Geant4-based simulations of charge collection in CMOS Active Pixel Sensors

Abstract

Geant4 is an object-oriented toolkit for the simulation of the interaction of particles and radiation with matter. It provides a snapshot of the state of a simulated particle in time, as it travels through a specified geometry. One important area of application is the modelling of radiation detector systems. Here, we extend the abilities of such modelling to include charge transport and sharing in pixelated CMOS Active Pixel Sensors (APSs); though similar effects occur in other pixel detectors. The CMOS APSs discussed were developed in the framework of the PRaVDA consortium to assist the design of custom sensors to be used in an energy-range detector for proton Computed Tomography (pCT). The development of ad-hoc classes, providing a charge transport model for a CMOS APS and its integration into the standard Geant4 toolkit, is described. The proposed charge transport model includes, charge generation, diffusion, collection, and sharing across adjacent pixels, as well as the full electronic chain for a CMOS APS. The proposed model is validated against experimental data acquired with protons in an energy range relevant for pCT. K: Detector modelling and simulations II (electric fields, charge transport, multiplication and induction, pulse formation, electron emission, etc); Solid state detectors; Instrumentation for hadron therapy 1Corresponding author.

The role of Monte Carlo simulation in understanding the performance of proton computed tomography

“…1, as well as on publications applying this simulation framework to research questions. While studies focusing on this scanner prototype, the longest in operation, have been selected to be discussed in detail, Monte Carlo methods were used to investigate other scanner prototypes as well [96,97,53,98,99,100,101,102,27]. Since these studies did not explicitly investigate the influence of the scanner on image quality for human-scale objects, we have chosen not to discuss them extensively.…”

Comparison of CsI:Tl and Gd2O2S:Tb indirect flat panel detector x‐ray imaging performance in front‐ and back‐irradiation geometries

“…Thin‐film a‐Si:H field‐effect transistors and photodiodes have been shown to retain acceptable performance at ~10 4 Gy cumulative dose, which greatly exceeds the expected lifetime dose for radiography and fluoroscopy detectors (<10 2 Gy) . CMOS APS, however, are less resistant to radiation‐induced damage and more susceptible to image noise from direct interactions due to their bulk Si wafer, thicker depletion region and higher carrier mobility‐lifetime product . Combining the intrinsic advantages of BI with the low electronic noise of CMOS APS would otherwise be desirable for both improving detector DQE and achieving quantum noise‐limited performance at low dose.…”

A large area CMOS Active Pixel Sensor for imaging in proton therapy

“…A CMOS Active Pixel Sensor, named DynAMITe, whose performance for proton imaging has been extensively studied both with experimental data [23][24][25] and simulations [29], has been used to compare the response of the PRaVDA CMOS sensors for individual proton imaging. Details of the sensor architecture, electro-optical performance and radiation hardness are reported elsewhere [19,22,28].…”