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 (Cosmic Ray Shower Paradigm) Atmospheric Depth  Shield Thickness

Radiation Protection and Safety Culture for Astronauts NOTE In 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)

Radiation shielding and Space radiation dosimeters Asssortment of dosimeters used by Mir and ISS astronauts during 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 Belt In 1958 Explorer 1 *, the 1 st 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 fields b) Solar storm c)Space weather d)Aurora Boreales/Aurora Australis e)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: Photons Main Symptom: Irriversible failure Vulnerability: 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 „ procedure Note: 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 241 Am/Be source (2) Neutrons moderated with 6.9 cm H 2 O 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 FPGA 15mm Lead + 6mm Boronated Rubber Unshielded FPGA Based on radiation sensitive SRAM (Static Random Access Memory) chips CPU / 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: 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: Table J1, J2: Jars (16 and 33 cm radius respectively) P: Stand S: 241 Am-Be Neutron source T: 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 241 Am/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 H 2 O), En (av) = 4.1 MeV (c) Moderated (15.9 cm H 2 O), En (av) = 3.2 MeV The total areas of the bins (a), (b) and (c) are normalised to unity. Legend Tmod = Moderator (H2O) Thickness SDD = 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 241 Am/Be source. Nucl. Instr. Meth. A 363(1995)

A Digital Signal Processing Board (COTS) under Gamma Irradiation A medium activity 60 Co 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 241 Am/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 Attention === Questions ??