Slim edges in double-sided silicon 3D detectors

Abstract

Minimization of the insensitive edge area is one of the key requirements for silicon radiation detectors to be used in future silicon trackers. In 3D detectors this goal can be achieved with the active edge, at the expense of a high fabrication process complexity. In the framework of the ATLAS 3D sensor collaboration, we produced modified 3D silicon sensors with a double-sided technology. While this approach is not suitable to obtain active edges, because it does not use a support wafer, it allows for a new type of edge termination, the slim edge. In this paper we report on the development of the slim edge, from numerical simulations to design and testing, proving that it works effectively without increasing the fabrication complexity of silicon 3D detectors, and that it could be further optimized to reduce the insensitive edge region to less than 100 µm.

First production of new thin 3D sensors for HL-LHC at FBK

“…All the pixelated sensors are designed with slim edges [10]. Compared to the 200-µm design used for the ATLAS IBL pixels, the possibility to use a reduced pitch for the columns here allows for more aggressive designs, down to 75-µm size [11].…”

Development of new 3D pixel sensors for phase 2 upgrades at LHC

“…also including surface fF for the 50×50 μm 2 and ainly due to the different e breakdown voltage before the ratio of the signal after was simulated using the 3-fied as described in [10] Besides allowing for high radiation hardness, the small inter-electrode distance also allows to minimize the dead area achievable by using the slim-edge concept introduced with the ATLAS IBL pixels [1,7]. This design is based on an ohmic column fence that confines the depletion region spreading from the outermost junction columns so that it does not reach the highly damaged cut region [11]. When their density is higher, the blocking action of the ohmic columns is even more effective, so that the depletion region is confined within a very short distance from the junction columns.…”

Simulations of 3D detectors

“…As an alternative, a border region featuring multiple rows of ohmic (p) columns was developed. Simulations, later confirmed by measurements [24], showed how the depletion region, extending from the outermost junction -n -columns, stops at the first p-column row, allowing a very short safe distance (order of 100 m) between active area and scribe line. The possibility to implement slim edges comes out to be another strong motivation to prefer 3D to planar sensors.…”