Charged particle detection using a CMOS active pixel sensor

Abstract

Active Pixel Sensor (APS) technology has shown promise for next-generation\nvertex detectors. This paper discusses the design and testing of two\ngenerations of APS chips. Both are arrays of 128 by 128 pixels, each 20 by 20\nmicro-m. Each array is divided into sub-arrays in which different sensor\nstructures (4 in the first version and 16 in the second) and/or readout\ncircuits are employed. Measurements of several of these structures under Fe55\nexposure are reported. The sensors have also been irradiated by 55 MeV protons\nto test for radiation damage. The radiation increased the noise and reduced the\nsignal. The noise can be explained by shot noise from the increased leakage\ncurrent and the reduction in signal is due to charge being trapped in the epi\nlayer. Nevertheless, the radiation effect is small for the expected exposures\nat RHIC and RHIC II. Finally, we describe our concept for mechanically\nsupporting a thin silicon wafer in an actual detector.\n