Combining TCAD and Monte Carlo methods to simulate CMOS pixel sensors with a small collection electrode using the Allpix2 framework

Abstract

Combining electrostatic field simulations with Monte Carlo methods enables realistic modeling of the detector response for novel monolithic silicon detectors with strongly non-linear electric fields. Both the precise field description and the inclusion of Landau fluctuations and production of secondary particles in the sensor are crucial ingredients for the understanding and reproduction of detector characteristics.In this paper, a CMOS pixel sensor with small collection electrode design, implemented in a high-resistivity epitaxial layer, is simulated by integrating a detailed electric field model from finite element TCAD into a Monte Carlo based simulation with the Allpix 2 framework. The simulation results are compared to data recorded in test-beam measurements and very good agreement is found for various quantities such as cluster size, spatial resolution and efficiency. Furthermore, the observables are studied as a function of the intra-pixel incidence position to enable a detailed comparison with the detector behavior observed in data.The validation of such simulations is fundamental for modeling the detector response and for predicting the performance of future prototype designs. Moreover, visualization plots extracted from the charge carrier drift model of the framework can aid in understanding the charge propagation behavior in different regions of the sensor.

Transient Monte Carlo Simulations for the Optimisation and Characterisation of Monolithic Silicon Sensors

“…While the comparison of the transient current pulse with transient 3D TCAD will be performed for all three pixel flavours, the comparison with test-beam data is only shown for the flavour with continuous n-implant, using a 100 µm thick sample. The comparison for the flavour with no n-implant and the one with segmented n-implant produce similar results and can be found elsewhere [2,7].…”

“…The Monte Carlo simulations performed in this paper largely follow the setup outlined in [2], with a few key differences with respect to energy deposition, charge carrier transport and signal formation. They were performed with Allpix 2 version 2.0 and profited significantly from the multithreading capabilities introduced with this version.…”

“…The module uses Geant4 [12,13] to simulate the creation of secondary particles and a more realistic interaction of the incoming particle with the detector material. The corresponding configuration can be obtained from [2].…”

“…The combination of 3-dimensional finite-element simulations using Technology Computer-Aided Design (3D TCAD) with the Monte Carlo framework Allpix 2 [1] was validated for a monolithic CMOS sensor with a small collection electrode and it was shown that the advantages of both simulation approaches can be exploited simultaneously: detailed sensor modelling and high simulation rates that enable the inclusion of statistical fluctuations [2]. The Allpix 2 framework allows for an end-to-end simulation of the response of a silicon sensor to the traversal of highly energetic particles, from initial energy deposition to signal digitisation.…”

Silicon Vertex and Tracking Detector R&D for CLIC

“…For verification, the response of the sensor to a particle beam was studied in a combination of Monte Carlo (MC) and electrostatic TCAD simulations. For this purpose, electrostatic sensor simulations in 3D TCAD were imported into the Geant4-based MC framework Allpix 2 [12], thereby harnessing the full potential of the accurate sensor modelling in TCAD and the high statistics thanks to the MC approach [13].…”