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"Radiation Tolerant and Intelligent Memory for
Space T. Dargnies1, J. Herath2, T. Ng2, C.
Val1, J.F. Goupy1, and J.P. David3 1 3D PLUS2
NASA Langley Research Center 3 ONERA 2005 MAPLD
International Conference September 7-9,
2005 Washington DC
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• Contents
• Introduction
• Preliminary design / heritage / radiation
  assessment
• Radiation testing / radiation results
• 3.1 FPGA Radiation results
• 3.2 SDRAM Radiation results
• 3.3 Voltage regulator results
• Design completion
• Prototypes results / functional validation
• Conclusion
• Authors information

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• Introduction
• In space applications such as earth observation
  or scientific missions, data storage requirements
  are always increasing. Moreover, environmental
  and radiation stress on electronics in space is
  very harsh. 3D PLUS, whose assembly process is
  certified by ESA and NASA has designed and
  manufactured for several years many modules
  (memory based, CPU, converters) for space
  applications.
• In partnership with NASA Langley Research Center
  under NASA Contract NAS1-0364, 3D PLUS developed
  the first high density and fast access time
  memory module tolerant of space radiation
  effects. This brand-new module operates like a
  simple SRAM (Addresses / Data / Control signals),
  and has a maximum capacity of 3Gb.
•  Radiation requirements of this SRAM-like module
  are
• ü             TID tolerant up to 100 krad(Si)
  (reference chosen orbit is Geosynchronous /
  duration is 15 years)
• ü             Single Event Effects immunity up to
  60 MeV/mg.cm² (Latchup and Upsets)
• To manage TID and SEE radiation effects on
  electronics, specific hardware and software
  protections are embedded in order to respect
  previous requirements. This module decreases
  design complexity for space based boards
  requiring memory with its simple interface and
  internal radiation tolerance management
  (shielding, EDAC, over current protections,).
  The first prototypes have been manufactured and
  tested by 3D PLUS in April 2005, first flight
  parts will be launched in 2006 or 2007..
• This module is to be directly connected to a
  processor or equivalent and considered as a
  radiation tolerant device.
• ACRONYMS CPU Central Processing Unit, EDAC
  System Error Detection And Correction System,
  ESA European Space Agency, FPGA Field
  Programmable Gate Array, MEU Multiple Event
  Upset, S(D)RAM Synchronous (Dynamic) Random
  Access Memory, SEE Single Event Effects, SEFI
  Single Event Functional Interrupt, SEL Single
  Event Latchup, SET Single Event Transient, SEU
  Single Event Upset, TID Total Ionizing Dose

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2. Preliminary design / heritage / radiation
assessment   Previous 3D PLUS memory modules for
space applications have embedded ELPIDA (former
HITACHI) SDRAMs. In fact, 3D PLUS has a long
history and significant experience with the 512
Mb monolithic die EDS5108ABTA which has been
fully characterized versus TID (CO60 TID
characterization) and SEE. This experience and
knowledge is why this particular memory was
chosen as the basis for this design.
Simplified schematic of the module Note1 Each
active component is also protected with a
specific thermal shutdown (over current
protection) component. Note2 Internal CLK 100
MHz (SDRAM operation). Note3 All components and
signals are not represented in this simplified
schematic.
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• To ensure that the proposed design would meet or
  exceed the radiation requirements, the radiation
  characteristics of all active components on the
  bill of materials were analysed. Radiations
  effects on components were considered in 3 steps
• Step 1 Latchup events If component is not
  latchup immune with LET lt 60 MeV/mg.cm² component
  will not be used. If immune, with LET gt 60
  MeV/mg.cm² component may be chosen.
• Step 2 Total Ionizing Dose Depending on
  components TID tolerance, specific shielding
  (tantalum, 3D PLUS FP4450 resin) will be
  considered.
• Step 3 Other events (SEU/MEU/SET) Depending on
  components tolerance, design will be adapted and
  specific software will be embedded.

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• 3. Radiation testing radiation results
• To ensure that requirements are respected,
  several radiation testing have been performed TID
  on all active components
• SEL on VIRTEX II FPGA, SDRAM memories and
  voltage regulator (Eeprom memory purchased in
  space quality level)
• SEU/MEU/SEFI on SDRAM memories
• SET on Linear regulator
• Sum up the of radiation results

Note 1 Test performed by ONERA at Toulouse
(France), 2 Test performed by RAD at TAMU (USA),
3 Test performed by 3D PLUS at TAMU (USA)
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Lets focus on the three main and critical
components tested under radiation effects (EEPROM
radiation characteristics are guaranteed by
Xilinx Datasheet because purchased in space
quality level. 3.1 Xilinx XQ2V1000 FPGA Radiation
results / SEL Testing SEL Testing at Texas AM
University
The Xilinx FPGA showed no SEL events at LETs of
86.6MeV-cm2/mg (normal incidence irradiation) and
at 124MeV-cm2/mg (effective LET at 45-degrees
angle of incidence irradiation). Each irradiation
was performed to a total effective fluence of
1E7ions/cm2).
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3.2.1 ELPIDA EDS5108ABTA SDRAM Radiation results
(TID) CO60 TID Testing up to 50Krad(Si)
ICC2PS Standby current ICC1 Operating current at 40 MHZ
Functional testing Functional testing
Conclusion SDRAM is within specifications at 50
Krad(Si)
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3.2.2 SDRAM Radiation results (SEL / SEU / SEFI)
Heavy Ions Testing up to 74 MeV/mg.cm²
SEU X-Section as a function of LET SEFI X-Section as a function of LET

SEL X-Section as a function of LET In addition,
the SDRAM memories showed no SEL events at LETs
of 40, 60, and 80MeV-cm2/mg at a temperature of
85ºC. Test was performed at higher temperatures
and the parts showed no SEL events at a LET of
80MeV-cm2/mg at temperatures of 85, 100 and
125ºC.
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3.3.1 Voltage Regulator Radiation results
(TID) CO60 TID Testing up to 15Krad(Si)
Conclusion Voltage Regulator is within
specifications at 10 krad (Si)
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3.3.2 Voltage Regulator Radiation results (SEL /
SET) Heavy Ions Testing up to 60 MeV/mg.cm²
Chemical opening for front side exposure SET observed at a LET of 60 MeV/mg.cm²

SEE Testing conclusion This component show
Single Event phenomenon at LET of 86.6 MeV.cm²/mg
and ambient temperature. A high internal current
is observed after an unexpected shutdown of the
output voltage of the part. This unexpected
shutdown of the regulator may be the consequence
of the impact of ions on the digital part of the
die that embed the automatic thermal shutdown and
other electronics. No SEL is observed at both
LET of 60 MeV.cm²/mg and 86.6 MeV.cm²/mg,
however, at these LET, Single Event Transients
are observed on the output voltage .
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4. Design completion

• Based on these radiation test results, we were
  able to use for each radiation phenomenon
  specific design rules.
•  1 Latchup events No Latchup events were
  detected on any of the tested parts. This bill of
  material will fit the SELth gt 60 MeV/mg.cm²
  requirement.
• For system safety, thermal shutdown protection is
  provided to every active part (memories, FPGA,
  regulator).
•   2 Other events (SEU / MEU / SEFI /SET)
• SEU/MEU/SEFI on FPGA Triple Modular Redundancy
  and scrubbing is used to mitigate upsets in the
  FPGA.
• SEU/MEU/SEFI on SDRAM  The FPGA interfaces with
  the 6 SDRAMs in two possible modes
• Triple redundancy (same data on 3 banks/16 bits).
  Full module data storage size is 1 Gb.
• EDAC system. Two banks are used for data storage.
  Full module data storage size is 2 Gb
• SET on voltage Regulator During Latchup testing,
  at a LET of 60 MeV/mg.cm² (fluence of 1E7
  ions/cm²), some Single Event Transients were
  observed on the output voltage of the regulator.
  Additional embedded energy capacitors of 940 uF
  were added to compensate for these voltage
  transients.
•    3 Total Ionizing Dose TID tolerance is
  different from one active component to another.
• For TID, a Geosynchronous orbit and a mission
  duration of 15 years was chosen. With these
  parameters, OMERE simulation software provides us
  the associated curve of TID versus Al thickness
  (see figure 1).

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Figure 1 Dose Vs Al thickness for
Geosynchronous orbit
TID requirement is 100 Krad(Si). Based on Figure
1 simulation results and components testing TID
results, we added specific shielding on
components. Epoxy resin HYSOL FP4450 (density
1.77 g/cm3) is the moulding resin used by 3D
PLUS. With AutoCAD software and design file of
the module, minimum thickness of epoxy resin
around a component in X, Y and Z axis is
calculated. When required extra Tantalum (density
16.6 g/cm3) shielding is added on parts. To
manage the TID requirement, we added 250 µm of
Tantalum on all the active parts (3 axis
protection) except for TPS75715 and MAX803
components (750 µm). Three dimensional
calculations performed by 3D PLUS for each active
component permits to conclude that 100 krad(Si)
requirement for a Geosynchronous Orbit and a
mission duration.
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5. Prototypes results / functional validation
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6. Conclusion 3D PLUS, in partnership with NASA
LaRC, designed and manufactured the first high
density and fast access time SRAM-like memory
module (1Gb or 2Gb available) TID tolerant to 100
krad (Si) and SEE immune up to 60 MeV/mg.cm². The
real improvement of this brand-new memory is the
significantly reduced board design time (no
complex controller, no SEU management, no TID
management required anymore). This module is to
be directly connected to a processor or
equivalent and considered as a radiation tolerant
device. Related paper Presentation of Tak-kwong
Ng and Jeffrey Herath of NASA LARC on hardware
and software design of this module (A208).
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7. Author Information
Corresponding (and Presenting) Author Timothée
Dargnies, 3D PLUS, 641 rue H. Boucher 78532 Buc
(France), phone [phone], fax 33 1
39 56 25 89, email tdargnies_at_3d-plus.com   Contri
buting Authors Jeff Herath, NASA LaRC, Mail Stop
488, Hampton VA23681 (USA), phone [phone]
1098, email jeffrey.a.herath_at_nasa.gov Tak-kwong
Ng, NASA LaRC, Mail Stop 488, Hampton VA23681
(USA), phone [phone], email
t.ng_at_nasa.gov Christian Val, 3D PLUS, 641 rue H.
Boucher 78532 Buc (France), phone [phone]
26 51, fax [phone], email
cval_at_3d-plus.com Jean Francois Goupy, 3D PLUS,
641 rue H. Boucher 78532 Buc (France), phone
33 1 30 83 26 53, fax [phone], email
jfgoupy_at_3d-plus.com Jean-Pierre David, ONERA,
Complexe scientifique 2 avenue E. Belin, 31055
Toulouse Cedex (France), phone  [phone]
37, email  jean-pierre.david_at_onecert.fr