Development of the focal-plane CMOS detector for the GEO-X mission

We report a development status of a focal plane detector for the GEO-X (GEOspace X-ray imager) mission that will perform soft X-ray (≤2 keV) imaging spectroscopy of Earth’s magnetosphere from a micro satellite. The mission instrument consists of a microelectromechanical systems (MEMS) X-ray mirror and a focal plane detector. A sensor with fine positional resolution and moderate energy resolution in the energy band of 0.3 to 2 keV is required. Because the observing target is the magnetosphere around the day-side Earth, the visible-light background must be decreased by shortening the integration time for readout. To satisfy the above requirements, a high-speed X-ray CMOS sensor is being evaluated as a primary candidate for the detector. Irradiating the flight candidate sensor with monochromatic X-rays, we obtained the energy resolution of 205 eV (FWHM) at 6 keV by cooling the devices to −15°C. Radiation tolerance of the sensor, especially in terms of total dose effect, is investigated with 100 MeV proton. The amount of degradation of energy resolution is <50 eV up to 10 krad, which ensures that we will be able to track and calibrate the change of the line width in orbit.