X 線検出素子（Silicon Drift Detector）用Si基板の高抵抗率化:　シミュレーションによる評価

摘要

環境問題の高まりから有害物質に対する規制が多く設けられている．有害物質検査の短時間化を計るために，可搬できる蛍光X 線検出器が望まれている．しかし，動作時にX 線検出素子を液体窒素温度まで冷却するため冷却装置が必要であり，蛍光X 線分析装置が大型化する．現在は，室温付近（ベルチェ冷却）で動作するX 線検出素子として，Si基板を用いたSilicon Drift Detector（SDD）が市販されているが，歩留まりが悪いため高価であり，さらにCd の蛍光X 線（23．5keV）の吸収率は約15％しかない．SDD を簡素化させ，MOSFET を含まないリング本数3本の構造に対する研究を行った．今回は基板の高抵抗率化を行い，Cd の蛍光X 線の吸収を高めるためにSi基板を厚くした際の問題点を解消する方法を検証する．%Several regulations for hazardous substances have been enforced due to the increase of awareness of environmental issues. To reduce those measurement times, it is required to carry out ready measurements. Since past X-ray detectors were operated at liquid nitrogen temperature, however, X-ray analysis equipments with those X-ray detectors were grown in size. Recently, silicon drift detectors (SDD) cooled by Peltier devices have been used. Because the structure of SDD with many p-rings is complicated, the cost of SDD rises. Moreover, the SDD can detect only 15 % of the X-ray fluorescence (23.5 keV) of Cd due to thin Si substrate. We have proposed and developed the simplified structure of X-ray detectors with only three p-rings. In this study, we aim to solve problems in our detectors fabricated using thicker Si substrate with higher resistivity in order to absorb a large part of the X-ray fluorescence (23.5 keV) of Cd.