P4-006: ASTRO-H 衛星搭載 SXS-XCS 検出器Kazuhisa Mitsuda1, Richard L. Kelley11, Kevin R. Boyce11, Gregory V. Brown12, Elisa Costantini15, Michael J. DiPirro11, Yuichiro Ezoe2, Ryuichi Fujimoto3, Keith C. Gendreau11, Jan-Willem den Herder15, Akio Hoshino3, Yoshitaka Ishisaki2, Caroline A. Kilbourne11, Shunji Kitamoto4, Dan McCammon14, Masahide Murakami5, Hiroshi Murakami4, Mina Ogawa1, Takaya Ohashi2, Atsushi Okamoto6, Naomi Ota7, Stéphane Paltani16, Martin Pohl16, F. Scott Porter11, Kosuke Sato8, Yoichi Sato6, Keisuke Shinozaki6, Peter J. Shirron11, Gary A. Sneiderman11, Hiroyuki Sugita6, Andrew Szymkowiak14, Yoh Takei1, Toru Tamagawa9, Makoto Tashiro10, Yukikatsu Terada10, Masahiro Tsujimoto1, Cor de Vries15, Noriko Y. Yamasaki1

1: ISAS/JAXA; 2:Tokyo Metropolitan University; 3:Kanazawa University; 4:Rikkyo University; 5:Tsukuba University; 6:ARD/JAXA; 7: Nara Womens’Univ.; 8: Tokyo Univ. of Science; 9:Riken; 10: Saitama University; 11:NASA/GSFC; 12: Lawrence Livermore National Laboratory; 13:Univ. of Wisconsin; 14: Yale University; 15:SRON; 16:Geneva University;

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1. SXS-XCS に期待されるサイエンス 2014 年打ち上げ予定の ASTRO-H 衛星に搭載される SXS-XCS はマイクロカロリメータの技術を使用した精密分光器であり、以下の 3 つが主なサイエンスとして期待される。(1) 銀河団高温ガスの熱エネルギーと運動エネルギーの総量を知ることで、銀河団の全体像を知る。(2) ブラックホールのごく近傍の重力ポテンシャルで決まる物質の運動を測定し、相対論的時空を解き明かす。 (3) 銀河団のダークマター分布を求め、異なる年齢の銀河団の質量を決めることで、銀河団の進化にダークマターとダークエネルギーの果たす役割を調べる。

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Parameter RequirementEnergy resoluion 7 eV (4 eV goal) FWHMEnergy range 0.3 - 12 keVResidual background 1.5 x 10-3 cts/s/keVField of view 2.9 x 2.9 arcmin2

Detector array 6 x 6Pixel size 800 µmAngular rsolution 1.7 arcmin (1.3 arcmin) HPDEffective area 160 / 210 cm2 (at 1 / 6 keV)Lifetime 3 years (5 years goal)Counting rate 150 cts/s full array with <5% dead timeEnergy scale accuracy +/- 2 eV (+/- 1 eV goal)

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NASA Goddard Space Flight Center AS T R O -H/SXS

SXS EM Array – complete

Anti-Co detector also complete.

Performance and environmental testing are next

No. 1] The Suzaku High Resolution X-Ray Spectrometer (XRS) S81

are in Brekosky et al. (2004). In this paper, we provide a briefdescription of the design and fabrication method.

The process starts with a silicon-on-insulator (SOI) wafer,which consists of a thin layer of silicon separated from the bulksilicon substrate of the wafer by a very thin oxide buffer. Thisburied oxide serves as both an etch stop and a diffusion barrier.Reactive-ion etching (RIE) is used to create thermally-isolatedpixels. RIE is a dry etch process that permits the etchingof silicon into any shape that can be defined by means ofphotolithography. Deep-RIE etches (DRIE) through a 400-µmwafer with nearly straight side walls. Etching from the frontcreates patterns in the top 1.5-µm layer of silicon, and etchingfrom the back up through the thick substrate to the oxide layerdefines the suspended silicon membrane of each sensor. Aphotolithographically patterned structural polymer is used tocreate a controlled interface between the implanted Si and theabsorber.

For the absorber attachment points, we formed four10 µm-thick spacers of NanoTM SU-8 on each pixel. SU-8 is apolymer that is patterned like photo-resist, but bonds stronglyto silicon like epoxy. The thermistor was formed by dopingwith phosphorus (P) compensated with boron (B). The thick-ness of the top silicon layer of an SOI wafer determined thethermistor depth. After capping with an oxide, we implanteda single dose each of P and of B into the 1.5 µm-thick SOIlayer. The wafer was then annealed at high temperature for anextended period of time to diffuse the dopants to a uniformdensity throughout the 1.5 µm depth, remove damage, andallow the dopants to occupy substitutional lattice sites. Weeliminated the effects of lateral diffusion by implanting overan area larger than the thermistor area and then defining thethermistor edges with the etch. We used degenerately dopedleads to contact the thermistor. A lower density implant wasused on the membrane in order to limit the heat capacityof the thermal sensor; a heavier dose was used on the solidframe. The room-temperature resistivity of the lighter dosewas ! 200 !/square, and the heavier was 12 !/square. Theresistivities drop by less than a factor of 2 on cooling to 4 K.

The combination of SOI and RIE enabled the fabrica-tion of silicon links of the desired thermal conductance andminimum resonant frequency while maintaining a compactdesign. Though the thermal conductance achieved in the flightdesign was about a factor of two higher than expected fromscaling measurements of straight beams fabricated on previousgenerations of devices, the conductance was uniform acrosspixels, across arrays, and across different fabrication runs.The resulting exponential decay time was 3–4 ms, dependingon bias. The finite thermal conductance of the link betweenabsorber and thermistor contributed to this time constant;modeling indicated a fall time of 2 ms would have resulted withperfect thermal coupling between the absorber and thermistor.

Due to a concern that applying epoxy or SU-8 directly tothe thin silicon of the thermistor element could result in strain-induced changes in its electrical properties, we added tabs tothe edges of each thermistor and placed cylindrical spacers onthe tabs. Figure 4 shows an optical image of an individualpixel with an electron micrograph inset of an SU-8 spacer.A benefit of this attachment technique is that the line responsewas greatly improved compared with previous techniques that

Fig. 4. Photos of a single XRS microcalorimeter thermometer. Thesquare section is implanted to form the thermistor. There are foursupport beams and also four absorber “tabs” on which the HgTeabsorber is subsequently attached. The thermistor area and supportbeams are 1.5 µm thick.

Fig. 5. XRS line spread function on a single pixel as obtained usingX-rays from an X-ray monochromator tuned to Cu K!.

had the absorber, or an intermediate spacer, attached directlyto the thermistor volume. Each pixel now has a nearly perfectGaussian response to monochromatic X-rays. An example ofthe line shape is shown in figure 5.

There is a small penalty for this attachment scheme,however. The thermal conductance between the absorber and

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4 4 Preliminary Design Review, March 10-12, 2010

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Total mass=360kg, Power= 580 W

• SXS の cooling chain は 2段スターリング冷凍機 (2ST) 2 台 (~20 K)、 4.5 K ジュールトムソン冷凍機 (JT) 1 台、超流動ヘリウム (~1.2 K)、2段式断熱消磁冷凍機 (ADR; 50 mK) から成り、さらに、cryogen free 観測を行うため ADR をもう一段搭載している。

•液体ヘリウムの寿命は 3.2 年、一台の冷凍機が故障しても >1.6 年以上が期待されている。

•3rd ADR を用いることで、液体ヘリウムが無くなった後も、機械式冷凍機と ADR が健全である限り、科学観測を続けることが出来る。

•カウントレートが 20 counts/s/pixel 以上の場合、半分以上のデータが “low-res” となり、エネルギー分解能は >>10 eV となるため、明るい天体からの X 線を制限するためのフィルターホイールを搭載する。フィルターホイールには Be filter (低エネルギー用), neutral density filter (全エネルギーを 25% 減光する), optical blocking filter を搭載する。

•フィルタホイールには modulated X-ray sources も搭載する。これは、機上でのエネルギースケールを追い、サイエンスの観測を損ねることなく ~1eV/10 min 程度の精度を実現する。

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銀河団高温ガス中の高階電離イオンからの輝線の微細構造が分離できる。また、100 km/s 程度の速度の運動が検出可能である。

7. 開発の現状•コンポーネントの EM (engineering model) を製作、試験中。•SXS 全体の EM の組み上げ中。本年中頃に全系の試験を行う。•FM (flight model) の製作も本年開始する。

Collecting area Energy resolution

EM dADREM double-stage Stirling-cycle Cooler (2ST)

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2. SXS-XCS への要求と期待される性能

3. SXS-XCS システム4. 検出器アレイ

6. SXS-XCS Cooling chain

5. 軌道上キャリブレーション