Development of an n-channel CCD, CCD-NeXT1, for Soft X-ray Imager onboard the NeXT satellite
Abstract
NeXT (New X-ray Telescope) is the next Japanese X-ray astronomical satellite mission after the Suzaku satellite. NeXT aims to perform wide band imaging spectroscopy. Due to the successful development of a multilayer coated mirror, called a supermirror, NeXT can focus X-rays in the energy range from 0.1 up to 80 keV. To cover this wide energy range, we are in the process of developing a hybrid X-ray camera, Wideband X-ray Imager (WXI) as a focal plane detector of the supermirror. The WXI consists of X-ray CCDs (SXI) and CdTe pixelized detectors (HXI), which cover the lower and higher X-ray energy bands of 0.1 80 keV, respectively. The X-ray CCDs of the SXI are stacked above the CdTe pixelized detectors of the HXI. The X-ray CCDs of the SXI detect soft X-rays below ∼10keV and allow hard X-rays pass into the CdTe detectors of the HXI without loss. Thus, we have been developing a “back-supportless CCD” with a thick depletion layer, a thinned silicon wafer, and a back-supportless structure. In this paper, we report the development and performances of an evaluation model of CCD for the SXI, “CCD-NeXT1”. We successfully fabricated two types of CCD-NeXT1, unthinned CCDs with 625-μm thick wafer and 150-μm thick thinned CCDs. By omitting the polishing process when making the thinned CCDs, we confirmed that the polishing process does not impact the X-ray performance. In addition, we did not find significant differences in the X-ray performance between the two types of CCDs. The energy resolution and readout noise are ∼140eV (FWHM) at 5.9 keV and ∼5 electrons (RMS), respectively. The estimated thickness of the depletion layer is ∼80μm. The performances almost satisfy the requirements of the baseline plan of the SXI.
- Publication:
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Nuclear Instruments and Methods in Physics Research A
- Pub Date:
- November 2007
- DOI:
- 10.1016/j.nima.2007.08.158
- arXiv:
- arXiv:0710.0785
- Bibcode:
- 2007NIMPA.582..546T
- Keywords:
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- Astrophysics
- E-Print:
- 20 pages, 10 figures, Accepted for publication in NIMA