Speaker
Description
Current X-ray astronomical satellites carry CCD cameras that have moderate performance in imaging, spectroscopy and timing. Future X-ray telescopes with large effective areas and sharp point spread functions require quick readout of focal plane sensors to realize imaging spectroscopy without photon pile-up nor intermittency of its exposure time. To fulfill the requirements, we are developing a hybrid sensor of CCD and CMOS. The former has readout nodes for every column, and the latter equips corresponding columnar analog-to-digital converters. Both parts are implemented in the same package. Vertical transfer frequency of 100~kHz enables us to readout the whole frame within 10ms even with 1k-by-1k pixel format. Our first test device with pixel format of 128 x 1024 and pixel size of 11 um square has been cooled down to -23$^{\circ}$C and evaluated with monochromatic X-rays from $^{109}$Cd. X-ray events are successfully detected, and the energy resolution is 966eV (full width at half maximum) at 22 keV for the events whose signal charges are concentrated in a single pixel. This performance compares favorably with a conventional CCD with a thick depletion layer (750eV FWHM at 22keV @ -70$^{\circ}$C). On the other hand, approximately 30% of charges are lost for the multi-pixel events, which is probably due to a drain structure in every pixel for the case of charge saturation and can be omitted in the next fabrication.
