Setups for eliminating static charge of the ATLAS18 strip sensors

Setups for eliminating static charge of the ATLAS18 strip sensors Pavla Federičová 1,* on behalf of the ITk Strip Sensor Project 1. Academy of Sciences of the Czech Republic, Institute of Physics, Na Slovance 2, 18221 Prague 8, Czech Republic * Corresponding author, pavla.federicova@cern.ch Construction of the new all-silicon Inner Tracker (ITk), developed by the ATLAS collaboration to be able to track charged particles produced at the High-Luminosity LHC, started in 2020 and is expected to continue till 2028. The ITk detector will include 22,000 highly segmented and radiation hard n+-in-p silicon strip sensors (ATLAS18), which are being manufactured by Hamamatsu Photonics. Mechanical and electrical characteristics of produced sensors are measured upon delivery for acceptance at several institutes participating in a complex testing program (the Quality Control (QC)). The Quality Control (QC) tests performed on each individual sensor check the overall integrity and quality of the sensor. These tests include sensor visual inspection measurement of the sensor bow and thickness, as well as current-voltage (IV) and capacitance-voltage (CV) electrical tests. Additional QC tests applied on a subset of the delivered sensor batch were introduced to verify the uniformity of channel responses across a sensor and long-term stability of the sensor leakage current. During the QC production testing of the ATLAS18 strip sensors, an increased number of sensors that failed the electrical tests was observed. In particular, IV measurements indicated an early breakdown, while large areas containing several tens or hundreds of neighbouring strips with low interstrip isolation were identified by the full strip tests, and current instabilities were measured in a long-term leakage current stability setup. Moreover, a high surface electrostatic charge reaching a level of several hundreds of volts was measured on a large number of sensors and on the plastic sheets, which mechanically protect these sensors in their paper envelopes. Accumulated data indicates a clear correlation between observed electrical failures and the sensor charge up. To mitigate the above described issues, the QC testing sites significantly modified the sensor handling procedures and introduce sensor recovery techniques based on irradiation of the sensor surface with UV light or application of intensive flows of ionizing gas. In this presentation, we will describe the setups implemented by various QC testing sites to treat silicon strip sensors affected by static charge, and evaluate the effectiveness of these setups in terms of improvement of the sensor performance.