A method for correcting cosine-law errors in SEU test data

Single-event upset tests often change the angle of the ion beam relative to the device to mimic a change in ion linear energy transfer, and the data are then converted via an assumed cosine law. The converted data are intended to represent device susceptibility at normal incidence, but the cosine law sometimes contains considerable error. The standard method for correcting this error is based on the rectangular parallelepiped (RPP) model. However, exact analytical expressions derived from this model are not particularly simple, so specialized computer codes are needed unless approximations are used. This paper starts with an alternate physical model, utilizing a charge-collection efficiency function, and derives an exact analytical result (called the alpha law here) that replaces the cosine law but is almost as simple as the cosine law, even when device susceptibility has a strong azimuthal dependence. The same model can be used to calculate (via numerical integrations) rates in a known heavy-ion environment. An alternative is to use model parameters to construct the parameters for an integrated RPP calculation of rates.