It seems super impressive that we are able to fabricate this sensor to be so small that we can fit so many of them, you can read more about it here https://www.researchgate.net/publication/3138768_Design_fabrication_and_test_of_CMOS_active-pixel_radiation_sensors
It seems super impressive that we are able to fabricate this sensor to be so small that we can fit so many of them, you can read more about it here https://www.researchgate.net/publication/3138768_Design_fabrication_and_test_of_CMOS_active-pixel_radiation_sensors