COMETH: a CMOS pixel sensor for a highly miniaturized high-flux radiation monitor

The need for miniaturized and versatile real-time radiation monitors has become a general trend for spacecraft applications. It requires a highly integrated detection system with the ability to count and identify ion species in a high-flux with mixed particles environment. We have proposed a new strategy to meet these requirements with a single CMOS pixel chip. This sensor is based on a matrix of 50×50 µm 2 pixels, read out in rolling-shutter mode, and features columns ended by 3-bit ADCs with tuneable threshold. An embedded digital algorithm extracts the particle properties from the pixel information to provide the radiation flux online. A reduced scale prototype with 32×32 pixels and 32 column-level ADCs has been designed and fabricated in a 0.35 µm CMOS process. The layout of the identifying and counting algorithm, downstream the pixel matrix, was developed in the same process. A full simulation of this layout for a subset of columns was used to check the algorithm output against a variety of inputs. The prototype was tested with X-rays, β- particles and laser illumination. Results confirm previous simulations addressing gain and linearity. Column-level ADCs also perform as expected. Those measurements validate the possibility to monitor proton and electron fluxes up to 10 7 particles·cm -2 ·s -1 and to distinguish protons from electrons for energies lower than 50 MeV. A brief review of this first prototype design and tests is presented in this paper.