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Failures in Aerospace Applications, Part 6

The previous blogs of this series describe the failures that can occur on ICs for aerospace applications:

All the listed failures are due to the creation of e /p+ because of the presence of radiation sources (proton/heavy ion) that impact the IC surface and cross the material. To determine the product's sensitivity to the heavy ions or to the protons, and to compare the products among themselves, main parameters have been defined:

  • LET (MeV/mg/cm2 ): Linear energy transfer is the amount of energy transferred to the material by the impacting heavy ion/proton.
  • LET threshold : This is the minimum starting LET from which SEE may occur on a component. The higher the threshold is, the better the component is.
  • Fluence (#/cm2 ): It is the number of ions per unit area that hit the component.
  • Cross-section (cm2 ): For a fixed LET , it is the ratio between the number of events detected on the device and the fluence .
  • Saturated cross-section (cm2 ): From a certain LET , the number of events occurring on the components will reach a saturation level. The saturated cross-section is the maximum number of events divided by the fluence .

All these parameters are summarized on the Weibull curve (see Figure 1).

Figure 1

The Weibull curve of an IC for aerospace applications. The curve contains LET, LET threshold,cross-section, and saturated cross-section.

The Weibull curve of an IC for aerospace applications. The curve contains LET, LET threshold,
cross-section, and saturated cross-section.

The listed parameters (LET, LET threshold, cross-section, fluence, and saturated cross-section) are very useful to help the engineering team evaluate the robustness of the silicon technology which constitutes the IC to the displacement damages (DD).

There are two main sources of DD: protons and neutrons. These particles are massive compared to the atoms contained in the ICs, so they can create modifications in the structure of the IC as they pass through. The neutrons are neutral particles that don't generate any e /p+ pairs, but the neutrons generate only DD. The protons are charged particles, which can thus generate both SEE and DD. All electronic components are composed of N or P doped silicon, which has internally free electric charges that can easily circulate inside these structured crystal lattices. If a neutron or a proton passes through the crystal structures, it disorganizes the crystal, and the disorganized electric charges don’t circulate anymore (see Figure 2).

Figure 2

The displacement damage caused by a proton/neutron when radiation passesthrough an N doped silicon material.(Source: ESA)

The displacement damage caused by a proton/neutron when radiation passes
through an N doped silicon material.
(Source: ESA)

An IC may be more or less sensitive to the DD, depending on the internal structure of the IC. Let's consider, as an example, a N-channel MOSFET transistor. When the N-MOS is properly biased, the electrons flow from the source to the drain, inside a non-doped area, that is insensitive to the displacement damages, due to the absence of free charges (see Figure 3).

Figure 3

Due to its internal structure, an N-channel power MOSFET is insensitive to displacement damage.

Due to its internal structure, an N-channel power MOSFET is insensitive to displacement damage.

In another widely utilized integrated power switch, the IGBT, the situation is different. The conduction of the electrical charges happens in doped areas that may be affected by DD.

Did you ever evaluate the radiation performance of an IC for an aerospace application by means of its Weibull curve? What do you think of the effectiveness of this curve in comparing some products for aerospace applications? Have you ever experienced a DD on an IC?

11 comments on “Failures in Aerospace Applications, Part 6

  1. etnapowers
    May 8, 2014

    The Displacement damages cannot affect low doped areas of an IC but might create a charge trapped inside the gate oxide , thus the treshold voltage of a NMOS transistor may vary accordingly.

  2. etnapowers
    May 8, 2014

    The fluence parameter describes the number of ions impacting the surface of the IC, this parameter is often associated to the dose rate parameter because the effects of the impacting ions are different in the the case of low dose rate or high dose rate.

  3. etnapowers
    May 8, 2014

    The protons and the  can cause either displacement damages or one of the Single event effects, among whom there is the SEGR, that is destructive. The irradiation of protons and heavy ions is hence two times dangerous for an IC in a aerospace environment.

  4. Netcrawl
    May 9, 2014

    @etnapowers compared to heavy ions, protons can generate more transient in electropnics components as they can easily penetrate the spacecraft and affect the components. In designing radiation mitigation plan its very important that we consider trapped protons and its variations.      

  5. yalanand
    May 10, 2014

    Protons and neutrons are the sources of DD, and it is a fact that they can create modification in the IC structure. When an N doped silicon material is used, then there will be a hold in charge circulation due to the displacement effects of neutrons and protons when radiation is included. And it is very interesting how IC structure can be modified to be insensitive to this damage. The N-channel power MOSFET is the solution.

  6. etnapowers
    May 12, 2014

    @Netcrawl: that's true, the protons can penetrate the spacecrafts more easily than heavy ions, due to the dimensions. The prevention of the damages created by heavy ions is very important too, because the circuitry that is external to the aircraft, may be heavy impacted by heavy ions.

  7. etnapowers
    May 12, 2014

    Agreed. The N-channel power MOSFET is one of the solutions because each device that works by a circulation of the electric current trough a low doped area is suitable.

  8. etnapowers
    May 12, 2014

    “The N-channel power MOSFET is the solution”

    I have worked on a project of a circuit for power management in a aerospace module, utilizing N-channel Mosfets and P-channel Mosfets. Both of these devices are quite insensitive to radiation displacement damages.

  9. Netcrawl
    May 13, 2014

    @etnapowers MOSFET is a key for power concersion, known to be resistant to high-energy charged particles, they have high-input impedance, they do not suffer from thermal runway or second breakdown, a perfect fit for most of today's space applications. 

  10. etnapowers
    May 13, 2014

    The only limitation to the usage of the mosfet in aerospace environment is the control of charge trapped inside the gate oxides, this control is very difficult to perform, in most cases.

  11. samicksha
    May 14, 2014

    Yes you are right, in fact low power losses and gate charge while also optimizing the maximum current rating.

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