Optical Blocking Performance of Ccds Developed for the X-Ray

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arXiv:2007.07608v2 [astro-ph.IM] 16 Jul 2020 iouiUchida Hiroyuki einadta h RS Csstsytemsinrequireme mission Keywords: the satisfy CCDs XRISM the that and design rpitsbitdt ora fL of Journal to submitted Preprint Uchida) (Hiroyuki apeCDadirdaei ihotcllgtt vlaeth evaluate backs to the light e on optical are layer with it aluminum irradiate extra and an CCD sample added data also Hitomi observat in and (ASTRO-H) recognized CCDs problems Hitomi XRISM largest design lost the basic of the one the of is While that that as 2021. same in the launched almost be ( to Devices planned Charge-Coupled XRISM, P-channel developing been have We Abstract h ioh Tomida Hiroshi Hayashida olg fSineadEgneig at aunUniversit Gakuin Kanto Engineering, and Science of College htr Sakuma Shotaro Yamauchi q ∗ eateto pc n srnuia cec,Sho fPh of School Science, Astronautical and Space of Department p pia lcigPromneo CsDvlpdfrteX-ra the for Developed CCDs of Performance Blocking Optical Uchiyama aaoh Kohmura Takayoshi mi address: Email author Corresponding aa eopc xlrto gny nttt fSaeand Space of Institute Agency, Exploration Aerospace Japan g ff aa eopc xlrto gny nttt fSaeand Space of Institute Agency, Exploration Aerospace Japan f rjc eerhCne o udmna cecs sk Un Osaka Sciences, Fundamental for Center Research Project cieyrdcdcmae ihta fteHtm Cs eth We CCDs. Hitomi the of that with compared reduced ectively d e eateto hsc,Fclyo cec,Nr oe’ Uni Women’s Nara Science, of Faculty Physics, of Department eateto at n pc cec,OaaUiest,1- University, Osaka Science, Space and Earth of Department e,f c -a eetr,Cag-ope eie XRISM device, Charge-coupled detectors, X-ray sm Hatsukade Isamu , n j n iooiMatsumoto Hironori , aut fLbrlAt,Thk aunUiest,211Te 2-1-1 University, Gakuin Tohoku Arts, Liberal of Faculty cec dcto,Fclyo dcto,Siuk Univers Shizuoka Education, of Faculty Education, Science auaaYamaoka Kazutaka , a k eateto hsc,KooUiest,KtsiaaaOi Kitashirakawa University, Kyoto Physics, of Department c [email protected] eateto hsc,TkoUiest fSine -,Ka 1-3, Science, of University Tokyo Physics, of Department g a, aut fEgneig nvriyo iaai - Gakuen 1-1 Miyazaki, of University Engineering, of Faculty ohaiKanemaru Yoshiaki , ∗ b e i o l aak Tanaka Takaaki , m eateto hsc,TkoUiest fSine 61Ya 2641 Science, of University Tokyo Physics, of Department eateto hsc,Kna nvriy -- oaa,H Kowakae, 3-4-1 University, Kindai Physics, of Department eg Hattori Kengo , aut fEuain aaUiest fEuain Takaba Education, of University Nara Education, of Faculty eateto hsc,Ngy nvriy uoco Chiku Furo-cho, University, Nagoya Physics, of Department eateto hsc,KasiGki nvriy - Gaku 2-2 University, Gakuin Kwansei Physics, of Department hnihr Takagi Shin-ichiro i oih Hagino Kouichi , r A aaas htnc .. 161 cioco Hamamatsu, Ichino-cho, 1126-1, K.K., Photonics Hamamatsu T E Templates X -- ohn-a,CuuK,Sgmhr,Kngw 252-52 Kanagawa Sagamihara, Chuou-Ku, Yoshino-dai, 3-1-1 c aah Sako Takashi , e o ym Ishikura Ayami , e,f a aaouOzaki Masanobu , uiAmano Yuki , aoHanaoka Maho , c i Sato Jin , i r ioh Murakami Hiroshi , eih Sugimoto Kenichi , aelt XRISM Satellite l aaoh Nobukawa Masayoshi , c ohyk Takaki Toshiyuki , ,15- usuaiah,Knzw-u ooaa Kanaga Yokohama, Kanazawa-ku, Mutsuurahigashi, 1-50-1 y, a ioih Okon Hiromichi , 5-20 Japan 252-5210, e sclSine,SKNA TeGaut nvriyfrAdv for University Graduate (The SOKENDAI Sciences, ysical srnuia cec,311Ysiodi hok,Sagam Chuo-ku, Yoshino-dai, 3-1-1 Science, Astronautical ioh Nakajima Hiroshi , e srnuia cec,211 egn skb,Iaai30 Ibaraki Tsukuba, Sengen, 2-1-1, Science, Astronautical p ooaeYoneyama Tomokage , aaauDotani Tadayasu , vriy - ahknym-h,Tynk,Oaa560-004 Osaka Toyonaka, Machikaneyama-cho, 1-1 iversity, pia lcigpromne sarsl,lgtleakages light result, a As performance. blocking optical e eaotdadul-ae pia lciglyro the on layer blocking optical double-layer a adopted We . ahknym-h,Tynk,Oaa5004,Japan 560-0043, Osaka Toyonaka, Machikaneyama-cho, 1 est,Ktuynsimci aa aa6080,Japan 630-8506, Nara Nara, Kitauoyanishi-machi, versity, jnaa zm-u edi iai9139,Japan 981-3193, Miyagi Sendai, Izumi-ku, njinzawa, o omlg n srpyis(SA,tefourth the (ASCA), Astrophysics Satellite and Advanced the Cosmology as- on for X-ray use of first field their the since tronomy, in spectrometers imaging as used Introduction 1. t,86Oy,Srg-u hzoa4282,Japan 422-8529, Shizuoka Suruga-ku, Ohya, 836 ity, r j hg .Kobayashi B. Shogo , h Atsumi Sho , aeco ay,Koo yt 0-52 Japan 606-8502, Kyoto Kyoto, Sakyo, wake-cho, hreCuldDvcs(Cs aebe widely been have (CCDs) Devices Charge-Coupled tfrteSXI. the for nt Cs o h poigXryAtooySatellite Astronomy X-ray upcoming the for CCDs) uaaa ijk-u oy 6-85 Japan 162-0825, Tokyo Sinjuku-ku, gurazaka, r,w r lnigt euete“ih leakages” “light the reduce to planning are we ory, iaaa ih,Myzk 8-12 Japan 889-2192, Miyazaki Nishi, Kibanadai aeco aa aa6082,Japan 630-8528, Nara Nara, take-cho, fteCDcmr Sf -a mgr X)is SXI) Imager: X-ray (Soft camera CCD the of ak,Ngy,Aci4480,Japan 464-8602, Aichi Nagoya, sa-ku, aai oa hb 7-50 Japan 270-8510, Chiba Noda, mazaki, gsiOaa sk 7-52 Japan 577-8502, Osaka igashi-Osaka, c uaTerada Yuta , a d fte.W eeo el eindtest designed newly a develop We them. of ide n ad,Hoo6913,Japan 669-1337, Hyogo Sanda, en, aeh .Tsuru G. Takeshi , scnld htteisei ovdb h new the by solved is issue the that conclude us l uioUrabe Yukino , h aioSaito Mariko , p,q r ioh Tsunemi Hiroshi , uiaTanaka Fumiya , 3-58 Japan 435-8558, e oiOkazaki Koki , 0 Japan 10, c oiMori Koji , k uueNishioka Yusuke , m d uk .Hiraga S. Junko , a uioK Nobukawa K. Kumiko , iouiNoda Hirofumi , r e e c auoiAsakura Kazunori , iaoiSuzuki Hisanori , Astronomy y iaiKashimura Hikari , hr,Kanagawa ihara, a2680,Japan 236-8501, wa -55 Japan 5-8505, ne Studies), anced c Makoto , ,Japan 3, m e,f uy1,2020 17, July Hideki , Kiyoshi , r d,b , e h , , , Japanese X-ray observatory launched in 1993. Because CCDs are sensitive to visible and ultra-violet light as well, it is required to block such out-of-band light that may increase the background noise level. For this rea- son, past X-ray satellite missions installed an optical- blocking filter in front of sensors (e.g., XMM-Newton [1]; Suzaku [2]). The recent Japanese satellite Hitomi launched in 2016 (formally known as ASTRO-H [3]) introduced an optical blocking layer (OBL) directly deposited on CCDs. Although the OBL makes the camera system simple and future missions such as Athena [4] are planning to adopt a similar design, the Hitomi OBL suffered of light leakages [5]. Figure 1: LED-irradiated images with Hitomi (left) and XRISM We have been developing P-channel CCDs for the CCDs (right), which use the same color scale. The bright region indicates light leakages. Note that most of the white dots seen in the next Japanese X-ray observatory, X-Ray Imaging and XRISM CCD image are of X-ray events from a calibration source Spectroscopy Mission (XRISM [6]), planned to be 55Fe. The number of pinholes is given in the text. launched in the Japanese fiscal year 2021. The CCD camera system, soft X-ray imager (SXI1 [7]) aboard XRISM is required to reduce light leakages. We there- the CCDs. The instrument was, however, suffering from fore changed the design of the OBL as described in the significant light leakages. The phenomenon was ob- following section. served only during a specific time when the back side This paper is structured as follows. Section 2 de- of the satellite was toward the day earth (MZDYE [5]). scribes light leakages found in the Hitomi data and de- The main light path is presumed to be holes provided sign modifications of the SXI aboard XRISM in terms for other instruments in the base panel of the space- of the optical blocking performance. In Section 3, we craft, which indicates that the origin of light leakages explain the performance of a sample CCD, the design is the Earth’s albedo i.e., reflection of the sunlight from of which is the same as that of the flight model (FM) of the Earth. The obtained false signals are categorized the SXI. The obtained results are discussed in Section 4 into two types according to their event positions: point- and the optical blocking performance of FM CCDs is like events (pinholes) scattered across the imaging area also summarized in Section 5. The errors quoted in the and end-surface leakage seen only near the edges of the text and error bars displayed in the figures represent a chips. The left panel of figure 1 reproducesthe MZDYE 1-σ confidence level. light leakagesby a groundtest with a FM spare CCD for Hitomi.

2. Description of XRISM SXI CCDs in Terms ofOp- 2.2. Improvement for XRISM tical Blocking Performance While XRISM is designedto close the holes that were While the basic design of the XRISM SXI is almost the main cause of the problem, we further introduced the same as that of Hitomi, we are planning to improve a fail-safe design so that the CCD instrument itself can several critical points related to light leakages. Since a minimize the effect of light leakages. We took measures detailed device description of the CCD is presented by ensuring that additional design changes can resolve the (Hayashida et al. [7] and Kanemaru et al. submitted above two problems. Below we summarize the causes to NIMA), here we focus on its optical blocking perfor- of each type of light leakages and detailed design mod- mance. ifications of the XRISM SXI CCDs. Figure 2 indicates a schematic view of the new design for a XRISM CCD 2.1. Light Leakages Found in Hitomi Data in comparison to that of Hitomi. In the case of the CCD instrument aboard Hitomi 2.2.1. Pinholes (similarly named as SXI [8]), an aluminum optical The origin of “pinholes” is voids generated in the blocking layer (OBL) was deposited on the surface of aluminum OBL deposited on the Hitomi CCDs with a thickness of 100 nm. According to a Transmission Elec- 1The SXI and the X-ray Mirror Assembly (XMA) are collectively tron Microscope image of the OBL, the typical size of called Xtend. these voids is ∼1 µm, which is much smaller than the 2 pixel size of the CCD (24 µm × 24 µm). When visible light passing through the voids is scattered in the silicon dioxide layer between the OBL and silicon substrate, false signals are generated as a single- or multi-pixel event at each position under the pinholes and its sur- roundings (within 3×3 pixels at a maximum). A similar phenomenon is reported on a ground-base test of CCDs for Origins, Spectral Interpretation, Resource Identifica- tion, Security, Regolith Explorer (OSIRIS-REx [9, 10]). Figure 2: Schematic side views of the Hitomi (left) and XRISM (right) They indicate that it is possibly due to particles or sur- CCDs (not to scale). Expected light paths are drawn as the red arrows. face irregularities of the silicon substrate under the aluminum layer. backside leakage. To block the entering light, we addi- In our case, the main cause of the voids is consid- tionally formed an aluminum filter on the backside elec- ered to be a deterioration of the OBL due to a resist trode (under the passivation) layer of the XRISM CCDs stripper used before aluminum vapor deposition. A with a width of 2 mm from the edge of the silicon sub- follow-up test revealed that changing the type of the re- strate. The width of the filter is enough longer than the sist stripper can significantly reduce the number of pin- attenuation length of the scattered light, and because its holes. However, even with this change a slight increase parasitic capacitance is small enough to ignore, it does of the number of pinholes over year was observed. We not affect the charge transfer performance of the CCDs therefore introduced a double-layer aluminum deposi- as well. tion with a thickness of 100 + 100 nm, so as to de- crease the probability of pinhole formation on the OBL 3. Performance Test (figure 2). Although a reduced quantum efficiency in the soft X-ray band is a trade-off, we confirmed that it We evaluate an optical blocking performance of the still satisfies the requirement of XRISM SXI. Note that new CCD with a test sample that has the same design as the double-layer design has also been applied for the the FM for XRISM. The CCD was cooled to −100 ◦C light filter of a PNCCD detector aboard extended Roent- and illuminated with a monochromatic light using a gen survey with an imaging telescope array (eROSITA light emitting diode (LED). The wavelength was set to [11, 12, 13, 14]) launched in July 2019, and no impact ∼ 568 nm, which is near the peak wavelength of the on in-orbit data has been reported. sunlight. Note that in this experiment we also simulta- neously irradiated the CCD with X-rays from an 55Fe 2.2.2. End-surface Leakage source for the purpose of calibration. The “end-surface leakage” is another problem that The right panel of Figure 1 shows a CCD image un- we found in the Hitomi data. Significant light leak- der the illumination of the above LED obtained with the ages were seen near the field of view of the SXI dur- test sample. The LED flash duration was 0.1 s for a sin- ing MZDYE, which seems similar to that reported by gle frame. For comparison, we also display an image Tsunemi et al. [15] in day-time data of MAXI/SSC. obtained with a Hitomi FM spare CCD under the same They speculate that the light entered through the edge condition in the left panel. It has a large number of pin- of the MAXI CCD, whereas in our case the bound- holes and also the end-surface leakage with an irregu- ary around the imaging area of the Hitomi CCD has a lar pattern originating from wrinkles of the die bond- dummy pixel region with a width of 250 µm, that is ing sheet. These features are the same as those taken larger than the attenuation length of visible light from with Hitomi, indicating that our ground test reproduces the Sun. We thus conclude that the Hitomi CCD has an- the in-orbit light environment. The XRISM CCD im- other light path and that a sidewall coating of a silicon age shows, on the other hand, a significant reduce both layer (e.g., [10]) is less effective for our case. of the number of pinholes and the end-surface leakage As shown in figure 2, the lateral structure of the SXI region. The results demonstrate a substantial improve- hints at the true origin of the end-surface leakage. In ment of the optical blocking performance. the design of the Hitomi CCD, a transparent die bond- ing sheet was used to adhere the silicon substrate and 4. Analysis and Results a silicon base. It was possible for the light scattered in the sheet to enter the imaging area. Similar cases are To give a quantitative evaluation of the optical block- reported by (Bautz et al. [16] and Ryu et al. [10]) as ing performance of the XRISM CCD, here we define a 3 Figure 3: Increase of pulse height amplitude caused by light leakages. Left: The green open circles correspond to values for pinhole pixels, whereas the filled circles show a result of a normal region. The dotted lines correspond to different transmission factor TX,Y according to equation (5). Right: Same as the left panel, but results of the end-surface leakage are shown. The green squares and diamonds indicate values obtained at the outermost edge (PH324,1−200) and 3 pixel inward (PH322,1−200), respectively

transmission factor (optical transmission) TX,Y at a pixel as position (X, Y) as × −3 · · 2 ΦOBL = 1.46 10 EOBL pbpx = 3.36 × 10−12 W TX,Y = EX,Y/EOBL, (1) QOBL =ΦOBL · t (3) = 3.36 × 10−13 J where E and E are the illuminance of light col- X,Y OBL × 6 lected by the pixel and that at the OBL surface. = 2.10 10 eV,

Given the luminous intensity of the LED ILED is where pbpx = 48 µm and t = 0.1 s are the size of a 10 mcd from a speciﬁcation sheet, we can estimate the binned pixel and the duration time of the LED illumina- value of EOBL as follows: tion, respectively. Thus, the expected increase of a pulse height amplitude PHX,Y (hereafter, “light leakages”) in − analog-to-digital unit (ADU) can be represented as a I d 2 f ≈ × LED util function of the photon energy ελ (eV) at a wavelength EOBL 1 lx, (2) − 10 mcd 0.1m! 1 ! of λ (nm) and the CCD gain g (e /ADU):

−1 PHX,Y = PH0 + (TX,Y · QOBL/ελ) · g ADU where d and f are the distance from the LED to the (4) util · · · −1 CCD and the so-called utilization factor, respectively. = PH0 + (TX,Y ΦOBL t/ελ) g ADU, While an accurate value of futil depends on the room in- where PH0 is an offset due to fluctuations of the dark dex and reflectance of the camera chamber, we approx- level between the LED-on and -off data: a few ADU in imately set futil ≈ 1. Since the reflectance of inner walls our experiment. The photon energy is fixed at ελ=568 = of the aluminum chamber is roughly close to 90%, our 2.2 eV and the gain g ∼ 1.67 e−/ADU. calculation may be an underestimation on EOBL. Also, Consequently, if the 0.1-s illumination results in an the LED has a slight directivity, which may give a larger increase of PHX,Y, the transmission factor can be calcu- EOBL. These factors result in that the following evalu- lated as ation of TX,Y is given under the most strict condition; −1 smaller TX,Y in reality would be expected than the cal- −6 t TX,Y = 1.8 × 10 · (PHX,Y − PH0) · . (5) culation below. 0.1 s Since 1 lx at ∼ 560 nm corresponds to 1.46 × From equation (5), if an increase of ∼ 1000 ch is caused −3 2 10 W/m , the radiant flux ΦOBL and the integrated by a 1-s illumination at (X, Y), the pixel has a transmis- −4 luminous energy QOBL absorbed per pixel are estimated sion factor TX,Y ∼ 1.8 × 10 . 4 Figure 4: Left: Pulse height profiles near the edge of the test sample for XRISM (green) and that of a spare CCD for Hitomi (cyan). The results assuming the in-orbit environment are drawn as the dotted lines with the same colors. The result of Hitomi taken during MZDYE is plotted as the black line. The mission requirement for the XRISM SXI is drawn as the red dotted line. Right: Same as the left panel but for the XRISM FM CCDs. The results of the selected four and the others are drawn in the solid and dotted lines, respectively.

4.1. Pinholes inward from the edge. The right panel of figure 3 in- From mission requirements for the XRISM SXI, the dicates the average values of light leakages measured number of pinhole pixels should be reduced less than at the outermost edge (PH324,1−200) and that at 3 pix- 1.8% of all. The definition of the “pinhole pixels” given els inward (PH322,1−200). Although the illuminance at by the XRISM team is those whose transmission factor the end-surfacepixel should be somewhat different from −4 is TX,Y < 1 × 10 . For instance, from equation (5), EOBL, it can still be concluded that almost all inward an equivalent threshold with the definition is PHX,Y ∼ pixels (Y ≤ 322) are well below the threshold. 600 ch for a 1-s illumination. The left panel of figure 4 shows comparison between To measure TX,Y for each pixel in the test sample a profile of average PHX,1−200 near the edge of the test CCD, we irradiated it with the LED light for various sample and that of the Hitomi FM spare CCD. The end- durations (0, 0.1, and 1 s). Increases of PHX,Y at each surface leakage at the outermost column is measured to pixel were measured by subtracting the average pulse be PH324,1−200 = 100 and 1231 ADU for XRISM and heightfrom LED-on data (t = 0.1, 1s)tothatofLEDoff Hitomi, respectively. The result indicates a significant (t = 0 s). In the left panel of figure 3, we plot obtained improvement on the end-surface leakage roughly by an values of light leakages at several example pinhole pix- order of magnitude with the new design. els and that of the surroundingnormalregion. The result In the same figure, we also plot the result of Hitomi indicates that the pinhole pixels significantly exceed the taken during MZDYE, in which the value of light leak- −4 threshold transmission TX,Y = 1 × 10 , whereas the ages is PH324,1−200 = 373 ADU at the edge. Given that normal region entirely satisfies the requirement. the Hitomi FM and its spare CCDs have the same op- The number ratio of the pinhole pixels npinhole is 0.2% tical blocking performance, the result implies that our (60/25, 000 pixels) in the analyzed area. Since pinhole ground test is in more luminous environment than Hit- affected pixels tend to cluster within a few pixels, the omi in orbit, although the configuration (i.e., futil) of real number of pinholes would be less than 0.1%. In the camera chamber is different between the ground test the same way we calculated npinhole of the Hitomi FM system and the Hitomi SXI. If this is the case, the end- CCD as4.1%(1, 027/25, 000pixels). We therefore con- surface leakage of the XRISM CCD is almost ignorable clude that light leakages originated from pinholes were even at the outermost edge (the dotted line in figure 4). addressed by the double-layer OBL. 5. Optical Blocking Performance of FM CCDs 4.2. End-surface Leakage It is requested for the XRISM mission to suppress the Since we confirmed that the new design is effec- −4 end-surface leakage up to TX,Y = 1 × 10 at 3 pixels tive for suppression of both types of light leakages, we 5 JP20H01947 (H.N.), JP16H03983 (K.M.), JP18H01256 Table 1: Ratio of pinholes in twelve FM CCDs for XRISM. (H.N.), and JP17K14289 (M.N.).

Numbering RatioofPinholes SXIName References segmentAB segment CD FM02-01 0.06% 0.04% — [1] Turner, M. J. L., Abbey, A., Arnaud, M., Balasini, M., et al., The european photon imaging camera on xmm-newton: The FM02-02 0.03% 0.04% CCD2 mos cameras, A&A 365 (1) (2001) L27–L35. FM02-03 0.05% 0.03% — [2] K. Koyama, H. Tsunemi, T. Dotani, M. W. Bautz, et al., X-Ray FM02-05 0.27% 0.17% — Imaging Spectrometer (XIS) on Board Suzaku, Publications of FM02-06 0.17% 0.30% — the Astronomical Society of Japan 59 (sp1) (2007) S23–S33. [3] T. Takahashi, M. Kokubun, K. Mitsuda, R. L. Kelley, et al., Hit- FM02-07 0.21% 0.16% — omi (ASTRO-H) X-ray Astronomy Satellite, Journal of Astro- FM02-08 0.21% 0.28% — nomical Telescopes, Instruments, and Systems 4 (2018) 021402. FM02-09 0.05% 0.03% CCD3 [4] M. Barbera, G. Branduardi-Raymont, A. Collura, A. Comas- FM02-10 0.06% 0.04% CCD1 tri, et al., The optical blocking filter for the ATHENA wide field imager: ongoing activities towards the conceptual design, FM02-11 0.06% 0.04% — Vol. 9601 of Society of Photo-Optical Instrumentation Engi- FM02-12 0.02% 0.03% — neers (SPIE) Conference Series, 2015, p. 960109. FM02-13 0.02% 0.03% CCD4 [5] H. Nakajima, Y. Maeda, H. Uchida, T. Tanaka, et al., In-orbit performance of the soft X-ray imaging system aboard Hitomi (ASTRO-H), PASJ 70 (2) (2018) 21. [6] M. Tashiro, H. Maejima, K. Toda, R. Kelley, et al., Concept of the X-ray Astronomy Recovery Mission, Vol. 10699 of Society evaluated the optical blocking performance of twelve of Photo-Optical Instrumentation Engineers (SPIE) Conference FM CCDs in a screening test. In the following anal- Series, 2018, p. 1069922. ysis, we estimated in-orbit values of light leakages by [7] K. Hayashida, H. Tomida, K. Mori, H. Nakajima, et al., Soft x-ray imaging telescope (Xtend) onboard X-ray Astronomy correcting an expected illuminance based on compari- Recovery Mission (XARM), Vol. 10699 of Society of Photo- son of the end-surface leakage at the outermost column Optical Instrumentation Engineers (SPIE) Conference Series, PH324,1−200 between the screening test and the Hitomi 2018, p. 1069923. MZDYE. [8] T. Tanaka, H. Uchida, H. Nakajima, H. Tsunemi, et al., Soft X- ray Imager aboard Hitomi (ASTRO-H), Journal of Astronomical The results for the pinholes and the end-surface leak- Telescopes, Instruments, and Systems 4 (1) (2018) 1 – 15. age are summarized in table 1 and in the right panel of [9] K. K. Ryu, B. E. Burke, H. R. Clark, et al., Development of figure 4, respectively. The ratios of pinholes for each CCDs for REXIS on OSIRIS-REx, in: Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray, Vol. 9144, CCD show that all the CCDs except several segments International Society for Optics and Photonics, SPIE, 2014, pp. satisfy the requirement, which will remain unchanged 1431 – 1438. by the end of life of XRISM, even taking into account a [10] K. K. Ryu, M. W. Bautz, S. E. Kissel, P. O’Brien, V. Sunthar- possible increase of the pinholes. As shown in figure 4, alingam, Journal of Astronomical Telescopes, Instruments, and Systems 3 (3) (2017) 1 – 7. we also confirmed that all the pulse height profiles of [11] N. Meidinger, R. Andritschke, J. Elbs, S. Granato, et al., Status the FM CCDs are below the given threshold. The plot of the CCD camera for the eROSITA space telescope, in: UV, indicates that the end-surface leakage as well satisfies X-Ray, and Gamma-Ray Space Instrumentation for Astronomy the requirement. XVII, Vol. 8145, International Society for Optics and Photonics, SPIE, 2011, pp. 33 – 44. We thus conclude that the issues of light leakages [12] N. Meidinger, R. Andritschke, F. Aschauer, J. Elbs, et al., De- found in the Hitomi data are totally solved by changing sign and performance of the eROSITA focal plane instrumenta- the optical blocking design and that the XRISM CCDs tion, in: High Energy, Optical, and Infrared Detectors for As- tronomy V, Vol. 8453, International Society for Optics and Pho- enough meet the mission requirement for the SXI. From tonics, SPIE, 2012, pp. 191 – 201. these results, we selected best four CCDs to be in- [13] S. Granato, The response of silicon pnccd sen- stalled in the SXI, also based on several criteria such sors with aluminium on-chip filter to visi- as the energy resolution and charge transfer efficiency ble light, uv- and x-ray radiation, Available at http://inis.iaea.org/search/search.aspx?orig q=RN:44052575. (Yoneyama et al. submitted to NIMA). [14] S. Granato, R. Andritschke, J. Elbs, N. Meidinger, et al., Charac- terization of erosita pnccds, IEEE Transactions on Nuclear Sci- ence 60 (4) (2013) 3150–3157. Acknowledgements [15] H. Tsunemi, H. Tomida, H. Katayama, et al., In-Orbit Perfor- mance of the MAXI/SSC onboard the ISS, Publications of the Astronomical Society of Japan 62 (6) (2010) 1371–1379. This work is supported by JSPS KAKENHI Grand [16] M. Bautz, S. Kissel, R. Masterson, K. Ryu, V. Suntharalingam, Numbers JP19K03915 (H.U.), JP15H02090 (T.G.T.), Directly-deposited blocking filters for high-performance silicon 6 x-ray detectors, in: Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray, Vol. 9905, International Society for Optics and Photonics, SPIE, 2016, pp. 1384 – 1391.