Radiation Effects in
Microelectronics
EE-698a Course Seminar by
Aashish Agrawal
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.
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.
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.
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.
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).
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.
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.
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.
Field Oxide Leakage Reduction
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.
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/radtest/intro.html#
SEE
•
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/hma
n187_eldrs_nsrec_portable03sep17.pdf