Development of CCDs for the SXI. We have developed 2 different types of CCDs for the SXI in parallel. . *Advantage =>They are successfully employed for current satellites. *Disadvantage =>The maximum thickness of the depletion layer is 100 m m.
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We have developed 2 different types of CCDs for the SXI in parallel.
=>They are successfully employed for current satellites.
=>Themaximum thickness of the depletion layer is 100 mm
1, P-type CCDs, fabricated on p-type Si wafer.
2, N-type CCDs, fabricated on n-type Si wafer.
=>mobility of major carrier is 3 times larger
=>higher resistivity of silicon wafer
N-type CCDs have 2-3 times thicker depletion layer than p-type.
=>They have never been employed onboard detectors.
=>The performance for X-rays are hardly investigated.
* L. Strüder et al. developed pn-CCDs with 300 mm thickness of the depletion layer, and it had already employed for XMM-Newton
* Steven Holland et al. fabricated MOS CCDs with high resistivity n-type Si wafer and successfully obtained a 300 mm thick depletion layer.
Development of the n-type MOS CCDs is under way with a collaboration of Osaka U., Kyoto U.,
NAOJ (National Astronomical Observatory of Japan)
and HPK (Hamamatsu Photonics K.K.).
Specification (design value)
Pixel size 14.5 mm x 15 mm
Format 328 x 320
Wafer thickness 200 mm
Depletion layer 200 mm
Illuminated method FI (Front illuminated)
of cross section
Depletion layer : 200 mm
Fully depleted CCD
Pulse height [ADU]Basic performance
Operation temp -70oC
Readout speed 60 kHz
Spectrum of 55Fe
1 pixel size is 14.5 x 15 um
Energy resolution 143 ± 3 eV
Readout noise 7 electrons
Basic performance was comparable to that of p-type CCD
spectrum of oxygen K line
We investigated the responsivity for soft X-ray by using
Oxygen K line : 527 eV
FWHM = 81 ± 1 eV
We confirmed that this CCD completely collects the signal charges
Because this peak has no low energy tail.
Oxygen K line
Pulse height [ADU]
This CCD have good responsivities for soft X-ray down to 0.5 keV.
Pulse height [ADU]Thickness of the depletion layer
Detection efficiency based on
We measured the thickness of depletion layer from the detection efficiency.
Solid line : 172 mm
Dotted line : 70 mm
Spectrum of 109Cd
Thickness of the depletion layer
172 ± 13 mm
Energy resolution 574 eV at 22.4 keV.
To improve the efficiency below 0.5 keV,
We have developed the BI (Back illuminated) CCDs.
We will evaluate the performance of this device.
Large imaging area (3 x 6 cm)
Photograph of engineering model