Detecting SEUs in Noisy Digital Imagers with small pixels

Abstract

Camera sensors are susceptible to the same transient (non-permanent) errors that occur in standard digital semiconductors, known as Single Event Upsets (SEUs). These result from the charge deposited by cosmic ray particles on the semiconductor. In a camera sensor, SEUs manifest themselves as one or more brighter pixels in a dark-frame image during long exposure times. Since the value of brighter pixels is related directly to the deposited charge, SEU analysis of digital imagers provides essential information about the nature and amount of charge deposited by particle hits, their occurrence rate, and the charge spread area. In this paper we describe an experimental approach to collect this information from pixels of size of $7\mu\mathbf{m}$ (DSLR cameras) down to $1.2\mu \mathbf{m}$ (cell phone cameras). High gain (ISO) images allow us to detect lower energy SEUs but at the cost of a noisier background. The smaller pixels $(1.2\mu \mathrm{m})$ are more sensitive to lower energy SEUs, but have considerably noisier background levels. It is important to observe the SEU information over a range of gains (ISOs) and pixel sizes, to obtain the energy and spatial distribution of the SEUs, which is valuable for understanding the nature of SEUs in other circuits. The problem is that SEUs, by their transient nature, appear randomly in both time and location in a series of images. It is important to separate those from the noisy imager random excursions above the background level. We implement a new algorithm that is more effective in separating SEUs from random noise by leveraging thousands of images to obtain the noise distribution of each individual pixel.