Development of silicon pixel detectors for radio-isotopic molecular imaging

In this paper we present an imaging module composed by an 8x8 array of p-i-n photodiodes, to be coupled with CsI(Tl) scintillators for use in scinti-mammography. The whole detector is optimized for the Technetium radiation (γ-ray:140 KeV). A special fabrication process was implemented to allow back side illumination from the crystal, forcing all the contacts to be placed on the front side of the detector. Square photodiodes, 1900x1900 µm wide and 300 µm thick, will be operated above the full-depletion voltage at a reverse bias of 75V, resulting in an expected capacitance of about 2pF and a typical dark current density in the order of 10nA/cm2. We are currently studying two different solutions of the array edge termination, having one or three guard rings. The array is planned to be used in a modular way, allowing the modules to be stacked side by side, with the aim of obtaining a large area (16x16cm2) camera, with a millimetric spatial resolution