Radiation hardening

Radiation hardening is the process of making

Most semiconductor electronic components are susceptible to radiation damage, and radiation-hardened (rad-hard) components are based on their non-hardened equivalents, with some design and manufacturing variations that reduce the susceptibility to radiation damage. Due to the extensive development and testing required to produce a radiation-tolerant design of a microelectronic chip, the technology of radiation-hardened chips tends to lag behind the most recent developments.

Radiation-hardened products are typically tested to one or more resultant-effects tests, including total ionizing dose (TID), enhanced low dose rate effects (ELDRS), neutron and proton displacement damage, and single event effects (SEEs).

Problems caused by radiation

Environments with high levels of ionizing radiation create special design challenges. A single

• heavy ions, together with X-ray and gamma-ray radiation. Most effects are caused by particles with energies between 0.1 and 20 GeV. The atmosphere filters most of these, so they are primarily a concern for spacecraft and high-altitude aircraft, but can also affect ordinary computers on the surface.^[5][6]
• Solar particle events come from the direction of the sun and consist of a large flux of high-energy (several GeV) protons and heavy ions, again accompanied by X-ray radiation.
• geomagnetic field. The particle flux in the regions farther from the Earth can vary wildly depending on the actual conditions of the Sun and the magnetosphere
  . Due to their position they pose a concern for satellites.
• Secondary particles result from interaction of other kinds of radiation with structures around the electronic devices.
• Nuclear reactors produce
  gamma radiation and neutron radiation which can affect sensor and control circuits in nuclear power plants
  .
• Particle accelerators produce high energy protons and electrons, and the secondary particles produced by their interactions produce significant radiation damage on sensitive control and particle detector components, of the order of magnitude of 10 MRad[Si]/year for systems such as the Large Hadron Collider.^[7]
• Nuclear explosions produce a short and extremely intense surge through a wide spectrum of electromagnetic radiation, an electromagnetic pulse (EMP), neutron radiation, and a flux of both primary and secondary charged particles. In case of a nuclear war they pose a potential concern for all civilian and military electronics.
• error-correcting codes
  to detect and often correct DRAM errors.

Radiation effects on electronics

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Fundamental mechanisms

Two fundamental damage mechanisms take place:

Lattice displacement

Lattice displacement is caused by

Single-event effects (SEE) have been studied extensively since the 1970s.[8] When a high-energy particle travels through a semiconductor, it leaves an ionized track behind. This ionization may cause a highly localized effect similar to the transient dose one - a benign glitch in output, a less benign bit flip in memory or a register or, especially in high-power transistors, a destructive latchup and burnout. Single event effects have importance for electronics in satellites, aircraft, and other civilian and military aerospace applications. Sometimes, in circuits not involving latches, it is helpful to introduce RC time constant circuits that slow down the circuit's reaction time beyond the duration of an SEE.

Single-event transient

SET happens when the charge collected from an ionization event discharges in the form of a spurious signal traveling through the circuit. This is de facto the effect of an electrostatic discharge. Soft error, reversible.

Single-event upset

SEL can occur in any chip with a parasitic PNPN structure. A heavy ion or a high-energy proton passing through one of the two inner-transistor junctions can turn on the thyristor-like structure, which then stays "shorted" (an effect known as latch-up) until the device is power-cycled. As the effect can happen between the power source and substrate, destructively high current can be involved and the part may fail. Hard error, irreversible. Bulk CMOS devices are most susceptible.

Single-event snapback

Single-event snapback is similar to SEL but not requiring the PNPN structure, can be induced in N-channel MOS transistors switching large currents, when an ion hits near the drain junction and causes avalanche multiplication of the charge carriers. The transistor then opens and stays opened, a hard error, which is irreversible.

Single-event induced burnout

SEB may occur in power MOSFETs when the substrate right under the source region gets forward-biased and the drain-source voltage is higher than the breakdown voltage of the parasitic structures. The resulting high current and local overheating then may destroy the device. Hard error, irreversible.

Single-event gate rupture

SEGR was observed in power MOSFETs when a heavy ion hits the gate region while a high voltage is applied to the gate. A local breakdown then happens in the insulating layer of silicon dioxide, causing local overheat and destruction (looking like a microscopic explosion) of the gate region. It can occur even in EEPROM cells during write or erase, when the cells are subjected to a comparatively high voltage. Hard error, irreversible.

SEE testing

While proton beams are widely used for SEE testing due to availability, at lower energies proton irradiation can often underestimate SEE susceptibility. Furthermore, proton beams expose devices to risk of total ionizing dose (TID) failure which can cloud proton testing results or result in pre-mature device failure. White neutron beams—ostensibly the most representative SEE test method—are usually derived from solid target-based sources, resulting in flux non-uniformity and small beam areas. White neutron beams also have some measure of uncertainty in their energy spectrum, often with high thermal neutron content.

The disadvantages of both proton and spallation neutron sources can be avoided by using mono-energetic 14 MeV neutrons for SEE testing. A potential concern is that mono-energetic neutron-induced single event effects will not accurately represent the real-world effects of broad-spectrum atmospheric neutrons. However, recent studies have indicated that, to the contrary, mono-energetic neutrons—particularly 14 MeV neutrons—can be used to quite accurately understand SEE cross-sections in modern microelectronics.^[9]

Radiation-hardening techniques

Physical

Hardened chips are often manufactured on

Magnetoresistive RAM, or MRAM, is considered a likely candidate to provide radiation hardened, rewritable, non-volatile conductor memory. Physical principles and early tests suggest that MRAM is not susceptible to ionization-induced data loss.^[14]

Choice of substrate with wide band gap, which gives it higher tolerance to deep-level defects; e.g. silicon carbide or gallium nitride.^{[citation needed]}

Shielding the chips themselves (from neutrons) by use of depleted boron (consisting only of isotope boron-11) in the borophosphosilicate glass passivation layer protecting the chips, as naturally prevalent boron-10 readily captures neutrons and undergoes alpha decay (see soft error).

Use of a special

Use of SRAM cells with more transistors per cell than usual (which is 4T or 6T), which makes the cells more tolerant to SEUs at the cost of higher power consumption and size per cell.[19]^[17]

Use of Edge-less CMOS transistors, which have an unconventional physical construction, together with an unconventional physical layout.^[20]

Logical

Error correcting code memory (ECC memory) uses redundant bits to check for and possibly correct corrupted data. Since radiation's effects damage the memory content even when the system is not accessing the RAM, a "scrubber" circuit must continuously sweep the RAM; reading out the data, checking the redundant bits for data errors, then writing back any corrections to the RAM.

Redundant elements can be used at the system level. Three separate microprocessor boards may independently compute an answer to a calculation and compare their answers. Any system that produces a minority result will recalculate. Logic may be added such that if repeated errors occur from the same system, that board is shut down.

Redundant elements may be used at the circuit level.

Hardened latches may be used.[22]

A watchdog timer will perform a hard reset of a system unless some sequence is performed that generally indicates the system is alive, such as a write operation from an onboard processor. During normal operation, software schedules a write to the watchdog timer at regular intervals to prevent the timer from running out. If radiation causes the processor to operate incorrectly, it is unlikely the software will work correctly enough to clear the watchdog timer. The watchdog eventually times out and forces a hard reset to the system. This is considered a last resort to other methods of radiation hardening.

Military and space industry applications

Radiation-hardened and radiation tolerant components are often used in military and aerospace applications, including point-of-load (POL) applications, satellite system power supplies, step down

However, not all military-grade components are radiation hardened. For example, the US MIL-STD-883 features many radiation-related tests, but has no specification for single event latchup frequency. The Fobos-Grunt space probe may have failed due to a similar assumption.^[13]

The market size for radiation hardened electronics used in space applications was estimated to be $2.35 billion in 2021. A new study has estimated that this will reach approximately $4.76 billion by the year 2032.^[24][25]

Nuclear hardness for telecommunication

In

Notes

1. Nuclear hardness may be expressed in terms of either susceptibility or vulnerability.
2. The extent of expected performance degradation (e.g., outage time, data lost, and equipment damage) must be defined or specified. The environment (e.g., radiation levels, overpressure, peak velocities, energy absorbed, and electrical stress) must be defined or specified.
3. The physical attributes of a system or component that will allow a defined degree of survivability in a given environment created by a nuclear weapon.
4. Nuclear hardness is determined for specified or actual quantified environmental conditions and physical parameters, such as peak radiation levels, overpressure, velocities, energy absorbed, and electrical stress. It is achieved through design specifications and it is verified by test and analysis techniques.

Examples of rad-hard computers

• The
  System/360
  architecture.
• The
  8-bit CPU
  , introduced in 1976, was the first serially-produced radiation-hardened microprocessor.
• PIC 1886VE, Russian 50 MHz microcontroller designed by Milandr and manufactured by Sitronics-Mikron on 180 nm bulk-silicon technology.
• m68k based:
  • The
    Coldfire
    M5208 used by General Dynamics is a low power (1.5 W) radiation hardened alternative.
• MIL-STD-1750A based:
  • The
    GEC-Plessey
    .
• The Proton 100k SBC by
  Space Micro Inc., introduced in 2003, uses an updated voting scheme called TTMR which mitigates single event upset
  (SEU) in a single processor. The processor is Equator BSP-15.
• The
  320C6Xx series digital signal processor
  . The Proton200k operates at 4000 MIPS while mitigating SEU.
• MIPS based:
  • The
    RH32 is produced by Honeywell
    Aerospace.
  • The Mongoose-V used by NASA is a 32-bit microprocessor for spacecraft onboard computer applications (i. e. New Horizons).
  • The KOMDIV-32 is a 32-bit microprocessor, compatible with MIPS R3000, developed by NIISI, manufactured by Kurchatov Institute, Russia.
• PowerPC / POWER based:
  • The
    RAD6000 single-board computer (SBC), produced by BAE Systems, includes a rad-hard POWER1
    CPU.
  • The RHPPC is produced by Honeywell Aerospace. Based on hardened PowerPC 603e.
  • The SP0 and SP0-S are produced by Aitech Defense Systems is a 3U cPCI SBC which utilizes the SOI PowerQUICC-III MPC8548E, PowerPC e500 based, capable of processing speeds ranging from 833 MHz to 1.18 GHz.^[26]
  • The Proton400k SBC by
    Space Micro Inc.
    , a Freescale P2020 cpu based on PowerPC e500.
  • The
    PowerPC 750
    processor, is the successor to the RAD6000.
  • The SCS750 built by
    PowerPC 750 cores against each other to mitigate radiation effects. Seven of those are used by the Gaia spacecraft
    .
  • The
    Boeing Company
    , through its Satellite Development Center, produces a radiation hardened space computer variant based on the PowerPC 750.
  • The BRE440 by Broad Reach Engineering. IBM
    system-on-a-chip, 266 MIPS, PCI, 2x Ethernet, 2x UARTS, DMA controller, L1/L2 cache ^[27]
  • The RAD5500 processor, is the successor to the RAD750 based on the PowerPC e5500.
• SPARC based:
  • The ERC32 and LEON 2, 3, 4 and 5 are radiation hardened processors designed by Gaisler Research and the European Space Agency. They are described in synthesizable VHDL available under the GNU Lesser General Public License and GNU General Public License respectively.
  • The Gen 6 single-board computer (SBC), produced by Cobham Semiconductor Solutions (formerly Aeroflex Microelectronics Solutions), enabled for the LEON microprocessor.^[28]
• ARM
  based:
  • The Vorago VA10820, a 32-bit ARMv6-M
    Cortex-M0.^[29]
  • NASA and the United States Air Force are developing HPSC, a Cortex-A53 based processor for future spacecraft use ^[30]
  • ESA DAHLIA, a Cortex-R52 based processor^[31]
• RISC-V based:
  • Cobham Gaisler NOEL-V 64-bit.^[32]
  • NASA Jet Propulsion Laboratory has selected Microchip Technology to develop a new HPSC processor, based on SiFive Intelligence X280^[33][34][35]

See also

• Communications survivability
• EMC-aware programming
• Institute for Space and Defense Electronics, Vanderbilt University
• Mars Reconnaissance Orbiter
• MESSENGER Mercury probe
• Mars rovers
• Tempest (codename)
• Juno Radiation Vault

References