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RADSAFE - An Integrated Radiation Effects
Simulation Framework Robert A. Weller, Robert A. Reed
& Marcus H. MendenhallVanderbilt University
9-10 May 2005
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RADSAFE - The Objective
To create a system for first-principles predication of device, circuit and system response to
radiation.
RADSAFE is a strategy for implementation of the “third paradigm” of scientific discovery
in the field of the interaction of semiconductor electronics with physical
systems, in general, and with radiation, in particular.
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The RADSAFE System
A revolutionary, modular computational system for predicting the radiation response of electronic devices, circuits, and systems from basic device structure, circuit topology, and fundamental radiation characteristics. Its goals – to be informed by the best available physics, implemented by robust algorithms, enabled by supercomputer technology, and calibrated by data.
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Implementation? How it works…
ISE TCAD (DESSIS)
Geometry
VUmps (GEANT4)
Mathematica& Python
C++ Tools,Scripting
AutomaticMeshing
QuickTime™ and aMPEG-4 Video decompressor
are needed to see this picture.
Events
Gaussian charge generation
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The single event - a collection of segments
Particle TrajectoriesIncident proton: blue
Electrons: red Energy in the transistor: 44.7 keV
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The single event - trajectory segment math
• The radiation event is a collection of trajectory segments
• Each segment has an associated energy• Each segment is convolved with a
Gaussian yielding:
f (
rx, t) =
Q(2π )3/2vσ 2τ
e
rr⋅
rv( )2 −v2r2
2v2σ 2 erf(v2 −2
rr ⋅
rv
2 2 vσ) + erf(
v2 + 2rr ⋅
rv
2 2 vσ)
⎡
⎣⎢
⎤
⎦⎥
e−
t−t0( )2
2τ2
1+erf (t0
τ 2)
rx0 ≡
12(rx1 +
rx2 )
rv≡
rx2 −
rx1
rr ≡
rx−
rx0 v=
rv etc.
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TCAD geometry parsing
• The key simulation step: Importing a TCAD structure
• The strategy: Reduce the structure to tetrahedra
• A constructive solid tetrahedron has been created for Geant4
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TCAD Geometry Interface - Complex layers
Device Description
Radiation Events
• High energy protons incident on advanced CMOS integrated circuit
• Interaction with metallization layers dramatically increases energy deposition
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Displacement Damage (Screened scattering)
• Screened Rutherford scattering is not part of Geant4• However - It is vital for displacement damage• MRED includes screened scattering using algorithms
that have been tested for more than a decade• Results accomplish the intent of NIEL but with
enhanced microscopic detail• Results point to an important research area for the
future
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A Displacement Single Event
How does energy translate to electrical activity?
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Single Event Simulation
• System: Si diode, a 5 µm cube.
• Events: 1 GeV/nucleon 12C. 106 total incident.
• Pre-selection: >1.5 MeV in a 1 µm cube, 0.5 µm below the junction. 267 candidate events.
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The radiation event - Trajectories
Event037
Event267
Event256
3.8 MeV 14.1 MeV10.6 MeV
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Ion Tracks for Event 037
1018 e-/cm3 1014 e-/cm3
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Ion Tracks for Event 256
1018 e-/cm3 1014 e-/cm3
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Ion Tracks for Event 267
1018 e-/cm3 1014 e-/cm3
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Radiation event: Meshing
Event267
Slice at y = 1.0 µm Slice at x = 0 µm
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RADSAFE - Future Developments (12-24 mos.)
• Unified xml-based command and geometric description language using W3C xercesc parser
• Additional Python integration (Replacing Geant4-style message passing in VU code)
• Output Mathematica®/xml selectable• Improved sensitive volume definition -
coincidences• Time-stamped segments in TCAD• FLOODS integration-With U. Florida (USAF
MURI)
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Outstanding Scientific Issues and Questions
• Experimental and computational tests of heavy-ion nuclear reactions. All ions. E < 1 TeV/nucleon
• Theory-based heavy ion stopping (Sigmund theory?) including spatial and energy distribution of electron-hole pairs
• Energy deposition in sub 100 nm structures• Energy deposition and persistent defects• Structure of electrically active defects• Fundamental device modeling in the quantum
regime• Spatially-dependent tensor mobility - Next talk!• “Deep Impact” - Core vacancy effects