Development of CMOS pixel sensors for tracking and vertexing in high energy physics experiments

Abstract

CMOS pixel sensors (CPS) represent an emerging technological approach to charged particle detectors. CMOS processes allow to integrate the sensitive volume and the readout electronics of the pixel detector in a single silicon die allowing for small pixel pitch ( 20 µm) and low material budget (∼ 0.2-0.3% X 0 per layer). These characteristics make CPS an attractive option for vertexing and tracking systems of high energy physics experiments requiring high spatial resolution. Moreover, thanks to the use of commercial CMOS processes for the CPS fabrication, the construction cost can be significantly reduced in comparison to the custom technologies used so far. However, the attainable performance level of the CPS in terms of radiation hardness and readout speed is mostly determined by the fabrication parameters of the CMOS processes available on the market rather than by the CPS intrinsic potential itself. The constant evolution of commercial CMOS processes towards smaller feature sizes and high resistivity epitaxial layers enhances steadily the radiation hardness and allows for the implementation of more complex, accelerated readout circuits. The TowerJazz 0.18 µm CMOS process, being one of the most relevant examples, recently became of interest for several future detector projects. The most imminent of them is an upgrade of the Inner Tracking System (ITS) of the ALICE detector at LHC. It will be followed by the Micro-Vertex Detector (MVD) of the CBM experiment at FAIR. Other experiments like ILD consider CPS as one of the viable options for flavour tagging and tracking sub-systems. Following the successful tests of the first prototypes in 2012 proving that the radiation hardness of the technology complies with the requirements of the new ALICE-ITS and CBM-MVD, the PICSEL group of IPHC-CNRS in Strasbourg (France) started to develop two CPS (MISTRAL and ASTRAL) dedicated to these projects. The present contribution describes the current status of this development. Results of the laboratory and beam tests of several prototype chips manufactured in Spring and tested during Summer 2013 are presented.

Study on the tolerance of partially and fully depleted CPS to non-ionizing radiation

“…The surface of the collection diode varies from 1 to 15 µm 2 [IPH18]. Some first beam test results were presented in[Sen+14]. All MIMOSA-34 measurements in this thesis were performed with an integration time of 32 µs.The high-resistivity epitaxial layers in MIMOSA-34 sensors are either 18 µm or 20 µm thick (see Section 4.2.2) and, for this thesis, are denoted as HR18 and HR20, respectively.…”