Speaker
Description
We have been developing the X-ray SOI (Silicon-On-Insulator) pixel sensor named XRPIX for the future astronomical satellite FORCE. XRPIX is a monolithic active pixel sensor composed of high-resistivity Si sensor, thin SiO2 insulator and CMOS pixel circuits by utilizing the SOI technology. Since XRPIX is capable of event-driven readout, it can achieve a high timing resolution better than ∼10 μs, which enables a low background observation by adopting the anti-coincidence technique.
XRPIX onboard the FORCE satellite will be put into the low earth orbit, and will suffer from the radiation effects mainly due to the geomagnetically trapped cosmic-ray protons. From the previous studies of the radiation effects in the SOI pixel detectors, positive charges trapped in the thin oxide layer have a large impact on the detector performance. To improve the radiation hardness of the SOI pixel detectors, we introduced a double-SOI structure, where an additional middle Si layer was added in the oxide layer. The negative potential applied on the middle Si layer compensates the radiation effect due to the trapped positive charges. Although the radiation hardness of the double-SOI detectors for application at high energy accelerators was evaluated, radiation effects on the X-ray imaging spectroscopic performances in the double-SOI detectors was not yet evaluated. In order to evaluate the radiation effects of the X-ray double-SOI detectors, we carry out an irradiation experiment with 6 MeV proton beam with a total dose of ~5 krad, corresponding to a few tens of in-orbit operation. This experiment reveals that the radiation hardness is improved in the X-ray double-SOI detectors. The energy resolution in full-width half maximum for 5.9 keV X-ray is increased by 7±2% with 5 krad irradiation. In this presentation, we present results of the proton irradiation experiment of the X-ray double-SOI detectors, and discuss the possible mechanisms of the degradation of the energy resolution.
| Submission declaration | Original and unpublished |
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