Simulations of planar pixel sensors for the ATLAS high luminosity upgrade

A physics-based device simulation was used to study the charge carrier distribution and the electric field configuration inside simplified two-dimensional models for pixel layouts based on the ATLAS pixel sensor. In order to study the behavior of such detectors under different levels of irradiation, a three-level defect model was implemented into the simulation. Using these models, the number of guard rings, the dead edge width and the detector thickness were modified to investigate their influence on the detector depletion at the edge and on its internal electric field distribution in order to optimize the layout parameters. Simulations indicate that the number of guard rings can be reduced by a few hundred microns with respect to the layout used for the present ATLAS sensors, with a corresponding extension of the active area of the sensors. A study of the inter-pixel capacitance and of the capacitance between the implants and the high-voltage contact as a function of several parameters affecting the geometry and the doping level of the implants was also carried out. The results are needed in order to evaluate the noise and the cross-talk among neighboring pixels when connected to the front-end electronics.