipolar transistors.

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Displacement Damage

• N-Type Si V-P, V-O, V-V are stable defects.
• P-Type Si V-O, V-V are stable defects.
• Electrical activity of an energy level
• NT Trap Concentration.
• ET Energy level.
• Capture cross section for electrons and holes.

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Displacement damage hardening

• Doping atom Ga doped Si preferable over B.
• Non-doping impurities like C and O. (ie reduction
  of V2O centres which introduce an acceptor level
  near mid-gap).
• Sn doping of Si for high solubility of Sn and
  form stable Sn-V complexes.
• Operation at low temperatures. ( vacancies and
  interstitials are frozen).
• Periodic high temperature annealing which leads
  to clustering of the defects into larger stable
  defects.

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Field Oxide Leakage Reduction
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Conclusions

• Single Event Effects (SEE), LET.
• Total Ionizing Dose (TID), RAD.
• Displacement Damage. ET, NT.
• TID is the primary damage mechanism in MOS and
  Bipolar devices due to formation of Oxide and
  Interface Traps.

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References

• Claeys C. and Simoen E., Radiation effects in
  Advanced Semiconductor Materials and Devices
  (Springer, 2002).
• A.H. Johnston, Radiation effects in advanced
  microelectronics technologies, in IEEE Trans.
  Nuc. Sci., 45(3) 1998.
• http//parts.jpl.nasa.gov/docs/Radcrs_Final.pdf
• http//www.maxwell.com/microelectronics/products/r
  adtest/intro.htmlSEE
• H.P. Hjalmarson, R.L. Pease,Mechanisms for
  Radiation Dose-Rate Sensitivity of Bipolar
  Transistors. http//www.cs.sandia.gov/departments
  /9235/papers_pdf/2003_pdf/hman187_eldrs_nsrec_port
  able03sep17.pdf