Design of the OBELIX monolithic CMOS pixel sensor for the Belle II vertex detector upgrade

Abstract Targeting a peak luminosity of 6 × 10 35 cm -2 s -1 , the Belle II experiment at the SuperKEKB in Japan is considering an upgrade of its interaction region. This upgrade involves the vertex detector, which will be replaced by a new fully pixelated vertex detector (VTX). A monolithic CMOS pixel sensor named OBELIX (Optimized BELle II pIXel) is proposed to be used in the VTX. Based on the existing TJ-Monopix2 chip initially developed for the ATLAS Inner Tracker (ITk) upgrade, OBELIX is designed in a 180 nm CMOS process with an improved pixel matrix and additional functionalities such as new on-chip voltage regulators and digital periphery. This paper will review the overall design of the VTX and the OBELIX sensor.