Thin photodiodes for a neutron scintillator silicon-well detector

In the development of new neutron imaging applications, it is crucial to achieve a detector combining high spatial resolution, fast response, and high detection efficiency. To achieve such features, we have proposed a new design for position sensitive radiation sensors, which we called the micromachined Si-well scintillator pixel detector. It consists of an array of scintillator crystals encapsulated in silicon wells with photodiodes at the bottom. In the following, we describe such a detector, which makes use of a powder of ⁶Li₆ ¹⁵⁸Gd(BO₃)₃(Ce³⁺). The first experiments obtained with a prototype detector using a thermal neutron beam show the presence of a signal above the detector noise tail. In addition, to improve the characteristics of the well-type silicon sensor, we have investigated the deep reactive ion etching on silicon-on-insulator wafers. The process to etch 700-μm-wide vertical wells into a 500-μm-thick silicon wafer has been optimized. Test detectors with 10-μm-thick photodiodes at the bottom have been fabricated by means of this process