Dependence of SEUs in Digital Cameras on Pixel size and Elevation

Determining how Integrated circuits' (ICs) soft (transient) errors (also known as Single Event Upsets or SEUs) change with elevation is important in many applications, both on Earth and in aerospace. We have been studying SEUs using camera sensors, which record SEUs as bright spots in a dark image. The most important advantage of camera pixels for this study is that they integrate the information over time until read out, creating a record of when/where cosmic ray particles collide with the IC, and the amount of the deposited charge. The study was done by collecting large numbers (100's - 1000's) of images at exposures of similar to 30 sec. SEUs appear as brighter spots above the noise background of the sensor, typically 1 or 2 per image, that appear in a single dark frame within a stream of images. At higher camera gains (ISO) we can detect weaker SEUs but must deal with the noise at these long exposures. We use a Pixel Noise Distribution, obtained from the same set of images, to distinguish SEUs from the background noise. Previously we noted that the SEU rate/area changes with the elevation of the camera, as has been found in other ICs. We have measured this rate at elevations from 0 to 1100m, using cameras with pixel sizes from 4.1 to 6.5 microns at several gain (ISO) levels (as higher ISOs magnify weaker SEUs). We then compared our results to previously developed models of cosmic radiation changes with elevation.