Study and characterization via Monte Carlo simulation of ionizing radiation damages in hybrid pixel detectors

Hybrid pixel detectors are being consolidated as one of the best approaches for X-ray imaging techniques, addressing synchrotron and medical applications. In both applications, detector failures can result in severe data loss. The radiation incident on the sensor, in the case of higher energies and smaller efficiency, can be partially transmitted by the sensor, reaching the reading electronics of each pixel, which is located behind it. In the case of the modern synchrotron applications, this radiation tends to high intensities, compromising the detector's life cycle. This work aimed to understand the phenomena behind the effect of radiation on image data, recognize patterns among the possible effects and quantitatively relate the deposited dose with damages in the data provided by the detector, seeking to establish limits for a data quality assurance for the various applications, as well as the frequency of possible maintenance procedures to ensure the best performance of the detector. The dose values in the oxide layers of the CMOS transistors were obtained through Monte Carlo simulation, based on the PENELOPE code. This parameter was chosen once there is a consensus in the literature that the phenomena related to damage in the considered energy range of 2 to 100 keV corresponds to dose deposition in these layers. The effects of charge dispersion in the sensor, which are relevant in pixelated detectors, were implemented in the code. This correction enabled a comparison between the experimentally obtained image and detected spectrum with the ones resulting from the Monte Carlo simulation. Thus, it was possible to verify their correlation and support the feasibility of using the deposited dose obtained via Monte Carlo simulation as an estimation of the deposited dose value. Low dose (809 ± 6 Gy) and high dose (6230 ± 20 Gy) experiments were performed at a Medipix3RX single chip detector, bonded to a 200 𝜇m thick silicon chip. It was possible to establish a metric to evaluate the low dose effects, which proved to be recoverable through time. For high doses, different damage patterns were verified and hypotheses were made to understand their different behaviors. Visible damages were verified starting at 2616 ± 13 Gy, and a guarantee of at least 90% healthy pixels until 3746 ± 23 Gy was calculated. It was also possible to obtain a quantitative estimation of the detector recovery time scale: half of the saturated pixels were recovered at 110.4 ± 1.3 minutes. (author)