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Description
AstroPix is a novel high-voltage CMOS active pixel sensor being developed for a next generation gamma-ray space telescope, AMEGO-X, and the ePIC electron-iron collider detector. AstroPix has to be $500~\rm{\mu m}$ thick and to be fully depleted by supplying bias voltage. The energy resolution must be < 6 keV (FWHM) at 60 keV and the pixel pitch should be $500\times500~\rm{{\mu m}}^2$. Furthermore, given the space-based nature of AMEGO-X, the power consumption of AstroPix needs to be limited ($<1.5~\rm{mW/{cm}^2}$). The first version of AstroPix was developed based on the experience of the developments of both ATLASPix and MuPix. The third version of AstroPix, AstroPix3, reached the target pixel pitch with a mean energy resolution of 6.2 keV (FWHM) at 60 keV and its power consumption is $4.1~\rm{mW/{cm}^2}$ (Y. Suda et al 2024 NIMA 1068). The latest version of AstroPix, AstroPix4, features an improved time stamp generation and readout architecture, aiming to achieve a time resolution of 3 ns (N. Striebig et al 2024 JINST 19). The pixel capacitance was reduced by improving the routing and minimizing the metal-to-n-well capacitance, which resulted in lower noise floor. As a result, most of the pixels in the tested AstroPix4 chip can detect the 14 keV photopeak from Co-57, which could not be detected with AstroPix3. In this work, we report about basic performance of AstroPix4, such as I-V, noise, energy calibration/resolution/threshold, and depletion depth.
