The purpose of our testing this week was to observe the performance of a population of VA10820 MCUs under a Total Ionizing Dose (TID) exposure of radiation. The Cobalt-60 radiation source is located in a pool of water behind the 12.7mm aluminum ‘window’ that sits in a 3 ft. thick densified concrete wall.
This is an important test for devices that are used in space, where electronics are exposed to an accumulation of radiation over time that results in a degradation of performance (and thereafter complete failure). As radiation particles strike the device, charges are built-up on the gate and field oxide areas. This charge leads to a shift (downwards) of threshold voltage, signal propagation delays and increased leakage.
A rad (Si) is a unit of energy absorbed in the silicon by radiation. A commercial MCU would typically withstand ~ 3K rad (Si) of TID before the device exhibits the derogatory effects of space radiation. VORAGO microcontrollers are tested at up to 450K rad (Si) and specified at 300K rad (Si).
Now it should be obvious why commercial off-the-shelf MCUs are not expected to survive for very long in space.