Reliability and Radiation Effects on Advanced CMOS Technologies




Depending on the radiation environment in which the chips are immersed, ionizing radiation can have different effects. Concerning CMOS circuits, there are two broad categories of radiation effects: single event effects (SEE), which are due to a single strike of a particle with high ionizing power; and total ionizing dose (TID) effects, which are due to the progressive build-up of defects caused by the passage of many particles, such as electrons or protons.

Single Event Effects

A particle passing through a semiconductor can give rise to several phenomena, depending on the type and bias conditions of the struck device and on the features of the impinging particles:

Single Event Upset (SEU) also known as soft error, because it results in a loss of information and not in permanent damage to the affected circuit (hard error). When a particle strikes a memory cell, it may cause a flip in the stored value, what was memorized as a '0' may become a '1' and viceversa. More information on soft errors can be found in this section.

Single Event Latch-up (SEL) occurs when the impinging particle activates parasitic BJT structures, causing high currents to be drawn from the power supply. A power-cycle is needed to restore proper operation, even though permanent damage may occur to the device during the high-current condition.

Single Event Functional Interruption (SEFI) occurs when a state machine controlling a device, such as a Flash memory or an FPGA, is upset by a heavy ion, causing a stop in the device operation.

Single Event Gate Rupture (SEGR) occurs when a particle with a high ionizing power impinges on a device biased over a critical voltage causing the rupture of the gate oxide, i.e., the formation of a conductive path which effectively shorts the anode and the cathode.

Total Ionizing Dose

Total ionizing dose effects are related to the progressive build-up of radiation-induced trapped charge and defects inside the exposed devices, caused by low-LET particles.

Charge trapping and interface state generation in the gate oxide were the biggest concern in older CMOS generations. Nowadays, thanks to the thickness reduction, gate oxide is no more a problem, and the Achilles' heel of modern processes is the shallow trench isolation (STI), where parasitic structures can be activated by radiation-induced defects.

Microdose Effects

Microdose effects are similar to TID effects, but are generated by the localized energy deposition of heavy ions.




LET, Linear Energy Transfer, is the amount of energy released by an ion in matter, due to ionization processes.