9.5.3 Prediction of SEE rates of protons and neutrons

a. Except in the case specified in requirement 9.5.3b, the proton or neutron contribution to error rate shall be calculated as follows:

1. Using the integral or differential energy spectra for protons or neutrons specified in the radiation environment specification, obtain:

(a) the cross-section experimental curve giving saturation, and

(b) two other cross section/energy points in the following ranges:

- For protons, in the energy range 10 MeV - 200 MeV.

- For neutrons, from thermal energies to 200 MeV.

2. Use one of the following formulas to calculate the SEE rates:

o From the environment proton or neutron fluxes and SEE cross sections:

o By considering the dependence of the angle of incidence, but assuming not azimuth angle dependence:

o By simplifying the previous formula, by

- defining σ_max(E) as the value of σ(E,q) at the angle q where the cross section maximises for that energy, and

- If the incident proton or neutron flux is anisotropic (and therefore cannot be approximated to an isotropic flux), approximate dΦ/dE to the angle-averaged incident flux if used in conjunction with the maximum cross section data, σ_max(E).

where:

dΦ/dE = differential proton or neutron flux spectrum as a function of energy;

E_Min = minimum energy of the differential energy neutron spectrum;

E_Max = maximum energy of the differential energy spectrum;

σ_nucleon(E) = proton or neutron SEE cross section as a function of energy.

b. If the heavy ion cross-section experimental curve exist, the proton or neutron contribution to error rate may be calculated as follows:

1. Obtain the proton cross-section curve by simulation and correlation with experimental data, using a simulation tool agreed with the customer.

2. Using the integral or differential energy spectra for protons or neutrons specified in the radiation environment specification, obtain two other cross section/energy points in the following ranges:

o For protons, in the energy range 10 MeV - 200 MeV.

o For neutrons, from thermal energies to 200 MeV.

3. Calculate the SSE rate, from ion-beam irradiations, by using the following formula:

where:

dΦ/dE, : E_Min, E_Max, and σ_nucleon(E) have the same meaning as in 9.5.3a2, and:

dP/de(E,e) = differential energy deposition spectrum for protons/neutrons of energy E depositing energy e within the sensitive volume;

e_C = critical or threshold energy deposition for inducing SEE;

e_Max = maximum energy deposition defined for energy deposition spectrum;

σ_ion(LET) = SEE cross section for ions as a function of LET for normally incident ions;

h = height of sensitive volume;

ρ = mass density of semiconductor;

s_sample = area of cell sampled by proton/neutron simulation to obtain energy deposition spectrum.

NOTE Rational and discussion on the calculation of SEE rates of protons and neutrons can be found in Section 8.5.5 to 8.5.7.