"电子产品辐射手册-TI:详解空间与地面辐射原理及应对方法"

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The "Radiation Handbook for Electronics" by Texas Instruments (TI) is a comprehensive guide that delves into the principles, impacts, and mitigation methods of radiation in electronic products. This handbook is a valuable resource for engineers and designers working in space, industrial, and terrestrial applications. The handbook begins with a foreword from Texas Instruments that highlights their expertise and experience in space flight. Chapter 1 explores the different radiation environments, including the space radiation environment, terrestrial radiation environment, and artificial radiation environments. By understanding these environments, engineers can better protect electronic devices from the damaging effects of radiation. Chapter 2 delves into radiation effects and mitigation strategies. By understanding how radiation impacts electronic components, designers can implement protective measures to ensure reliable performance in harsh environments. The handbook also provides practical tips and techniques for reducing radiation effects in electronic products. One valuable resource highlighted in the handbook is a compendium of blog posts on op amp design topics by Bruce Trump. These blog posts offer practical insights and advice for designing electronic circuits that can withstand radiation exposure. Overall, the "Radiation Handbook for Electronics" is a valuable resource for engineers and designers working in the field of electronic products. By understanding the principles of radiation, its impacts, and mitigation strategies, engineers can design robust and reliable electronic products that can withstand the rigors of space, industrial, and terrestrial applications. Texas Instruments' expertise in this field shines through in this comprehensive and informative handbook.

Radiation Handbook for Electronics Texas Instruments

neutrons; however, its reaction cross-section is nearly 1 million

times smaller, and its reaction products (gamma rays) generally do

not cause problems. The thermal neutron capture cross-section

B is extremely high compared to most other isotopes present

in semiconductor materials (three to seven orders of magnitude

higher), as illustrated in Figure 1-18.

Unlike most isotopes that emit relatively harmless gamma photons,

after absorbing a thermal neutron, the

B nucleus breaks apart

with an accompanying release of energy in the form of an excited

Li recoil nucleus and an alpha particle. A prompt gamma photon

is also emitted from the lithium recoil soon after ﬁssion occurs. In

the

B(n,a)

Li reaction, the alpha particle and lithium nucleus are

emitted in opposite directions to conserve momentum. The lithium

nucleus is emitted with a kinetic energy of 0.840 MeV 94% of the

time and 1.014 MeV 6% of the time. The alpha particle is emitted

with an energy of 1.47 MeV, as shown in Figure 1-19.

The lithium recoil has a peak LET of 25 fC/μm, while that of the

alpha particle is 16 fC/μm. In most cases, calculations have shown

that the range of the alpha particle and lithium recoils in silicon and

silicon oxide is very limited: less than 1.5 mm. If the reaction occurs

more than 1 mm away from sensitive device nodes (deeper in the

substrate or in the layers over the silicon), neither the lithium recoil

nor alpha particle will have sufﬁcient energy to induce SEEs.

Figure 1-20 shows the lineal charge generation and range of

both secondary products. Generally, only

B in close proximity to

the active silicon layer needs to be considered. For conventional

semiconductor processes, BPSG is the dominant source of boron

reactions, and in some cases can be the primary cause of soft

errors.

[41-43]

The alpha and the lithium recoils are both capable

of inducing SEEs in microelectronics, particularly in advanced

low-voltage technologies. The event rate from the

B(n,a)

mechanism is a function of the thermal neutron ﬂux, the thermal

neutron cross-section for the reaction and the amount of

in the device close to the active silicon device layers. Several

groups have measured the terrestrial thermal neutron ﬂux and it is

between 4-20 n/cm

-hr, basically a little less or similar in magnitude

to the high-energy neutron ﬂux. The

B(n,a)

Li reaction has a

thermal neutron cross-section of 3,838 barns (1 barn = 10

-24

per nucleus).

Assuming a 1-cm

device area covered with a 1-mm layer of BPSG

doped with 8% boron, an upper bound for the SEE event rate can be

calculated by assuming that one of the two secondary products will

produce a detectable SEE. Because the secondaries are emitted in

opposite directions, only one of them will traverse the active devices.

Actually, since the secondary products will be emitted in or near

the active silicon device volumes, it is very likely that each event will

be capable of upsetting a sensitive volume. In any case, using the

assumptions above, an event rate of 0.0126 reactions/hr-cm

the upper bound, or, assuming that each event is an upset, a failure

rate of 17 kFIT. Clearly, this is an overestimation, but compared to

Figure 1-18. Comparison of thermal neutron capture cross-sections

for

B and several common semiconductor materials. This plot

demonstrates the anomalously high thermal neutron reaction

cross-section of

B. Note, a “barn” is a nuclear physics unit of area

equivalent to 10

-24

Figure 1-20. Differential charge generation and range in silicon as a

function of particle energy from the alpha particle and lithium recoil

produced by the

B(n,a)

Li reaction.

[44]

Figure 1-19. Capture of a thermal neutron by a

B nucleus and the

secondary products: an alpha particle, a lithium recoil nucleus and

prompt gamma photon.

18- 3387 Rotation Graphics Chapter 2

Round 2

Figure 2.20 Figure 2.21

Thermal neutron

1.47 MeV

0.84 MeV

dQ/dx (fC/µm)

Range in silicon (µm)

Ion energy (MeV)

0.0 0.5 1.0 1.5

Li dQ/dx in silicon

He dQ/dx in silicon

He range in silicon

Li range in silicon

18- 3387 Rotation Graphics Chapter 2

Round 2

Figure 2.20 Figure 2.21

Thermal neutron

1.47 MeV

0.84 MeV

dQ/dx (fC/µm)

Range in silicon (µm)

Ion energy (MeV)

0.0 0.5 1.0 1.5

Li dQ/dx in silicon

He dQ/dx in silicon

He range in silicon

Li range in silicon

18- 3387 Rotation Graphics Chapter 2

Round 2

Figure 2.17 Figure 2.19

% Change in neutron ﬂux

Time

-30%

-25%

-20%

-15%

-10%

-5%

11/1997 3/1999 8/2000 12/2001 5/2003 9/2004

Solar eruptions follow the

“11-year sun-spot cycle”

nth

(barns)

-3

-2

-1

Boron-10

Boron-11

Tungsten

Titanium

Arsenic

Cooper

Nitrogen

Aluminum

Silicon

Phosphorus

Oxygen

Radiation Handbook for Electronics Texas Instruments

the other two mechanisms (the terrestrial thermal neutron ﬂux and

the alpha particles), the

B(n,a)

Li mechanism can cause reliability

issues in microelectronics that have BPSG layers close to the silicon

substrate, or those that use borane-based fabrication processes

and leave

B residue near the active silicon.

It’s possible to mitigate SEEs caused by the activation of

in BPSG in several ways. The ﬁrst and most direct is simply to

eliminate BPSG, borane or other boron-containing compounds

from the process ﬂow. Due to the limited range of the alpha and

lithium recoil emitted during the

B(n,a)

Li reaction, there is no

need to replace or modify concentrations of

B outside this range

because the secondary products will never reach active silicon. In

cases where the unique reﬂow and gettering properties of boron

are needed, or the boron compound is required in the process, the

boron source material should be replaced with one enriched with

B, thereby mitigating

B without changing the desired physical

or chemical properties and without requiring new equipment or

processing steps.

Finally, if the process cannot be changed, such as in the case

of a foundry process, the packaging materials can use materials

rich in

B to provide a thermal neutron shield. For example, in a

plastic molded package, the silica ﬁller could be doped with

thus providing effective shielding for thermal neutrons. Because

the resultant secondary alpha-particle and lithium recoils only have

a range of <2 μm, they would be completely absorbed by the

silica and mold compound or die materials long before any of the

radiation would reach the sensitive active silicon device volume.

1.3 Artiﬁcial radiation environments

This section focuses on man-made artiﬁcial radiation environments,

situations where microelectronics are exposed to – and must function

in – radiation environments produced in a host of medical, industrial

and defense applications. In medical applications, the radiation

exposure occurs most often in diagnostic or treatment equipment

such as X-ray and proton-beam therapy machines. High doses of

electron-beam (e-beam) or gamma-ray irradiation are also used

for sterilizing surgical instruments and implantable electronics in

operating rooms.

There are numerous industrial uses of radiation. A wide range of

applications rely on X-ray, gamma- and e-beam irradiation, from

waste treatment to inspection to security screening. Microelectronics

are exposed to doses of neutrons and gamma rays when used in

high-radiation areas inside nuclear power plants. In the defense

environment, electronics must be hardened against brief but intense

gamma-ray and neutron exposures, as well as against follow-on

electromagnetic pulse (EMP) effects from nuclear detonations. For

microelectronics in most medical and industrial applications, TID is the

primary radiation effect concern, while in the defense environment,

the concern includes the full spectrum of SEEs, TID, DDD and

prompt-dose (high-dose-rate) effects.

Medical radiation environments

In the medical ﬁeld, devices that produce X-rays are ubiquitous, from

simple dental X-ray machines to full-body scanners (dental X-rays,

ﬂuoroscopes, computerized axial tomography [CAT] scanners, etc.).

Figure 1-21 shows an evacuated tube with electrodes at each end

producing X-rays. One electrode, the ﬁlament, is heated by running

a high current through the wire ﬁlament. The ﬁlament current is the

source of electrons for the acceleration process that produces the

X-rays. The heated wire emits electrons from the surface of the wire,

which is excited by thermionic emission.

In this process, the electrons gain enough kinetic energy from heating

to be able to overcome the work function of the material, which is

the energy required to liberate an electron from inside a material. The

ﬁlament itself is surrounded by a grounded metal cup with an aperture

at the end, facing the other electrode. The other electrode, the target,

is biased with a high positive voltage with respect to the ﬁlament cup

(usually 10-150 KeV) such that the high electric ﬁeld immediately

sweeps the electrons emitted through the aperture in the cup toward

the target electrode. Because the electrons are traveling in a vacuum,

they suffer no energy-robbing collisions with gas molecules and thus

are accelerated to high energies by the ﬁeld.

When these energetic electrons collide with the target (usually a

high-z metal such as tungsten), various scattering effects (see

Chapter 2) produce X-rays. The target is usually canted at an angle

to enable the X-ray radiation to radiate out of the side of the tube,

unobstructed. The amount of radiation exposure in diagnostic

applications near the equipment or in the patient is not high enough

to pose a risk to microelectronics because the X-ray dose is tightly

controlled (humans are much more sensitive to radiation exposure

than electronics), and the X-ray equipment is heavily shielded so that

no X-rays radiate outside the target treatment area.

As an example of a typical patient dose, consider the very popular

computer tomography (CT) or CAT scanner, which provides cross-

sectional images of the body constructed from a series of multiple

X-ray exposures from different radial positions, as illustrated in

Figure 1-22.

[45]

This type of diagnostic will usually give a maximum

X-ray dose, as a large number of X-ray exposures is required to build

up the image.

Figure 1-21. Cross-sectional diagram of an X-ray tube.

Filament

current

Vacuum

X-rays

Tungsten

target

High-voltage

anode

Glass envelope

Filament

Grounded Cathode

shield

Accelerated

electrons

Radiation Handbook for Electronics Texas Instruments

Table 1-2 shows a comparison of the patient dose received as a

function of the type of X-ray diagnostic. The unit of millisieverts (mSv)

deﬁnes an “effective dose” received from radiation exposure based on

different tissue types and their relative sensitivity to speciﬁc types of

radiation. To put this into perspective, with regards to doses relevant

to microelectronics, 1 mSv is equivalent to 0.1 rad(Si).

For a microelectronic device implanted in a patient, given a single

CT abdomen scan, you would expect a maximum dose of ~2 rad(Si).

Even the weakest commercial electronics would not be sensitive to

such a low dose.

What about SEEs occurring during irradiation? To be certain that

CT scans do not interfere with implanted devices, several medical

studies used CT scanner X-rays to directly irradiate the electronics

of pacemakers and cardio deﬁbrillators (simulating a coronary CT

angiography or multipass abdomen CT scan). While some did report

“electronic interference,” the probability that this interference would

cause clinically signiﬁcant adverse events was deemed extremely low.

For example, the interference observed on an internal node did not

translate into a functional interruption during irradiation.

It is possible to completely avoid the risk of any interference when

the implantable device is outside the primary X-ray beam of the

CT scanner. In general, microelectronics implanted in patients are

unlikely to be exposed to any radiation that would damage them

because of the high-dose sensitivity of the human body compared

to silicon devices.

The one medical environment where microelectronics may be exposed

to high chronic doses of X-rays is in the solid-state detectors and

supporting electronics housed inside of an X-ray machine. In these

locations, the patient receives an X-ray dose; therefore, a single

exposure will represent a relatively low dose. However, the fact that the

machine is used on many patients over hours, days, months and years

of service means that internal electronics can accumulate high TIDs.

Vendors of such equipment alleviate this problem by ensuring that

metal of sufﬁcient density/thickness shields all microelectronics that

are not physically part of the actual imaging, so that X-ray exposure

is minimized or eliminated completely. Image sensors will necessarily

be exposed to X-rays and will accumulate signiﬁcant doses over

time.

[47-49]

In cases such as these, even well-designed or radiation-

hardened imagers and support circuits will likely suffer dose effects

and will need to be replaced occasionally. Since dose failures involve

the shifting of device parametrics over dose (time), self-test startup

routines can detect when an imager is reaching its end of life and alert

users that a replacement is required.

In the medical environment, there is an increasing use of ionizing

radiation to sterilize surgical instruments and implantable devices that

would otherwise be damaged by the high temperature and humidity

of autoclave sterilization.

[50-52]

Sterilization by irradiation with e-beams,

X-rays and gamma rays works because the radiation has sufﬁcient

energy to ionize atoms. Ionization directly damages DNA and creates

reactive free radicals. One major free radical forms when the ionizing

radiation breaks the covalent bond between two oxygen atoms in an

oxygen molecule (O

). The two oxygen-free radicals are energetically

predisposed to ﬁnd an additional electron, causing them to become

highly reactive. The free radicals cause additional damage to the cell

and further degrade its DNA.

Figure 1-23 shows the DNA of the cell’s control and reproduction

mechanism being affected by radiation. With a sufﬁcient dose,

enough damage accumulates such that the cell no longer functions

properly, cannot reproduce and ultimately dies.

Table 1-2. The effective doses of various diagnostic X-ray

procedures.

[46]

Figure 1-23. Sterilization of bacteria and viruses is possible by using high

doses of ionizing radiation that irrevocably damage their DNA/RNA such

that the cells can no longer function or reproduce and ultimately die off.

CT-abdomen and pelvis, repeated with/without contrast 20 mSv

CT – colonography 6 mSv

Coronary computed tomography angiography (CTA) 12 mSv

Radiograph – lower GI tract 8 mSv

Radiograph – spine 1.5 mSv

Radiograph – extremity 0.001 mSv

CT – chest 7 mSv

CT – lung cancer screening 1.5 mSv

Radiograph – chest 0.1 mSv

Dental intraoral X-ray 0.005 mSv

Bone densitometry (DEXA) 0.001 mSv

Mammography 0.4 mSv

Figure 1-22. Diagram of a CT scanner. Because the image is built

up from numerous X-ray “shots,” the radiation exposure from a CT

scan can be many times higher than that of a single X-ray.

Rotating direction

Rotating

X-ray source

Fan-shaped

X-ray beam

Motorized table

Rotating X-ray

detectors

Radiation Handbook for Electronics Texas Instruments

Studies on inactivating viruses and bacteria by ionizing radiation

indicate that a single exposure is sufﬁcient to sterilize a sample,

provided that the dose is high enough. Because no patient is

involved and the bacteria and viruses must be neutralized to a very

high degree (usually to 10

-6

or better), sterilization using radiation is

performed at extreme dose levels – a maximum dose considered to

fully sterilize a sample is ~50 kGy (5 Mrad). This type of dose actually

exceeds most defense and space application requirements and thus

poses a real challenge for any microelectronics located in a piece

of equipment that must be sterilized. However, most electronics in

devices being sterilized will be powered down during irradiation,

which can signiﬁcantly reduce the amount of charge trapped and

somewhat lessen the effective dose.

The medical radiation environment is primarily limited to X-ray,

gamma-ray or e-beam exposures. Proton-beam therapy is also

used for cancer treatments, but these are characterized by highly

focused, targeted exposures that deliberately steer clear of implanted

electronics. It is unlikely that medical microelectronics implanted in a

patient would suffer permanent dose-related damage because the

irradiation is limited by dose allowances that patients can tolerate

(very low dose levels). Even microelectronics inside X-ray machines or

other devices that produce ionizing radiation are usually shielded to

keep the dose to a manageable level.

Electronics that must be in a radiation beam (like imagers) constitute

the primary exception. They will eventually accumulate enough

doses that they may need to be replaced occasionally. The radiation

doses encountered in medical sterilization applications are also

extremely challenging, and most microelectronics will not be able

to tolerate these dose levels without being shielded or radiation-

hardened. TID effects are the primary concern for microelectronics

used in medical instrumentation or implantable devices sterilized

with ionizing radiation.

Industrial radiation environments

Industrial applications use radiation extensively: in the processing of

materials to induce chemical/physical changes, in the sterilization

of food and waste, for the inspection and monitoring of physical

properties of materials, for the mitigation of static in assembly

processes, in the defect inspection of manufactured components,

and in security screening applications.

[53-58]

Some examples of

industrial radiation applications are shown in Figure 1-24.

Radiation sources for industrial applications include many types and

geometries of sealed sources containing radioactive materials that

emit radiation continuously and machines that produce radiation

by accelerating particles (e-beam and X-ray machines). The sealed

sources are usually encapsulated in metal shields, with a shuttered

port or window that allows the radiation out. Sealed gamma-ray

sources most commonly use cobalt-60 (half-life ~5.2 years) and

have an advantage in that they do not require external power to

generate radiation.

The spontaneous ﬁssion of Californium-252 or sources that combine

a source of alpha particles with light (low-z) metals such as lithium

or beryllium will emit neutrons (for example, plutonium-beryllium,

americium-beryllium, americium-lithium) when bombarded by

alpha particles.

The main issue with many sealed source applications is that the

source intensity decays with time, because the source isotope

produces the radiation as a byproduct of the natural decay. Dose-

rate correction is necessary on a regular basis, with the time interval

deﬁned by the half-life of the isotope. Other issues with sealed

sources include the potential for contamination – the release of the

radioactive material into the environment if the seal is breached – and

ultimately their disposal when the radiation intensity has decayed

below a useful ﬂux, even though the source is still radioactive.

Accelerators and other powered devices energize charged particles

such as ions (most commonly protons) or electrons by using very

high accelerating voltages to give these particles a high kinetic

energy. At this point, they are used directly as a radiation source or

directed onto a target material converting the incident radiation into

secondary radiation.

Accelerated protons incident on metal targets generate neutrons,

while accelerated electrons on metal targets produce X-rays.

Accelerators require lots of energy to produce radiation, so they

tend to be large and in-place installations. Unlike sealed sources,

accelerators do not pose a portable contamination risk.

Figure 1-24. X-ray image of the contents of a bag in an airport

security line (top); a portable X-ray machine to scan for

pipe defects (bottom).

Radiation Handbook for Electronics Texas Instruments

Particle beams, however, especially ion and neutron beams, induce

nuclear reactions within any materials in the beam, potentially making

them radioactive. For lighter materials, the degree of activation

is usually not a concern, as the amount of radiation produced is

short-lived, but some heavier elements that can have longer-lived

radioactivity require caution. The activation produces gamma-ray

radiation, as the unstable isotopes created by the nuclear reactions

in the target material decay to stable ones.

Microelectronics are present in most industrial applications, either

as an integral part of the equipment producing the radiation or

embedded in equipment being irradiated. In places where operators

or other personnel are present, the radiation sources must be

well-shielded and controlled such that radiation emission and

contamination is either eliminated or constrained to levels deemed

safe for humans. Microelectronics in these types of areas are

usually not at risk. Additionally, microelectronics inside accelerators

(e-beams and proton beams), X-ray machines or sealed sources that

produce ionizing radiation are generally heavily shielded to keep dose

exposures low. The doses encountered in industrial applications are

extremely well-controlled.

There are two exceptions where dose exposure can accumulate to

levels that will damage or destroy microelectronics:

• In industrial applications, where the microelectronics are part

of the imaging or detection systems and must be in the

radiation ﬁeld during operation. This applies to X-ray imagers

as well as radiation, liquid-level and other detectors used in

nuclear power plants.

• In processing/sterilization applications, where the electronics

will be irradiated and will accumulate dose; for example, in

electronic radio-frequency identiﬁcation (RFID) tags used to

label foods and drugs.

Nuclear ﬁssion reactors operated by the power industry to produce

electricity also create high radiation areas rich in neutrons and gamma

rays from both the reactor vessel and spent fuel in the storage pools.

All power plants – whether nuclear-, coal-, oil- or gas- driven – boil

water to produce steam that actives turbines, which in turn produce

electricity. In nuclear reactors, the process of nuclear ﬁssion produces

the heat needed to obtain steam.

Most reactors are based on isotopes of uranium (

238

U and

235

U) that

have a high-ﬁssion cross-section.

[59]

Fission or splitting of the uranium

nucleus can occur spontaneously, albeit at a very low rate, or if it is

exposed to neutrons. The absorption of an extra neutron renders the

uranium nucleus much less stable. The excess energy of the uranium

nucleus is released when it splits into two energetic ﬁssion fragments,

emitting additional neutrons and gamma rays. This is a key point,

because ﬁssion of the nucleus without the production of additional

neutrons would not allow subsequent ﬁssions to occur. So uranium

nuclei ﬁssions release neutrons that feed follow-on ﬁssion reactions

such that the process can be self-sustaining, usually referred to as a

controlled chain reaction. The uranium fuel consists of small pellets

assembled into long fuel rods placed in the main reactor vessel in

vertical bundles, as illustrated in Figures 1-25 and 1-26.

IInterspersed between the array of uranium fuel bundles are rods

of neutron absorbers. They consist of elements that are capable of

absorbing many neutrons without themselves undergoing ﬁssion.

These control rods slow down or speed up the rate of ﬁssion

reactions by modifying the number of neutrons available to drive the

ﬁssion process. By adjusting the height of the control rods within

the reactor vessel, the ﬁssion rate adjusts, as does the rate of steam

production and ultimately the power output of the reactor.

The heat energy is actually derived from the kinetic energy of the

ﬁssion fragments created during the reaction. The entire fuel assembly

is submersed in a deep pool of water. The water itself absorbs some

neutrons, but its main purpose is to keep the core below melting

temperatures while converting the waste heat by turning water

into steam, which in turn drives a turbine and generator to create

electricity. While uranium fuel is used in the reactor, it gradually

accumulates ﬁssion products – transuranic elements (the production

of nonﬁssile isotopes by neutron absorption) that cause an increase

in the neutron absorption of the reactor components. The control

rods can be adjusted to compensate, but after several years, the

increasing neutron absorption, along with the structural changes

Figure 1-25. Nuclear reaction core cross-section.

Figure 1-26. Photograph of a nuclear reactor core in operation. The blue

color is Cherenkov radiation given off as charged particles pass through

the water at speeds greater than the speed of light in water, an effect

analogous to the sonic boom produced by aircraft traveling faster than

the speed of sound in air.

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