Characterization of proton irradiated 3D-DDTC pixel sensor prototypes fabricated at FBK

Abstract

In this paper we discuss results relevant to 3D Double-Side Double Type Column (3D-DDTC) pixel sensors fabricated at FBK (Trento, Italy) and oriented to the ATLAS upgrade. Some assemblies of these sensors featuring different columnar electrode configurations (2, 3, or 4 columns per pixel) and coupled to the ATLAS FEI3 read-out chip were irradiated up to large proton fluences and tested in laboratory with radioactive sources. In spite of the non optimized columnar electrode overlap, sensors exhibit reasonably good charge collection properties up to an irradiation fluence of 2 x 10 15 n eq cm −2 , while requiring bias voltages in the order of 100 V. Sensor operation is further investigated by means of TCAD simulations which can effectively explain the basic mechanisms responsible for charge loss after irradiation.

3D irradiation results

“…As far as 3D-DDTC sensors are concerned, the charge collection performance after irradiation of the first samples made at FBK was limited by the non-optimized column depth, which resulted in the presence of low field regions. Nevertheless, pixel sensor assemblies using the ATLAS FE-I3 read-out chip have shown signal efficiency values in response to radioactive sources of 76% and 64% at 1×10 15 n eq cm -2 and 2×10 15 n eq cm -2 , respectively [11]. The same sensors have been further characterized in several beam tests with good results in terms of hit efficiency, charge collection, and charge sharing up to a fluence of 1×10 15 n eq cm -2 [12].…”

3D Silicon Detectors

“…Nevertheless, it should be mentioned that the considered radiation damage model was validated up to irradiation fluences in the order of 1x10 15 n eq /cm 2 and tends to underestimate the signal efficiency at higher fluences. As an example, the same model provided an excellent agreement with experimental data for 3D sensors from FBK irradiated with protons at 1x10 15 n eq /cm 2 [33]. On the contrary, it did not reproduce the charge collection properties of 3D sensors irradiated with protons at 2x10 16 n eq /cm 2 , and in particular it failed to predict the experimentally observed double-junction effect [27].…”

Pre- and post-irradiation performance of FBK 3D silicon pixel detectors for CMS

“…In addition, calibration of the deep-reactive ion etching (DRIE) process to obtain the desired depth was difficult and prone to create differences in electrode overlap [10].…”