Characterization of a CMOS Pixel Sensor prototype for the CEPC vertex detector

The proposed Circular Electron Positron Collider poses significant challenges for the vertex detector in terms of material budget, spatial resolution, readout speed, and power consumption. To address these challenges, a Monolithic Active Pixel Sensor prototype, named TaichuPix, has been developed based on a column drain readout architecture. The performance of the second version of this prototype, TaichuPix2, has been evaluated using a radioactive source, which exhibits a time walk of less than 100 ns corresponding to the threshold of 380 e− and amplitude variation of analog output from 300 mV to 500 mV. An infrared laser setup is utilized to estimate the single-point spatial resolution of this sensor for minimum-ionizing particles. The setup includes a high-precision three-dimensional translation stage and an optical system with a 1064 nm laser diode. With this setup, the spatial resolution is estimated to be about 4 µm. The performance for real particles is to be confirmed in a test beam.