Radiation effects on electronics Radiation hardening

1 radiation effects on electronics

1.1 fundamental mechanisms
1.2 resultant effects
1.3 digital damage: see
1.4 see testing

radiation effects on electronics
fundamental mechanisms

two fundamental damage mechanisms take place:

lattice displacement, caused neutrons, protons, alpha particles, heavy ions, , high energy gamma photons. change arrangement of atoms in crystal lattice, creating lasting damage, , increasing number of recombination centers, depleting minority carriers , worsening analog properties of affected semiconductor junctions. counterintuitively, higher doses on short time cause partial annealing ( healing ) of damaged lattice, leading lower degree of damage same doses delivered in low intensity on long time (ldr or low dose rate). type of problem particularly significant in bipolar transistors, dependent on minority carriers in base regions; increased losses caused recombination cause loss of transistor gain (see neutron effects). components certified eldrs (enhanced low dose rate sensitive) free, not show damages fluxes below 0.01 rad(si)/s = 36 rad(si)/h.
ionization effects caused charged particles, including ones energy low cause lattice effects. ionization effects transient, creating glitches , soft errors, can lead destruction of device if trigger other damage mechanisms (e.g. latchup). photocurrent caused ultraviolet , x-ray radiation may belong category well. gradual accumulation of holes in oxide layer in mosfet transistors leads worsening of performance, device failure when dose high enough (see total ionizing dose effects).

the effects can vary wildly depending on parameters – type of radiation, total dose , radiation flux, combination of types of radiation, , kind of device load (operating frequency, operating voltage, actual state of transistor during instant struck particle) – makes thorough testing difficult, time consuming, , requiring many test samples.

resultant effects

the end-user effects can characterized in several groups:

neutron effects: neutron interacting semiconductor lattice displace atoms. leads increase in count of recombination centers , deep-level defects, reducing lifetime of minority carriers, affecting bipolar devices more cmos ones. bipolar devices on silicon tend show changes in electrical parameters @ levels of 10 10 neutrons/cm², cmos devices aren t affected until 10 neutrons/cm². sensitivity of devices may increase increasing level of integration , decreasing size of individual structures. there risk of induced radioactivity caused neutron activation, major source of noise in high energy astrophysics instruments. induced radiation, residual radiation impurities in used materials, can cause sorts of single-event problems during device s lifetime. gaas leds, common in optocouplers, sensitive neutrons. lattice damage influences frequency of crystal oscillators. kinetic energy effects (namely lattice displacement) of charged particles belong here too.
total ionizing dose effects: cumulative damage of semiconductor lattice (lattice displacement damage) caused ionizing radiation on exposition time. measured in rads , causes slow gradual degradation of device s performance. total dose greater 5000 rads delivered silicon-based devices in seconds minutes cause long-term degradation. in cmos devices, radiation creates electron–hole pairs in gate insulation layers, cause photocurrents during recombination, , holes trapped in lattice defects in insulator create persistent gate biasing , influence transistors threshold voltage, making n-type mosfet transistors easier , p-type ones more difficult switch on. accumulated charge can high enough keep transistors permanently open (or closed), leading device failure. self-healing takes place on time, effect not significant. effect same hot carrier degradation in high-integration high-speed electronics. crystal oscillators sensitive radiation doses, alter frequency. sensitivity can reduced using swept quartz. natural quartz crystals sensitive. radiation performance curves tid testing may generated resultant effects testing procedures. these curves show performance trends throughout tid test process , included in radiation test report.
transient dose effects: short-time high-intensity pulse of radiation, typically occurring during nuclear explosion. high radiation flux creates photocurrents in entire body of semiconductor, causing transistors randomly open, changing logical states of flip-flops , memory cells. permanent damage may occur if duration of pulse long, or if pulse causes junction damage or latchup. latchups commonly caused x-rays , gamma radiation flash of nuclear explosion. crystal oscillators may stop oscillating duration of flash due prompt photoconductivity induced in quartz.
systems-generated emp effects (sgemp) caused radiation flash traveling through equipment , causing local ionization , electric currents in material of chips, circuit boards, electrical cables , cases.
single-event effects (see) phenomena affecting digital devices (see following section overview of various types of see).

digital damage: see

single-event effects (see), affecting digital devices, not studied extensively until relatively recently. when high-energy particle travels through semiconductor, leaves ionized track behind. ionization may cause highly localized effect similar transient dose 1 - benign glitch in output, less benign bit flip in memory or register or, in high-power transistors, destructive latchup , burnout. single event effects have importance electronics in satellites, aircraft, , other civilian , military aerospace applications. sometimes, in circuits not involving latches, helpful introduce rc time constant circuits slow down circuit s reaction time beyond duration of see.

single-event transient (set) happens when charge collected ionization event discharges in form of spurious signal traveling through circuit. de facto effect of electrostatic discharge. soft error, reversible.
single-event upsets (seu) or transient radiation effects in electronics state changes of memory or register bits caused single ion interacting chip. not cause lasting damage device, may cause lasting problems system cannot recover such error. soft error, reversible. in sensitive devices, single ion can cause multiple-bit upset (mbu) in several adjacent memory cells. seus can become single-event functional interrupts (sefi) when upset control circuits, such state machines, placing device undefined state, test mode, or halt, need reset or power cycle recover.
single-event latchup (sel) can occur in chip parasitic pnpn structure. heavy ion or high-energy proton passing through 1 of 2 inner-transistor junctions can turn on thyristor-like structure, stays shorted (an effect known latchup) until device power-cycled. effect can happen between power source , substrate, destructively high current can involved , part may fail. hard error, irreversible. bulk cmos devices susceptible.
single-event snapback, similar sel not requiring pnpn structure, can induced in n-channel mos transistors switching large currents, when ion hits near drain junction , causes avalanche multiplication of charge carriers. transistor opens , stays opened. hard error, irreversible.
single-event induced burnout (seb) may occur in power mosfets when substrate right under source region gets forward-biased , drain-source voltage higher breakdown voltage of parasitic structures. resulting high current , local overheating may destroy device. hard error, irreversible.
single-event gate rupture (segr) observed in power mosfets when heavy ion hits gate region while high voltage applied gate. local breakdown happens in insulating layer of silicon dioxide, causing local overheat , destruction (looking microscopic explosion) of gate region. can occur in eeprom cells during write or erase, when cells subjected comparatively high voltage. hard error, irreversible.

see testing

while proton beams used see testing due availability, @ lower energies proton irradiation can underestimate see susceptibility. furthermore, proton beams expose devices risk of total ionizing dose (tid) failure can cloud proton testing results or result in pre-mature device failure. white neutron beams — ostensibly representative see test method — derived solid target-based sources, resulting in flux non-uniformity , small beam areas. white neutron beams have measure of uncertainty in energy spectrum, high thermal neutron content.

the disadvantages of both proton , spallation neutron sources can avoided using mono-energetic 14 mev neutrons see testing. potential concern mono-energetic neutron-induced single event effects not accurately represent real-world effects of broad-spectrum atmospheric neutrons. however, recent studies have indicated that, contrary, mono-energetic neutrons—particularly 14 mev neutrons—can used quite accurately understand see cross-sections in modern microelectronics.

a particular study of interest, performed in 2010 normand , dominik, powerfully demonstrates effectiveness of 14 mev neutrons.

the first devoted see testing laboratory in canada being established in southern ontario under name re-labs inc..