RADIATION EFFECTS ON SPACE MICROELECTRONICS
COSMIC RAY TYPES
Cosmic Ray Air Shower
(a) Produced in upper atmosphere(b) A myriad of elementary particles(c) Cherenkov light, Air glow(d) Affects Airline pilots, Balloon flyers(e) Detrimental to radio communication(f) Long range: Mountain top to sea bed
Galactic Cosmic Rays GCR)
(a) Extra galactic origin(b) Omni directional(c) Shielded by earth magnetic field
(d) Source: H and He ions (most abun-dant in universe) to very high energy.
Astronauts during inter or extra planetory travels (in very near future) and long term habitants in space stations are affected by GCR. Radiation shielding for both astronauts and microelectronic based instruments and control systems becomes vitally important.
Radiations from High-Energy Particle Accelerators Radiations from High-Energy Particle Accelerators (Cosmic Ray Shower Paradigm)(Cosmic Ray Shower Paradigm)
Atmospheric Depth Atmospheric Depth Shield Thickness Shield Thickness
Radiation Protection and Safety Culture for Astronauts
NOTEIn EU member countries Pilots and Flight attendants of civil airlines already catagorised as „Radiation workers“, manadatory to carry personal radiation dosimeters (TLD badges)*.
*Bhaskar Mukherjee, Peter Cross and Roger Alsop, Measurement of the neutron and gamma doses accumulated during commercial jet flights from Sydney to several destinations in the northern and southern hemispheres. Radiation Protection Dosimetry 100(2002)515-518
Radiation shielding and Space radiation dosimeters
Asssortment of dosimeters used by Mir and ISS astronauts during 1990-2000.
Cosmonauts during daily work in Mir space station. Area dosimeters are attached to the internal wall of the cabin,
A typical example of space radiation shielding. A 250 mil (6.35 mm) thick aluminium plate found to be optimal.
The annual limit of occupational radiation exposure to astronauts is 50 mSv, whereas the limit for terrestrial radiation workers endorsed to be 20 mSv.
Discovery of the van Allen BeltDiscovery of the van Allen Belt
In 1958 Explorer 1*, the 1st US Satellite mapped the charged particle radiation field around the earth, the van Allen Belt
William Pickering, James van Allen and Wernher von Braun with the replica of Explorer 1
Professor Dr. James van Allen
* Explorer 1 (JPL, California) was in fact, the 1st space borne GEIGER COUNTER fully based on recently invented transistors
The Space Environment : van Allen Belts
The Morphology of Space Environment
a) Geomagnetic fieldsb) Solar stormc) Space weatherd) Aurora Boreales/Aurora Australise) Galactic Cosmic Rays
Detail Structure of the Van Allen Belt
a) Inner Belt => Protons dominate Operation zone => Low Earth Orbiting
(LEO) Satellites, ISS
b) Outer Belt => Electrons dominate Operation zone => Geo Stationary
Satellites, Communications Satellies
Total accumulated dose depends on Orbit altitude, Orientation and Time
Commercial Off The Shelf
COTS ?are far more cost effective than radiation hardend
(„military grade“) electronic components
Radiation Effects on Electronics: Summary
Single Event Upsets (SEU), also known as Soft Errors is non-detrimental, however, could severely interrupt the flawless function of microelectronics.
Types of Radiation induced Damage
Total Ionising Dose (TID) damage
Agent: PhotonsMain Symptom: Irriversible failureVulnerability: all types of (opto) electronic components
Displacement or Non-Ionising-Energy-Loss (NIEL) damage
Agent: Neutrons, Protons and Heavy charged particcles (HCP)Main Symptom: Irriversible failure Vulnerability: all types of (opto) electronic components
Single Event Upset (SEU) or Soft Error
Agent: Neutrons, Protons and Heavy charged particcles (HCP)Main Symptom: Temporary function inturruption Vulnerability: mainly electronic memory chips driving FPGA, CPU and Microcontroller etc.Characteristics: function revival by „switching on/off „ procedureNote: disussed in details in next slide
Mechanisms of Triggering a SEU
In a microelectronic circuit (M), embedded in the semiconductor substrate (S) a Single Event Upset (SEU) set off when the interacting ionising particle deposits sufficient energy in the sensitive volume enclosing the critical node (N). The SEU triggering mechanism could be divided in two broad categories:
The high energy heavy (HZE) particle, i.e. of cosmic origin (P) directly
interact with the critical node (N) by producing a track of electron/hole pairs,
thereby causing the SEU.
The primary particle, i.e. accelerator produced neutron undergo nuclear reaction with the primary atom (A) producing primary
knockout atom (PKA) and secondary charged particle (CP), causing the SEU.
(a) Direct Interaction
(b) Indirect Interaction
SEU in Static Random Access Memory (SRAM)
Radiation Effects Mitagation Strategies
Total Ionising Dose (TID) damage and Displacement damage (NIEL)
Optimised Lead or Concrete shielding for Gamma rays
Borated Polyethylene or Borated Concrete for Neutrons
Single Event Upset (SEU) in Memory Chips (SRAM and Flash Memories)
(a) Software based: Triple Mode Redundancy (TMR), Humming Code => SLOW (time lag)
(b) Hardware based: Thin composite-material neutron shielding =>FAST (instanteneous)
(c) Combination of Hardware and Software =>MOST RELIABLE
Incidance of SEU could have severe implications
(a) Power supplies (FPGA controlled) operating in radiation environement of High-Energy Accelerators => SEU induced faults in FPGA could cause fire due to malfunction of the P Suppy
(b) Patients with heart-pace makers (driven by very high density micro-chips) under going particle therapy, generating a copious secondary neutrons => SEU induced faults could stop the pace maker. Even a short interruption may result in patients heart failure.
(c) LEO Micro-Satellite instruemntaion system (controlled by FPGA based on fast SRAM chips), neutrons are produced by the interaction of protons with the satellite body => SEU induced fault may abruptly terminate the mission
Electronics in Radiation Environment: Summary
Semiconductors are highly susceptable to radiation.
Instrumentation and control devices of modern particle accelerators are solely based on microelectronics.
Highlighting the radiation damage threshold (neutrons.cm-2) of 1 MeV equivalent neutrons relevant to selected electronic components.
Reference
F. Wulf, A. Boden, D. Bräunig, GfW Hand-book for Data Compilation of irradiation tested electronic components. HMI Report B-353, TN 53/08, Vol. 1-6
MITIGATION TECHNIQUES
Implementation of Shielding
(a) Water/Polyethylene (b) Borated Rubber
(c) Borated Heavy concrete (d) Lead
Testing of Microelectronic Memories and CCD Cameras
We have irradiated the following microelectronic devices
(1) Commercially available SRAM chips of 256, 512, 1024 and 2048 kB memory density (s. Table below)
(2) Two miniature CCD Cameras
Radiation Source and Shielding Type
(1) Un-moderated neutrons from a 241Am/Be source
(2) Neutrons moderated with 6.9 cm H2O layer
(3) Moderated neutrons (as above), Electronics shielded with 3.5 mm thick Boron Rubber
Specifications of the SRAM (Static Random Access
Memory) Chips used in this Investigation.
Test Results
Number of SEU in 512 kB SRAM Chips induced by neutrons for three exposure modes.
Neutron induced SEU in CCD Cameras for two exposure modes.
Results showing the neutron irradiation effects in SRAM
chips of four different memory densities.
Boronated Rubber => Best Performance
Hydrogenous shield (Polyethylene, Water) without Boron => Worst Performance
Radiation Shielding for Power Control Devices
Power Control Crete
Power Control Card
Test-location under Acclerator Module
Shielded FPGA15mm Lead + 6mm Boronated Rubber
Unshielded FPGA
Based on radiation sensitive SRAM (Static Random Access Memory) chips
CPU / SRAMCPU / SRAM
TL-Glow Curves of TLD-600 chips:1st. Chip inside, 2nd. Chip outside
Shielding Efficacy was estimated by the ratio of TLGC areas
Gamma:A(in)/A(out) = 0.09
Thermal Neutron:An(in)/An(out) = 0.01
Both Cards were interfaced to DAC system and continuously monitored over 7 months
Unshielded Card: 2 SEU (Single Event Upset) recorded in every week
Shielded Card: No SEU was recorded in 7 months
Radiation Effects in Electronic Components and Mitigation provided by dedicated Shieldings
Photon
Shielding: 20 cm Heavy Concrete=> Dose reduction factor: 0.019
Neutrons
(as) lies above the gamma toleration threhold, hence, additional 5mm Pb to be added
Neutron Irradiation Set up for COTS Microelectronics
B: Thermal Neutron Shield (Borated Polyethylene)D: Device under Test (DUT)H: TableJ1, J2: Jars (16 and 33 cm radius respectively)P: StandS: 241Am-Be Neutron sourceT: Tripod (Source holder)
Photograph of the neutron Irradiation device showing diverse types of DUT (Device Under Test), in particular power control boards and Memory chips (SRAM) under irradiation.
Water moderated 241Am/Be Neutrons
Characteristics of the Neutron Test-Exposure Field
The Reference Neutron Spectra
((a) Un-moderated, En (av) = 5.2 MeV
(b) Moderated (6.9 cm H2O), En (av) = 4.1 MeV
(c) Moderated (15.9 cm H2O), En (av) = 3.2 MeV
The total areas of the bins (a), (b) and (c)are normalised to unity.
Legend
Tmod = Moderator (H2O) ThicknessSDD = Source to Detector Distance
Hnm = Measured Neutron Dose Equiv.Hnc = Calculated Neutron Dose Equiv.Hgm = Measured Gamma Dose Equiv.
*With thermal neutron shield
Reference
B. Mukherjee: Development of a simple neutron irradiation facility with variable average energy using a light water moderated 241Am/Be source. Nucl. Instr. Meth. A 363(1995)616-618
A Digital Signal Processing Board (COTS)under Gamma Irradiation
A medium activity 60Co point gamma source was placed behind the FPGA Chip
(FPGA = Free Programmable Gate Array)
Types of important radiation induced detrimental effects on electronics (SRAM chips and CCD camera) explained
Implementation of various mitigation strategies relevant to biomedical and space electronics discussed
Development and application of variable energy radiation delivery devices for testing of microelectronics are highlighted
SUMMARY AND CONCLUSION
These devices are based on isotopic neutrons from a 241Am/Be source and a 235 MeV proton therapy medical cyclotron
The application of a Isotope Poduction Medical (proton) Cyclotron for radiation hardness testing microelectronics is proposed.
Thank you all for your Thank you all for your AttentionAttention
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