CMOS monolithic sensors with hybrid pixel-like, time-invariant front-end electronics: TID effects and bulk damage study

Electronic circuits and systems are employed in a number of different fields where some degree of radiation tolerance is required. These fields include, to mention but a few, space and avionic applications, high-energy physics experiments, nuclear and (still at an exploratory stage) thermonuclear power plants, and medical diagnostic imaging and therapy. When operated in these environments, electronic systems may be directly struck by photons, electrons, nucleons or heavier particles, with a subsequent alteration of their electrical properties. Depending on the type and characteristics of the impinging radiation and on the fabrication technology of the circuit, different effects, either irreversible or (partially or totally) reversible, may arise. Knowledge of the mechanisms underlying the behavior under irradiation of electronic devices and circuits is of paramount importance for devising hardness assurance methodologies to guarantee that they can work reliably in the target environment and developing rad-hard circuits and design techniques to improve their tolerance to specific radiation effects in specific applications. The work focuses on the cumulative effects of ionizing radiation and neutrons on complementary metal-oxide semiconductor (CMOS) monolithic sensors, also known as monolithic active pixel sensors (MAPSs) or as CMOS image sensors (CISs), developed for particle tracking applications in high-energy physics (HEP) experiments. The analysis will focus on a couple of case studies, where the analog front-end electronics (the analog electronic circuits integrated in each of the elementary cells making up the sensor array) is more complicated than the typical three-transistor structure of CMOS MAPS and actually has the same architecture as the circuits used in hybrid pixel sensors (HPDs) for the readout of pixel sensors in a high-resistivity substrate. For this reason, the results discussed here can be of interest for the radiation-tolerant design not only of CMOS MAPS, but also more generally of circuits for the readout of capacitive detectors broadly used in fundamental physics experiments. The purpose is to draw the attention to the most critical points, as far as radiation tolerance is concerned, in the design of classical analog blocks for radiation detection applications. The chapter is organized as follows. After a short section about the development and use of CMOS MAPS in charged particle tracking applications, total ionizing dose (TID) effects will be discussed for two different MAPS devices: one fabricated in a 130-nm, triple-well CMOS technology, and the other in a 180-nm, quadruple-well CMOS technology. While CMOS circuits are known to be significantly affected by ionizing radiation, they are mostly insensitive to bulk damage. On the other hand, the collecting electrode of monolithic sensors, and in particular, its capability of collecting charge from the substrate to detect the transit of a particle, may be sizably degraded by neutron-induced increase in bulk trap density. This subject will be investigated for the same two devices, the 130-nm and 180-nm CMOS MAPS sensors, in the last section of the chapter