The Soft X-ray Imager ( SXI ) is an imaging spectrometer using charge-coupled devices ( CCDs ) aboard the Hitomi X-ray observatory .
The SXI sensor has four CCDs with an imaging area size of 31 ~ { } { mm } \times 31 ~ { } { mm } arranged in a 2 \times 2 array .
Combined with the X-ray mirror , the Soft X-ray Telescope , the SXI detects X-rays between 0.4 ~ { } { keV } and 12 ~ { } { keV } and covers a 38 ^ { \prime } \times 38 ^ { \prime } field-of-view .
The CCDs are P-channel fully-depleted , back-illumination type with a depletion layer thickness of 200 ~ { } \mu { m } .
Low operation temperature down to -120 ~ { } ^ { \circ } { C } as well as charge injection is employed to reduce the charge transfer inefficiency of the CCDs .
The functionality and performance of the SXI are verified in on-ground tests .
The energy resolution measured is 161 – 170 ~ { } { eV } in full width at half maximum for 5.9 keV X-rays .
In the tests , we found that the CTI of some regions are significantly higher .
A method is developed to properly treat the position-dependent CTI .
Another problem we found is pinholes in the Al coating on the incident surface of the CCDs for optical light blocking .
The Al thickness of the contamination blocking filter is increased in order to sufficiently block optical light .