Abstract: The Upgrade of the Belle II vertex detector (VTX) at the SuperKEKB accelerator in Japan is foreseen to improve tracking performance at the expected high beam backgrounds at target luminosity of 6 x 1035 cm-2s-1. The OBELIX-1 chip is specifically developed for this purpose and used as sensor on all VTX layers. OBELIX-1 is a depleted monolithic active pixel sensor in 180 nm technology. The pixel matrix is inherited from TJ-Monopix2, but the periphery of the chip is entirely reworked. A newly designed 2-stage pixel memory matches Belle II trigger requirements. OBELIX-1 includes LDO regulators and a precision timing module with less than 3 ns resolution. Furthermore, the chip can also contribute to the Belle II trigger system with low latency, low granularity real-time streaming of pixel data in parallel to regular operation. Details of the inner working of the trigger memory are presented, as well as performance simulations to validate the requirements for the VTX Upgrade. The trigger memory has been studied in simulation using realistic scenarios, including Landau distributed charge and clustering to evaluate performance. In order to allow post-production testing, an additional module is presented. This allows the injection of pseudo-random data early in the processing chain, and replaces the need for industry standard scan-chains. It can be used stand-alone or during analog charge injection, in order to reach the full trigger memory during testing.

Abstract: The Belle II experiment, operating at the asymmetric SuperKEKB e+e-collider, is preparing an upgrade of its vertex detector to cope with an increased luminosity of 6 & times; 1035 cm-2s-1. The upgraded vertex detector (VTX) will consist of five or six layers of depleted monolithic active pixel sensors (DMAPS), with a total material budget of approximately 3% X/X0. The OBELIX chip, derived from the TJ-Monopix2 sensor and fabricated using Tower-Jazz Semiconductor 180 nm CMOS technology, is being developed for this upgrade. It features a 33 & micro;m pixel pitch with a time-stamping binning of 50-100 ns, along with a dedicated digital periphery compatible with the Belle II trigger system, supporting rates up to 30 kHz. The sensor is designed to operate under the high background conditions expected at the target luminosity, with radiation tolerance up to 5 & times;1014 neq/cm2 and 100 Mrad, while targeting a power density of about 200 mW/cm2. This corresponds to hit rates up to 120 MHz/cm2. Beam test and irradiation studies of TJ-Monopix2 demonstrate that the operating sensor temperature should stay below 40 degrees C after irradiation up to 5 & times; 1014 neq/cm2. This report reviews the proposed VTX concept, sensor performance, and ongoing R&D activities.