Development of a novel HV-CMOS active pixel sensor AstroPix for gamma-ray space telescopes

All-sky medium-energy gamma-ray observations are essential to deepen our understanding of physics in high energy astronomical phenomena, and to further develop multi-messenger astronomy. Future all-sky MeV gamma-ray telescopes must have a large area detector and keep high sensitivities even in the energies in which Compton scattering is dominant. AMEGO-X is one of the proposed MeV gamma-ray missions and its gamma-ray detector consists of silicon trackers and calorimeters. In order to efficiently detect MeV photons and to have precise Compton reconstruction, the silicon sensors must be fully depleted (500 μm) and have a moderate position resolution (∼ 500 μm) with a good energy resolution (< 10% at 60 keV). On top of that, the power consumption of the silicon detector must be low (< 1.5 mW/cm²) given the required silicon area in the gamma-ray detector is huge (∼ 24 m²). We have been developing AstroPix, a high-voltage CMOS active pixel sensor, to fulfill such specifications. In this contribution, we report basic characterization of the third version of AstroPix chip (AstroPix3), such as I-V measurement, imaging capability, energy spectrum, and indirect depletion depth measurements using gamma-ray sources.