Speaker
Description
AstroPix is a novel high-voltage monolithic active pixel sensor being developed mainly for future gamma-ray space telescope, AMEGO-X. It is also expected to be used in the barrel imaging calorimeter in the ePIC electron-iron collider detector, USA. AstroPix has to be 500 μm thick and to be fully depleted by supplying bias voltage. The energy resolution must be < 10% (FWHM) at 122 keV and the pixel pitch should be 500×500 μm2. The dynamic range should be in the range from 25 keV to 700 keV. Furthermore, given the space-based nature of AMEGO-X, the power consumption of AstroPix needs to be limited (< 1.5 mW/cm2). We have been developing four different versions of AstroPix so far. The first version of AstroPix was developed based on the experience of the developments of both MuPix and ATLASPix. It was used to understand the sensor and to develop the data acquisition tools. The second version has an increased pixel pitch and a digital readout capability. The third version, AstroPix3, reached the target pixel pitch with a moderate energy resolution of 6.2 keV (FWHM) at 60 keV. The latest version of AstroPix, AstroPix4, is equipped with an improved time stamp generation and readout architecture to achieve 3 ns time stamping. Its power consumption is about 2 mW/cm2. The pixel capacitance is reduced by improving the routing and reducing the metal to n-well capacitance to achieve lower noise level. Thanks to it, most of pixels in a tested AstroPix4 chip detect 14 keV photopeak from Co-57, which could not be detected with AstroPix3. The mean energy resolution over the chip is 14% at 122 keV. The dynamic range is estimated to be in the range from 14 keV to ~250 keV. The bias voltage dependence of the measured depletion depth showed that the depletion depth growths as expected, but the achieved depth is only 90 um due to the fact that the resistivity of the used chip is not high enough to allow full depletion. We present an overview of our AstroPix development, selected results from AstroPix performance evaluations, design of the next version of AstroPix, and future prospects.
