Development of Double-Sided Full-Passing-Column 3D Sensors at FBK

We report on the main design and technological characteristics related to the latest 3D sensor process developments at Fondazione Bruno Kessler (FBK, Trento, Italy). With respect to the previous version of this technology, which involved columnar electrodes of both doping types etched from both wafer sides and stopping at a short distance from the opposite surface, passing-through columns are now available. This feature ensures better performance, but also a higher reproducibility, which is of concern in medium volume productions. In particular, this R&D project was aimed at establishing a suitable technology for the production of 3D pixel sensors to be installed into the ATLAS Insertable B-Layer. An additional benefit is the feasibility of slim edges, which consist of a multiple ohmic column termination with an overall size as low as 100 μm. Eight batches with two different wafer layouts have been fabricated using this approach, and including several design options, among them the ATLAS 3D sensor prototypes compatible with the new read-out chip FE-I4.