Development of low noise radiation hard sensors and cables for the CBM Silicon Tracking System

Abstract

The performance of Double Sided silicon Strip Detectors (DSSDs) and Kapton cables for the Silicon Tracking System (STS) of the upcoming Compressed Baryonic Matter (CBM) experiment at FAIR is being reported. The CBM STS will consist of 8 stations of DSSDs at a distance between 25-100 cm downstream of the target. These DSSDs have a pitch of around 58 μm, stereo angle of ± 7.5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> with double metallization on either side. Total integrated fluence is expected to reach 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eq</sub> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> for some of the STS stations. We present the first 3-D TCAD simulated results on DSSDs using tools from SYNOPSYS. To determine the radiation hardness of these sensors, we have irradiated some of the prototypes at KRI Cyclotron facility. Our radiation damage model implemented in TCAD simulations is able to reproduce the irradiated data. Besides the static characteristics, we have also extracted interstrip parameters relevant to understand strip isolation and cross-talk issues. Transient simulations have been performed to estimate the charge collection of irradiated sensors and the collected charge has been found to exactly mimic the variation of interstrip resistance with bias voltage. Also parameters relevant for noise calculations like metal trace resistance have been measured. For ENC calculations, it is also important to determine the contribution of analog kapton cables since the length of cables could reach up to 50 cm for inner modules. We present the first finite element simulations to extract the capacitive and series resistive noise contribution from kapton cables using RAPHAEL. In order to validate RAPHAEL, we have reproduced the D0 kapton simulations which were done using ANSYS. Present prototype kapton cables have been produced at Kharkov using Aluminum traces. This paper presents a detailed comparison between Aluminum and Copper traces in terms of noise and material budget. Copper seems to be better candidate for metal traces in cables.