Introduction
In this context, a failure means a detectable misbehavior of the circuit following a Single Event. A Single Event (SE) is the results of the impact of a single, high-energy charged particle that strikes a sensitive region of a circuit and deposits energy. The charged particle could be one of the following: ion, proton or alpha particle. These particles can also appear following the interaction between a high-energy neutron and the electronic device. The particles could be encountered in a natural environment or be produced (i.e. at a radiation facility).
When the number of particles is high, we may expect a higher occurrence probability for single events. The flux is defined as the number of particles passing through one square centimeter area per unit time. The flux is measured in particles/cm2·sec. The fluency is the particle flux integrated over the needed duration. The unit is particles/cm2.
Single Event Effects (SEE) are the results of SE, and their manifestations are many-fold. We may classify them in permanent (destructive) and non-permanent.
Single Event Latch-up (SEL) and Single Event Snapback (SES) consists in the activation of parasitic structures of CMOS devices and may produce high current consumption, above device specifications. The latched condition may destroy the device, affect other surrounding devices and destroy the power supply. These effects can be cleared by a power off-on reset. If the power is not removed quickly, the device can be damaged by excessive heating, metallization or bond wire failure.
Single Event Burnout (SEB) provokes the apparition of a very high and localized flow of electric charge and thus the local destruction of the transistor by melting of the silicon in the affected region.
Single Event Gate Rupture (SEGR) corresponds to the formation of a conducting path in the gate oxide. The electrical performances are compromised and the device may no longer function correctly.
Single Event Transients (SET) are analog pulses resulted from a SE, that are large or big enough to momentarily change the output of the cell to the opposite logic value.
Single Event Upsets (SEU) sometimes inadequately called Soft Error are SEEs which changes the logic state of a discrete sequential element, such as a latch of flip-flop or a the value of a memory cell.
The last two types of errors are not physically destructive and they disappear after a power-cycle.
Soft Errors may provoke a device error the dysfunction of the device, event that we will call Single-Event-Induced Failure.
The FIT rate is the measurement unit to assess the soft error sensitivity of electronic devices. A FIT is equal to: one failure per billion chip hours.
The FIT rate is linked to the characteristics of the working environment. The environment is defined by the type (neutron/proton/alpha/ion) and the characteristics of particles (Energy/Linear Energy Transfer) and by the occurrence of these particles in a unit of volume (flux).