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Setups for eliminating static charge of the ATLAS18 strip sensors
Construction of the new all-silicon Inner Tracker (ITk), developed by the
ATLAS collaboration for the High Luminosity LHC, started in 2020 and is
expected to continue till 2028. The ITk detector will include 18,000 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 their delivery at several
institutes participating in a complex Quality Control (QC) program. The QC
tests performed on each individual sensor check the overall integrity and
quality of the sensor. During the QC testing of production 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 leakage
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 per inch 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 introduced sensor recovery techniques based on
irradiation of the sensor surface with UV light or application of intensive
flows of ionized gas. In this presentation, we will describe the setups
implemented by the 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