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. In order 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 ⁶Li ₆¹⁵⁸Gd(BO₃)₃(Ce³⁺ ). The first experiments obtained using a thermal neutron beam show the presence of a signal above the detector noise tail. In addition, in order to improve the characteristics of the well-type silicon sensor, we have investigated the deep reactive ion etching on SOI wafers. The process to etch 700 μm wide vertical wells into 500 μm thick silicon wafer has been optimized. Silicon wells with 10 μm thick photodiodes at the bottom have been fabricated by means of this process