A single VIP unit module detector is made of 4 CdTe pixelated detectors (see Figure 1). CdTe can provide an energy resolution as low as 1.5% FWHM for a 511 keV incoming particle, which will make the contribution of scattered events to the final data-set negligible. Each one of the four detectors has a parallelepiped shape and consists of ∼ 200 voxels. Each voxel has a size of 1mm x 1mm x 2mm and is connected to its own independent readout channel for the energy, position, and arrival time of the gammas. Each readout channel is bonded to a microchip hosting a fully integrated front-end electronic as designed and developed by the VIP project.

The VIP unit detector module is bonded to a thinned read out chip (ROC) and then mounted on a kapton printed circuit board (PCB). A 2000 V high voltage is applied with the electric field directed perpendicular to the surface so that the detector can be run inside a magnetic field without affecting the signal, for hybrid MRI/PET operation. The ROC and the PCB are 50 µ m thick each, whereas for the conductive glue between the ROC, the PCB, and the CdTe detectors a thickness of 15 µm is assumed. The combined attenuation coefficient of the passive material accounts for less than 2% compared to 2 mm CdTe.

The VIP modular design is extremely versatile with the possibility to build virtually any detector geometry by stacking the needed number of modules in arbitrary patterns. The resulting detector has a 3-D segmentation with a channel density of ∼ 470 voxels per cm3.