Development of monolithic active pixel sensors for charged particle tracking

Monolithic active pixel sensors introduce a detection technique, where the active detecting element is a thin, moderately doped, and undepleted silicon layer and the readout electronics is implanted on top of it. The built-in potential, resulting from differences in doping, screens both parts, as well as it confines the charge diffusing to the readout electrodes. The R&D was triggered by the increasing need of high performance flavour identification capabilities that should be provided by future vertex detectors. The viability of the technology and its high tracking performances were demonstrated with small-scale prototypes, made of small arrays of a few thousands of pixels and more recently with a first prototype of a serviceable size of one million pixels. This paper summarizes results from tests performed with relativistic charged particles on prototypes essentially fabricated with a classical 3-transistor pixel configuration. Within the last year, two novel ideas optimising the pixel design for a vertex detector have been developed. They are presented with test results assessing their suitability. (C) 2003 Elsevier B.V. All rights reserved.