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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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development of ccds for the sxi
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

=>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.

*Advantage

=>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.

*Disadvantage

=>They have never been employed onboard detectors.

=>The performance for X-rays are hardly investigated.

background of developing ccds with thick depletion layer
Background of developing CCDs with thick depletion layer

* 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 of test device

4.8 mm

Specification of test device

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)

Schematic

of cross section

Depletion layer : 200 mm

electrode

Fully depleted CCD

basic performance

Mn ka

5.9 keV

Mn kb

6.5 keV

counts

escape

X-ray events

Pulse height [ADU]

Basic performance

Operation temp -70oC

Readout speed 60 kHz

Spectrum of 55Fe

X-ray image

1 pixel size is 14.5 x 15 um

n-type CCD

Energy resolution 143 ± 3 eV

Readout noise 7 electrons

p-type CCD

135 eV

5 electrons

Basic performance was comparable to that of p-type CCD

responsivity for soft x ray
Responsivity for soft X-ray

spectrum of oxygen K line

We investigated the responsivity for soft X-ray by using

Oxygen K line : 527 eV

Energy resolution

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

527 eV

counts

Pulse height [ADU]

This CCD have good responsivities for soft X-ray down to 0.5 keV.

thickness of the depletion layer

22.4 keV

24.9 keV

counts

Pulse height [ADU]

Thickness of the depletion layer

Detection efficiency based on

http://www-cxro.lbl.gov/optical_constants/

We measured the thickness of depletion layer from the detection efficiency.

Solid line : 172 mm

Dotted line : 70 mm

Spectrum of 109Cd

Detection efficiency

Energy [keV]

Thickness of the depletion layer

172 ± 13 mm

Energy resolution 574 eV at 22.4 keV.

future plan
Future plan

To improve the efficiency below 0.5 keV,

We have developed the BI (Back illuminated) CCDs.

We will evaluate the performance of this device.

Schematic

of cross-section

Large imaging area (3 x 6 cm)

Photograph of engineering model

BI

Depletion layer

electrode

FI

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